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A F OWl MANUAt
oiPHM-TECHNiaUE

CORNELL

UNIVERSITY

LIBRARY

FINE ARTS LIBRARY

TR 290.Jl'"l972"""""'"-"'"'^

mmmmmEim^ negative technique

3 1924 015 369 055

The original of tliis book is in
tlie Cornell University Library.

There are no known copyright restrictions in
the United States on the use of the text.

http://www.archive.org/details/cu31924015369055

The Manual of Photo-Technique

THE MANUAL OF PHOTO-TECHNIQUE

Camera Techniques

H. J. WALLS, B.SC, PH.D.

Exposure

W. F. BERG, D.SC, F.INST.P., F.R.P.S.

Optics

ARTHUR COX, M.A., B.SC, F.INST.P.

Enlarging

C. I. JACOBSON, PH.D. AND L. A. MANNHEIM, M.A.

Developing

C. I. JACOBSON, PH.D. AND R. E. JACOBSON, M.SC,
PH.D., A.R.LC.

Retouching

O. R. CROY, PH.D.

Basic Sensitometry

L. LOBEL, I.C.P. AND M. DUBOIS, I.C.P.

Stereo Photography

K. C. M. SYMONS, D.L.C., A.M.I.I.A.

Colour Prints

J. H. COOTE, F.R.P.S., F.B.K.S.

Colour Films

C. LESLIE THOMSON B.SC.

Colour Separation Negatives

PHILIP JENKINS

C. I. JACOBSON,/'^.Z>.

and

R. E. JACOBSON, M.Sc, PH.D., A.R.I.C.

Developing

THE NEGATIVE TECHNIQUE

EIGHTEENTH EDITION

FOCAL PRESS

London and New York

Distributed in the U.S.A. by

AMPHOTO

915 Broadway, New York, N.Y. 10010

First published in U.S.A. 1972

0-8174-0626-3

Library of Congress Catalogue Card No. 77-107002

stored in a retrieval system, or transmitted, in any form or by any means,

electronic, mechanical, photocopying, recording or otherwise, without

the prior permission of the Copyright owner.

First Edition

May,

1940

Second Edition

May,

1942

Third Edition

Dec.,

1943

Fourth Edition

Aug.,

1944

Fifth Edition

May,

1945

Sixth Edition

April,

1946

Seventh Edition

Jan.,

1947

Eighth Edition

Jan.,

1948

Ninth (U.S.) Edition

Oct.,

1948

Tenth Edition

Jan.,

1950

Eleventh Edition

Nov.,

1951

Twelfth Edition

Aug.,

1953

Thirteenth Edition

July,

1955

Fourteenth Edition

April,

1959

Fifteenth Edition

Feb.,

1961

Sixteenth Edition

Jan.,

1966

Seventeenth Edition •

April,

1970

Eighteenth Edition :

Mar.,

1972

In Spanish

EL REVELADO

1949

In Dutch

ONTWIKKELEN

1949

In Danish

FREMKALDELSESTI

:knik

1959

y^'

ALL INQUIRIES

relating to this book or to any photographic problem are

answered by the Focal Press without charge if a stamped

addressed envelope is enclosed for reply

FOCAL PRESS 31 FITZROY SQUARE, LONDON, W.l

Printed and bound in Great Britain
by Thomas Nelson (Printers) Ltd., London and Edinburgh

This book was first published in May 1940 and has been
reissued seventeen times since that date. There is probably no
other work on this subject that has served so many readers so
long and so well as an authoritative source of reference.

Every edition preceding the Seventeenth had been brought
up-to-date in the hght of current progress. Yet after thirty
years of wear and tear the time had come to reconsider the
subject as a whole and so the last edition was reshaped to suit
the prevailing trends.

Thirty years ago photographic processing was still some-
thing of a pastime which seemed to thrive on a spirit of
experimentation and even controversy. The changing social
structure, economics and technology of our day combine to
evoke more uniform and thus more reliable concepts of
developing standards and control. This is a field in which
increasing automation is both desirable and feasible.

The basics of processing chemistry may not have changed a
great deal, but the approach to its technology has. The range
of developing agents is as wide as ever but only a few of them
are consistently used in practice and optimum results are
simply achieved by an informed choice of the correct
formulation.

So the extensively revised Seventeenth and the present
Eighteenth Edition, which has undergone further revision,
present a very comprehensive survey of formulae, whenever
possible in compact comparative tables. Professional and
commercial practices are covered more extensively than in the
preceding editions.

In this latest Edition, the Eighteenth, techniques of pro-
cessing have again been revised to include rapid daylight
in-cassette processing of 35 mm. film and modern tube and
drum processors suitable for the professional. In the rapid
access field, formulae for ultra-rapid processing are given as
well as the Bimat and Dry Silver process.

Processing formulae have been brought up-to-date and
wherever possible general tables of developer formulae are
given. Low contrast and stabilised physical developer formulae
are now included.

Reversal processing has been completely revised and so
have formulae for processing of colour materials. Specific
formulae are given for processing a variety of currently avail-
able colour negative and colour reversal materials.

A short chapter on quality control has novi' been included
which gives details of typical practical process control systems
for both black and white and colour negative materials.

A. Kraszna-Krausz

Contents

DEVELOPMENT— WHAT IT IS AND WHAT IT DOES 21

The Negative 22

Development: A Reduction Process 22

Chemical and Physical Development 23

EMULSION SENSITIVITY AND GRADATION 24

Comparing the Sensitivity of two Films 24

Measurements of Sensitivity 29

Gradation 32

Characteristic Curves 32

Gamma 35

Time-Gamma Curves 35

Determination of Development Time 38

Contrast Index _ 40

Average Gradient (G, "Gee Bar") 40

Densitometers 42

"Diffuse Density" 42

Visual Densitometers 44

Photo-Electric Densitometers 44

IMAGE STRUCTURE 50

Grain and Development 50

Granularity and Graininess 54

Negative Granularity 54

, Print Graininess 55

Resolving Power 55

Irradiation 56

Halation 58

Image Sharpness 58

Modulation Transfer Characteristics 62

The Choice of Film and Developer 64

Optimum Exposure 66

Quality of the Negative 67

THE PROGRESS OF DEVELOPMENT 70

The Rate of Development 70

The Influence of Temperature 72

When is the Developer Exhausted? 74

Developer Replenishers 76

Development Effects 77

The Influence of Agitation 78

THE COMPOSITION OF THE DEVELOPER 80

The Preservative 80

The Alkali (or Accelerator) 84

Alkalies and pH Values

Restrainers

Other Additions to Developers

Wetting Agents

Organic Accelerators

Developing Agents

Superadditivity

101

Induction Period

104

PREPARING SOLUTIONS

106

Chemicals

106

Order of Dissolving

106

Temperature

107

Manipulation

110

Tap-water

110

Saturated Solutions

110

Percentage Solutions

111

Dilute Solutions

112

Water up to ... .

113

Weights and Measures

113

pH Determination

115

Indicator Solutions

116

Indicator Papers

118

pH Meter

119

ARRANGEMENT OF THE DARK-ROOM

120

Darkening the Room

120

Walls and Floor

121

Dark-Room Illumination

121

Sodium Safelamps

125

Ventilation

127

Heating

127

Light-Tight Entrance

128

The Working Place

128

Improvising a Dark-Room

128

METHODS AND APPARATUS

137

Individual or Timed Development?

137

Compensating Development

139

Dish or Tray Development

140

Judging The Negative

143

Small Tanks

145

Rapid Daylight Processing of 35 mm. Film

152

Large Tank Development

154

Types of Tanks

154

Automatic Processing Machines

155

Self-Threading Roller-Processors

165

Tube and Drum Processors

170

DEVELOPER FORMULAE

172

General Purpose Developers

173

High Contrast Developers

177

Low Contrast Developers 180

Other Developing Agents 194

Tank Developers 200

Fine Grain Developers 202

Principles of Fine Grain Development 203

Medium Fine Grain Developers 204

Emulsion Speed and Fine Grain Development 208

Super-Fine Grain Developers 208

Special Techniques with Meritol 211

Fiigh-Definition (High Acutance) Developers 214

Inversion Agitation • 217

Physical Development 218

Tanning Developers 222

Chromogenic Developers 223

Tropical Developers 226

Prc-Hardener 227

At Higher Temperatures 228

Addition of Sodium Sulphate 228

Special Tropical Developer Formulae 228

Low-Temperature Development 230

Factorial Development 23 1

Quick-Finish (Rapid Access) Developers 233

Two-Bath Development 234

Multi-Solution Technique 238

Inorganic Developers 240

Restrained Development 241

Reversal Development 243
Reversal of Process Materials by the Etch-Bleach Process 249

Electrolytic Development 249

Basic Formulae 250

Desensitising 251

INCREASING FILM SPEED 256

Hypersensitising 256

Bathing 257

Vapour Treatment 257

Fogging by Light 258

Latent Image Intensification 258

Vapour Latensification 259

Post-Exposure Fogging 260

High-Energy Development 260

Development to Completion 262

FIXING 263

What the Process is and how it Works 263

Rate of Fixation 265

Life and Capacity of Fixing Baths 268

Rinse and Stop-Baths 271

Plain or Neutral Fixing Bath 272

Acid Fixing Baths 272

Hardening and Fixing Baths 273

Rapid Fixing Baths 276

Fixing Bath Maintenance and Regeneration 276

Monobaths 278

Fixing at Low Temperatures 282

The Recovery of Silver 282

Determining the Amount of Silver in Fixing Baths 283

Electrolytic Recovery of Silver 285

Precipitation of Silver by Other Metals 286

Precipitation of the Silver by Sulphide 287

Precipitation with Sodium Hydrosulphite 289

Regeneration of the Fixing Bath 289

WASHING AND DRYING 290

Technique of Washing 290

Washing in Sea Water 291

Control of Washing 291

Shortening Washing by Chemical Means 292

Drying 294

Stabilization 296

Formulation of Stabilizers 299

Improvement of Stability 299

RAPID ACCESS PROCESSES 301

Cell and Chamber Processors 301

Viscous Layer Applicators 304

Porous Plate and Roller Applicators 305

Jet Spray and Slit Processors 306

Roller Applicators 307

Saturated Web Applicators 314

"Dry" Development 314

"Photo" Development 316

Dry Silver Process 317

Chemical Transfer Processing 318

Combined Camera-Processors- Viewers 337

Formulae for Rapid Processing 337

AFTER TREATMENT OF THE NEGATIVE 339

Reduction 339

Subtractive Reducers 342

Proportional Reducers 343

Super-Proportional Reducers 344

Re-Development 345

Intensification 347

Mercury Intensifier 348

Mercuric Iodide Intensifier 350

Uranium Intensifier 350

Chromium Intensification 351

Copper-Silver Intensifier 351

Quinone-Thiosulphate Intensifier 352

RETOUCHING 354

Plan of Work 354

Partial Reduction or Intensification 355

Shading and Blocking Out 356

Spotting 357

Dry Reduction 357

Knifing 35g

PendJ Retouching 359

Varnishing 359

Applying the Varnish 361

Pencils for Retouching 36i

PROCESSING COLOUR FILMS 363

"OflBcial" and "Substitute" Formulae 364

Colour Negative Film 369

Colour Development 37O

Stop-Bath 371

Hardening Bath 372

Bleach- and Fixing-Baths 372

Colour Reversal Processing 374

First Development 375

Colour Development 377
General Simimary of Operations for Colour Processing 380

QUALITY CONTROL 384

Process Control Chart 384

Colour Process Control 386

PRESERVING THE NEGATIVE 388

Plate and Flat-Film Negatives 388

Roll-Film Negatives 388

Cleaning FUm 389

Dealing with Scratches and Abrasions on Film 389

DARK-ROOM HINTS 390

Antidotes for Poisons 390

Prevention of Dermatitis 390

Removing Developer Stain from the Hands 390

Removing Developer Splashes from Qothes 391

Cleaning Solution for all Non- Metal Vessels 391

Releasing Jammed Glass Stoppers 391

Disinfecting of Wood and Composition Tanks 392

Saving Cracked or Broken Plates 392

Giving Greater Transparency to Paper Negatives 393

Writing on Negatives 393

DEFECTS IN NEGATIVES 394

Faults in the Gradation of the Negative 394

The Negative is Fogged 395

White Deposit on or in the Film of the Negative 397

Dark or Light Streaks or Blotches on the Negative 398

Spots, Flecks and Linear Markings 399

Less Common Negative Faults 400

PHOTOGRAPHIC CHEMICALS 401

RECOMMENDED FURTHER READING 407

INDEX 408

List of Tables

n.
m.

IV.

VI.

vn.
vm.

K.
X.
XI.

XII.

xin.

XIV.
XV.
XVI.

xvn.

xvin.

xrx.

XX.

XXI.

xxn.
xxm.
xxrv.

XXV.

xxvi.
xxvn.
xxvm.

XXK.
XXX.

XXXI.

xxxn.
xxxni.
xxxiv.

XXXV.

xxxvr.
12

Time-temperature table for standard developer

groups 72
Keeping properties and useful capacity of

developers 76

Equivalent quantities of alkalies 83
Equivalent quantities of crystalline and anhydrous

salts 85

pH values 89

pH values of chemicals and solutions 90
Lengthening of development time by the addition

of potassium bromide 92
Characteristics of developing Agents 102
Fahrenheit and Centigrade degrees of temperature 108
English, American and metric exact values 1 14
Avoirdupois and metric weight measure equiva-
lents 114
British liquid and metric measure equivalents 115
U.S. liquid and metric measure equivalents 115
Indicators for pH determination 116
Colour change of universal pH indicators 118
Safelight filters 126
Varying of Focal Universal M.Q. Developer 16 141
General purpose M.Q. developers — Soft 173
General purpose M.Q. developers — ^Normal 174
General purpose M.Q. developers — Contrasty 174
General purpose M.Q. developers — Two-solution 175
Special developers — High contrast 178
Special developers — High contrast (Two solutions) 178
Special developers — Extreme contrast 179
Special developers — Low contrast 194
Chlorquinol developers 195
Glycin developers 196
p-Aminophenol developers 197
Phenidone-Hydroquinone (P.Q.) developers 199
Special M.Q. developers — ^Tank 201
Special M.Q. developers — Fine grain 206
Special developers — Super-fine grain 210
Quantities of Meritol stock in working developer 213
Special developers — High definition 215
Approximate time of physical development 219
Chromogenic developer substances and couplers 225

xxxvn. Development times in non-sulphated and sulphated

developers 229

xxxvra. Special developers — Tropical 229

xxxrx. Watkins' factors 232

XL. Special developers — Quick finish 235

XLi. First developers for reversal processing 246

xtn. Bleach baths for reversal processing 247

XLm. Clearing baths for reversal processing 247

XLiv. Second developers for reversal processing 248

XLV. Reversal processing — processing steps and formulae 248

XLvi. Etch-bleach reversal processing 249

XLvn. "Basic" developer formulae 252

XLvm. Fixing baths 264

XLix. Effect of ammonium chloride on clearing time 266

L. Qearing time in sodium thiosulphate 267

LI. Clearing time in sodium and ammonium thio-

sulphates 268

Ln. Capacity of a fixing bath 268

Lm. Stop baths 270

Liv. Stop and hardening baths 271

Lv. Acid hardening fix baths 274

Lvi. Acid hardening fix baths — with chrome alum 275

Lvn. Acid hardening stock solution 275

Lvra. Monobaths 280

Lix. Colour developing agents 370

Lx. Colour negative developers 371

LXi. Bleach baths for colour negative films 373

Lxn. Fixing baths for colour negative films 373

Lxm. Colour negative processing procedures — processing

steps and formulae 375

Lxiv. First developers for colour reversal processes 376

Lxv. Stop and hardening baths for colour reversal

processes 377

Lxvr. Colour developers for colour reversal processing 378

Lxvn. Bleach baths for colour reversal processing 379

Lxvrn. Fixers for colour reversal processing 380

LXK. Colour reversal processing procedures — processing

steps and formulae 381

List of Formulae

1. Soft M.Q. developer D165 173

2. Soft M.Q. developer ID3 173

3. Soft M.Q. developer G215 173

4. Soft M.Q. developer G212 173

5. Soft M.Q. developer AN40 173

6. Normal M.Q. developer D61a 174

7. Normal M.Q. developer G214 174

8. Normal M.Q. developer AN47 174

9. Normal M.Q. developer AG46 174

10. Normal M.Q. developer AN61 174

11. Contrasty M.Q. developer Dll 174

12. Contrasty M.Q. developer ID2 174

13. Contrasty M.Q. developer AN30 174

14. Contrasty M.Q. developer G201 174-

15. Contrasty M.Q. developer D72 174

16. Contrasty M.Q. developer Focal Universal 174

17. Two-solution M.Q. developer M.Q.I 175

18. Two-solution M.Q. developer M.Q.II 175

19. Two-solution M.Q. developer Metol 175

20. Two-solution M.Q. developer Hydroquinone 175

21. High contrast developer D19b 178

22. High contrast developer D19bR 178

23. High contrast developer ID 19 178

24. High contrast developer ID19R 178

25. High contrast developer AN30 178

26. High contrast developer G209a 178

27. High contrast developer AG30 178

28. High contrast developer D82 178

29. High contrast developer D178 178

30. High contrast (Two solution) developer D153 178

31. High contrast (Two solution) developer ID 13 178

32. High contrast (Two solution) developer AN70 178

33. High contrast (Two solution) developer G220 178

34. High contrast (Two solution) developer AG70a 178

35. Extreme contrast developer AN79b (Two solution) 179

36. Extreme contrast developer AN79/D85 (One solution) 179

37. Extreme contrast developer DP7d (One solution) 179

38. Low contrast developer T/O, XDR-4 194

39. Low contrast developer POTA 194

40. Single-solution pyrocatechin developer 194

41. Two-solution pyrocatechin developer 195

42. Two-solution chlorquinol developer 195

43. Single-solution chlorquinol developer 195

44. Single-solution chlorquinol developer 195

45. Two-solution pyro developer 196

46. Glycin developer AN72 196

47. Glycin developer ID60 196

48. Glycin developer AGS 196

49. Glycin developer G204 196

50. Two-solution p-aminophenol developer 197

51. Single-solution p-aminophenol developer 197

52. Single-solution p-aminophenol developer 197

53. p-Aminophenol-Hydroquinone developer 197

54. Amidol stock solution 198

55. P.Q. developer ID62 199

56. P.Q. developer ID67 199

57. P.Q. developer ID68 199

58. P.Q. developer ID68R 199

59. P.Q. developer ro72 199

60. P.Q. developer ID72R 199

61. P.Q. developer concentrated normal 199

62. P.Q. developer concentrated contrasty 199

63. M.Q. tank developer DK50 201

64. M.Q. tank developer DK50R 201

65. M.Q. tank developer ID6 201

66. M.Q. tank developer ID6R 201

67. M.Q. tank developer AN47 201

68. M.Q. tank developer AN47R 201

69. M.Q. tank developer Focal 201

70. M.Q. tank developer FocalR 201

71. M.Q. Tank developer G210 201

72. M.Q. tank developer G210R 201

73. M.Q. tank developer AG45 201

74. M.Q. tank developer AG46 201

75. M.Q. tank developer AG61 201

76. M.Q. tank developer AN48m 201

77. M.Q. tank developer AN48mR 201

78. M.Q. tank developer ID34 201

79. M.Q. tank developer 1D34R 201

80. M.Q. fine grain developer D76 206

81. M.Q. fine grain developer D76R 206

82. M.Q. fine grain developer D23 206

83. M.Q. fine grain developer D25 206

84. M.Q. fine grain developer D25R 206

85. M.Q. fine grain developer D76d 206

86. M.Q. fine grain developer ID 11 206

87. M.Q. fine grain developer IDl IR 206

88. M.Q. fine grain developer AN12 206

89. M.Q. fine grain developer ANl 7 206

90. M.Q. fine grain developer AN17R 206

91. M.Q. fine grain developer G206 206

92. M.Q. fine grain developer G207 206

93. M.Q. fine grain developer AG44 206

94. Phenidone-Hydroquinone fine grain developer 207

95. Super fine grain developer Sease 210

96. Super fine grain developer Meritol 210

97. Super fine grain developer Meritol-metol 210

98. Super fiaie grain developer Windisch 210

99. Super fine grain developer Focal 210

100. Super fine grain developer FXIO 210

101. Super fine grain developer Kodak 210

102. Super fine grain developer M. & B. 210

103. Super fine grain developer M. & B. 210

104. Meritol-caustic fine grain developer 211

105. High definition developer Beutler 215

106. High definition developer Windisch 215

107. High definition developer FXl 215

108. High definition developer FX2 215

109. High definition developer FX13 215

110. Forebath for physical development 219

111. Physical developer 219

112. Forebath for physical development (F. R. McQuown) 220

113. Physical developer (F. R. McQuown) 220

114. Stabilized physical developer 221

115. Tanning developer 223

116. Tanning developer D 175 223

117. Focal colour developer 225

118. Pre-hardener 227

119. Tropical developer Dl 3 229

120. Tropical developer DK15 229

121. Tropical developer DKl 5a 229

122. Tropical developer AN64 229

123. Tropical developer G222 229

124. High energy developer for low temperatures 230

125. Amidol-pyrocatechin developer for very low

temperatures 231

126. Time-temperature developer 232

127. Quick finish developer Orlando 235

128. Quick finish developer FortmiUer 235

129. Quick finish developer Duffy 235

130. Quick finish developer D8 235

131. Two-bath developer 236

132. Two-bath fine grain developer 236

133. Two-bath DK20 developer 237

134. High speed two-bath developer 238

135. Metol-hydroquinone multi-solution developer 239

136. Titanium developer 240

137. Amidol developer for intermittent development 242

138. Metol developer for intermittent development 242

139. Reversal developer D 168 246

140. Reversal developer D19+thiocyanate 246

141. Reversal developer ID36+hypo 246

142. Bleach bath for reversal processing 247

143. Bleach bath for reversal processing R21A 247

144. Clearing bath for reversal processing 247

145. Clearing bath for reversal processing R21B 247

146. Second developer for reversal processing D158 248

147. Second developer for reversal processing D8 248

148. Etch-bleach bath (Kodak EB-3) 249

149. Bath for electrolytic development 250

150. Basic developer— Soft 252

151. Basic developer — Normal 252

152. Basic developer — Contrast 252

153. Basic developer — Fine grain 252

154. Basic developer — Tank 252

155. Basic developer — High contrast 252

156. Basic developer — Rapid 252

157. Basic developer — Rapid contrast 252

158. Phenosafranin desensitiser 253

159. Desensitiser (B. T. Denne) 254

160. Pinacryptol desensitiser 255

161. High energy developer SD 19a 261

162. Fixing bath F24 264

163. Fixing bath F52/D18F 264

164. Fixing bath 264

165. Fixing bath IF2 264

166. Fixing bath G304 264

167. Fixing bath G305 264

168. Fixing bath 264

169. Fixing bath 264

170. Fixing bath 264

171. Stop bath 270

172. Stop bath 270

173. Stop bath 270

174. Stop-hardening bath 270

175. Stop-hardening bath 270

176. Stop-fix bath 270

177. Hardening stop-fix bath 270

178. Stop and hardening bath SBl 271

179. Stop and hardening bath SB3/AN216 271

180. Stop and hardening bath SB4 271

181. Stop and hardening bath 271

182. Stop and hardening bath OP207 271

183. Stop and hardening bath D2S 271

184. Stop and hardening bath G357 271

185. Acid hardening fix bath 274

186. Acid hardening fix bath F6 274

187. Acid hardening fix bath F7 274

188. Acid hardening fix bath FIO 274

189. Acid hardening fix bath AN204 274

190. Acid hardening fix bath G306 274

191. Acid hardening fix bath IF19 274

192. Acid hardening fix bath AG305 274

193. Acid hardening fix bath ATF5 274

194. Acid hardening fix bath ATF2 274

195. Acid hardening fix bath F16/AN202 275

196. Acid hardening fix bath AG306 275

197. Acid hardening fix bath AG308 275

198. Acid hardening stock solution F5a 275

199. Acid hardening stock solution F6a 275

200. Acid hardening stock solution 275

201. Acid hardening stock solution D2FH 275

202. Rapid thiocyanate fixer 276

203. Monobath— Keelan 280

204. Monobath— Levy 280

205. Monobath— Orlando 280

206. Monobath— Kodak 280

207. Monobath— Sasai and Mii 280

208. Monobath— Crawley 280

209. Ultra rapid monobath 281

210. Test solution for determining silver 284

211. Hypo test solution 291

212. Silver test solution 292

213. Hypo remover 293

214. Hypo ehminator for paper materials 293

215. Hypo eliminator for negatives 294

216. Bath for rapid drying 296

217. Alternative bath for rapid drying 296

218. Alternative bath for rapid drying 296

219. Stabilizing solution 300

220. Farmer's reducer 342

221. Belitzki's reducer 343

222. Permanganate reducer 343

223. Permanganate-persulphate reducer 343

224. Stain remover 344

225. Ammonium persulphate reducer 344

226. Alternative ammonium persulphate reducer 344

227. Benzoquinone reducer 345

228. Bleach bath for re-development 345

229. Fine grain re-developer 345

230. Bleach bath for super-proportional reducing 346

231. Gold chloride bath 346

232. Bleach bath for mercury intensification 348

233. Blackening bath for mercury intensification 348

234. Single solution mercury intensifier 350

235. Mercuric iodide intensifier 350

236. Uranium intensifier 350

237. Chromium intensifier 351

238. Alternative chromium intensifier 351

239. Copper-silver intensifier 351

240. Blackening bath for copper-silver intensifier 352

241. Quinone-thiosulphate intensifier 352

242. Matt varnish 356

243. Dry reducer 358

244. Alternative dry reducer medium 358

245. Water varnish 359

246. Alcohol varnish 359

247. Cold varnish 360

248. Alternative cold varnish 360

249. Normal matting varnish 360

250. Rapid matting varnish 360

251. Celluloid varnish 361

252. Colour negative developer for Kodak films 371

253. Colour negative developer for Agfa films 371

254. Colour negative developer for 3M (Ferrania) films 371

255. Stop bath for colour negative films (E. Gehret) 372

256. Intermediate bath for Agfacolor CNS and CN17

films (E. Gehret) 372

257. Hardener for colour negative films (E. Gehret) 372

258. Bleach bath for Kodak colour negative films 373

259. Bleach bath for Agfa colour negative films 373

260. Bleach bath for 3M (Ferrania) colour negative films 373

261. Fixing bath for Kodak colour negative films 373

262. Fixing bath for Agfa colour negative films 373

263. Fixing bath for 3M (Ferrania) colour negative films 373

264. Bleach-fix bath (G. Theilgaard) 374

265. Bleach-fix bath (H. Gordon) 374

266. First developer for Ektachrome E3 colour reversal films 376

267. First developer for Ektachrome E4 colour reversal films 376

268. First developer for Agfa colour reversal films 376

269. First developer for 3M (Ferrania) colour reversal

films RC131 376

270. First developer for Ansco colour reversal films 376

271. Pre-hardener for Ektachrome E4 process (E. Gehret) 376

272. Neutraliser for Ektachrome E4 process (E. Gehret) 377

273. Stop bath for Ektachrome E3 colour reversal films 377

274. Stop bath for Ektachrome E4 colour reversal films 377

275. Stop bath for Agfa colour reversal films 377

276. Stop bath for 3M (Ferrania) colour reversal films VC233 377

277. Stop bath for Ansco colour reversal films 377

278. Colour developer for Ektachrome E3 reversal films 378

279. Colour developer for Ektachrome E4 reversal films 378

280. Colour developer for Agfa reversal films 378

281. Colour developer for 3M (Ferrania) reversal films RC125 378

282. Colour developer for Ansco reversal films 378

283. Bleach bath for Ektachrome E3 colour reversal films 379

284. Bleach bath for Ektachrome E4 colour reversal films 379

285. Bleach bath for Agfa colour reversal films 379

286. Bleach bath for 3M (Ferrania) colour reversal films

VC212 379

287. Bleach bath for Ansco colour reversal films 379

288. Fixer for Ektachrome E3 colour reversal films 380

289. Fixer for Ektachrome E4 colour reversal films 380

290. Fixer for Agfa colour reversal films 380

291. Fixer for 3 M (Ferrania) colour reversal films FC200 380

292. Fixer for Ansco colour reversal films 380

293.

Stabilizer bath (E. Gehret)

294.

Film cleaner

295.

Anti-scratch solution

296.

Preventive against metol dermatitis

297.

Stain remover

298.

Cleanser

299.

Stain remover

300.

Cleanser

301.

Vessel cleanser

302.

Disinfectant

303.

Hardening bath

304.

Plate stripping solution

305.

Cement

306.

Writing solution

307.

Hardening bath

308.

Fog remover

309.

Fog remover

310.

Amidol re-developer

380
389
389
390
390
391
391
391
391
392
392
392
392
393
396
396
397
397

Development:

What it is and what it does

If we expose a photographic film in the camera the closest
visual examination fails to disclose any perceptible change
in the sensitive coating which, in general, consists of a sus-
pension of silver bromide in gelatine and to which the name
emulsion is given.

Yet we all know there has been a change and that the
apphcation of a developer will reveal it. We say that the
action of the Ught on the sensitive material has produced a
latent image. Latent here means imrevealed or undeveloped.

The development of this latent image by means of the
developer is one of the most important and interesting of all
photographic processes, and upon its successful operation
depends in very large measure the nature of the end product,
that is, the finished photograph, which is our goal.

In order to render the latent image visible we make use of
certain substances known as developers, which have the
property of changing the exposed silver bromide into black
metallic silver. Hence we think of two processes, first a
photochemical change brought about by light during ex-
posure, second a chemical change by which the exposed
silver bromide, that is the latent image, is changed or re-
duced to metalMc silver and so rendered visible.

The chemists call this second process reduction.

If we were to introduce an unexposed film into the de-
veloper, a very small amount of silver bromide at most would
be reduced to silver. Only the exposed silver bromide res-
ponds to the action of the developer and is reduced or
changed to metallic silver.

It is most important to notice that those parts of the
sensitive emulsion which receive most light provide the
heaviest deposits of reduced silver and are therefore blackest.
Where only a small quantity of light acts on the silver

bromide the amount of silver reduced is much less. If we
examine the result very carefully we find that the greater the
amount of light allowed to act on the sensitive material the
greater the amount of reduced silver.

THE NEGATIVE

This gives us a very interesting result: we have now got a
developed picture in which all the light values of the original
object photographed are reversed. The lightest parts of the
original are darkest in our picture while the dark parts of
the original are light in our result. That is why we call the
result a negative.

This reversal of light values must always be borne in mind
if we are to understand rightly the process of development
and to read our negatives correctly.

We remember then that the darkest parts of the negative
represents the lightest parts of the subject photographed.
Therefore the highlights of our subject provide the blackest
areas in our negative.

Similarly, the lighter parts of the negative represent the
darker or less well-lit areas in our subject. Hence the shadows
of our subject provide those areas in the negative with the
lightest deposit of silver, or perhaps not even a light deposit,
but clear gelatin.

development: a reduction process

We have already seen that photographic development is
a reduction process in which the developer acts as a reducing
agent. But photographic developers are a special kind of
reducing agent, because they act only on silver bromide that
has been exposed to hght.

The chemist knows many reducing agents capable of
reducing silver bromide to metallic silver, but they act
differently to the photographic developer. They fail to
discriminate between silver bromide which has been exposed
to light and that which has not. A plate or film placed in
such an agent would be completely blackened, irrespective
of whether it had been wholly or partially exposed.

Just why the photographic developer reduces only the
silver bromide that has been exposed to light is a question

we do not propose to answer in this book. Our interests
are purely photographic, and a discussion of the many
physico-chemical problems involved would not necessarily
increase our understanding of the essentials of photographic
development.

CHEMICAL AND PHYSICAL DEVELOPMENT

One small chemical point we must know is that in the
process of reducing silver bromide to silver, soluble bromide
is set free and passes into the developer solution. This is an
integral part of the reduction process and is of importance
because it can, under certain circumstances, cause various
troubles.

In such a development process as we have described it is
clear that the silver which builds up the image in the negative
is derived from the sensitive film of emulsion on the plate or
film, and that it is produced by the chemical reduction of the
silver bromide.

We therefore call this process chemical development, to
distinguish it from another process, called physical develop-
ment, in which silver, already present in solution in the
developer, is deposited on the latent image, a method which
might be likened to silver-plating.

The composition of the developer and the method of
development can naturally influence the character of the
negative produced, and by suitable methods it is possible to
exercise a large measure of control in the development
processes. To do this with some degree of confidence we
need to know something of the properties of the sensitive
materials.

Emulsion Sensitivity
and Gradation

In choosing photographic material the question of sensitivity
is naturally of considerable importance, but it would be a
mistake to think that it was the only criterion. It would be
wrong to think, for example, that the fastest, or most sensi-
tive, film was necessarily the best. Other properties such as
graininess may well play an important part and influence
the final result quite as much.

On the other hand, if we have chosen the fastest and most
sensitive film, then we want to feel that we know just how
to develop it so that we do not lose in the processing of it
just those qualities which the manufacturer has been at such
pains to confer upon it.

COMPARING THE SENSITIVITY OF TWO FILMS

We may desire to compare the sensitivity of two films one
with another. A quite simple experiment enables us to do
this, and also to understand and investigate other properties
of the sensitive material. We start from the concept that a
film of high sensitivity is one requiring a small exposure
to light. To put it another way, it requires only a small light
impression to produce on development a given degree of
blackening beyond that produced in an unexposed area,
which is known as "fog".

We take two strips of the films we wish to compare and
expose successive areas to a light soiirce such that a reason-
ably long exposure is necessary to produce full blackening
of the exposed film-strips when developed. We do this by
covering up the strip with an opaque card step by step during
exposure so that each successive portion of the film receives
an exposure double the time of the previous exposure, for
example, 1, 2, 4, 8 seconds, and so on.

SOFT GRADATION. The scale of gradation is long and
comprises a wide range of densities which build up the above
soft negative. It will be seen that the fairly long blackening curve
does not rise at a high angle, hence the gamma value (see page 34)
is not high.

HARD GRADATION. If this negative is compared with that
on page 25 it will show the diflference between a soft and a hard
negative. In the latter the scale of blackening is short and the
curve is steeper, hence the gamma is higher. The curve also rises
much higher, hence the negative has higher or greater densities
particularly in the highlights.

SI'

PROGRESS OF DEVELOPMENT IN A RAPID
DEVELOPER. In such a case the image develops so that all the
details, shadows as well as highlights, appear almost at the same
time {top). As the development proceeds, density grows all over
and hence a strong and contrasty negative is seen {centre) until
finally the required contrast is reached {bottom). — See page 70.

PROGRESS OF DEVELOPMENT IN A SLOW
DEVELOPER. Here the highlights appear first {top), then the
middle tones (centre) and finally the shadows (bottom). The
negative builds up slowly from the first appearance of the high
lights to the final filling up of detail in the shadows, by which
time it has the necessary gradation and density. — See page 70.

When we develop these strips, we obtain what we can call
blackening scales (see page 25) for the two films.

These scales will show that the two strips differ in the
position occupied by the first visible trace of reduced silver.
The faster film may show it at the 1 -second step. In the
slower film it may not appear until the step exposed for
4 seconds.

But that is not all the strips will tell us. We shall also
learn that in those parts of the film which have only
received a small exposure to light a certain development
time is essential for full blackening. If the time of develop-
ment is cut short, the eff"ect of small exposures to light is
lost and we lose some of the advantage of using a fast
film.

To put this another way, if a film is under-developed
shadow detail is lost (see page 27). In fact, the film which is
developed for too short a time behaves as if it were much
less sensitive than is actually the case. Hence we see that the
time of development is of great practical importance and
has a real influence on the practical sensitivity of our material.
If we desire to utihse fully the whole sensitivity of our material
we must develop it completely.

We can extend our experiments with strips of sensitive
material by using difi"erent developers or by using developers
of the same composition but of varying temperature. We
shall find that all these factors are capable of influencing the
result.

MEASUREMENTS OF SENSITIVITY

Our experiments have introduced us to the rudiments of
sensitivity measurements but it is important to bring out a
few of the essential requirements when undertaking such
sensitometric investigations. These are:

(1) A light-source that can give a constant and con-
trollable hght output so that identical conditions of exposure
can be repeated time after time. Moreover, as in the great
majority of cases it is the sensitivity of materials to dayUght
that we are interested in, we must ensure that our light-source
provides light of such colour composition, or spectral com-
position as it is called, that it approximates closely to dayhght.
Such a source is a timgsten filament, gas-filled lamp fitted

with the necessary control of electric current to maintain a
constant light output.

To this must be added a filter which transmits light of
almost exact daylight quality. For the photographer who
desires to make only a few measurements now and again it
will be sufficient to use one of the filters supphed for trans-
forming artificial light to daylight. This filter is fixed in a
frame in front of the lamp house carrying the tungsten
filament lamp. This daylight filter should not be the gelatine
film type, as these are liable to change in time and with use.
It should be the all-glass type which is permanent and un-
affected by age or use.

A light source and filter as described can be used for
determining the sensitivity of any photographic material,
whether ordinary, orthochromatic or panchromatic, and is
particularly useful for comparing the relative sensitivity of
materials in general use with new products or with materials
which have not hitherto been in common use.

(2) An exposure machine or apparatus. This takes the
place of the opaque cover used in simple experiments and
may consist of a wedge scale of blacknesses, or, as is more
usual and convenient, a step wedge in which the relation of
the density or blackness of the steps to one another is known.
Another method is to make use of a sector wheel which
has been so cut as to provide a range of accurately deter-
mined exposures during a single revolution. For simple
measurements the step wedge is recommended as being
the easier to obtain and costing less than more elaborate
apparatus.

Whichever type of exposure apparatus is used, the effect
is to produce a graded series of exposures on the sensitive
material being tested. These exposures always bear a constant
relation to one another and the only factor the operator has
to watch is the control of the light source. This should be
arranged at such a distance from the exposure apparatus
that an exposure of, say, ten seconds suffices for a very wide
variety of sensitive materials. The reason for choosing an
exposure of ten seconds or so is that an error of one-tenth
of a second in switching the fight on or off will mean only a
one per cent error in exposure, whereas if the exposure time
were only one second the same error would be ten per cent
and therefore serious. For more accurate measurements, a

shutter must be used, producing a short exposure time in
the order of the average camera exposure.

(3) Developer for the test-strips. This is of the utmost
importance and calls for careful consideration, if only because
the relation between sensitivity and development is the biggest
factor involved in the actual technique of development. We
have already seen that development can affect the result of
any determination of sensitivity, for if we do not develop
fully, then the sensitivity of the material being tested will
appear to be lower than it really is. Hence if we are to obtain
comparable results our methods of development must be most
carefully controlled, so that they not only give comparable
but also reproducible results. That means a developer of
definite composition, used for a definite time at a definite
temperature, with a well defined method of agitation. We
may decide to use a reasonably energetic developer for such
a time and at such a temperature that we know the strips
will be fully developed. Or we can use a particular developer
to attain a predetermined gradation (see page 35). What-
ever method we use, it must be capable of giving identical
results with identical materials as many times as we desire —
and that is not the simplest thing in the world.

(4) A means whereby we can measure the degree of
blackening on our developed strips. This may be some form
of comparator in which the density or blackening of the
developed strip is compared visually with a standard wedge
of known densities and gradation. There are various types
available, some of which are discussed at the end of this
chapter.

In determining or measuring sensitivity, and particularly
in comparisons between diiferent materials, a most important
criterion is the smallest perceptible blackening which the
exposure has caused, or to put it another way, the smallest
light effect which is developable on our test strip. It is
particularly important that we should be able to measure
this accurately, and we want also to remember that we are
not dealing with the least perceptible blackenmg that the eye
can detect; what we are considering is blackening or density
which is capable of being copied when we make a print from
our negative. That is the practical side of the question, and
we are much more interested in a threshold value that we
can reproduce in our print than in some faint deposit just

perceptible to the eye but which is without influence in
reproducmg a negative in positive form and is therefore
outside the useful sensitivity of our material.

If we study the various methods of determining and
expressing the sensitivity of photographic materials, such as
the ASA, BS and DIN systems, we shall find that in the
modern view it is not the first perceptible trace of light effect
that coimts, but the lowest density capable of reproduction
when the negative is printed.

Now we must leave questions of sensitivity to discuss those
other properties of photographic materials which are of
importance to us in considering development and par-
ticularly the way in which they can be affected or influenced
by it.

GRADATION

Our experiment in exposing strips of film to produce a graded
series of exposiures provides us with a means of investigating
a very important property of sensitive materials, namely
gradation, and of understanding how this is related to or
afi"ected by development. In order to do this we have to
consider the whole range of our strips and not merely one or
two of the steps or exposures on our scale of blackening.

When we do this we can see just how any particular
sensitive material reacts to a graded series of exposures, so
arranged that they bear a constant ratio to one another.
Such a scale of blackenings or exposures indicates what we
call the gradation of any particular material, and materials
can vary greatly in character as we shall see.

For example, the film on page 25 has a long range of steps
between the deepest black and the lightest deposit, whereas
on page 26 there are only a few steps over the same range.
We call the first a soft gradation film, and the second we
designate as hard. Between these two extremes there may be
many diff"erent degrees of gradation and particularly that
which we should call normal.

CHARACTERISTIC CURVES

These terms soft, normal, hard, etc., have no exact signi-
ficance, they are relative and only take on a quantitative

value when used in comparing properly prepared blackening
curves of sensitive materials. The average photographer is
rather repelled by curves and mathematical formulae, yet the
expression of properties by a curve is a tremendous help in
visualising clearly a collection of observations. It is infinitely
easier to read and understand than are columns of figures.
We have only to think of the ease of handling statistics of a
recurrent character over any period of time to realise that
a moment's glance at a curve can convey information which
otherwise might take minutes or even hours.

So if we desire to visualise the relation between the
exposure to light and the blackening it produces on sensitive
material, the simplest way to do it is to produce a curve.
If we wish to compare more than one material then we simply
draw the curves on the same diagram.

Up the side of the diagram (see page 37) we plot units of
density or blackening. The definition of density and the
method of measuring it are indicated in the inset of the
diagram. If we let a beam of light^of intensity I^ fall on to our
photographic density D, the intensity is reduced to a value 1 2.
We call our density one where it reduces the measuring
light intensity to 1/lOth, two, where it reduces to I /100th,
three, where it reduces to 1 /1000th, etc. Thus on oiu' density
axis we allot equal decrements of the intensity I^ to a density
unit. For example, if any two densities differ from one another
by the lighter density transmitting twice as much light as the
heavier one, the spacing between these two densities will be
constant (and equal to 0.3) whatever the actual values of the
densities may be. (For the mathematically minded it will be
clear that we are defining density as the logarithm of the
ratio of transmitted to incident light intensity.)

Along the base of the diagram we have divisions which
represent equal increments of exposure intensity. The ex-
posure increment axis is very similar to the density axis in
that any two exposures which are in a certain ratio to one
another (as for example 2 to 1) are spaced a constant distance
apart on the increment axis (in this instance 0.3). (Again the
mathematically minded will notice that we plot the character-
istic curve on a logarithmic intensity axis.)

Now the curve itself is obtained from a series of measure-
ments of densities which have been produced by certain
exposures. On the axis described we erect verticals at

corresponding values of density and exposure; where these
verticals cross we have the point of the curve. In this way
we can build up and compare the blackening curves for
different materials.

On pages 25-26 we have the two curves of the strips of
two films that we have already spoken of, and at once we
see how great a difference there is in their gradation.

In order to understand more thoroughly how to read and
interpret such curves, let us consider first of all the long
straight sloping portion of the curve on page 37. Here, on
increasing the exposure by, for example, ten times, the
amount of hght transmitted by the developed density drops
to one tenth since the curve rises at an angle of 45° to the
axis ; this is correct whichever exposure we start from as long
as we stay on the straight-line part of the curve. In this case
we speak of a correct reproduction in densities of the varying
quantities of light forming these densities.

Now the actual characteristic curve is straight over only
a limited range of exposures and densities. The curve bends
both at the lower and the top part. With any complete
characteristic curve there comes a point where increasing
exposure does not increase the density. Thus at the top end
of the curve is situated the region of over-exposure.

In the same way at the beginning of the curve there is a
region where exposure to Hght causes no change in the
density, followed by a region where density increases more
and more rapidly with increasing unit increments of exposure
— until the straight-line part is reached. The very lowest part
of the curve is the region of under-exposure.

The most usual normal exposures reach from somewhere
in the lower bent portion of the curve well into the straight-
line portion. The region of normal or correct exposure may
be said to reach from halfway up the lower bent part of the
curve all the way up the straight-line part.

Looking now at the two curves on pages 25-26, we can
see that there is a notable difference in their slope and there-
fore in the angle which their straight-line portion makes with
the horizontal axis or base of the diagram. Moreover, we
notice that neither curve fulfils the ideal condition of being
a straight Une at an angle of 45° to the horizontal axis and
in this respect they differ from the curve on page 37. The
curve of the soft gradation film makes a much smaller angle,

that of the hard gradation film a much larger angle with the
axis.

GAMMA

Gamma (y) is the tangent of the angle produced when the
straight line portion of the characteristic curve is prolonged
to meet the horizontal axis. It will be obvious that as the
curve is steeper or less steep, so the angle will vary and so,
too, the Gamma, and therefore the gradation.

Gamma, or the tangent of the angle, is measured as shown
in the diagram on page 37.

In our diagram the slope of the curve is 45 degrees, hence
BC and AC are identical in length and so BC/AC = 1, which
is the Gamma.

If now we take the other examples, our soft and hard
films on the pages 25-26, and measure them in the same way,
we shall find the soft gradation film has a Gamma of 0.6 and
the hard film a Gamma of 1.5.

Now that we know how we can give a numerical valae to
the gradation of our sensitive material, we can get on with
investigating the relation between gradation and develop-
ment, a matter of the utmost practical importance. For this
purpose we prepare a series of strips, all with the same series
of step wedge exposures and then develop them in the same
developer for varying times. When this has been done and the
strips fixed, washed and dried, we shall see that the develop-
ment has reached a definite maximum value. If we measure the
densities and plot curves for the strips we find that the steep-
ness of gradation and also the Gamma value reach a definite
maximum and then increase no more.

That really gives us two maxima, namely maximum
density (D max) and maximum Gamma (y max), or more
usually Gamma infinity (y oo). The two values D max and
y 00 just mean the maximum density and gamma that can be
obtained by prolonging development.

TIME-GAMMA CURVES

The results we have obtained with our developed strips can
now be used in another valuable direction, namely in pre-
paring a curve which clearly indicates the relation between

the length of time of development and the growth of Gamma.
In other words we can prepare a time-gamma curve. To do
this we arrange a diagram in which time of development
appears along the horizontal axis, while on the vertical axis
we have the Gamma values. As we can easily determine the
Gamma from our blackening curves, so it is a simple matter
to produce time-gamma curves in turn.

On page 39 curves are given for two different developers
and the differences between them are apparent at a glance.
The developer of curve B causes a slow increment in Gamma
and the maximum reached is only low; this is a weakly
active and slow-working developer. With curve A the oppo-
site is the case, not only is the maximum Gamma reached with
a comparatively short development time, but it is a high
figiure at that. Here we have an energetic and hence quick-
working developer.

From these two examples it will be clear that in time-
gamma curves we have an excellent means of characterising
developers. We can see at a glance all the really important
things we want to know about them, such as their relative
energy as developers, the time required to reach a particular
gradation or gamma and, for any particular material, the
maximum gamma attainable.

In practice, time-gamma curves are not always available.
Various film manufacturers supply such curves for their own
material when developed with a prescribed developer. But
the photographer who uses the various formulae given in
this book may well ask himself what is the practical time of
development for some particular film with a particular
developer, not necessarily either the film or the particular
developer recommended and supplied by any particular firm.
To answer this question with exactitude would require a
time-gamma curve for every developer and for every film or
plate sold. This is obviously impossible in view of the tre-
mendous variety of developers and materials available. Not
only is it impossible, but it is also quite xmnecessary.

It is very easy to exaggerate the importance, as well as
the value, of the time-gamma curve in actual practice. On
the one hand we know that with a normal developer a
variation of half a minute either side of full development will
not seriously affect gamma, and on the other hand we know
that the range of modern printing papers is so wide that we

CHARACTERISTIC CURVE AND GAMMA

D
3

1000 ▼▼▼▼▼▼

■xposu

1000

B
re-H

I 10000

1 , ID

1 1 l2
1 ^^^^ ^ ^^

■ 100 <i°X

10 /

Xi Intensity of I

/ 10 \ 100

A 1 2 3

Log (Intensity of Exposure) — »
-U X N )e

C 4

The characteristic curve of photographic material is a plot of density
against the logarithm of exposure necessary to produce that density on
development. Density is defined as the logarithm of the incident divided
by the transmitted light intensity; D = log Ii/Ij, Ii and la being the
intensities illustrated in the insert diagram. The values of the ratio of
1] /Iz are shown against the density values D, and similarly the exposure
intensity values are shown against the log exposure in order to illustrate
the logarithmic relationships. The region of under-exposure is indicated
by U, that of normal exposure by N, that of over-exposure by O along
the exposure axis. Gamma is a figure which expresses the contrast of a
negative. It is measured or determined by extending the straight-line
part of the curve until it meets the horizontal axis at A and a vertical axis
erected at a point C anywhere along the exposure axis. Then gamma (y) =
BC/AC = tan u.. In the above example gamma is 1, for the angle a is
45° and so AC and BC are equal.

5 37

can obtain a good print from almost any negative whether it
is hard or soft.

On these grounds it is obviously unnecessary to develop
a negative so that it just exactly reaches a given gamma
value, for example, 0.8. What we want is a negative that is
developed to such a gamma value that it will produce a
good print or enlargement. That is, it should fall between
the limits of gamma 0.7 and 1.0. Once the practical value of
this is reahsed the question of the right development time
can soon be dealt with in the following simple manner.

DETERMINATION OF DEVELOPMENT TIME

In practice, we can regard most films as falling into three
groups, according to their speed rating. Group A includes
slow films rated up to about 80 ASA; Group B is for medium
speed films from 125-320 ASA; Group C for fast films rated
faster than 320 ASA.

The middle group (Group B) is that which requires normal
development time, i.e. the time given in the various formulae
for developers. The films in the other two groups (A and C)
call for either a shorter or a longer development time, i.e.
a l/3rd decrease for Group A or a one-half increase for
Group C.

Example. — Suppose we choose a fine grain developer
formula and that the average normal development time for
this developer is 12 minutes. This will hold good for all
films of Group B. If now we have a film of Group A, then
the development time must be reduced to 2/3rds, that is to
eight minutes. If, on the other hand, we are dealmg with a
film belonging to Group C, we must increase the develop-
ment time by one-half, that will be 18 minutes.

The normal development times given with the various
developer formiilae are all chosen so that they will give a
gamma of an average of 0.8 in that time, and if the above
instructions relating to the three groups of films are followed
then the average gamma of all negatives developed should
not diverge notably from 0.8.

It is perfectly true that the rate of development may vary
between films of the same group. It can even vary between
films of the same grade and maker, but the divergences from
the general mean which can occur in this way should be

TIME-GAMMA CURVE

TIME

The time-gamma curve shows how the contrast of a negative increases
with the development time. In order to produce such a curve, the hori-
zontal axis of the diagram shows development time, while the vertical
axis shows the Gamma values. In the diagram the effect of two types of
development is shown. The curves A and B have been produced by
developers with very different properties. A is a rapid-working and
contrasty developer. The curve rises steeply and reaches a high Gamma
value in 6 minutes. B is a slow and soft-working developer. Hence the
curve rises gradually and the Gamma value is much less than that in curve
A. In this case 10 minutes was required to reach even this low Gamma.

quite easily dealt with by the choice of a suitable printing
paper.

CONTRAST INDEX

With modern emulsions and processing techniques gamma is
frequently difficult to measure because of the unusual curve
shapes obtained. Also many exposures are made in the toe
region of the characteristic curve. These difficulties have led
to the definition and use of the term Contrast Index and
similar concepts. Contrast Index is the Kodak term, defined
in their Data Sheet SE-IA as the slope of a straight line
joining two points on the characteristic curve that represent the
approximate minimum and maximum densities used in practice.
Development of different films to a given gamma generally
aff"ords negatives that are best printed on different grades of
paper. Development of different films to the same CI value,
however, gives negatives that yield acceptable prints on the
same grade of paper.

To determine the CI two arcs are drawn from a common
point on the base+fog axis. The intersection of the smaller
arc of radius 0.2 density (or log exposure) units with the
characteristic curve gives the low-density point (A). The inter-
section of the larger arc of radius 2.2 density (or log exposure)
units with the characteristic curve gives the high-density point
(B). The slope of the line joining the points A and B is the Con-
trast Index (page 41). For easy measurement of the Contrast
Index Kodak recommend the use of a transparent template.

AVERAGE GRADIENT (G, "GEE BAR")

Ilford have adopted the criterion of average gradient (G,
"gee bar") as a measure of contrast in place of gamma. This
is slightly easier to measure than contrast index and both give
similar variations with development time although their
absolute values are slightly different. At the present time there
is, unfortunately, no universally accepted alternative to
gamma as a measure of contrast and both contrast index and
average gradient are commonly used. Kodak express develop-
ment data for their products in terms of contrast index
whereas Ilford use average gradient.

In order to measure average gradient a point A is located

CHARACTERISTIC CURVES: CONTRAST
INDEX AND AVERAGE GRADIENT

1-0-

1 1

// / \

// // \ y

.20

1 // X
0/7 // ^\

^rj^j;^^^

D=0-2 ___^

"^^ LOGE=20

Base+Foa Densitv i i i 1

Top: The slope of the line between the points A and B gives the contrast
index (CI). Points A and B are obtained from the intersection of arcs of
radii 0-2 and 2-2 density units, drawn from a common point on the
base + fog axis, with the characteristic curve.

Bottom: The slope of the line between the points A and B gives the average
gradient (G). Point A is 01 density units above base + fog density and
point B is 1-5 log exposure units to the right of A

on the characteristic curve 0.1 density units above the fog
level and a point B is located on the curve 1.5 log exposure
units to the right of point A. The slope of the line joining
points A and B is the average gradient (page 41).

DENSITOMETERS

The densitometer is an important accessory and is useful in a
number of different ways for testing photographic materials
and for the control of processing generally. To plot the
characteristic curves discussed in a previous chapter, a
densitometer is required to measure the density of the
photographic materials. Density measurements may, on the
face of it, appear to be very simple and all that is necessary is
to take an exposed and processed sample, place it in a hght
beam and measure how much of the incident light is trans-
mitted. However, things are not quite so simple, as the silver
deposit is in the form of relatively large particles which do
not only scatter the light, but also absorb it. Some of the
incident light will also be lost by reflection on the surface of
the sample.

DIFFUSE DENSITY

Depending on how measurement is made, a multiplicity of
numerical values of density may be obtained for a given
sample. "Specular density" is obtained when the illumination
on the sample is direct and only the directly transmitted light is
included. "Dififuse density" is measured when the illumina-
tion is direct and all the transmitted light is included in the
measurement or when the illumination on the sample is
diffused and only directly transmitted light is included in the
measurement. "Double diffuse densities" are obtained when
the illumination is diffused and all the transmitted light is
measured. The ratio of the specular to the diffused density
is known as the "Callier Co-efficient" and is related to the
graininess of the material and the conditions of exposure and
development. The type of density closely related to most
conditions of photographic practice is the "dijfuse density"
as defined in the British Standard No. 1384/1947.

OPTICAL REFLECTION-TRANSMISSION
DENSITOMETER

Densitometric control is of great assistance in producing negatives and
prints of consistently high quality. A simple but accurate instrument for
this purpose is the optical reflection-transmission densitometer. The
drawing shows the Kodak instrument of this type which makes reading
the densities of negatives, transparencies and prints a straightforward job.
Its versatility is based on a dual lighting system whereby densities are
measured visually by either transmitted or reflected light. The parts are
(a) eye piece, (b) reflection zeroing screw, (c) transmission zeroing knob,
(d) optical disc, (e) scale wheel filter holder, (f) reflection zeroing screw,
(g) reflection transmission switch.

VISUAL DENSITOMETERS

To measure the diffuse density of photographic materials,
two main types of densitometer are available, visual and
photo-electric instruments. In visual densitometers, two
beams of light are brought together in a circular field and
when the illumination of both beams is the same, the field
is of uniform brightness. When the density to be measured is
inserted in one of the beams, that portion of the field will get
darker and to restore both portions to the same illumination,
the comparison beam has to be reduced by a known amount.
In most visual densitometers in use today, the intensity of the
comparison beam is compared by a neutral wedge.

An instrument of this type is the Kodak reflection-
transmission densitometer. For transmission densities the
hght is provided by a lamp mounted in the base below a
flashed opal disc. Another lamp moimted immediately behind
the rotatable annular wedge in the measuring head provides
the comparison field. Two lamps, fitted at the lower end of the
measuring head provide the illumination for measurement by
reflected light. The annular density wedge itself is made of
methyl methacrylate and contains a carbon pigment. Its
construction ensures a uniformly linear density scale and a
high degree of stability.

Before measurement, the zero setting is first adjusted so
that the two fields seen in the eyepiece are in balance, i.e. the
outer and inner fields match in brightness. The sample to be
measured is then placed over the opal disc with the area to
be measured inside the guide lines. The light source in the
base iUuminates the sample which is seen through a small
apertiu-e in a mirror. This sample field appears in the centre
of the finder lens. The comparison light source projects the
beam through the wedge and collecting lens via the mirror,
to the finder lens, thus giving the comparison field. The
density is measured by rotating the wedge imtil the outer
comparison field again matches the inner sample field in
brightness.

PHOTO-ELECTRIC DENSITOMETERS

Photo-electric instruments are more convenient and rapid
in use. They use vacuum photocells or selenium cells. The
Baldwin densitometer belongs to the first group. It consists of

VACUUM-CELL DENSITOMETER

Using vacuum photo-cells, the Baldwin Densitometer consists of two
main units, the photometer and the density unit. The photometer {left)
consists of (a) photocell, (b) amplifier, (c) meter, (d) recorder (optional).
The transmission density unit {right) contains (a) photocell, (b) shutter,
(c) filter, (d) sample to be measured, (e) diffuser.

two main units, the photometer and the density unit. The
photometer, which houses the amplifier, has two controls
besides the on /off switch. One of these selects the density
range to be used while the other adjusts the zero setting.
The mirror scale is cahbrated to show densities between
and 1.0, and there is no compression of the scale at the upper
densities.

The range selector switch is marked 0, +1, and +2 and
in the last position densities up to 3.0 can be read. Owing to
the sensitivity of the photocell used in this instrument,
densities as high as 6.0 can be measured accurately by placing
neutral density filters of known value in the filter holder prior
to zeroing the instrument. The high sensitivity of the densito-
meter makes it useful for colour work as well: there is no
difficulty in reading colour densities through filters.

The other unit is the transmission densitometer which is so
designed that measurements can be made at any distance up to
12 in. from the nearest edge of the negative or transparency
being measured. A sliding filter holder with four openings is
available for colour work. Two aperture plates are provided
with the densitometer allowing readings to be taken of den-
sities in areas 1/16 in. and 3/16 in. in diameter.

Instead of the transmission unit, a reflection density unit
can be used for the measurement of the density of positive
prints in colour or black and white. It measures the light
reflected from a small spot about 1 in. diameter which is
illuminated by a light beam at an angle of 45 deg. The light
is reflected perpendicular to the illuminated siuface before
entering the photocell. Provision is made for the insertion
of colour filters. The density range of the reflection densito-
meter is to 3.0 accurate to within 0.02, and 3.0 to 4.0 with
a slightly lower accuracy.

An instrument based on the use of selenium cells is the
Eel Universal densitometer which is available in two models,
the Minor for surfaces up to 12 in. wide and the Major for
surfaces up to 24 in. wide. There are three apertures available:
1 mm., 2 mm. and 4 mm. diameter. To avoid errors in reading
the higher densities on the logarithmic scale two range con-
trol buttons are located on the front panel. In this way
densities from to 3 can be easily read. A layout of the Eel
Densitometer is shown on page 47.

The reflection head is available as a plug-in accessory to

SELENIUM-CELL DENSITOMETER

m n

P q

The Eel vmiversal densitometer is based on the use of selenium cells. A
standard 12-voIt, 36-watt automobile-type lamp (q) is supplied from a
stabilising transformer (k). The light beam passes through a condenser
lens (p), heat absorbing glass filter (o), an iris control for zero setting (n),
and two gauzes each of density 1.0 (m). The beam is then deflected by an
angled mirror (1) to another lens system (b) to focus on the aperture (f).
The Ught passes through the sample (d) and falls on a barrier layer photo-
cell (e) mounted at the end of the moveable friction loaded arm (g). The
current generated by the photocell is fed directly into a microammeter (i),
having an inverse logarithmic scale for direct readings of optical density.
The two gauzes (m), each of density 1.0, are controlled by two push
buttons (h). The iris control is operated by the knob (j).

PHOTOMULTIPLIER TUBE DENSITOMETER

The Macbeth Quantalog Densitometer TD-102 uses a photomultiplier
tube (c). A 6-3 volt, 40 amp tungsten bulb (m) is powered from a stabilised
source. After passing through a lens, dichroic filter and heat absorber (n)
and deflection by a mirror (1) the light beam is focused on the aperture
disc, (k) The sample is placed between the aperture disc (k) and the
diffuser (j). The light beam is then focused on the photomultipUer tube
cathode (g) by the lenses (i and h). The appropriate filter (d) may be
selected by rotating the filter selector (e).

Calibration of the instrument is accomplished by the use of a calibrated
step wedge by adjustment of the zero adjust control (a) and the calibration
control (b) so that the scale reads the correct density values.

the Universal Densitometer. A neutral filter of density 1 .0 is
normally in the light beam within the instrument and after
adjusting the iris to obtain zero reading on a white surface,
reflection densities up to 1.0 are read directly from the meter.
For higher densities, the neutral filter may be swung aside
when the meter indicates densities between 1.0 and 2.0.

Another instrument used for the rapid determination of
transmission densities is the Macbeth Quantalog densitometer
model TD-102 which uses a photomultiplier tube as the
detector. This instrument has a filter turret assembly for use in
colour as well as black and white measurements. Densities
within the range 0-4.0 and 0-6.0 density units may be measured
for colour and black and white respectively. In addition to
calibration of the instrument by adjusting the calibration
control after zeroing the instrument by the zero adjust and
using a caUbrated step wedge, the cahbration reference control
may be used. This is an internal reference filter which may be
interposed in the optical system simply by moving a lever. For
colour measurements the instrument is calibrated as before
but when the colour filters are placed in the light beam the
filter trim controls are adjusted so that the instrument gives
the required reading.

Image Structure

We have learned something of the way in which the charact-
eristic curve can throw light on development processes in
general (see page 33). Now let us follow the process of
development somewhat more minutely, especially as it
proceeds in the actual emulsion and afifects the structure of
the developed image.

If we examine an average negative with the naked eye it
appears to consist of a homogeneous deposit of black silver
with quite as regular a texture as a layer of black pigment.
If, however, we use a fairly strong lens, we shall see that the
silver deposit consists of numerous grains of quite varied
and irregular structure.

In enlargements from the negative this irregularity some-
times attracts attention in an unexpected and often unpleasant
fashion. This is graininess and it is caused by the granu-
larity of the negative image. It is the reason why one of
the most important problems in photography is the reduc-
tion of the grain size of emulsions and the use of the correct
development technique.

GRAIN AND DEVELOPMENT

Let us take a step further in our investigation of grain and
granularity and call to o^xr aid a microscope giving us a
much greater magnification. First, let us glance at an un-
developed emulsion (page 53). We can see the individual
grains of silver bromide and we note that they show crystalline
form. What happens to these grains during development?
Fortunately it is not necessary for us to carry through an
extended investigation to answer this question. That has been
done by many workers using photomicrography and cine-
micrography and their resuhs are at our disposal. From them

GRAIN AND GRANULARITY

50 ASA

125 ASA

320ASA

If we examine an average negative with the naked eye it appears to
consist of a homogeneous deposit of black silver, with quite as regular
a texture as a layer of black pigment. If, however, we use a fairly strong
lens, we shall see that the sUver deposit consists of numerous grains of
quite varied and irregular form. The larger the individual sUver grains in
an emulsion, the more sensitive it is. A film of 320 ASA is enormously
more grainy than one of 50 ASA, while a film of 125 ASA is mid-way
between the two. In an enlargement from the negative, this irregular
structure might become obtrusive and unpleasant. That is graininess,
caused by the granularity of the negative image. It emphasises the need to
choose the film and development technique most suited to the result
required.

we know that the actual process of development does not
begin equally over the whole surface of one of the grains: it
starts from some particular point on the grain. This occurs
on many grains simultaneously and gradually each grain is
reduced to black metallic silver. Where two or more grains
touch one another the whole mass tends to be reduced to a
clump of silver whose form bears no resemblance to the
original grains. Generally the developed silver grains have a
very irregular character and are much larger than the original
grain of the emulsion.

Page 53 illustrates various stages in the process of develop-
ment. We see grains in which development has just begun,
others in which it has advanced some distance and yet others
where development is complete and the whole grain has been
reduced to metaUic silver.

Both the character and the size of the silver grains can be,
and are, enormously influenced by the development process.
For example, by developing for a short time, we can obtain a
very fine-grained silver deposit, but only by sacrificing all that
full development can give us, and particularly the advantage
of the full sensitivity of our material.

The granularity of negatives is naturally a fxmction of
the properties of the emulsion itself and the photo-
graphic manufacturer exercises all his ingenuity and care
to ensure that his emulsions shall be as fine-grained as
possible. Nor do his efforts cease with the attainment of
small single grain size. He equally takes every possible pre-
caution against any clumping together of the grains in the
emulsion.

The graininess which so often mars an enlargement is not
due to the size of single grains, for these are far too small to
cause such an effect. It is caused by apparent clumping
together of the grains. In a photographic film there may be up
to 40 or 50 grains in layers on top of one another. De-
veloped photographic deposits thus appear irregular; there
seem to be large masses of grains which produce compara-
tively large masses of reduced silver in the negative. The mere
touching of grains in the emulsion can help to this end, for,
as we have seen in our study of the development process, a
developable grain in contact with another which has re-
ceived no exposure usually means that both are developed.

THE SILVER BROMIDE GRAIN

This diagrammatic representa-
tion of two emulsion grains at a
very high magnification shows
that development begins at definite
centres on the grain (top). These
centres grow and soon the original
form of the grain is altered by the
appearance of reduced silver, which
alters the outward form of the grain.
As the development proceeds, it is
seen that the reduced silver in the
two adjacent grains bridges the gap
between them and so forms one
large, irregular grain of developed
silver ^bottom). The effect of a fine-
grain developer is to develop the
single grains and to obviate the
clumping together of adjacent
grains.

GRANULARITY AND GRAININESS

The terms "granularity" and "graininess", as used in the
preceding paragraph have very definite meanings, although
they are often misused.

Granularity refers to the grainy structure of the photo-
graphic silver image itself and can be evaluated in measurable
terms. Graininess is the inhomogeneity we see as a result of
granularity, i.e. the visual subjective appearance of this
pattern. The graininess produced by a material of a certain
granularity varies with the conditions under which we look
at the result.

The cause of the granularity of the negative has
already been considered. The grainy structure — granu-
larity — is responsible for the visible efifect of graininess
in the print, which becomes worse at greater degrees of en-
largement.

The subjective impression of graininess depends also on
the viewing distance and is less noticeable as the distance
increases. In practical photographic terminology we use
granularity mainly in connection with the negative while
graininess refers mainly to the print. These terms have a
different meaning although they are often used in the same
sense.

NEGATIVE GRANULARITY

The granularity of the negative depends on:

(1) the negative emulsion. The granularity of an emulsion
increases with an increase in speed. High-speed emulsions
have a high granularity and the graininess becomes noticeable
at enlargements of 8-10 diameters. Medium-speed emulsions
can be enlarged by more than 10 diameters without producing
an objectionable degree of graininess.

(2) the exposure. The negative density should be kept low
as higher density leads to an increase in granularity. The
exposure should therefore be as short as it is consistent with
good tone reproduction.

(3) the developer. The correct choice of developer is of
primary importance, as is explained on pages 64-66.

(4) the conditions of processing. To achieve the optimum
result with the chosen developer, time and temperature must

be controlled carefully. These conditions have to be adjusted
in such a way that the correct gamma is obtained (page 38).

PRINT GRAININESS

The graininess of the print is influenced by the following
factors:

(a) The type of enlarger.

(b) The contrast and the surface structure of the
paper.

Contrast in enlarging increases graininess. If the same
negative is enlarged on two papers with different degrees of
contrast, the print on the more contrasty paper shows more
graininess. This does not provide an easy method of con-
trolling graininess because the choice of paper is determined
by the contrast of the negative. We choose the paper that
gives the best possible relationship between the tone repro-
duction of the print and that of the original scene. Graininess
in the print can, however, be somewhat suppressed by the
choice of a paper with a matt or, still more, a grained surface.

In a similar manner, the condenser-type enlarger en-
hances contrast and leads to more noticeable grain than a
diffused ("softer") Ught source. Any measure which reduces
the sharpness or contrast of the print, such as the use of
soft-focus lenses or similar devices will, of course, reduce
graininess too.

Graininess is much less obvious if the enlargement is
viewed from a distance. The grain may therefore be less
noticeable in very big enlargements which can be viewed from
comparatively large distances.

RESOLVING POWER

The grain size of the film emulsion effects the quality of the
print not only because graininess depends on it, but also
because it controls the image resolution. Fineness of grain
results in smoothness of tone in the picture and also affects
its fineness of detail. This ability of the emulsion to record
fine details is its resolving power.

The resolving power is measured by photographing on a
reduced scale a test object consisting of sets of lines of

decreasing size separated by spaces having a width equal
to the width of the lines. The photographic test is examined
under magnification to determine the finest set of Unes which
can be individually distinguished. The numerical value of
resolving power is the number of lines per millimeter.

Resolving power depends mainly on the grain size of the
emulsion and to a lesser degree on the type of the de-
veloper. A high-energy developer, while producing maximum
speed, leads to greater granularity than one of lower activity.
To obtain minimum graininess the first rule is to chose the
finest-grain film that has sufiicient speed for the pmrpose in
question.

The fineness of the silver grain is, however, not the only
factor determining the visual quality of the picture. Often,
an image which appears sharper than another is actually
much coarser in grain.

IRRADIATION

To understand the difference between the effects of these two
factors (grain size and developer energy) on the image
quality, we must give a little attention to another phenomenon
which takes place in the emulsion. We must investigate the
way in which a beam of hght acts and how it progresses as it
passes into the photographic layer.

The photographic emulsion is what the physicist calls a
turbid medium and one of the notable properties of turbid
media is their power of scattering hght. Hence, when a beam
of light falls on a photographic emulsion it does not pass
directly through it as would happen with a transparent
medium. It is scattered and so may reach areas which are not
subject to direct illumination.

This is illustrated on page 57 where we have a highly
magnified section of a film, protected by an opaque mask
which allows a very fine ray of hght to pass through a tiny
aperture. This ray of hght is scattered by the turbid medium,
the emulsion, and so spreads laterally, thus affecting areas
which are actually protected from direct light by the mask.

It is quite easy to see that if the mask had two tiny
apertures close together, each allowing a tiny beam of light
to fall on the emulsion, the lateral spread or scatter of the
hght in the emulsion would result not in two points affected

IRRADIATION

The photographic emulsion is a turbid medium and therefore has the
property of scattering light, a process which can seriously affect the
sharpness of the image. The diagram shows a highly-magnified section of
an emulsion which has been covered by a sheet of metal with a small
aperture through which a beam of light falls on to the emulsion. With
a very short exposure, only the point where the light meets the emulsion
will be developed. But if the exposure is longer, the light is scattered so
that it spreads beyond the area protected by the metal, and hence irradia-
tion takes place, although the area affected by the scattered light is actually
protected by the metal cover.

by light, but in one diffuse area much larger in extent than
either of the points due to the direct action of light on the
film. It is obvious that this scattering of light will affect the
image quaUty and interfere with its sharpness.

HALATION

If we follow the track of light further through the emulsion
and into its support, we shall see that when it meets the film-
base /air inter-face at a particular angle, it is reflected back
into the film and can reach the emulsion again, thus producing
halation. Various methods of reducing halation are shown
on page 61. A light absorbing filter layer is coated either on
the back of the film base or — better — between the emulsion
and its support. Another method consists in dying the film
base itself. By these means halation can be restricted but never
completely eliminated.

IMAGE SHARPNESS

These two phenomena of irradiation and halation, in addition
to the grainy structure of the emulsion, can have a very
adverse effect on the quaUty of the image. They cause blurring
of the image and the sharpness of line suffers. The change in
density along the line of separation between a light area and a
dark area is not sufficiently abrupt and sharp to produce a
crisp image. It is the degree of abruptness of the change in
density along the hard line of separation between a Ught and
a dark area that determines the "sharpness of definition" or
"image sharpness".

The physical measiuement of image sharpness, in this
sense, is called acutance. It is a measiure of the abruptness of
the change in density along the Une of separation between a
light and dark area. The steeper the transition, the higher
the acutance. The ability to obtain negatives of high acutance,
capable of producing pictures of the best possible sharpness,
depends in the first place on the properties of the film (see
page 63).

When the bulk of camera work involved mainly contact
printing or low degree enlargements from negatives of fair
size, the interests of the majority of camera users were con-
sidered to be best served by films having the maximum

EMULSION THICKNESS

Top: A ray of light which enters the emulsion of the film is scattered
inside, so that a sharply- defined point is not formed in the negative.
Instead, a dark circle is formed round the central black dot, which becomes
less and less dense towards its edge. The "definition" of a film is thus
greater when its emulsion is thin than when it is thick.

Bottom: Increasing the exposure latitude of a film by using a double-
coated emulsion. The lower emulsion is less sensitive than the upper one,
and if a flat image appears in the top one because it is given excessive
exposure, the lower emulsion is affected and adds density where the single
top emulsion would have lost it.

ORIGIN OF HALATION

When a beam of light of sufficient strength falls on the emulsion, it
not only passes through the emulsion but also through the film support.
When it reaches the film-air boundary, it will be reflected back to a greater
or lesser extent, depending on the angle at which it meets the boundary
surface. In this way, it again reaches the emulsion on the under side and so
produces a developable spot or halation. In the diagram, two forms of
reflection are shown. In the case of the light falling at a steep angle, part
of it is not reflected back and the part which is reflected is therefore of
comparatively low intensity. The light which falls at a wider angle suffers
almost complete reflection and hence the effect is much more marked.

PREVENTION OF HALATION

.i/i II ■;■!'.'• ' ■.•; ' • ' !■ ' • • • 1 . 1 > Ti

. Emulsion
Anti-halo Layer
Glass

;:j:|:i:i:W:i:::::::::::;:::::::::::::::::::::v:::::::::::::::v:;:

"WW

v:;:v:;:;:;:i:|:

-Emulsion
Glass
- Anti-halo Layer

-Emulsion
-Coloured Support

In the diagram, three methods are shown whereby halation can be
prevented. First, by the introduction of an anti-halo layer between the
emulsion and the support. Secondly, by the coating of the back of the
film with an anti-halo layer. This absorbs any light which passes through
the emulsion and prevents it being reflected back. Third, halation is
prevented by coating the emulsion on a coloured support. This method is
used largely with films for miniature cameras.

exposure latitude. This led to the introduction of double-
coated roll films capable of recording a wide range of
exposures.

These films consist of a highly sensitive upper coating
which rests directly upon a much less sensitive emulsion. The
combined action of these two emulsions confers a wide lati-
tude in exposure to the film. In cases of overexposure, for
example, which would normally produce a flat, inferior
negative, the lower and less sensitive emulsion takes over to
increase the total range and so ensure a printable negative
(see page 59).

From the point of view of image sharpness, however,
such films are far from ideal. The thick, double coating is
particularly susceptible to scattering of light and the image
is more or less blurred. Where only contact copies or small
enlargements are required, this may not be a matter of great
importance. The lack of definition is, in fact, hardly noticeable.
But for greater enlargements the double-coated film or indeed
any thick-coated film is totally unsuitable.

As modern camera technique prefers the use of small
negatives requiring high degrees of enlargement, the question
of good exposure latitude must take second place to good
definition. Thinner coatings of higher turbidity offer less
opportunity for scatter within the emulsion and the image
sharpness is consequently increased. These films, with a single
thin coating, have a comparatively hmited exposure latitude,
but this is no problem for the modern photographer with an
automatic camera or a rehable exposure meter at his disposal.

MODULATION TRANSFER CHARACTERISTICS

Modulation transfer characteristics indicate the effects on
the microstructure of the image caused by diffusion of light
within the emulsion. The results can also be modified to a
certain extent by development effects.

The term "modulation transfer" has been introduced by
Kodak Research Laboratories in place of what has been
variously called "sine-wave response", "contrast transmission
fimction" etc., in accordance with recommendations made
by the International Commission for Optics.

In obtaining these data, patterns having a sinusoidal
variation m illuminance in one direction are exposed on to the

ACUTANCE OF EMULSIONS

Exposure

A highly magnified section of a film protected by an opal mask (A).
With increasing exposures the light is scattered and may reach areas which
were not subjected to direct illumination (B, C and D).

film (see page 65). After development, the photographic image
is scanned in a microdensitometer, the densities of the trace
are interpreted in terms of exposure, and the effective modula-
tion of the image is calculated. The modulation transfer is the
ratio of the modulation of the developed image to the modula-
tion of the exposing pattern. The modulation transfer curves
show a plot of this ratio as a function of the spatial frequency
of the patterns in cycles per millimeter. By multiplcation of
ordinates of the individual curves, the modulation transfer
data for a film can be combined with similar data for the
optical system with which it will be used, to predict the final
image-detail characteristics.

In the illustration, page 65, the bottom panel is the sinu-
soidal test object, the next panel the photographic image
magnified to the size of the original test object, and above
that the microdensitometer trace of the image. After the
characteristics of the lens have been taken out, a plot of
the eff"ective exposure of the film alone is shown in the curve,
i.e. the effective distribution of light in the test object. This
is the modulation transfer response of the film alone. Usually
the scale of frequencies is either linear or logarithmic, but in
the illustration it is arranged so as to correspond to the
frequency of the original test object.

Two typical modulation transfer curves are shown on
page 65, one representing a high speed negative film, the
other a low speed positive film. The right-hand graph in each
case is on an arithmetic scale, while the left-hand graph is on
the logarithmic scale. The latter-type curve not only has
theoretical advantages, but is also easier to use when curves
must be combined with technical data for other components
of a system for study and evaluation of the overall perform-
ance characteristics.

THE CHOICE OF FILM AND DEVELOPER

The modern high-acutance films are not only inherently
capable of giving improved image sharpness, but they also
lend themselves to a special processing technique which
artificially enhances image sharpness. This method involves
the use of so called "high definition" developers (see
page 214) which take advantage of the edge-effects described
on page 77. This results in the production of a much harder

MODULATION TRANSFER CHARACTERISTICS

{Right, bottom): The sinu-
soidal test object and the
phocographic image magnified
to the size of the origmal test
object. {Right, centre): The
microdensitometer trace of the
image. {Right, top): A plot of
the effective exposure of the
film, i.e. effective distribution
of light in the test object.

(Below): Typical modulation
transfer curves representing
in the upper pair a high-speed
negative film and in the lower
pair a low-speed positive film.
In each case, the left-hand
graph is on a logarithmic
scale, the right-hand on an
arithmetic scale.

\„

SfAIlM FtlOUINCT {itc\nl'"f\

s ^

and more abrupt change of density across the line between
light and dark areas, which gives the impression of much
increased sharpness. The term acutance is applied to a rather
complicated mathematical measurement of the rate of change
of density across this edge (see page 216).

Wherever circumstances allow it, it is clearly best to
choose a high-acutance film to be processed in a high-
definition developer. A limitation to the use of these thin-
coated films, however, is their comparatively slow speed.

In general the choice of a negative developer is governed
in the first place by the size of the negative in question, apart
from cases where the nature of the negative material itself
requires special developers. For sizes larger than 2J X SJ in.
any type of standard negative developer is likely to prove
entirely suitable. For roll films, the first choice will usually
be a standard fine-grain developer (Table XXXI). For minia-
ture films there is the choice between fine-grain, super fine-
grain and high-definition developers as we shall see later (page
202).

In all cases, for the best results the degree of development
of the negative must be adjusted to the characteristics of the
printing (or enlarging) equipment and material. Basically it is
best, from the points of view of print quality and working
convenience, to adopt a technique by which the majority of
average negatives print best on to medium-contrast paper
under normal conditions of enlarging. Expressed in gamma
values (page 35) this means that sheet films should be de-
veloped to a gamma of approximately 0.8, while a somewhat
lower gamma — 0.6 to 0.7 — is generally adopted for roll and
miniature films.

OPTIMUM EXPOSURE

Every photographer should be aware of the fact that his
success depends in the first place on the correct exposure
of the film in the camera. First, however, let us define what
we mean by the term "correct exposure".

In the early days of photography, the aim was for all the
tones of the negative to lie in the straight-line portion of the
gradation curve (page 37). This is useful insofar as the nega-
tive then renders the various brightness areas of the scene in
their true ratio of values. But this does not necessarily mean

that the same is true for the print, because we also have to
take into consideration the curve of the paper which is by
nature much shorter than that of the negative. This deficiency
in the tone rendering properties of the paper can be com-
pensated for to some extent by the deviation of the negative
curve from the straight-line form. To achieve this, the camera
exposure must be kept on the short side so that the shadow
values of the scene fall on the "toe" of the gradation curve
(page 37).

The old rule that it is better to over-expose than to
under-expose, still stands in cases of emergency when the
photographer is in doubt about the correct exposure. To
make sure of a printable result it is certainly better to choose
an ample exposure rather than a too short one. But this does
not mean that over-exposure is advisable as a general rule.
On the contrary, for the reasons explained above it is the
modern practice to reduce camera exposure to the minimum
consistent with good rendering of shadow details.

QUALITY OF THE NEGATIVE

Finally let us summarise the main factors on which negative
quality depends:

(1) Tone gradation.

(2) Fineness of grain.

(3) Sharpness of definition (acutance).

(1) Tone gradation. From the practical point of view, it is
desirable that the tone gradation of the negative allows the
choice of a paper of medium contrast. To produce such
negatives is mainly a question of correct development, a
suitable developer at the right developing time. By adequate
exposure we have made sure that the shadow details of the
subject will be rendered in the negative, provided of course
that this is not spoiled by under-development. Likewise we
have to make sure that the high-light areas in the negative
are printable. For the visual assessment of the negative we
can use the following procedure: If the negative is held close
to a printed sheet in good light, the letterpress should just be
readable through the densest parts of the negative.

To produce negatives of good printable quality, the
gamma (page 35) of the characteristic curve should be kept

within 0.7-0.9 by controlling the developing time. This range
of ganuna permits, too, quite a good exposure latitude.

For special purposes, such as press or industrial photo-
graphy, negatives of a gamma between 0.9 and 1.2 are often
preferred. The exposures must then be more accurate to
avoid the production of negatives which are very dense and
therefore rather inconvenient to print.

Correct exposure and correct development will lead to
a negative of good tone reproduction. There is however,
another factor that might seriously interfere with the result,
namely the non-image forming glare light. This can arise
from several sources, such as hght scattered or reflected by
the glass-air surfaces of the lens system, by flare in the glass
of the lens and by dust or finger prints on the lens surfaces.
Light can also be reflected from the lens mount, the iris and
the shutter blades. Flare light can reduce the tone scale
considerably because it has a much greater effect on the
shadows than on the highlights. While a certain amount of
flare light is inevitable, it should be kept to the minimum by
cleaning the lens and by using a lens hood.

(2) Fineness of grain. Granularity is primarily a property of
the film emulsion and is largely determined by its speed.
However, we have already seen that the development has a
certain effect on the quality of the negative in this respect,
too. To obtain a negative of low granularity, exposure should
be kept to the minimum and a fine grain developer should
be used.

The finer the grain of the emulsion, and the better it is
preserved by correct negative technique, the higher the image
resolution (page 55), i.e. the ability of the film to record fine
details. Even under these conditions a kind of graininess can
be obtained which is in fact due to microreticulation caused
by unsatisfactory control of the temperature of the processing
solutions. It is therefore important to control not only the
temperature of the processing solutions themselves carefully,
but — imder extreme conditions — even the temperature of the
wash-water.

(3) Sharpness of definition (acutance). The quaUty of the
image does not depend only on the fineness of the grain. In-
deed, it has been found that an image which appeared sharper
than another was in fact considerably coarser in grain. We
have therefore to deal with two different factors: the fine-

ness of the grain determines the resolution i.e. the rendering
of fine details, whereas the sharpness of the contours of the
objects of the scene depends on the acutance of the negative.

Assuming the optical system can produce a sharp image,
the degree of sharpness actually obtained depends on certain
properties of the photographic emulsion and on the pro-
cessing technique. We have already dealt with the emulsion.
So, where good definition is of primary importance, a high-
acutance film should be chosen, i.e. film with a thinly coated
emulsion of high turbidity (page 62).

The image sharpness can further be enhanced by the
choice of a high-definition developer. These developers make
use of the adjacency effects (page 214) and we shall have to
deal with their formulation and application later on.

The Progress of Development

It might be expected that in the case of thinly-coated
emulsions the process of development would take place
through the whole film simultaneously ; this is, in fact, rarely
the case. Development almost invariably commences at the
surface exposed to the developer and only slowly progresses
into the interior of the emulsion (see page 71).

This is partly dependent upon the fact that the gelatine of
the emulsion layer must swell in order to permit the de-
veloper to diifuse into it. Also as the developer acts on the
silver bromide it naturally is used up or exhausted and
development can only progress if the used-up developer is
replaced by fresh solution. Naturally, the exposed silver bro-
mide is not distributed evenly throughout the film.

THE RATE OF DEVELOPMENT

The manner in which the developer acts and the speed with
which it penetrates the emulsion layer is largely dependent
on the nature of the developer. Later on we shall discuss the
differences between surface and depth developers in some
detail.

One factor which plays an important part is the energy of
the developer; an energetic developer produces a heavy
density at the surface of a film before it has had time to
penetrate to any depth, whereas a less energetic or slow-
working developer will produce an equal density only when
it has had time enough to penetrate into the emulsion and
to develop the deeper layers. This difference is shown
diagrammatically on page 73. Both films have the same
density to transmitted fight, but the distribution of the
developed grains is different, those in the film developed with

PROGRESS OF DEVELOPMENT IN THE FILM

""* y,t\:':-j

V.'i'.; ..vj ij-.'„.-.?'..'.i j...V.'v-^

The clock faces show the passages of time during development and
the sections show how development proceeds. We see that development
begins at the surface of the film and progresses downwards into the
thickness of the film. This method of progress is dependent upon various
factors. First, the gelatine must swell to permit the difiusion of the
developer. Next, as the developer is used up in development, it is essential
that there should be a free flow or diffusion of the developer in order that
action may take place in the deeper layers of the film. Hence while progress
at the surface is rapid, later on more time is required for the developer
to penetrate and act on the inner portion of the emulsion.

the weak developer being much more widely and deeply
distributed than is the case in the film treated with the ener-
getic developer.

THE INFLUENCE OF TEMPERATURE

As is the case with most chemical reactions, and photo-
graphic development is a chemical reaction, the rate of
development depends upon temperature. The higher the
temperature of the developer the more rapid and energetic
will be the progress of development. This rule holds good
for all developer substances but the actual degree of accelera-
tion for a given rise of temperature varies with the different
developers.

The increase in speed of development with an increase
of 10°F. is taken as the Temperature Coefficient of the
developer. For example if we find that a particular de-
veloper works twice as quickly at 75°F. as it did at 65°F.
then we say that it has a Temperature Coefficient of 2.
The following table gives a rough guide to the time-tempera-
ture relationship of the three main types of developer,
assuming Temperature Coefficient of 1.8 for standard MQ
developers, 1.6 for fine-grain and 2.3 for super fine grain
developers.

I.— TIME-TEMPERATURE TABLE FOR STANDARD DEVELOPER GROUPS

Super

M.Q.

Fine Grain

Fine Crain

"F.

°C.

Min.

Temperature

Coefficient

1.8

1.6

2.3

The Temperature Coefficient is not solely influenced by
the developer substance; the formula, and in particular the

RAPID AND SLOW DEVELOPMENT

The diagram shows two plates, each of which has been given a long
exposure on one half and a short exposure on the other half. In the case
shown on the left the negative has had a rapid development, that on the
right a slow development. But in both cases overall blackening has
resulted. The energetic developer A has caused a strong blackening on
the surface of the film, while the slower developer has attained a like
blackening, but has required much more time. The developer A gives a
strong surface image, while developer B has given rise to an image which
is much deeper in the film, although both pictures appear to have the
same contrast when examined by transmtited light.

quantity and type of alkali present, plays a part. Thus, each
developer has its own Temperature Coefficient. Nevertheless,
for most practical purposes, this can be taken as 2. That
means that development time should be halved for each 10°F.
(6°C.) rise in temperature.

A development temperature of 20°C. (68°F.) is usually
considered as normal, but there is a trend towards using a
higher temperature (24°C.,75°F.) as it is easier to warm a
solution than to cool it.

For convenience most manufacturers pubhsh charts for
their particular films and developers from which it is possible
to read the appropriate development times for various temper-
atures. A typical time- temperature chart for the development
of negative materials is illustrated on page 75. In order to
estimate the development time at a temperature other than
20°C. (68°F.) the diagonal line from the recommended time at
20°C. is followed until it cuts the horizontal line representing
the actual temperature to be used. The new development
time at this temperature is then read from the bottom line of
the chart vertically below the intersection. Thus if the recom-
mended development time is 8 minutes at 20°C. (68°F.), at
24°C. (75°F.) the required development time will be 5^ minutes
and at 18°C. (65°F.) it will be 10 minutes.

WHEN IS THE DEVELOPER EXHAUSTED?

This very practical question is difficult to answer by any
simple and generally applicable formula, because the useful
life of any developer depends upon a whole series of factors
not easily assessable.

Of these the most important is the quantity of negative
material which a given volume of developer solution wiU
develop. It is also important to consider whether all the
developing will be done in one big operation or, on the other
hand, if intervals of time will occur between one batch of
developing and another. The class of material developed will
also play a part, the thickness and the type of emulsion, its
content of stabihsing constituents and the extent to which
they will retard the development process. Another factor
is the amount of surface of the developer exposed to the
influence of atmospheric oxidation and the time of such
exposure.

TIME-TEMPERATURE CHART

75-

\ \

5 6 7

8 9 10 li 14 1

6 18 20 2

i 30

, s,

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V ^

s \

\ '

A\\ V

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V^3a\^~'^^^

Vvu '^ \ \ '^

AAA

v\K \ \\

^68

■ 1

2—

-r

3 '

— 5-6-7
\ \ \

-8-9-10-12-14-1
\ \ \ \ \

S-18-20

\ \ \

Va^-

^A^XAA

^^A=

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^^U^^

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-S ^^

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V T

^^r-0>AA

^r-VV

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aZ-^ ^

vA^Aav

A VV

b o

3" \^

5^V^A

VV^

v-^ A

v^Xvv

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Vv-'^r

A v^AA

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22 0)

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7 (D

a
6-E

r/2 2 2^2 3 4 5 6 7 8 9 10 12 14 16 18 20 25 30

Time of Development in Minutes

A typical time-temperature development chart published by Ilford Ltd
from which it is possible to read development times at temperatures other
than 20°C. (68°F.).

Finally it must not be overlooked that it is not the
total area of film that is to be thought of as contributing to
the exhaustion of the developer but only that part which
has actually imdergone development.

For all these various reasons any direct or comprehensive
answer to our question is not easy. For the majority of
developers in use today, details will be found in the directions
for use which will indicate the quantity of material develop-
able by unit quantity of developer and wiU also usually say
what extra time of development should be allowed after a
certain number of films have been developed. In some cases
the necessary replenisher is given and this is a matter that
should receive the attention of all careful and economical
workers.

Table II gives approximate figures for the keeping
properties and useful capacities of various developers in
common use.

II.— KEEPING PROPERTIES AND USEFUL CAPACITY OF DEVELOPERS

♦Stock **Sheets8' x 10'

solution Working Solution per I gallon

in full (4.5 litres)

bottles Dish Tank

D76, DK20 6 months

24 hours

1 month

D23, D25 6 months

24 hours

1 month

Dll, D50, D93, IDII.

ID36, ID62, ID68, D60a 6 months

24 hours

1 month

DI9, IDI9, ID72 6 months

24 hours

1 month

60-80

♦Partially-filled bottles one-third of full-bottle life.

** Approximate equivalents: I rollfilm 120; 2 rollfilms 127; I 35 mm. film (36 exposures);
I i sheets 6^ X 8i in. or 18 X 25 cm.; 2i sheets 4i X 6i in. or 13 X IS cm. 4 sheets 4 X 5in. ;
6 sheets BJ x 4i or 9 X 12 cm.

DEVELOPER REPLENISHERS

The decrease in developer activity with use can be overcome
up to a degree by increasing the development time. The better
procedure and the only one when large quantities of solutions
are involved is to compensate for developer exhaustion by
adding small quantities of replenisher solutions at intervals
as required. These replenishers are usually of such strength

that when used to replace the developer carried out on the
film, the developer activity is kept approximately constant.

The quantity of developer carried out with the film varies,
of course, according to the processing conditions. If after
replenishment the developer is still below normal activity
some of the old developer must be discarded and more
replenisher added. If, on the other hand, the developer tends
to gain strength from replenishment the replenisher should
be diluted with water (say, two parts replenisher with one
part of water). The diluted solution is then added to maintain
the working solutions at the required level.

Small volumes of developers are best replenished by the
addition of a definite quantity of replenisher for each roll or
sheet film, processed. Usually the developer activity will be
satisfactorily maintained by adding 1 oz. of replenisher for
each 80 sq. in. of film.

This is equivalent to:

1 sheet 8 in. x 10 in.
or 4 sheets 4 in. x 5 in.
or 1 roll film 120 (620)
or 1 35 mm. film of 36 exposures

The following procedure is recommended. After pro-
cessing, for instance, one roll film, pour 1 oz. of replenisher
solution into the empty developer storage bottle. Then return
enough used developer to the bottle to bring it up to the
original volume, discarding any excess. If the original volume
is not reached add imused developer solution or replenisher
diluted two parts with one part of water.

It is naturally inadvisable to exhaust and replenish a
developer indefinitely because the solution accumulates a lot
of foreign matter such as particles of gelatine, silver sludge
etc. The developing solution should be examined carefully
and discarded when its condition makes it advisable. De-
veloped films should also be inspected carefully in order to
find out whether they show any indication of the developer
giving trouble such as variation of contrast and density,
stain, and fog, etc. Test strips can be used for this purpose.

DEVELOPMENT EFFECTS

Some development effects are phenomena of only scientific
interest and we shall not deal with them here. Others have

an important bearing on the course of development and
even on the quahty of the result.

These phenomena can best be demonstrated by giving one
half of a film a strong exposure, the other half only a weak
exposure. The sharpness of the boundary between the two
areas of diiferent density suffer not only from the emulsion
effects of "irradiation" and "halation" (pages 56, 58) but also
from adjacency effects in development. In the area of low
exposure the developer has little work to do. So, relatively
fresh developer passes to the area of intense exposure and
assists its development just across the border line, where it
produces a small region ofincreased density. This phenomenon
is called the border effect.

On the other hand, reaction products from the develop-
ment of the heavily exposed area diffuse into the lightly
exposed part and retard its development near the boundary.
This creates a region of lower density than that of the re-
mainder of the lightly exposed area. This phenomenon is
referred to as Xht fringe effect. The two lines so created have
also been called Mackie lines.

A microdensitometer curve showing the variation in
density across the line between the two areas has the appear-
ance shown on page 216. The two edge effects are rep-
resented by the increase in the density on one side of
the border and by the depression in density on the other side.

A special form of the border effect is the Eberhard effect.
Between two small areas of different size, but equal exposure,
the smaller area will in general have the higher density.
Again the reason is the action of the non-exhausted de-
veloper which is available for this area.

As we shall see in the next chapter, these development
effects can cause trouble. We shall, however, also learn that
controlled use of these developing effects can actually im-
prove the quality of the negative. It is worth mentioning that
Phenidone developers give much weaker edge effects than
MQ developers.

THE INFLUENCE OF AGITATION

It is self-evident that agitation of the developer can have
a considerable influence on the development effects described
in the preceding paragraphs.

Let us consider first an extreme case in which the solution
is completely undisturbed and suffers no agitation whatever.
In such a case the areas close to highlights will be occupied
by increasing quantities of exhausted and bromide-rich
developer and as a result the development will be slowed
down.

In the shadow area of the negative the developer will
naturally be only slightly affected because only small amounts
of silver bromide have to be reduced; therefore development
proceeds unaffected. This means that in the highlights
development is restrained and the contrast of the negative
is diminished. In addition, markings of varying density may
be developed which, as we shall see later, (page 394) can
produce serious faults.

Next, let us consider a case in which the negative or the
developer solution has hardly been stirred, certainly not
sufficiently to move the exhausted developer away from the
surface of the negative quickly. That means that the major
part of the developing has to be done by this exhausted
developer and that entails a greater or lesser degree of
retardation of the development. This emphasises the fact
that the agitation of the developer is no matter of insignifi-
cant influence on the speed of the development but is of
particular importance as regards the time of development
and the contrast of the negative.

Hence we should ensure by good agitation of the de-
veloper that the exhausted solution is replaced by fresh de-
veloper as quickly as possible and that throughout the process
the developer is maintained in a well-mixed condition. This
does not necessarily mean constant agitation, although steady
movement is advisable.

As an example of the effect of agitation on the progress of
development, it may be taken that where intermittent agitation
is used about 50 % longer development time should be given
than would be considered necessary with constant movement.

The Composition of the Developer

A developer consists of many different chemicals, mainly:

(1) The developer substance,

(2) The preservative,

(3) The alkali (or accelerator),

(4) An agent which restricts fog formation or slows
the action of the developer as a whole.

The nature of the chemicals, as well as the relative quantities
present, govern the properties of the developer to so great
an extent that it is important to understand exactly the role
of each constituent.

While it is correct to say that the most important consti-
tuent of any developer is the developing agent itself, it does
not appear correct to commence a description of a developer
with the actual developing agent for the simple reason that
it is the composition of the solution that plays the dominant
part in determining the photographic properties of the
developer. We know, for example, that many developing
agents can provide slow acting and weak, or rapid and
contrasty developers according to the composition of the
solution and the relative amotmts of preservative and alkali
present. The photographic behaviour of the developing
agent is therefore less a fimction of the substance itself than
of the total composition of the developing solution. Hence
it appears logical to deal first with the other constituents and
to explain their effect on the developer substance.

THE PRESERVATIVE

Development, as we have already seen (page 22) is a reduction
process, in which silver bromide is reduced to silver and the
developer substance itself undergoes a change, being oxidised.

It has to be noted, however, that the development process
itself is not necessary for the oxidation of the developer.
Mere exposure to the oxygen of the atmosphere will quickly
oxidise the developer and render it useless. To prevent this
oxidation taking place, or at least to reduce its rate, a pre-
servative is added to the developer and the most widely used
substance for this purpose is sodiiiin_.sulphite.

Sodium Sulphite

Sodium sulphite plays an important part in the developing
process itself. The oxidation products of the developing
agents, formed during the reduction of the silver halide,
have an undesirable eifect on the developing process. Some of
these products can accelerate the developing process, while
others have a retarding effect. Both effects are undesirable
because they make control of development considerably more
difficult.

Furthermore, most of the oxidation products decompose
to usually coloured compounds which stain the gelatine of
the emulsion. In certain cases use is made of this effect by
the controlled addition of a limited amount of sulphite to
the developer. The stained oxidation products are then
formed in situ with the dyed image which can be useful to
;increase the printing density of the negative.

By adding a sufficient quantity of sulphite, the formation
'of these products can be almost completely prevented. In the
case of hydroquinone for example, its oxidation product
quinone combines with sulphite to produce a sulphonate.
This is a colourless, water-soluble product which has practic-
ally no effect on the course of development.

Another important property of sulphite is its solvent
action for silver halide. It can therefore have a noticeable
influence on the graininess of the silver image. This action
of the sulphite will have to be considered in greater detail
in the chapter on fine grain developers.

Sodium sulphite comes in two forms, as a crystallised
salt and as an anhydrous powder. The crystalline form is
more commonly used, but the anhydrous salt is to be
preferred. One part by weight of the anhydrous salt is the
equivalent of two parts by weight of the crystalline. In all
other respects the two salts are similar in their action.

The anhydrous salt is often preferred because of its better
keeping qualities; the crystallised salt tends to change in the
air and the decomposition gives rise to sodium sulphate
which does not act as a preservative in developers. Another
advantage of the anydrous salt is that it dissolves quickly and
easily.

Generally speaking the purity of the anhydrous sodium
sulphite on the market leaves nothing to be desired. This
is of particular importance in compoimding fine-grain de-
velopers which often contain a high proportion of sulphite
and in which the sulphite plays quite an important role other
than that of preservative.

As, however, the principal object of adding sulphite to a
developer is to guard against the oxidation of the developer
substance by the oxygen of the air, it is naturally important
to adopt a definite sequence of operations in compounding
a developer and in general the order of addition of the
components to the solution should be:

1. Sulphite. 2. Developer substance. 3. Alkali.

This order should not be varied unless special instructions
are given with any formula for some other order to be
followed.

Bisulphites

It is sometimes advantageous to replace sulphite by bisulphite,
and the salt most generally used for this pmT)ose is either
potassium or sodium metabisulphite.

There is an important difference between sulphites and
bisulphites in that solutions of sulphites are weakly alkaline
whereas solutions of bisulphites are distinctly acid. This
difference materially affects the properties as well as the
applications of the two salts.

Developing agents or substances, with certain special
exceptions, are only active in alkaline solution, hence when
bisulphites are used there must be sufiicient alkali present
in any normal developer to neutralise the free acid and
convert the bisulphite into sulphite. In practically all pub-
lished formulae it will be seen that the proportion of alkali
present is ample for this purpose, the only exceptions to this
rule being special developers such as those based on amidol

and cenaiii of the fine grain and physical developers which
will be discussed later in this book (pages 202 and 218).

Potassium metabisulphite is sometimes objected to on
account of expense and sodium bisulphite suggested as a
substitute. The sodium bisulphite of commerce is mainly
sodium metabisulphite and not the sodium hydrogen sulphite
which comprises true sodium bisulphite. This is no disad-
vantage to the photographer and he can at all times replace
potassium metabisulphite by an equal weight of the sodium
sah, as the properties of the two materials are practically
identical.

Another form in which bisulphite is sometimes recom-
mended, especially in Europe, is bisulphite lye, which con-
sists of a concentrated solution of sodium bisulphite con-
tainmg about 10 oz. of sohd bisulphite in 32 oz. of solution.
(It has a specific gravity of 1.32 at 60°F. and is designated as
35° Baume.) It is but Httle used by photographers either of
Britain or the United States. One hundred parts by weight of
potassium metabisulphite are equal to 205 parts by volume in
bisulphite lye, i.e., 10 oz. by weight metabisulphite = 20|
fluid oz. of lye.

The amounts of the alkalies commonly used in photo-
graphy which neutralise unit quantities of potassium meta-
bisulphite are given in the following table by L. P. Clerc.

III.— EQUIVALENT QUANTITIES OF ALKALIES

To neutralise 100 parts by Of sodium carbonate anhydrous 95 parts

weight of potassium mefo- „ sodium carbonate crystal 2S8 ,,

bisulphite take „ potassium carbonate dry 124 ,,

„ sodium hydroxide (caustic

soda) 36 „
„ potassium hydroxide

(caustic potash) S0| „

Sulphite or Bisulphite?

We have seen that the addition of alkah to a bisulphite
converts it into a sulphite. Why, then, should we use a bisul-
phite in preference to sulphite?

In the first case, it is fairly common to make up developers
in two solutions, one of which contains the developing sub-
stance and the sulphite, and the other the alkaU. In such a

case bisulphite should replace sulphite because with its acidity
it inhibits oxidation, aud thus solutions will keep much better.
Quite unnecessarily some formulae still use sulphite in such
a case : they are given in this book in the form in which they
are pubhshed.

Next there is a decided advantage in using bisulphite in
more than usually concentrated solutions of developer,
owing to the greater solubility of the bisulphites.

Another point which must not be overlooked is that in
the case of a one-solution developer in which sodium
sulphite and bisulphite occur with sodium carbonate, the
sodium bisulphite neutralises an equivalent amount of sodium
carbonate in accordance with the following reaction: Sodium
bisulphite + sodium carbonate = sodium sulphite + sodium
bicarbonate. In this way the proportion of alkali is reduced,
an apparent restraining action is exerted and the life of the
developer is prolonged because some of the alkali has been
destroyed.

In addition to its action as a preservative, sulphite has
another valuable property which is made use of in develop-
ment processes. When silver bromide is in a finely divided
condition, sulphite has a certain amount of solvent action on
it and so is made use of in certain fine-grain developers
which act in part as chemical but also in part as physical
developers as will be seen when we come to discuss these
processes.

THE ALKALI (OR ACCELERATOR)

Solutions of developer containing only siilphite have, as a
rule, only very weak developing powers, and may, indeed,
show none at all. In order to develop their full action, the
addition of alkali is necessary.

The alkalies most widely used in photography are sodium
carbonate, potassium carbonate and the caustic alkahes
sodium and potassium hydroxide. The quantity and the
character of the alkalies exert a profound influence on
the properties of developers. There is a notable difi"er-
ence between the action of the alkali carbonates, that is,
sodium and potassium carbonates, and the caustic alkalies,
the latter giving developers of much greater energy than the
carbonates.

Sodium Carbonate

This is the most widely used of all the alkalies, and appears
on the market in three forms.

Crystal sodium carbonate, contains ten molecules of
water and so is called deca-hydrated and has about 37 per
cent by weight of anhydrous sodium carbonate.

Next there is anhydrous or desiccated sodium carbonate
which theoretically is free from water and contains nominally
about 98 per cent pure sodium carbonate.

The third form contains one molecule of water and is
termed mono-hydrated sodium carbonate, and contains 85
per cent by weight of anhydrous carbonate. The equivalent
weight relation which these three varieties bear to one another
is shown in the following table.

IV.— EQUIVALENT QUANTITIES OF CRYSTALLINE AND
ANHYDROUS SALTS

100 parts by weight of crystal sodium carbonate = 37J parts by weight

of anhydrous
„ „ „ „ „ „ „ „ = 8SJ parts by weight

of monohydrate
lOOpartsby weightofanhydroussodiumcarbonate= 270 parts by weight

of crystal salt

,, „ „ =120 parts by weight

of monohydrate

These equivalents are not exact, but are quite near enough
for all practical purposes.

Potassium Carbonate

Potassium carbonate, or carbonate of potash, occurs only
in one form, the anhydrous salt. It is, however, a very
hygroscopic material which absorbs water rapidly from a
moist atmosphere. Hence it should never be kept in paper
packets but always in bottles with either a close-fitting glass
stopper or better still a well-waxed and sound cork.

In general there is nothing to be gained by substituting
potassium carbonate for sodium carbonate in developer
solutions. Where it has an advantage is in the preparation of

6 85

concentrated developers, as its solubility is much greater than
that of sodium carbonate. It can be used in practically the
same proportions, or more exactly 13 parts by weight of the
potassium carbonate are equal to 10 parts by weight of sodium
carbonate.

Caustic Alkalies

These are much more energetic in their action than the
alkali carbonates, and are only used in those cases where
a powerful and quick-acting developer is required. As might
be expected, developers compoimded with caustic alkali
have poor keeping properties and are soon exhausted. The
reason for this difference in properties between developers
compounded with carbonates and those made with caustic
alkalies is of sufficient interest to call for a little special
explanation.

When sodium carbonate is dissolved in water, part of it
is split up, or as the chemist calls it, hydrolysed. As a result,
caustic soda and bicarbonate of soda are formed although
only in small quantities at any one moment. When develop-
ment is taking place the caustic soda or sodium hydroxide is
used up and as that happens more carbonate hydrolyses.
Hence the carbonate acts as a sort of reservoir of caustic
alkali. If we had caustic soda in place of the carbonate to give
the same alkalinity, it would soon be used up and the activity
of the developer would cease. Obviously the use of sodium
carbonate allows us to use a small concentration of alkali
and get the utmost work out of it. The above explanation
also shows why it is rarely possible to substitute caustic
alkalies for carbonates in normal developers.

As their name implies, caustic alkalies possess corrosive
properties, a fact which must be remembered when handling
them. They can burn the skin, are very dangerous to the eyes
and act vigorously on other materials of both organic and
inorganic origin. They are also intensely hygroscopic and so
must be preserved from contact with moist air if they are to be
kept in solid form. They are usually sold in sticks which are
kept in bottles with well-fitting waxed corks, or in pellet
form in tins with close-fitting lids.

There is no difference between the potassium and sodium
hydroxides so far as photographic uses are concerned, other

than that 10 parts by weight of the sodium salt are the
equivalent of 14 parts by weight of the potassium.

Among other energetic alkalies mention may be made of
sodium metasilicate (Metso). This substance, as the table on
page 87 shows, is almost as alkaline as the hydroxides and
equal to the carbonate. It has the advantage that it does
not attack gelatine and also that it tends to reduce any
excessive swelling. As a result it helps toward the quick
drying of films developed in formulae containing it.

Substitution of Alkalies

We have already given the proportions in which one alkali
can be substituted for another, but it will be realised that
such substitution is only possible between members of the
same group. For example, one can substitute one carbonate
for another, or one caustic alkali for another, but it is not
possible to substitute the alkah of one group by that of an-
other group.

Of late years another form of substitution has come into
use, and in some formulae one finds formalin or paraformal-
dehyde substituted for caustic alkali. Formalin is a solution of
formaldehyde gas in water (40% w/v.) and paraformaldehyde
is a white powder which produces formalin when dissolved in
water. One of the most useful properties of formalin is its
hardening eff'ect on gelatine, and it is widely used for hardening
the emulsion of photographic materials. It can exercise this
property when added to a developer, but it also has another
action. It reacts with sodium sulphite and one of the products
of that reaction is sodium hydroxide.

Formaldehyde + sodium sulphite + water = Formal-
dehyde-bisulphite + sodium hydroxide. Hence the result of
adding formalin to a developer containing sulphite but no
alkali is equivalent to adding caustic soda to the developer. It
is mainly used to prepare highly active and contrasty hydro-
quinone developers.

The formaldehyde-bisulphite compounds keep the sulphite
concentration at a low and constant level. The keeping quali-
ties of the developer are not seriously affected, but the
hydroquinone is more easily oxidised to quinone and semi-
quinone. The latter acts as an accelerator causing rapid
development of silver halide grains and also a reduction of

grains adjacent to those already developed. This process of
"infectious" development gives gradation curves with very
high gamma and short toe as required for lith materials.

Mild Alkalies

For some yeais now another group of alkalies has found
appUcation in photographic practice to which the name
"mild alkalies" might be given. Of these the most widely
used is borax, or sodium biborate, which finds its widest use
in the compounding of fine-grain developers.

Another compound which falls in this group is Kodalk
introduced by Kodak, which is more alkaline than borax and
somewhat more easily soluble, but less alkaline than car-
bonate. When used as a substitute for carbonate, two parts by
weight of Kodalk are the equivalent of one part by weight of
carbonate in normal developers. As Kodalk contains no free
carbonate there is no danger of bubbles of carbonic acid gas
being formed when an acid stop-bath is used, a very real
advantage in certain circumstances. (For formulae containing
Kodalk, see page 206.)

In the chapter on fine-grain developers certain other mild
alkalies will be discussed as well as organic substances
such as triethanolamine, acetone, etc. The properties of
tribasic sodium phosphate, the action of which lies between
that of carbonate and caustic alkalies, will also be dealt with.

ALKALIES AND pH VALUES

So far in this book we have spoken of alkalies as caustic,
energetic or mild, a description which from a scientific
standpoint leaves much to be desired. The alkahnity or
acidity of any solution can be exactly measured and equally
exactly described in terms of its pH value (see pagell5). A full
understanding of exactly what is meant by pH value* is
not necessary for the photographer; it is sufficient to know
that pure water, which is neither acid nor alkaUne but neutral,
has a pH value of 7, that any pH below 7 indicates acid or
above 7 indicates alkaline and that the higher the pH value the
more alkaline the solution.

*V. Gold, pH Measurements, their Theory and Practice, Methuen,
London, 1956.

v.— pH-VALUES

pH-yalue

Solution IS.

0—2

strongly acid

3—4

acid

5—6

weakly acid

neutral (pure water)

8—9

weakly alkaline

10—11

alkaline

12—14

strongly alkaline

In Table VI (page 90), pH values are given for a series of
alkalies and preservatives, mixtures of these developer
constituents, and processing solutions.

Where the percentage strength of solutions is not given
the value relates to saturated solutions.

Although in the table the differences between the pH
values of the various solutions appears small remember that
the pH figures are logarithm values and so a solution of pH
10 is ten times more alkaline than a solution having a pH
value of 9. This latter in turn is ten times as alkahne as a
solution with a pH value of 8 and so on, thus a small change
in pH indicates a notable variation in alkalinity. As the table
shows, the pH values of developers cover a very wide range
from strongly alkaline through weaker and very weak alka-
line to neutral.

The table also allows us to draw a conclusion of particular
value in connection with fine-grain developers. As we shall
see later (page 202) solutions of low alkalinity are important for
fine-grain developers. In the preparation of such solutions
two possibilities offer themselves. Either we can use a strong
alkah in weak concentration or a mild alkali in higher
concentration, for example we can take a 0.1 % solution of
sodium carbonate or even weaker, or a 0.2% or stronger
solution of borax. Which will give us the best result?

The answer is that we shall obtain a more constant work-
ing and a better keeping developer by using a mild alkali
at relatively high concentration than if we use a weak
solution of a strong alkah. Similar considerations enter into
the use of the so-called "Buffer-mixtures" in developers.
Perhaps the best known example is the Buffered Borax
Developer No. 84 (page 206). This formula contains a relatively
large quantity of borax as alkali and in addition a quantity
of acid, namely boric acid. This has the effect of stabilising

VI.— pH VALUES OF CHEMICALS AND SOLUTIONS

Alkalies

Sodium hydroxide 4%, potassium hydroxide

5.6%

14.0

Sodium hydroxide 0.4%, potassium hydroxide 0.5%

13.0

Sodium hydroxide 0.04%, potassium hydroxl

de 0.05%

12.0

Sodium carbonate 5 — 10%

11.5— 11.6

Potassium carbonate 5 — 10%

11.6

Trisodium phosphate 3 — 4%

12.0

Trisodium phosphate 1%

11.3

Sodium metaborate 1 — 5%

10.5—10.8

Sodium metasilicate 1%

12.6

Sodium metasilicate 0.1%

11.5

Ammonia 3 — 4%

11.6

Ammonia 0.3%

ll.l

Ammonia 0.03%

10.6

Borax 0.1%

9.5

Kodalk 0.2%

9.9

Sodium sulphite S— 10%

8.0—9.9

Triethanolamine 10%

10.6

Disodium hydrogen sulphate 1%

8.0

Sodium sulphite 10% + borax 0.2%

9.5

Sodium sulphite 10% + borax 0.2% + Bori(

: acid 1.4%

8.1

Acids

Hydrochloric acid 3—4%

I.I

Sulphuric acid 1%

1.2

Citric acid 2%

2.2

Acetic acid 6%

2.4

Acetic acid 0.6%

2.9

Acetic acid 0.06%

3.4

Potassium alum 5%

3.2

Boric add 0.5%

5.2

Sodium dihydrogen phosphate 1%

4.2

Sodium metabisulphite 1%, potassium metab

isulphite 1%

4.3-4.9

Buffer Mixtures

Acetic acetate, sodium acetate

4.6

Potassium dihydrogen phosphate, disodium phosphate

6.8

Boric acid, borax

8.5

Boric acid, sodium hydroxide

9.2

Disodium phosphate, sodium hydroxide

11.5

Processing Solutions

Hydroquinone and p-aminophenol developer

with

hydroxide

12.0—12.5

M.Q.-sodlum carbonate

10.0—10.5

M.Q.-borax

8.6

M.Q.-buffered borax

7.9

Metol — sodium sulphite with bisulphite

7.2

Hardening fixing baths

Acid fixer

4.8

Stop bath with potassium metabisulphite

4.6

Stop bath with acetic acid

2.9

the pH value and acting as a buffer against any violent
change, hence its name. Such developers are characterised
by their constant and even working properties as well as good
working life.

RESTRAINERS

The great majority of developers fulfil, more or less com-
pletely, the important function of acting only on the ex-
posed silver bromide in sensitive materials and leave im-
attacked that portion of the emulsion which has not re-
ceived any exposure. Their action is selective and does
not lead to a general fogging of the whole of the sensitive
surface.

In order to ensure that they shall produce an image com-
pletely free from fog, a restrainer is made use of and the
substance most widely used for this purpose is potassium
bromide.

Potassium Bromide

acts not only as a fog preventer but also as a restrainer, that
is, it slows down the rate of development. This action varies
with different developers. In many cases the restraining
action is very strong, in others the effect is only small. It is
important to remember this difference and take it into account
when compounding developers for special or even general
purposes.

In the following table there are set out examples of the
relative lengthening of development time caused by the
addition of an equal quantity of potassium bromide.

It will be seen that a metol-carbonate developer is
relatively insensitive to the action of potassium bromide
whereas a hydroquinone-caustic developer is strongly
affected and the development time notably prolonged. This
emphasises the important fact that the effect of potas-
sium bromide as a restrainer depends almost wholly on
the composition of the developer. It should also be remem-
bered that the addition of potassium bromide usually
results in a reduction of the contrast in the developed
image. Excessive bromide may thus produce as undesirable
an effect as slight fogging.

VII.— LENGTHENING OF DEVELOPMENT TIME BY THE ADDITION
OF POTASSIUM BROMIDE

Developer Percentage lengthening of

development time

Gl/cin-potassium carbonate 300%

Glycin-caustic soda 200%

Hydroquinone-caustic soda 400%

p-Aminophenol-potassium carbonate 17%

Amidol 150%

Hydroquinone-potassium carbonate 140%

p-Aminophenol-caustic potash 100%

Pyrogallol-potassium carbonate 80%

Metol-potasslum carbonate 25%

Various Restrainers

Some formulae contain potassium iodide which also acts as
a restrainer and an anti-fogging agent, but the quantity
should always be very small, very much less relatively than
is permissible with potassium bromide. Potassium iodide in
appreciable quantities is a disadvantage because it produces
silver iodide in the sensitive material which is not very
soluble in fixing baths and so lengthens unduly the fixing
time. On the whole the use of potassium iodide as a restrainer
is not recommended.

Certain organic compounds, notably nitrobenzimidazole
and benzotriazole, have the interesting properties of acting as
anti-fogging agents without aff'ecting in any way other proper-
ties of the developer. They are used in very small quantities,
one part in ten thousand of the developer being a perfectly
satisfactory proportion to use.

The use of compounds of this type is sound practice in
every-day work, as they afford real protection against any
tendency to fogging by the developer itself, or by variations
in its preparation, too high temperature or even prolonged
development. They also have an excellent effect when some-
what stale or badly stored sensitive material has to be used.

OTHER ADDITIONS TO DEVELOPERS

When hard water is used for the compounding of developers
a milkiness or turbidity is often produced; this is caused by
the action of alkali carbonate and sulphite on the Ume salts

present in the water. If the amount of hme salt is excessive
a troublesome precipitate of calcium carbonate and sulphite
may be deposited on the sensitive film unless the developer
has been filtered or the precipitate destroyed in some other
manner. The formation of this precipitate of carbonate of
lime can be prevented by the addition of certain sequestering
agents.

Calgon is a proprietary compound put on the market
for this purpose; it is essentially sodium hexametaphosphate
and is added to the developer solution. In general, one part
per thousand is sufficient, except for very hard water. Where
the amount of lime present is high the proportion of Calgon
can be slightly increased. For the same purpose EDTA —
ethylenediaminetetraacetic acid — can be used.

WETTING AGENTS

Wetting agents are used in many branches of industry with
most useful results and in recent times have found successful
application for photographic purposes, particularly as addi-
tions to developers.

In order to understand the action of a "wetting" agent
we must know what the operation of wetting really is. It may
be defined as the forming of a continuous adsorbed film of
liquid upon the surface of any desired sohd or on that of
another liquid. The capacity of a liquid for wetting depends
to a large extent upon its surface properties.

The surface or interface of a liquid where, for example, it
is in contact with air, behaves diff'erently from the liquid
layers lying beneath it. If a needle be stroked by the fingers
sufficient grease will remain or be transferred to the needle
to repel water and allow it to float so long as it is laid down
carefully lengthwise on water. If, however, one end be
pressed so that it penetrates the water the needle instantly
sinks. Thus the surface of the water behaves as though it
were a thin membrane and resisted rupture. There is, in
fact, a force, which is called surface tension, acting along the
surface of the water which tends to prevent the surface
being broken. This surface tension is also the force which
tends to prevent liquids from spreading evenly over a surface
and so wetting it completely and evenly. Wetting agents are
substances which have the power of lessening this surface

tension and so facilitating the spreading or wetting of a liquid
or another surface.

A simple experiment will demonstrate this. If we take a
vessel full of water and plunge a piece of old film into it,
quickly withdrawing the film we shall see that the whole of
the surface of the film is by no means wetted, that on the
contrary the moistening has only been in patches here and
there. If now we repeat the experiment with the difference
that we add a wetting agent to the water, usually one part
per thousand is ample, we at once observe a very notable
difference for the whole surface of the film is now covered
by a complete even film of water.

Of what benefit will this wetting effect be in practice?

The first and obvious advantage is in the assurance of a
quick and even wetting of film or plate in the developer and
the safeguarding in this way against air bubbles or bells and
other inequalities of wetting. This is of quite special impor-
tance when using daylight developing tanks (page 145) in which
the spiral leads for the film leave but little space for contact
between film and developer. Quick and even wetting of the
film is equally of importance for high speed development
as described on page 233. Wetting agents, suitable for
photographic purposes, are commercially available. Most of
them belong to the group of sulphonate, sulphated or
carboxylated fatty alcohols.

ORGANIC ACCELERATORS

The charge barrier of the silver halide grain can be neutralised
or even completely changed by a different class of agents
which have no developing action whatsoever but are strongly
electroactive and possess a positive charge, accelerating the
action of the developer. This effect can be produced by
certain cationic surface active agents of the quaternary type
in a concentration of about 0.05-0.1 %. Suitable compounds
are for instance:

Cetyl-trimethyl-ammonium bromide (Cetavlon)
Cetyl-pyridinium bromide
Dimethyl-benzyl-lauryl-ammonium chloride
Lauryl-pyridinium chloride
Lauryl-pyridinium-p-toluene sulphonate
Beta-phenylethyl-alpha-picolinium bromide.

These agents are only effective in developers which have
normally a noticeable induction period, i.e. a negative charge,
for instance hydroquinone or to a lesser degree metol. They
are of no use for developing agents which have no charge and
practically no induction period, such as p-phenylendiamine
and its derivatives (see page 104).

DEVELOPING AGENTS

We have already learned that developing agents or sub-
stances are reducers (see page 22), but that not every reducing
agent can act as a photographic developer. For a reducing
agent to act as a developer it must possess the property of
reducing only the exposed silver bromide and of leaving the
unexposed material unaltered.

Fortunately there are many compounds which possess this
quality, although they differ notably in both chemical and
photographic properties and their action is to a very large
degree dependent on the composition of the developer in
which they play the part of reducing agent. From the chemical
point of view, reducing agents have to fulfil a number of
conditions to be suitable as developing agents. Aromatic
organic compounds must have either two hydroxy (OH)
groups or two amino (NHj) groups or one hydroxy and one
amino group. Aromatic compounds can be considered as
those organic compounds that possess a benzene nucleus :

Only ortho and para compounds have developing action but
not meta compounds. Ortho (o) compounds are those com-
pounds that have two substituents in the 1 and 2 (or 1 and 6)
positions of the benzene nucleus, para (p) compounds have
two substituents in the 1 and 4 positions and meta (m) com-
pounds are 1:3 (or 1:5) disubstituted benzene compounds.
The hydrogen atoms of the amino group can be replaced by
alkyl groups but not those in the hydroxy group which would
destroy the developing power. If, however, the hydrogen atoms
of the benzene nucleus are replaced by alkyl or halogen or

further hydroxy or NHj groups the developing power is not
decreased but may be increased. The same rules are true for
naphthalene derivatives but there are no developing agents of
practical importance in this group.

In judging the properties of developing agents the follow-
ing points are all of importance and due consideration must
be given to them.

(1) Solubility.

(2) Fogging effect and /or discoloration of film or
fingers.

(3) Reaction to changes of temperature.

(4) Reaction to bromide addition.

(5) Behaviour with carbonate and caustic alkalies.

(6) Keeping properties and rate of exhaustion.

(7) Influence on graininess.

(8) Toxicity.

(9) Cost.

Metol
N-Methyl-p-aminophenol sulphate

Metol is easily soluble in water and permits the preparation
of concentrated stock solutions. If these are beyond a certain
concentration a precipitation of the metol base by the alkali
sulphite may occur. This can be remedied either by ensuring
that the whole of the metol is dissolved before any further
addition is made or by the addition of alcohol in the pro-
portion of one-tenth by volume to the solution.

Acetone can also be used in even smaller proportion,
namely 55 parts per 1,000.

Metol responds well to the addition of bromide, giving a
very clean working developer without any staining of either
film or fingers. The energy of the developer is only slightly
affected by low temperature, and is also but slightly reduced
by the addition of bromide.

Metol alone with either sodium or potassium carbonates
gives a rapid working developer when the alkalies are in
high concentration, but the speed of development can easily
be controlled by dilution.

The use of caustic alkali with metol is not recommended
as there is a tendency to excessive fog.

When used with sulphite alone without alkali, metol

provides a slow-working, fine-grain developer, but it is
preferable to use a mild alkali such as borax, which accelerates
the rate of development without increasing the grain-size
of the image appreciably.

Developers containing metol as the sole developing agent
are not very widely used, but in combination with hydro-
quinone it provides the most widely used developer.

All metol developers keep well and are only slowly
exhausted.

Metol had the reputation of causing skin poisoning
(dermatitis); this was traced to certain impurities and not to
the metol itself. Today good quality metol is free from such
impurities, but some people are even sensitive to the
purest type. p-Aminophenol developers are free from this
trouble, and can thus be used instead of metol developers
which they resemble. Still better, use Phenidone developers
(page 198) or amidol developers (page 99).

Hydroquinone
p-Dihydroxybenzene

Hydroquinone is fairly soluble in cold, easily soluble in
warm water. In general it is a clean-working and non-staining
developer.

In some respects its properties are in marked contrast to
those of metol: it is notably affected by low temperature and
below 50°F. (10°C.) its action slows down very considerably.
It is also extremely susceptible to the action of bromide.
When compounded with alkali carbonates it gives somewhat
slow-working but contrasty developers, while with caustic
alkalies its action is very rapid and gives the highest possible
contrast. For this reason it is the most widely used developer
in technical practice, especially in process work where the
highest attainable contrast is essential. In the presence of
caustic alkali, i.e. at high pH, it is not especially temperature
sensitive and can be used for low-temperature developing.

Hydroquinone developers keep reasonably well and are
only slowly exhausted.

In normal photographic practice hydroquinone alone is
not largely used, but in combination with metol or Phenidone
it provides a universal developer of outstanding value. By
varying the relative quantities of metol and hydroquinone

and adjusting the quantities of sulphite and carbon-
ate, almost any desired contrast or rate of development
can be obtained (seepage 173). The combination can also be
used as a fine-grain developer by suitably modifying the
formiila.

Chlorquinol
Chlorhydroquinone

Less soluble in cold water than hydroquinone, but easily
soluble in hot water, rather more energetic in action than
hydroquinone and almost equally sensitive to the action of
bromide.

Its main use is as a warm-tone developer for papers when
heavily restrained with bromide. As a negative developer
it has no advantage over metol-hydroquinone.

Pyrocatechin
Catechol, o-Dihydroxybenzene

Easily soluble in warm water, chemically closely akin to
hydroquinone but with some quite special properties, notably
the fact that it oxidises very readily and its oxidation products
tan gelatine. When used without sulphite or with very low
sulphite content it gives a heavily stained image and tans the
gelatine in proportion to the density of the image. This
property has led to its use for a number of special purposes,
such as high-definition and tanning developers, for a descrip-
tion of which see pages 214 and 222.

Pyrocatechin with caustic alkali provides a very rapid
developer.

Pyrogallol
Pyrogallic acid, Pyro. 1, 2, 3-Trihydroxybenzene

Readily soluble in water, very easily oxidised, and the oxida-
tion products tan gelatine and also colour the film and stain
the fingers. Pyrogallol was at one time a universally used
developer, but today equal results can be obtained by modern
developers without the disadvantages of pyrogallol, which
has poor keeping qualities.

In combination with metol it has some vogue among press

photographers on account of its rapid action and the behef
that the yellow stain on the film adds printing quality. It is
also used for tanning developers.

Pyrogallol in combination with Phenidone has been shown
to exhibit superadditivity (see page 101) and to be quite stable
when left in an open tray overnight.*

Glycin
p-Hydroxyphenyl glycine

Almost insoluble in water but dissolves readily in alkahne
solutions. Oxidises very slowly, very clean working. Used
mainly in developers for papers until fine-grain developers
assumed importance; now sometimes used in combination
with other developers for this purpose.

Glycin is very sensitive to bromide and also to low
temperature; with alkah carbonates it makes slow- working
developers which have good keeping properties and give low
contrast.

p-Aminophenol hydrochloride

Very soluble in cold water, its principal use is in the prepara-
tion of very concentrated developers with caustic alkalies
which will stand dilution from 20 to 100 times. These con-
centrated solutions keep well and should only be diluted
immediately before use.

They work rapidly, are free from fogging properties and
do not stain. They are not sensitive to variations of tempera-
ture nor do higher temperatures affect their clean working.
They can, however, cause excessive swelling at high tempera-
ture because of high pH and low concentration. The diluted
solutions are suitable as high-definition developers.

Alkah carbonate should not be used with this substance
as they precipitate out the base and prevent the preparation
of any but very dilute solutions.

Amidol
Diaminophenol. 2 : 4 Diaminophenol hydrochloride

Very soluble in water or in sulphite solution. Amidol has
the interesting property of acting as a developer in sulphite
*M. Levy, Photogr. J., 105, 303 (1965).

solution without the necessity of adding any alkali. The
solution is easily prepared but does not keep, although its
keeping properties may be somewhat improved by the
addition of a weak acid such as lactic acid. Solutions of
amidol with bisulphite have the noteworthy property of
beginning their development in the depth of the film and not,
as is usually the case, at the surface. So far no practical
use appears to have been made of this depth-development
effect.

As amidol develops in the absence of alkali there is not
the excessive swelling of the film that takes place with other
developers and amidol is therefore favoiu-ed as a tropical or
high temperature developer, although it is possible to prepare
other developers having like properties without the dis-
advantage of the poor keeping properties of amidol.

p-Phenylenediamine
1:4 Diaminobenzene

Only slightly soluble in water when in the form of the base,
but much more soluble as the hydrochloride salt. Its par-
ticularly valuable property is that it supplies a very fine-grain
developer. For various formulae with p-phenylenediamine
alone, and in combination with other developer substances,
see page 210.

Unfortunately p-phenylenediamine suffers from a number
of drawbacks: it is poisonous and has also a very strong
tendency to staining and wherever a particle of powder rests
it causes a brown spot very diflBcult to remove. It will also
stain both film and fingers unless very carefully handled.

These many disadvantages have naturally led to attempts
at discovering developers which would give fine-grain de-
velopers without the troublesome properties. One such
material is o-phenylenediamine which must, however, be
quite free from any trace of the para compound (see page
209).

p-Phenylenediamine forms addition products with various
other developing agents, in particular with hydroquinone and
pyrocatechin. To this group belongs Meritol, a fine-grain
developer which is less poisonous and less staining than
p-phenylenediamine. Derivatives of p-phenylenediamine have
found wide apphcation for colour development (see page 366).

100

Phenidone
1 -phenyl-3-pyrazolidone

Phenidone is a colourless crystalline compound which is
moderately soluble in hot and shghtly in cold water. It is,
however, readily soluble in both aqueous acids and alkalies,
including solutions of alkaU bisulphites and carbonates, so
that it can easily be incorporated into developer solutions.
When used alone in sodium carbonate-sulphite solutions, it
gives very fast but extremely soft working developers. The
developing properties of Phenidone (Trade Mark registered
by Ilford) were discovered by J. D. Kendall, who worked out
a process suitable for the large-scale manufacture of this
compound. In mixture with hydroquinone, Phenidone is
highly active and retains its activity well. Phenidone has a
low oral toxicity and is unlikely to cause dermatitis. Sufferers
from metol poisoning have been able to use Phenidone
developers without any ill effects.

SUPERADDITIVITY

The phenomenon of superadditivity is of the greatest im-
portance for the formulation of modern developers. As a
matter of fact, by far the majority of all developers in use
today are based on this effect.

Developing agents are said to be superadditive if the sum
of their combined action is greater than the sum of their
actions used separately. The best known example of such
a superadditive combination is metol-hydroquinone. Metol is
— as we already know (page 96) — a developing agent of fast
action, while hydroquinone develops slowly. If we combine
them in one formula, however, we obtain a developer which
can be still faster than metol alone and which can produce
contrast equal to or even higher than that of hydroquinone
alone.

This phenomenon is still more pronounced in the com-
bination Phenidone-hydroquinone. Phenidone on its own is
quite useless as a developer; it acts fast but the contrast of the
negative is very low. Added in a comparatively small quantity
to a hydroquinone developer, however Phenidone retains its
high activity and combines with it the contrast hydroquinone
is able to produce.

7 101

VIII.— CHARACTERISTICS OF
A In alkaline carbonate solution. B In coustic

Developer

{\) Fog forma- (2) sensitivity (3) sensitivity
tion and stain- to temperature to bromide
ing

METOL

A
B
C

none slight
appreciable slight
none moderate

slight
slight
moderate

HYDROQUINONE

A
B
C

none strong
none moderate
not suitable

strong
moderate

PYROCATECHIN

A
B
C

none strong
none slight
not suitable

strong
slight

PYROGALLOL

A
B
C

stains moderate
not suitable
not suitable

moderate

AMIDOL

B
C

none moderate

not suitable
not suitable

moderate

PHENIDONE

none slight

slight

GLYCIN

A
B
C

none very strong
none strong
not suitable

very strong
strong

P-AMINOPHENOL

A
B
C

not suitable
none slight
not suitable

slight

CHLORQUINOL

A
B
C

none moderate
none slight
not suitable

moderate
slight

P-PHENYLENE-
DIAMINE

strong moderate

staining

properties

moderate

O-PHENYLENE-
DIAMINE

none moderate

moderate

102

DEVELOPING AGENTS

alkali solution. C As a fine-grain deve/oper.

(4) Speed of
deve/opment

(5) Gradation

(6) Keeping
properties

(a) separately

(b) mixed

(7) Properties
See pages

(8) Examples of
Formu/ae
See Nos.

normal-rapid

rapid

slow

soft
soft
soft

a and b good
a good, b bad
a and b good

1—29

slow
rapid

contrast/
contrast/

a and b good
a good, b bad

1—29 30—37

normal
rapid

normal
contrast/

a and b good
□ good, b bad

43—44

normal

soft

□ good, b bad

normal

solutions do
not keep

normal

soft

a and b good

55—62

slow
rapid

normal-soft
normal

a and b good
good, b bad

46—49

normal-

rapid

normal-soft

good, b bad

50—53

normal
rapid

normal
contrast/

a and b good
a good b bad

40—42

slow

soft

varies with
formula

slow

soft

good

103

The maximum developing speed is reached when the
developer contains 7 % Phenidone based on its hydroquinone
contents. Such a developer is 50% faster than a metol-
hydroquinone developer under comparable conditions, i.e.
containing the optimum quantity of 28 % metol with regard
to hydroquinone. As a matter of fact, Phenidone is about 18
times more efficient as an activator than metol.

At a practically useful Phenidone to hydroquinone ratio,
Phenidone has the tendency to produce fog. This fog can,
however, easily be controlled by the addition of organic
restrainers (page 92), such as benzotriazole, used in a quantity
of 0.1-0.2 gram per litre of developer.

INDUCTION PERIOD

To understand the phenomenon of superadditivity and also
the influence of certain agents on the course of development
(see page 94), we have to consider the surface condition of
the silver halide grain in the emulsion. Development can ob-
viously only take place if the developing agent can reach
the surface of the silver halide grain.

However, the developer is opposed by an electrostatic
effect, and can not easily penetrate to the surface of the grain.
This electrostatic effect is caused by a negative charge barrier
which surrounds the grain and tries to prevent the approach
of negatively charged agents such as the developing substance.
Thus an induction period is produced varying with the
magnitude of the charge of the developing agent.

According to the length of the induction period develop-
ing agents can be divided into the following groups:

(A) Developing agents with no charge, such as
p-phenylendiamine and derivatives.

(B) Developing agents with one negative charge, such
as metol and Phenidone.

The developing agents in group (A) have practically no
induction period. Beginning immediately, the developing
process is at first rapid but soon slows down. Contrast and
maximum density of the negatives are very low. Developing
agents of group (B) start to react with some delay; develop-

104

tnent increases proportionally but the negatives have a
tendency to be soft. Developers of group (Q have a noticeable
induction period and start very slowly. Once a certain density
is reached, the density increases with development time. The
negatives have normal to high contrast.

The induction period can be explained in terms of a change
in the magnitude of the charge barrier surrounding the silver
halide grain. As the charge barrier is reduced, a larger
quantity of the developer can reach the surface and the rate
of reaction is increased. Developing agents with no charge are
not hindered by the barrier and the developer does not show
an induction period.

The phenomenon of superadditivity can be explained, at
least partially, by the effect which developing agents of
group (B) have on the potential barrier of the grain. By
breaking the barrier down, they reduce the induction period
and once this has been done, the developing agents of group
(C) can take over and carry on the development of the grain.
However, this process alone does not seem to explain the
powerful effect of Phenidone and similar substances which
is probably due to a triple action. First, the barrier layer
effect, as explained above. Secondly, a chemical reaction,
during which hydroquinone regenerates the Phenidone from
its reaction products. Thirdly, the formation of products
which can accelerate development. This intermediate product
has a positive charge and will therefore decrease very
efficiently the charge of the barrier, thus facilitating the
approach of the negatively charged developing agent.

More recently it has been suggested that charge barrier
effects are less important than was previously supposed and
that the major contributory factor is the regeneration of the
primary developing agent (e.g. Phenidone or metol) at the
grain surface by the secondary developing agent (e.g. hydro-
quinone).

105

Preparing Solutions

CHEMICALS

The first point is to see that the chemicals used are of first-
class quality and are obtained from a dependable dealer. It is
more economical to buy in large than in small quantities, but
here the photographer must be guided by the amounts of
each chemical he is Ukely to use, and also by the keeping
properties of the chemicals. It must also be emphasised
that no chemical should be kept in paper packets or bags, in
which it will be exposed to the more or less damp atmosphere
of the dark-room.

ORDER OF DISSOLVING

It is usually of the greatest importance to dissolve constituents
in the order given in the formula.

Generally it is convenient to dissolve the sulphite first
because most developing agents are easily oxidised in water
in the absence of this preservative.

An exception to this is the case of metol which (see page
96) is only soluble with difiiculty in sulphite solutions.
Hence when making up developers containing metol, it
should be dissolved before the sulphite. This has no serious
effect on the keeping properties of the developer as metol
itself is not very easily oxidised.

Many practical workers prefer to dissolve a pinch of
sulphite, or a crystal or two of metabisulphite, in the water
before dissolving the metol. In such cases the small extra
amount of sulphite is ignored; it is insufficient to upset
the balance between sulphite and alkali in the finished
developer.

A basic rule in preparing developers is to make quite

106

certain that each constituent in turn is completely dissolved
before the next is added.

Where developers are bought in packet form this rule
cannot be obeyed in full because the packets do not contain
separate constituents, but usually consist of a small package
containing the developing agents and a much larger one
containing the other constituents. Even so, the rule can be
followed by dissolving the contents of the small packet first
and ensuring that the contents are completely dissolved before
the contents of the larger packet are added to the solution.

TEMPERATURE

With some few exceptions that do not interest us here, all
chemicals have the property of dissolving more rapidly and
more easily in warm water than in cold. Note that we say
warm, for it would be a mistake to go too far and to use
boiling water. In many cases this would cause decomposition
of the materials with the possible precipitation of insoluble
residues which would interfere with the properties of the
developer and with the development process. It must also
be remembered that too high a temperature accelerates the
tendency to oxidation and so reduces the keeping properties
of the solution.

When using warm water in the preparation of developer,
etc., it is not necessary to employ the whole volume called
for by the formula; it is preferable to use about two-thirds
and then to make up to the required volume with cold water
when solution is complete. Many modem formulae are set
out in this manner.

The temperature of a solution should not exceed 120°F.
(50°C.) unless the instructions with the formula definitely
prescribe a higher temperature.

When solution is complete the developer should be
cooled to normal temperature. By normal temperature is
meant that temperature at which processes such as develop-
ment and the like should be carried out, and that is taken as
68°F. (20°C.) in this book. A degree or two above or below
this temperature is not of great importance, but every
endeavour should be made to keep the temperature of the
solutions as close as possible to 68°F. when in use.

It should also be noted that where solutions have been

107

IX.— FAHRENHEIT AND CENTIGRADE

+ 212

+ 100

+ 169

+ 76.11

+ 126

+ 52.22

211

99.44

168

75.55

125

51.67

210

98.89

167

124

51.1!

209

98.33

166

74.44

123

50.55

208

97.78

165

73.89

122

207

97.22

164

73.33

121

49.44

206

96.67

163

72.78

120

48.39

205

96.11

162

72.22

119

48.33

204

95.55

161

71.67

118

47.78

203

160

71.11

117

47.22

202

94.44

159

70.55

116

46.67

201

93.89

158

115

46.11

200

93.33

157

69.44

114

45.55

199

92.78

156

68.89

113

198

92.22

155

68.33

112

44.44

197

91.67

154

67.78

III

43.89

196

91.11

153

67.22

110

43.33

195

90.55

152

66.67

109

42.78

194

151

66.11

108

42.22

193

89.44

150

65.55

107

41.67

192

88.89

149

106

41.11

191

88.33

148

64.44

105

40.55

190

87.78

147

63.89

104

189

87.22

146

63.33

103

39.44

188

86.67

145

62.78

102

38.89

187

86.11

144

62.22

101

38.33

186

85.55

143

61.67

100

37.78

185

142

61.11

37.22

184

84.44

141

60.55

36.67

183

83.89

140

36.11

182

83.33

139

59.44

35.55

181

82.78

138

58.89

180

82.22

137

58.33

34.44

179

81.67

136

57.78

33.89

178

81.11

135

57.22

33.33

177

80.55

134

56.67

32.78

176

133

56.11

32.22

175

79.44

132

55.55

31.67

174

78.89

131

31.11

173

78.33

130

54.44

30.55

172

77.78

129

53.89

171

77.22

128

53.33

29.44

170

76.67

127

52.78

28.89

108

DEGREES OF TEMPERATURE

+83

+ 28.33

+41

+ 5

— 1

—18.33

27.78

4.44

18.89

27.22

3.89

19.44

26.67

3.33

26.11

2.78

20.55

25.55

2.22

21.11

1.67

21.67

2';.44

l.ll

22.22

23.89

+ 0.55

22.78

23.33

22.78

—0.55

23.89

22.22

1.11

24.44

21.67

1.67

21.11

2.22

25.55

20.55

2.78

26.11

3.33

26.67

19.44

3.89

27.22

18.89

4.44

27.78

18.33

28.33

17.78

5.55

28.89

17.22

6.11

29.44

16.67

6.67

16.11

7.22

30.55

15.55

7.78

31.11

8.33

31.67

14.44

8.89

32.22

13.89

9.44

32.78

13.33

33.33

12.78

10.55

33.89

12.22

11.11

34.44

11.67

11.11

12.22

35.55

10.55

12.78

36.11

13.33

36.67

9.44

13.89

37.22

8.89

14.44

37.78

8.33

38.33

7.78

15.55

38.89

7.22

16.11

39.44

6.67

16.67

6.11

17.22

5.55

17.78

109

over-cooled, or when they have been kept in a cold place,
crystallisation of some of the constituents may occur; this
should be guarded against as much as possible.

MANIPULATION

Solutions should not be prepared in the vessels in which
they are to be used, e.g., tanks, dishes, etc., but in separate
vessels. Glass or porcelain jars or wide-mouthed bottles are
convenient, but metal receptacles other than stainless steel
should not be used, and this applies particularly to iron,
copper, aluminium or tinwares.

To ensure quick dissolving and perfect mixing the solution
should be well stirred or shaken. Stirring is best and for
small volumes a glass rod may be used. A hardwood stirrer
is best for large volumes. The same stirrer should not be
used for developer and fixing bath aUke; a separate stirring
rod should be provided.

TAP-WATER

Unless a formula specifically calls for distilled water, the
usual domestic supply can be used for almost all photographic
solutions and therefore for developers.

Where the water is very hard it can be treated as described
on page 92, so that no precipitation of lime salts occurs. If
this is not practicable, then the solution should be allowed
to settle and the clear supernatant liquor decanted off. This
procedure is sufficient in the case of most developers.

Where a perfectly clear developer is essential, filtration
is necessary, using a funnel and filter paper or cotton wool.
With rather large volumes the funnel and filter paper are too
slow and a quick and cheap method is to use filter cloth held
in a hardwood frame over the tank which is to hold the
developer. The filter cloth must be well washed after use and
care must be taken when filtering developer or aerial oxidation
may occur.

SATURATED SOLUTIONS

A saturated solution is a solution of any chemical which, at a
particular temperature, is incapable of dissolving any more

110

of that chemical. In general, normal room temperature, that
is about 68°F. (20°C.), is understood.

The preparation of a saturated solution is a comparatively
simple matter and is carried out as follows: The water or
other solvent is slightly warmed and the substance to be
dissolved is added with constant stirring until no more is
dissolved and a residue remains at the bottom of the vessel.
That is a sign that the solution is saturated. The solution is
now allowed to cool down to room temperature; in doing so
a further quantity of the substance will crystallise out. When
the solution has reached room temperature it can be filtered
or decanted from the residue.

It will be reahsed that the amount of salt required to
saturate a solution is dependent on temperature, but in
photography we are only interested in "cold" saturated
solutions, that is solutions at room temperature

PERCENTAGE SOLUTIONS

A certain amount of misunderstanding exists in some quarters
as to how a solution containing a prescribed percentage of a
particular constituent should be prepared.

Suppose we want a 10 per cent solution of potassium
bromide: we weigh out 10 parts of the bromide, it may be
100 grains or 10 grams, and we dissolve it, not in the full
quantity of water required, but in about three-quarters of
the amoimt. When the bromide is wholly dissolved we then
make up the liquid to the correct volume. If we have weighed
out 100 grains, then we require 1,000 grains of solution by
weight. That is, 2i ounces within a few minims. If we have
taken 10 grams we require exactly 100 millihtres, so as to
get a 10 per cent solution by weight. It is quite true that had
we dissolved 10 grams of bromide in 100 ml. of water, the
error would have been a small one and not of any significance
in photographic operations, but we should not have made up
an exact 10 per cent solution.

The use of correct weight per cent solutions is particu-
larly helpful when it is desirable to obviate the weighing of
numerous very small quantities. It is much easier and quicker
to measure out a few minims or a millilitre or so of solution
than to weigh a grain or the tenth of a gram, provided always
that the photographer uses the metric system. It has to be

111

admitted and is clear from the following example that when
working with the avoirdupois system the use of percentage
solution is not quite so convenient.

Suppose we required a solution having the composition

Potassium ferricyanide 100 grains 5 grams

Potassium bromide 30 grains 1.5 grams

Water to make 40 ounces 1000 ml.

If we have stock solutions of 10 per cent potassium ferri-
cyanide and 10 per cent potassium bromide, we make our
solution up by taking:

Potassium ferricyanide,

10% solution

2 ounces

50 ml.

Potassium bromide.

10% solution

5 drams

15 ml.

Water to make

40 ounces

1000 ml.

Certain chemicals which keep well in solution can also be
kept on the shelves in standard per cent solutions.

DILUTE SOLUTIONS

For preparing dilute solutions of known strength from
concentrated solutions it is, of course, essential that the per-
centage content of the concentrated solution be known.
If we are working on the metric system using cubic centi-
metres, the procedure is very simple.

Suppose we want a 10 per cent solution and our con-
centrated solution contains 40 per cent. We take 10 ml. of
the concentrated solution and add water to make the total
volume 40 ml., then we have 40 ml. of a 10 per cent solution.
If our concentrated solution contained only 32 per cent then
we should still take 10 ml. but we should add water to make
32 ml. Hence using metric volumes we take the number of
ml.'s representing the percentage we require in the dilute
solution and we add water to make up the number of ml.
equal to the percentage of the concentrated solution.

With English measures it is not so simple unless we
confine our volumes to minims or drams, when we can use
the same rule; hence to make a 10 per cent solution from a
40 per cent we should take 10 drams of the 40 per cent

112

solution and add water to make 40 drams (5 ounces) and so
on.

WATER UP TO . . .

In many formulae we find the instruction "water up to" or
"water to make" and then the required volume is given.
This is always a clear direction to dissolve the ingredients
called for by the formulae in a lesser volume of water,
generally about two-thirds, and then when solution is
complete to add further water to bring the whole to the
required volume.

As already mentioned, it is often the custom in modern
formulae to direct that a certain volume of the water shall
be used at a temperature of 120°F. (50°C.). In such formulae
the total volume of water required is usually indicated at
the bottom of the list of ingredients accompanied by the
sentence, "water to make", or sometimes "cold water to
make". The meaning of such directions should be quite
clear from the above account.

WEIGHTS AND MEASURES

Some formulae in this book are given first in English
Avoirdupois, and then in the metric system. It is to be noted
that the figures in the two systems are not interchangeable,
that is to say, a formula must not be compounded by
weighing some of the constituents on the English system and
some of the metric. The finished solutions, whether made by
the English or the metric system, will be similar.

It should also be noted that the English pint, quart and
gallon are not the same as the American measures of the
same names. The United States' gallon has 128 ounces
against the English gallon of 160 ounces. Hence, in the United
States, the pint is 16 ounces, the quart is 32 ounces and the
gallon is 128 ounces. Whereas in England the pint is 20
ounces, the quart is 40 ounces and the gallon is 160 ounces.

The conversion of British weights and measures to metric,
or vice versa, if carried out in the usual way by using exact
factors, is a somewhat troublesome procedure owing to the
fractions or decimals involved. As a result various con-
ventional conversion factors are employed which, while not

113

X.— ENGLISH, AMERICAN AND METRIC EXACT VALUES

I. — British Imperial Quart to U.S. Quart

Grains, ounces or pounds per British Imperial quart (40 fluid ounces)

multiplied by 0.833 = grains, ounces or pounds per U.S. quart (32 U.S.

fluid ounces).

2. — 6f/t/sh Imperial Quart to Litre

Grains per B.I. quart multiplied by 0.05696 = grams per litre
Ounces „ ,, „ „ by 24.92 = grams per litre

Pounds „ by 398.7 = grams per litre

3. — Litre to British Imperial Quart

Grams per litre multiplied by 17.54 = grains per B.I. quart

„ „ „ „ by 0.0401 = ounces „ „ „

, „ by 0.002506 = pounds

4. — U.S. Liquid Measure to Litre

Grains per U.S. quart multiplied by 0.06847 = grams per litre
Ounces „ „ „ „ by 29.96 = grams ,, „

Pounds „ by 479.3 = grams „ „

5. — Litre to U.S. Measure

Grams per litre multiplied by 14.6 = grains per U.S. quart

„ „ „ by 0.03338 = ounces

„ „ „ by 0.002086 = pounds „

6. — British Imperial Liquid Quart to U.S. Liquid Quart

Ounces (fluid) per British Imperial quart multiplied by 0.8 = ounces (fluid)
per U.S. quart.

7. — British Imberial Liquid Quart to Litre

Ounces (fluid) per British Imperial quart multiplied by 25.00 = millilitres
per litre.

8. — Litre to British Imperial Liquid Quart

Cubic centimetres per litre multiplied by 0.03999 = ounces (fluid) per
British Imperial quart.

9.— U.S. Liquid Quart to Litre

Ounces (fluid) per U.S. quart multiplied by 31.25 = millilitres per litre.

10. — Litre to U.S. Liquid Quart

Millilitres per litre multiplied by 0.032 = ounces (fluid) per U.S. quart.

XI.— AVOIRDUPOIS AND METRIC WEIGHT EQUIVALENTS
Pounds Ounces Grains Grams Kilograms

1.0

16.0

7000.0

453.6

0.4536

0.0625

1.0

437.5
1.0

28.35
0.0648

0.02835

0.03527

15.43

1.0

0.001

2.205

32.27

15430.0

1000.0

1.0

114

XII.— BRITISH LIQUID AND METRIC MEASURE EQUIVALENTS

Gallons

Quarts

Fl. Ounces

Fl. Drams

MillUitres

Litres

1.0

4.0

160.0

1280.0

4546.0

4.546

0.25

1.0

40.0

320.0

1136.0

1.136

1.0

8.0

28.41

0.02841

0.003125

0.125

1.0

3.551

0.003551

0.03520

0.2816

1.0

0.001

0.2200

0.8800

35.20

281.6

1000.0

1.0

XIII

.—U.S. LIQUID AND METRIC MEASURE EQUIVALENTS

Gallons

Quarts

Fl. Ounces

Fl. Dran)s

MillUitres

Litres

1.0

4.0

128.0

1024.0

3785.0

3.785

0.25

1.0

32.0

256.0

946.3

0.9463

1.0

8.0

29.57

0.02957

0.000975

0.0039

0.125

1.0

3.697

0.003697

0.03381

0.2705

1.0

0.001

0.2642

1.057

33.81

270.5

1000.0

1.0

exact, are sufficiently correct for all practical purposes. One
of these conventions has been used in this book throughout
(except in a number of cases where the author of a formula
has laid down definite avoirdupois and metric alternatives of
his own).

For example, it will be seen that the Avoirdupois ounce is
taken as being equivalent to 25 grams and the gram as being
equal to 20 grains, whereas their true equivalents are 28.35
grams to the ounce and 15.43 grains to the gram respectively.
Although such differences may appear appreciable, in actual
practice that is not so because the relative proportions of
soUd to liquid in the two formulae, that is, in the Avoirdupois
and the metric respectively, are much more nearly correct
than would appear at first sight, hence the percentage values
of the various solutions, when made up in accordance with
this convention are sufficiently accurate.

pH DETERMINATION

In many cases, especially in the processing of colour materials,
it is essential to maintain the pH of solutions at its correct
value. The simplest method to determine the pH is by the

115

use of indicators. These are substances which impart to the
solution to be tested a colour dependent upon its pH value.
For reasonably accurate pH determination, they must show
a definite and complete change of colour over a short range
of pH. The classical method using litmus paper is for this
reason a very unsatisfactory one because this paper changes
its colour from red to blue over the comparatively wide pH
range from 5.0 to 8.0. Litmus paper should, therefore, only
be used to determine roughly whether a solution is acid or
alkaline.

INDICATOR SOLUTIONS

For the actual pH determination, more sensitive indicators
have to be used of which there is a large number available.
A considerably shortened list of such indicators, arranged in
increasing order of pH is given in the following table.

XIV.— INDICATORS FOR pH DETERMINATION

Indicator

pH Range

Colour Change

Cresol Red

0.2—1.8

Red to Yellow

Thymol Blue

1.2—2.8

Red to Yellow

Bromophenol Blue

2.8—4.6

Yellow to Violet

Bromo-cresol Green

3.6—5.2

Yellow to Blue

Bromo-cresol Purple

5.2—6.8

Yellow to Violet

Bromo-thymol Blue

6.0—7.6

Yellow to Blue

Phenol Red

6.8—8.4

Yellow to Red

Phenol phthalein

8.3—10.0

Colourless to Violet-Red

Thymol Blue

8.0—9.6

Yellow to Blue

B.D.H. 901!

9.0—11.0

Yellow to Violet-Grey

B.D.H. 1014

10.0— 1 1.0

Green to Brownish-Grey

„

1 1.0— 12.0

Brownish-Grey to Pink

»f

12.0—13.0

Pink to Reddish-Orange

13.0—14.0

Reddish-Orange to Orange

The approximate pH value of a solution can be determined
by usuig universal indicators. These change colour over the
whole spectrum from red to violet within the range pH 3.0
topH 11.0.

To facilitate the assessment of the correct coloiu" change,
an indicator may be used in connection with a series of buffer
solutions having known pH values. A given amount of the
indicator is added to the test solution and to each buffer, and

116

PORTABLE pH METER

^^^^^

An EIL portable pH meter: (a) pH scale, (b) combined glass electrode
(pH sensitive) and reference electrode, (c) temperature compensator,
(d) set buffer control, and (e) control switch.

8 117

XV.— COLOUR CHANGE OF UNIVERSAL pH INDICATORS

pH 3.0 red

4.0 deeper red

5.0 orange-red

5.5 orange

6,0 orange-yellow

6.5 yellow
7.0 — 7.5 greenish-yellow

8.0 green

8.5 bluish-green

9.0 greenish-blue

9.5 blue
10.0 violet
10.5 reddish-violet
1 1.0 deeper reddish-violet

the pH of the test solution is that of the buffer with which
it matches. Comparators are also available which largely
overcome the necessity for preparing a series of buffer
solutions and which simplify correct matching in the case
of coloured or clouded test solutions. There are various
types of such comparators, some depending on a series
of standard buffer tubes, others using permanent colour
standards.

INDICATOR PAPERS

Another simple means of determining the pH value is with
the use of indicator papers. The best known material of this
type is litmus paper with which however, for the reasons
already mentioned, only acid from alkaline solution can be
distinguished. Modern test papers cover a much shorter
range of pH and are, therefore, more accurate. Most of the
indicators in Table XIV are available in the form of indicator
papers too and in addition there are special indicator papers
prepared from mixed indicators comprising "narrow range"
and "wide range" papers. "Narrow range" indicator papers
cover the range from pH 2.5-10.0 and the covers are printed
in the colours of the papers at intervals of 0.3 pH units.
The "wide range" indicator papers carry colour standards
for pH values at intervals of approximately 1.0. For
the best results, it is advisable to dip the papers into
the solution rather than to "spot" the liquid on to the
paper.

118

pH METER

In view of the fact that the change of pH in an aqueous
solution is essentially an electro-chemical phenomenon, the
determination of pH can be carried out in a very accurate way
by direct electrical means. The concentrations of the hydrogen
and hydroxyl ions are so related that only one of the two
need be determined. The electrical potential between a glass
electrode and the solution surroxmding it is indicative of the
hydrogen ion concentration. In order to measure this
potential with a meter, a constant potential reference electrode
(calomel) is used to complete the circuit. The meter scale is
cahbrated in units of pH which is defined as a negative
logarithm of the effective hydrogen concentration.

pH meters are available in a large variety of models,
either mains or battery operated, all of which are easy to
handle and give direct and accurate readings. For the
photographic worker a small portable unit will usually be
sufiicient (see page 117). The process of measuring consists
simply of dipping an electrode assembly into the solution and
observing the reading on the scale of the instrument after
cahbration of the meter by dipping the electrodes in buffer
solution(s) of known pH value.

The electrode should be treated with great care and never
left dry but always dipping in a beaker of distilled water.

119

Arrangement of the Dark- Room

The fact that the handling of sensitive photographic materials
requires a dark room does not mean that any inconvenient
comer should be chosen.

Not only should there be sufficient space to work in
comfort, but ventilation should be good and the conditions
such that even a prolonged spell in the dark-room should
be possible without any inconvenience and certainly without
any unhealthy influence. Photographic materials are just as
sensitive to bad conditions, poor ventilation, damp, etc., as
the human organism.

DARKENING THE ROOM

Darkening the room usually involves dealing with a window,
and there is a fairly wide choice of methods. The important
point is so to arrange matters so that the window can easily be
opened when required.

A very simple arrangement consists of a wooden frame
which fits snugly into the window opening, the frame being
filled with some opaque substance such as three-ply wood,
thick cardboard or even opaque cloth. If the edges require
seaUng this can be done with adhesive tape.

Where the window is fairly large, a very practical arrange-
ment is one in which the opaque material takes the form of
a roller blind running in slits at the side which form an
efi'ective light seal. Such frames are not now commercially
manufactured but the handyman can make one for himself
without much trouble.

The point to remember is that the slides at the side in
which the blind runs must be deep enough to form a good
Ught seal. They should be not less than 2 inches deep and
about l/5th inch across, and should be painted matt black

120

inside. The spring roller blinds can be obtained easily and
are built into a partly-enclosed cover at the top of the frame.

WALLS AND FLOOR

The old idea that the walls of a dark-room should be black
or some very dark colour is now dead. Modern darkrooms
have hght-coloured walls which allow reasonable light
in the room. Remember that the walls can only reflect
the light which falls upon them: if that light is safe for
photographic materials the hght they reflect is also safe.

The most serviceable colour for walls is a light grey or
even a pure light yellow: the ceiling and, if desired, the upper
part of the walls can be finished in white: this is particularly
useful when indirect hghting is used (see page 122).

The lower part of the walls should be finished with a
waterproof coat which wiU allow their being wiped down
and cleaned with a damp cloth. The area of the wall behind
the wet bench where developing and the like is carried out,
also behind sinks where they occur should be especially
protected against splashes, etc. This can be done either by
applying a couple of coats of a good oil paint or by fixing
plastic sheeting in such areas. Where a really large volume
of work is being done, thin sheet lead is very suitable.

Where rather dim light is much used, as when pan-
chromatic negative material predominates, a useful tip is
to paint the corners and edges of tanks, tables, cupboards and
the like with white. This renders movement in the dark-room
much easier and much more safe.

In a busy dark-room the floor calls for special considera-
tion. It should be protected against moisture and chemical
action. The best material is asphalt, or one of the special
chemical resistant concrete coatings, but these are expen-
sive and cannot be laid everywhere. The next best is a good
quality linoleum which is kept clean and well waxed. This
can be underlaid with bitumen paper as an extra precaution
against liquids getting through and damaging the actual floor.

DARK-ROOM ILLUMINATION

The adequate and comfortable handling of a negative material
in the dark-room is very largely dependent upon safe and

121

proper dark-room lighting. The lighting of a photographic
dark-room is a compromise between providing illumination
of such colour and intensity that the sensitive materials will
not be fogged and one which will nevertheless enable the
operator to work with minimum inconvenience. It is, there-
fore, essential that the correct safelight filter is selected and
that it is used in a housing of appropriate design and fitted
with a bulb of the correct wattage.

Safelight Filters. Ordinary blue-sensitive emulsions can be
handled in a quite high intensity of red, dark-brown or red-
brown Ught. Orthochromatic materials must be used in a
reasonable intensity of dark red light. Panchromatic films
are sensitive to all colours and require the use of a hght of
lower intensity and a dark green filter. These materials are
comparatively little sensitive to this colour while the eye is
appreciably more sensitive to green than to red particularly
at low intensities.

Special filters (see Table XVI), are used for X-ray and
infra-red materials. However, in all these cases the sensitive
material used must not be exposed to the light for a longer
period than necessary nor brought nearer than the minimum
recommended distance from the lamp.

Dark-Room Lamps. The actual lighting or illumination of
the dark-room depends upon whether it is a small room used
only occasionally, or a fairly large room in which developing
is being done fairly constantly. For the small dark room
direct lighting is sufiicient. As a general rule a 25-watt pearl
lamp should be chosen and the light source arranged about
4 ft. from the working place. For a larger dark-room where a
good volume of work has to be done, indirect lighting will be
required as general illumination. The reflecting surface,
usually the ceiling, shoiild be smooth and white. If theroomis
too high or the ceiling otherwise unsuitable, a reflector should
be suspended above the lamp.

A suitable set-up is a white ceihng board about 5 ft. X 4 ft.
fixed about 10 ft. from the floor with a ceihng-type dark-room
lamp suspended approximately 16 in. below it. A 25-watt
pearl bulb should be used.

Material which can be handled by indirect lighting should,
nevertheless, not be handled closer than 6 ft.-7 ft. from the
reflecting surface.

122

DARKROOM ILLUMINATION

\^^

For the adequate and compatible handling of a negative material, it is
essential that the correct safelight filter is selected and used in a housing of
appropriate design, fitted with a bulb of the correct wattage.
1. Standard lamp for bench use with 15 or 25 watt bulb. 2. Shelf lamp for
wall or bench use with a 40 watt bulb. The safelight may be swung back-
wards leaving a white glass panel for negative or transparency inspection.
3. Ceiling lamp with two safeUghts and 15 or 25 watt bulb. Provides both
direct and indirect illumination. 4. Lamp for wall fixing to give local
illumination with 15 or 25 watt bulb.

123

SODIUM SAFE LAMPS

These lamps provide maximum general illumination with adequate safety
for low-speed non-colour-sensitive materials. The greatly-increased level
of general illumination affords much greater working comfort with very
low running cost. The modem type of this lamp does not only contain
the sodium tube, but combines it with a tungsen bulb,
(a) A sodium tube, (b) 25-watt tungsten bulb, (c) Leak transformer, (d)
Ceiling box, (e) Second 25-watt tungsten bulb, (f) Capacitor.

124

The pyramid lamp, see page 123, is designed to provide
either direct or indirect illumination, as is the very similar
beehive lamp. These lamps can be himg from the ceiling or
fixed to the wall and can be adjusted to throw the light on
the place where it is required. Bulb, 25-watt pearl, distance
not closer than 4 ft.

The work-bench lamp is designed to give direct dififused
light on to the working place from the wall or shelf or the
bench itself. When the lamp is mounted on the wall a space
of at least 1 in. must be left to allow a clear passage of air at
the back to prevent overheating.

The ceiling lamp of the type shown on page 123 can also
be supplied in a model incorporating two safeUght filters,
one arranged in the bottom of the lamp for direct illumination
and one on top of the lamp for indirect illumination. Both
filters can be used simultaneously or separately. If both safe-
lamps are used the working distance should be not closer
than 4 ft. from the bottom of the lamp (bulb 25-watt pearl).

SODIUM SAFELAMPS

Sodium safelamps are especially suitable for large printing
rooms, not smaller than about 20 X 30 ft. They provide
maximum general illumination with adequate safety for low
speed non-colour sensitive materials. The design of these
lamps is such that the illumination from one sodium safelamp
is equal to that of about ten conventional dark-room lamps.
The greatly increased level of general illumination affords
much greater working comfort with very low running costs.

The modern type of this lamp not only contains the
sodium tube, but combines it with a tungsten bulb. DifiFusers
producing either an amber coloured light or an orange light
can be used. The light from one sodium safelamp consumes
an average of only 75-95 watts.

The working distance from the lamp should be at least
10 ft. When the lamps are to be used in smaller rooms, it is
essential to fit the special neutral density filters provided for
these lamps, to reduce the brightness of the light to a safe
level. The lamp shown on page 124 is cylindrical in shape,
the outside case and the two end pieces being plastic mould-
ings. One end piece is fitted with two bayonet cap lamp
holders for the sodium lamp and a tungsten lamp. The other

125

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H
I

Qo:

— '_!

Qo:

'e>

J c

^(5

•^m

LO to

DO CO

13§

0(j

? c

rt -D ro

126

end piece is fitted with one lamp holder for a second tungsten
lamp. The lamps are usually suspended in a horizontal
position on two chains from the ceiling. The electrical con-
nections from the safelamp are plugged into the sockets of the
ceiling box. A special transformer is required suitable for use
on 50 cycle AC supplies. Another necessary accessory is a
power factor capacitor.

VENTILATION

Every dark-room should be well ventilated, but the means
used to that end will naturally depend upon its size and the
volume of work done in it.

In large business establishments an installation is required
both to provide fresh air and to exhaust the used air.

In a room of normal size which is reasonably well ventil-
ated when in ordinary use, two openings, one at ground
level and one at ceiling level, should provide adequate ventil-
ation. Naturally they must be light tight, but this is not
difficult to arrange. The overall size of the openings should
be about 6 x 30 in.; the light traps are formed by thin
boards providing a double right angle channel which
effectually prevents any direct beam of light penetrating.
Each light trap must be painted matt black over the whole
of the interior. The two wings of the light trap can be about
3 in. apart (see page 131).

HEATING

Whenever possible it is best to maintain the temperature of
the dark-room at approximately 68°F. (20°C.). If central
heating or air-conditioning is not available electrical heaters
that do not give out any light are recommended, such as oil-
filled radiators or tubular heaters fitted with thermostatic
control. Paraffin and gas heaters should never be used since
not only do they emit light but they use up the oxygen of the
air and their fumes may affect photographic materials. If the
temperature of the dark-room can be kept close to the working
temperature thermostatic baths for maintaining the temper-
ature of the processing solutions are not required for small
scale processing.

In summer months or in hot climates where the temperature

127

is likely to be above 68°F. (20°C.) refrigeration units can be
used and for the professional or industrial dark-rooms full
air-conditioning that ensures adequate temperature control
and ventilation is recommended. For the amateur, however,
solutions will have to be cooled to the required temperature
or shorter development times used (see page 72).

LIGHT-TIGHT ENTRANCE

In the case of a busy dark-room where there is much move-
ment of personnel, the entrance should be some form of
light trap.

The simplest way is to build a Ught-tight space into
which the door can open, in front of which is hung a heavy
light-tight curtain. For large establishments an arrangement
with double doors and more space between them is necessary,
or the light-tight labyrinth (see page 130).

THE WORKING PLACE

As the greater part of the work in a dark-room consists of
handling solutions, an ordinary work bench is unsuitable,
and in planning a dark-room, provision should be made for
tanks or sinks to accommodate the various baths.

In the small dark-room stoneware sinks can be used, but
where a big volume of work has to be handled lead-lined
wood troughs or sinks are preferable. A wooden rack should
cover the bottom of the sink so that dishes and tanks can
stand on it to allow the free flow of liquid through the sink.
As an extra precaution against wet floors, etc., the under-part
of the tanks can be provided with a separate draining board
(see page 130).

In large installations it is usual for the fixed films to be
washed in a daylight or otherwise lit room; this involves the
provision of a light-tight trap for passing in and out.

IMPROVISING A DARK-ROOM

Such arrangements as have just been discussed are not for
the amateur, who frequently must make the bathroom his
dark-room. In such a case the best arrangement is to have a
wooden rack which fits on top of the bath (see page 129).

128

DARKROOM LAYOUT AND EQUIPMENT

Left Top and Bottom: TWO IMPROVISED DARK-ROOMS. Right, 1-4:
METHODS OF WASHING. Right, 5: MAKING A WOODEN TANK

OR SINK
(Seepages 128, 134)

129

DARKROOM LAYOUT AND EQUIPMENT

c :

Top: DARK-ROOM WITHOUT RUNNING WATER.

Right Bottom: GROUND PLAN OF LARGER DARK-ROOM.

Left: ARRANGEMENTS FOR LIGHT-TIGHT ENTRANCE

(Seepages 134-135)

130

DARKROOM LAYOUT AND EQUIPMENT

Top and Centre: DARKENING WINDOWS AND VENTILATION.
Bottom: LIGHT-TIGHT HATCH WITH SAFETY LOCKING DEVICE

(See page 135)

131

DARKROOM LAYOUT AND EQUIPMENT

ARRANGEMENT OF LARGE DARK-ROOM FOR BUSINESS
PURPOSES

(See page 136)

132

DARKROOM LAYOUT AND EQUIPMENT

QSB0

1. COOLING SYSTEM FOR TANKS. 2. HANGERS FOR ROLL

FILMS. 3. HANGERS FOR PLATES AND FLAT FILMS. 4. STANDS

FOR TANKS. 5. DRYING CUPBOARD

(See page 136)

t 133

On this can be placed a large enamelled dish which can be
supplied with water through a rubber tube from the tap.

Where a small room is available, then it can be arranged
so that everything required in ordinary dark-room work is
to hand (see page 130).

When possible, arrangements for drying as well as for
printing, enlarging, etc., should be separated from that part
of the room where developing and the like is carried out.
This can sometimes be done in a simple manner by dividing
the room into two by means of a light partition which allows
one part to be used in daylight while the other remains the
actual dark-room. In such a case only the apparatus which
really belongs to the dark-room is kept there; all other
operations, including the washing of materials if desired, are
then carried out in the other room in which all after-treatment
of the negative is done, including reduction or intensification
if necessary (see page 130).

Page 129 IMPROVISED DARK-ROOMS. The drawing shows a
method of improvising a dark-room in a bathroom or even a lavatory.
It consists in providing a wooden frame of such dimensions that it can
rest on the sides of the bath, or on small supports if a lavatory has to
be used. The frame supports either a metal tray or wooden dish which
has a drain hole and a rubber tube to carry away waste. The bottom
of the tray or dish has a wooden rack upon which dishes or tanks can
rest. In the upper drav/ing a daylight developing tank is shown. In
addition to the frame a shelf is provided upon which the necessary
additional apparatus can rest, such as a dark-room clock, the safelight,
measures, bottles, etc. In the upper drawing a simple dark-room lamp
is shown, but below is one with three safelights, yellow, green and red,
which are controlled from the switch at the side.

Page 129 (1-4): RIGHT AND WRONG METHODS OF WASHING.
However washing is done it is essential to remove the used wash water
which contains hypo. The hypo left in the emulsion diffuses out into
the water in the vessel and remains there unless special measures are
taken to remove it. In case 1 this is not achieved; unless the stream
of v-iater from the tap is very strong it simply overflows at the sides.
The arrangement in 2 is better, where the water flows in at the bottom
of the wash vessel; but 3 and 4 are better still, where the water is syphoned
away and constantly being renewed by fresh water straight from the
tap, so gradually removing all the hypo. In 3 the syphon is fixed at the
side of the tank, but in 4 it is built into it and is part of the outflow.

Page 129 (5): MAKING A WOODEN TANK OR SINK. The drawing
shows how the sink shown on page 125, left, can be built in a simple
manner using wood. The inside of the tank can be painted with bitumen
paint, or lined with thin lead or polythene sheet.

Page 130 (Top): DARK-ROOM WITHOUT RUNNING WATER.
Many a photographer has to manage without running water. The

134

drawing shows a good arrangement under such conditions. One-half
the working bench or table is made in the form of a sink, which has a
drain leading into a bucket. Above the sink, on a bracket, is a water
tank. Lighting is by means of a dark-room lamp, hung from the ceiling.
The drying rack for plates is on the shelf and a small developing tank
is in the sink. Dishes, measure, etc., are on the table.

Page 130 {Bottom): GROUND PLAN OF LARGER DARK-ROOM
FOR BUSINESS PURPOSES. The main part of the plan shows the
arrangement of the dark-room proper with light-tight entrance
communicating with the room on the left. A is the general work or sorting
table with shelf B. C is the cupboard for the developing hangers, D the
developing tank, E the rinsing tank between developing and fixing, F
fixing tank and G the washing tank. I is a large sink in which dish develop-
ment can be carried out. J and K are ceiling safelights and L is a light-tight
hatch. Taps, wall safeUghts, etc., are indicated by easily understood
symbols.

Page 130 {Left): ARRANGEMENTS FOR LIGHT-TIGHT EN-
TRANCE AND EXIT. (1) Door with heavy curtains hung either side of
the door openmg. (2) Small cubicle with double doors. (3) Labyrinth
without doors, allowing free ingress and egress, with or without curtains; if
the side passage can be made sufficiently long, curtains are not
necessary.

Page 131 {Top): SIMPLE WINDOW SHUTTER OF PLY-WOOD.
A wooden frame is fitted to the window and the sheet of ply-wood
screwed to it as shown in top left-hand diagram. Ventilation can be
assured, as seen in the top centre sketch, by means of a row of holes
cut in the ply-wood, over which is arranged a small light-lock, the details
of which are indicated in the top centre and right-hand sketches. The holes
in the main sheet of ply-wood are protected on the inside by the box-like
structure with opening at the top, while on the outer side another similar
structure carries a row of holes situated some inches above those in the
main sheet of ply-wood, thus providing a light-lock which allows free
access of air but prevents any light entering.

Page 131 {Middle): DARKENING BY ROLLER BLINDS. The
blind runs in slots at either side of the window which provide efficient light-
traps. If desired a ventilating trap can be arranged at the bottom of
the blind as shown in the sketch on the right-hand side. The arrangement
is similar to that described above, and can be at the side or across the
whole width of the window as desired.

Page 131 {Bottom): LIGHT-TIGHT HATCH WITH SAFETY
LOCKING DEVICE. The details can be seen from the three sketches.
Two iron levers, each with a weight which normally keeps them in the
locked condition, are fitted to the side wall of the hatch. Each door has a
countersunk catch into which one end of the levers can fall and also
a small ramp set opposite the other lever which prevents it locking so long
as the door is open. As soon as one door is opened, thus removing the
ramp, the corresponding lever falls by virtue of the weight and so auto-
matically locks the opposite door. When the open door is closed the ramp
again comes into action, raising the lever and so releasing the opposite
door.

135

Page 132: ARRANGEMENT OF LARGE DARK-ROOM FOR
BUSINESS PURPOSES. The space is divided into two rooms. On the
left the developing and fixing is carried out, while on the right the washing
is done. Communication between the rooms is by means of a hatch. The
tanks in both rooms are raised from the floor and so guarded that spots,
splashes or drops of fluid can drain away and not collect on or
damage the floor. A slightly raised gallery is provided which in fact is
a long, shallow tank or sink, in which is placed the wooden rack D
which acts as foot walk and support for the tanks 1, 1, 2, etc. The sink
or channel B is provided with a drain C and a pipe leading to the outside
drains. In the room on the left are three developing tanks, 1, 1, 1, a rinsing
tank 2 and the fixing tanks 3. These last are built into the wall H, so
that they project into the room on the right and are provided with light-
tight lids. This allows the fixed films to be taken out, with their holders
7, in the well-lit room on the right without interfering with the operations
in the dark-room. After they are taken from the fixing tanks they are
washed in the washing tanks 4, 4, 4. In the dark-room light is obtained
from the wall dark-room lamps 6, of which a sufficient number are
installed to provide safe but adequate lighting; in the room on the right,
wall lamps can be installed but safelights are not necessary. The tanks
are provided with taps E at the base, running into the underlying sink so
that they can be emptied as required. Ventilating spaces are provided in
the wall H just below the ceiling G with the necessary light-traps F, and
others at floor level to ensure plenty of fresh air.

Page 133 (1): COOLING SYSTEM FOR DEVELOPER AND FIX-
ING TANK. The importance of temperature and its effects in develop-
ment, see page 106, are such that every attempt should be made to ensure
that the correct temperature is maintained. To this end the simple arrange-
ment shovm here can help either in cooling in hot, or in warming in cold,
weather. The piping is usually of stainless steel. When used for cooling
the water can be used in the washing tank. Coimections are by flexible
rubber tubing.

Page 133 (2): HANGERS FOR ROLL FILMS. The films are secured
to the hanger by clips of suitable metal — stainless steel being the best;
the hanger rests on the walls of the tank; at the bottom of the film a
weight is attached to prevent curling of the film. When using such hangers
the films should not be loaded too closely together in the tanks.

Page 133 (3): HANGERS FOR PLATES AND FLAT FILMS. Here
the flat films are secured by clips while the plates are held in wire cradles.

Page 133 (4): STANDS FOR TANKS. Stands of varying shape and
size for raising tanks from the floor can be built, as shovra in the diagram,
of wood and lined with bitumen paper.

Page 133 (5): DRYING CUPBOARD. The quick and certain drying
of negative materials calls for warmed air in constant circulation and
a good supply of fresh air. The diagram illustrates a drying cupboard
in which the air is heated by an electric heating element and circulated
by a ventilator and baflles with a small electric fan.

136

Methods and Apparatus

There is a bewildering choice of possibiHties for the develop-
ment of photographic negative materials. There are hundreds
of formulae, dozens of methods and innumerable items
of apparatus. The simplest question is which method to
employ;

(1) Dish or tray development.

(2) A small developing tank.

(3) Large-tank development.

Which of these methods is the most practical depends
upon the character of the negative material and the quantities
that have to be handled.

Dish or tray development is suitable for single plates or
flat films. Roll film or film for the 35 mm. camera should
not be dish developed; such a method is unpractical and will
almost certainly result in scratches or streaks along the length
of the film. The process also becomes dirty and unpleasant.

The small developing tank is much used today for develop-
ing single roll films, including 35 mm. This is generally a
small cyhndrical tank taking just sufficient developer solution
for the correct development of one film. Multiple tanks are
also available to take a few films.

For the handling of both plates and films in quantity,
large-tank development is now the general rule everywhere,
because of the enormous saving in time and money.

INDIVIDUAL OR TIMED DEVELOPMENT?

In earlier days the question of individual development

played a great part in the selection of development methods.

Individual development involved influencing the character

of the negative by varying the time of the development at the

137

desire or caprice of the photographer. This meant that the
negative image had to be under observation during the de-
velopment process, and for this reason dish or tray develop-
ment was preferred to all other methods. The opposite
process was development by time, in which all negatives
were developed for a definite time without special control.

It was argued on behalf of individual development that
errors of exposure could be corrected and the gradation of
the negative controlled to suit the positive material.

In order to see just how far these claims are true, we must
examine the possibilities of influencing the negative character-
istics in and during development. Is there, in fact, any true
foundation for such claims?

We already know (page 35) that time of development has
an influence on gradation and density. The longer the develop-
ment, the steeper the gradation (higher gamma value), until
a definite limit is reached (gamma infinity). If we set out the
growth of blackening of the negative for different develop-
ment times in the form of a diagram showing the various
steps of blackening as on page 27, we shall reveal the actual
character of the development process. We shall see graphically
that with increasing time the steps are steeper, but that finally
they form a kind of platform (= maximum blackening
of the negative), and the density no longer increases.

The possibility of controlling gradation in this manner was
of importance in the early days of photography because the
photographer had only one type of paper at his disposal, and
that paper had only one gradation. In those far-off days, when
only albumen paper could be obtained, the photographer
aimed at obtaining a negative which would produce a good
print on that paper; that meant that he had to produce a
negative that was neither too hard nor too soft. Hence
when his subject was contrasty he developed for softness by
giving a comparatively short development, but when his
subject lacked contrast he had to give a long development and
to obtain a medium contrast negative. His desire for a de-
veloper of a versatile character and for a method which gave
reasonable control of the negative is therefore understand-
able. He preferred to work with a developer which changed
its properties on dilution, on variation of the relative quanti-
ties of its constituents, and which produced different results
according to the time of development appUed.

138

The position of the modern photographer is quite
different. He has at his disposal a range of papers of almost
infinite variety of contrasts and can therefore produce a good
print from any negative whether it be hard or soft in grada-
tion. Moreover, he cannot give individual treatment to a
single exposure because his film provides a series of exposures
which it is, in general, quite impracticable to handle separ-
ately. So, development by time is rarely possible.

The various formulae in this book, when used for the times
indicated in each case, produce negatives having the charac-
teristic of a "normal" negative as defined on page 65.
Where the negatives are of contrasty objects a soft gradation
paper is used, and a hard gradation paper for soft negatives.
Hence what the earlier photographer sought to obtain, often
unsuccessfully, by manipulating the development process is
today more easily and certainly obtained by choosing the
right grade of printing or enlarging paper.

COMPENSATING DEVELOPMENT

In a somewhat similar manner photographic technology
today deals with another question, namely the rectification
of errors in exposure. How it does this can be made clear
by reference to our density staircase or steps on page 25.

What efl'ect has an error in exposure on the building up
of the silver image of our negative? If we give too short an
exposure only the lower part of the staircase will be de-
veloped; with a longer exposure the scale will be extended
towards the upper part.

The great exposure latitude of modern negative material
permits so long a tone scale that there is actually room
for quite considerable errors of exposure. The actual dif-
ferences between negatives which have received different
exposures is not in gradation, as can be see on page 37, for
the steepness of the steps is the same over the whole range,
but in the fact that the densities of the longer exposed negative
lie higher up the scale than is the case with short exposures.
In printing this means that negatives of short or long exposure
can be printed on the same paper, but those with the heavier
or higher densities or blackening require a longer exposure in
printing as compared to those which have had a short or
normal exposure.

139

We can now ask what effect development time has on the
various exposed negatives? If we compare the range of
densities of a negative which has had a short development
time, with another which has received normal development,
we shall see that short development has given us a lower
contrast and densities. That means that we must use a
contrasty paper for printing and a short exposure. So far as
the finished prints are concerned there will be no serious
difference between them, and the same will apply in respect
of errors of exposure, whatever variations we may adopt in
the development process.

In fact, the great exposure latitude of modern sensitive
material is sufficient in itself to bridge over errors in exposure
in the great majority of cases. There are some special ex-
ceptions which we shall discuss in the section dealing with
developer formulae (page 172), but as a general rule it will
be well to avoid any tricks or special techniques in the actual
development.

DISH OR TRAY DEVELOPMENT

In early days this was the most widely-used method of
development. Today it finds application in the handhng of
single plates or films. We have already seen that it a8"ords
the possibihty of observing the growth of the image during
development and, to some extent, influencing the process.
Let us gather together the various factors that can influence
the character of the negative and arrange them as a short set
of rules.

(1) A strongly diluted developer results in a soft
negative.

(2) Increased development time increases contrast.

(3) The stronger the concentration of the developer
the more quickly it wiU develop, and the more
speedily wiU high contrast be reached.

(4) With home-compounded developers increasing
the alkali content provides a means of accelerating
the rate of development and therefore contrast.
This procedure requires great care, otherwise
there is the danger that fog will be produced.

The way in which the properties of a developer can be
varied by altering its composition is shown in Table XVII.

140

The table shows how it is possible to obtain nine variants
of this particular developer, so that almost every type of
result from a very soft to a hard gradation can be obtained.

A dash in the table denotes no change in the standard
formula under the particular heading of the column.

It will be seen that in No. 1 the hydroquinone content is
60 grains (3 grams) and the soda is 2 ounces (50 grams)
and a very soft working developer is obtained. No. 2 is some-
what more contrasty as only the hydroquinone is altered;
in No. 3 the hydroquinone is increased to 100 grains (5
grams) and the soda content is as in No. 1.

In No. 4, the higher hydroquinone content results in more
brilliant, that is somewhat harder, results. In the variations
5-9 the chemical composition of the developer is not altered
but the degree of dilution is varied and so an increasing degree
of brilhance or hardness is attained.

XVII.— VARYING OF FOCAL UNIVERSAL M.Q. DEVELOPER 16

Effect

Quantity of
Hydroquinone

Quantity of
All<ali

Degree of Minutes o
Dilution Developing

'1 60 grains or

2 ounces

<inft

3 grams
2 80 grains or

50 grams

4 grams
3 100 grains or

2 ounces

5 grams

SO grams

r4 100 grains or

Normal -

5 grams

6 —
^7 —

—

1
1

7
5

5-6

6-7

Hard /^ ~

—

1 :1-2
Undiluted

4-5
3-4

The temperature of the developer is very important, and
it should be kept at 68°F. (20°C.) as it greatly affects the
development process.

A low temperature slows down development and hinders
the building up of density, while a high temperature acceler-
ates the process and introduces the additional danger of
fogging.

Dishes or trays for developing are made of plastic, glass,

141

porcelain or stainless steel and should be rigorously reserved
for their special purpose. They should never be used for
other photographic purposes such as fixing, for which
separate vessels should be provided. If the dishes in use are
of the same size and material they should be marked with a
waterproof paint, D for developing, F for fixing, so that there
shall be no confusion and no mixing of dishes. Metal dishes
or tanks other than of stainless steel must be coated with a
good chemical (preferably rubber based) paint for protection.

Plates or films for development are laid into the dish
sensitive face upward, and care must be taken to ensure that
the developer flows evenly and quickly over the whole of
the surface. This is best achieved by tilting the dish slightly
so that the solution accumulates at the lower end, then
placing the plate or film in the dish, quickly lowering the
raised end so that a wave of developer flows quickly but
smoothly over the whole of the plate or film surface. A
little wetting agent added to the developer will avoid the risk
of air bubbles sticking to the surface of the emulsion and
retarding or even preventing development in those areas.

The dish should be kept in gentle movement, by rocking,
during the whole time of development to enstu^e even action
of the developer. This is particularly important in view of
the retarding effect of potassium bromide (see page 91),
which can accumulate locally in the developing film and
cause uneven development if the developer does not flow
freely over the developing surface.

One can now observe the beginning and the progress of
the development process, and if the necessity arises, make
such corrections as seem called for. In the normal handling of
negatives we may meet with the three following possibilities:
(1) Correct exposure. (2) Under-exposure. (3) Over-exposure.

(1) Correct Exposure. As we shall see later (see page 231),
the appearance of the first trace of the image and the way in
which the image builds up varies somewhat with different
developers, but the normal order of appearance and develop-
ment is as follows.

The first to appear are the highlights, those parts of the
subject photographed which were most brilliantly lit; next
come the well-lit parts, then the half tones and finally the
details of the shadows, that is, the darkest or least lit portion
of the picture.

142

The density and gradation of the negative can be roughly
judged by looking at the back of the plate or film and choosing
the right moment for stopping the development process, that
is, the moment that it has reached the desired character. If
the negative appears too soft or thin, development is con-
tinued until every important detail in the picture is visible. If
greater contrast is required, then the time of development
will be increased until it is obtained.

(2) Under-Exposure. This is shown during development
by the appearance of the highlights, then much more slowly
the other details and the half tones appear, but the details in
the shadows refuse to appear even after excessively long
development.

A badly imder-exposcd negative cannot be saved by any
manipulation of the developer. Those parts of it which
received no exposure or an insufficient amoimt cannot be
developed, for there is nothing there to develop. It is there-
fore quite wrong in such a case to attempt the use of a
concentrated developer, the effect of which will be to exag-
gerate the contrast of that part of the image which has
developed without in any way improving the rendering of
shadow detail.

The old-fashioned remedy of diluting the developer is
equally fruitless, for there is nothing in the negative to be
saved. At the best all that we can do is to make use of some
method of after-treatment (see page 339), or choose a more
suitable grade of printing paper.

(3) Over-Exposure. This shows itself in development by
the whole image flashing up quickly, and not merely the high
lights: that is always an indication of over-exposure.

It is not an indication to stop development; on the
contrary, the process should be continued until the negative
is fully developed right through. True, the image will be
dense and the whole negative dark but, thanks to the latitude
of modern materials, the gradation will be a usable one. If
the development be stopped too soon the negative will be
too flat.

JUDGING THE NEGATIVE

It must be accepted that a certain amount of experience
is necessary in order to judge correctly the character of a

143

negative during development. The creamy silver bromide in
the film is deceptive and appears to increase the covering
power of the developed silver. When a negative has been
fixed and the undeveloped silver bromide removed, the nega-
tive looks much less dense than it did before, and appears
to have "gone back" or retrogressed. Hence the old and
well-known rule that the negative examined by the dark-room
light must always appear somewhat denser than is actually
required in its finished state.

Owing to the high general and colour sensitivity of modern
materials, the negative should never be exposed for any length
of time to the dark-room hght. A short glimpse should suffice
to indicate the nature of the control required. Although
we speak of safelights, the term is a relative one and even
the safest red light can fog an orthochromatic film if it is
exposed long enough.

With panchromatic materials control is difficult, even with
a green safelight. The usual green safelight prescribed gives
sufficient illumination to enable one to move about the dark-
room in safety, and to see where apparatus is, but not suf-
ficient to allow judging a negative.

Hence for panchromatic material either time development
should be used (see page 38), or a desensitiser employed
(see page 251).

The emulsion layer on plates or films is very easily
damaged, either mechanically or chemically, at every stage
of the photographic process. It should be a rule never to
touch the emulsion surface with the fingers; a glass negative
should always be held by the edges — if it is a small one, then
the thumb and forefinger should suffice and only the edges
of the negative need be touched. Flat film or roll film
negatives must be held by an edge which is free from any
image.

If the face of an undeveloped plate or film is touched
there is always the danger of markings being caused either
through the natural oiliness of the skin, perspiration or
plain dirt or dust. In any case there is likely to be some
interference with the process of development.

Even after processing and drying the emulsion can easily
be marked and spoiled by being touched with moist or dirty
fingers and such markings are particularly troublesome when
enlargements have to be made.

144

SMALL TANKS

The difBculty of developing a long length of film in a dish
has already been mentioned, and although special long
narrow dishes were once produced for the purpose of
developing films, they did not prove popular. In addition, the
modern fine-grain developers call for a comparatively long
development time, and if the dish or developer container is
to be kept in constant movement while development is taking
place, a great deal of time is lost.

For similar reasons the drum-type of developing machine
did not achieve any great amount of popularity. It consisted
of a glass drum or barrel mounted on metal bearings. Under
the drum was a dish which contained the developer solution.
The film was threaded on the drum and as this revolved so
the film, passing through the developer, was developed. The
drum had to be kept in movement during the whole of the
process, and one real disadvantage was that for much of the
time the developing film was exposed to air which gave rise
to a number of troubles of which aerial fog was only one.
The drum idea has been revived for processing and details of
modern drum and tube processing are described on page 170.

A notable solution of the whole problem lies in the many
small developing tanks which have been evolved. The
essential principle of these is that the film is developed
whilst wound up in spiral form, and that only sufiicient
solution is required to develop a single film. The film is
wound in spiral form, in which it occupies minimum space,
but the conditions must be such that the turns of the film do
not touch one another and that the developing solution has
free access to the front of the films.

In practice this is achieved in two diff"erent ways: by
means of an apron or band which serves to keep the turns
of the film separate, or by a spiral lead in and guide attached
to the central bobbin.

The apron or band type. This was the earliest on the
market. The film and the apron or band are wound up
together on the centre spool of the tank. The apron, which
generally consists of celluloid, has projections on its surface
which serve to support both the front and the back of the
film to be developed, and also ensure the necessary space
for the flow of the developer, the apron is often perforated

145

to help in this direction. The tank itself is usually made of
plastic and has a light-tight lid or cover (seepages 147-148).

The spiral guide type. Here the apron or band is dispensed
with, and the film is held in position during development
by spiral leads or guides forming part of the central bobbin.
Small projections occur at regular intervals round the inside
of the spirals and so hold the film in position, and also allow
free circulation of the developer. This principle permits
of universal tanks which can be used for the development of
films of various sizes: to this end the spiral guides are
made adjustable and can be fixed in any desired position on
the centre axle (see page 148). Modern tanks of this type are
frequently constructed of stainless steel which makes them
more robust and easier to clean than plastic tanks.

The capacity of the smallest of such tanks is about 11
ounces (300 ml.), but those for miniature films take a much
smaller quantity and are therefore very economical.

The loading of the tank must be done in the dark-room,
but once the light-tight cover has been put on, the rest of the
procedure can be carried out in daylight.

Most models are supphed with inlet and overflow so that
the film can be rinsed with water when development is
completed, and then the fixing solution introduced without
necessity of opening the tank or using the dark-room.

Certain types are available which actually permit the
loading operation to be carried out in daylight, and so dis-
pense with the dark-room altogether. The idea is alluring,
but it has to be admitted that these tanks are not so simple
to operate, are somewhat less safe and are distinctly more
expensive (see page 149).

The usual procedure is to place the loaded spiral in the
tank and then pour in the developer. With modern, fast-
pouring tanks, this is usually quite safe. If development time
is at all short, however, it is advisable to fill the tank first
and lower the spiral gently into the developer.

Precautions must be taken against the formation of air
bubbles and their attendant dangers. Many developers now,
however, contain a wetting agent to obviate this problem.
Nevertheless, it is a sensible precaution to disperse any
bubbles that may have formed by giving the tank a short
but fairly strong shake just as development begins.

It is not convenient to maintain the tank in constant move-

146

DEVELOPING TANK, APRON TYPE

(See page 151)

147

DEVELOPING TANKS, SPIRAL GUIDE

(See page 151)

148

Daylight-loading tank

(See page 151)

149

LOADING OF SPIRALS

Development in spiral spool tanks is a weU-proved method, but has always
been subject to some practical difficulty in loading the spools particularly
when using longer films or when a larger number of spools is to be used.
These difficulties can be overcome by mechanical guides which feed the
film automatically into grooves from the centre outwards.
1 . Machine for loading spools automatically. 2. Device for threading film
into the spiral by hand. 3. Multiple-storey tank containing five spools.
4. Loader for longer length of film.

150

ment during development, but a certain amount of agitation
is essential. In many cases this is brought about by revolving
and/or raising and lowering the spiral by means of a rod
projecting through the Ud of the tank. Most modern tanks
are spill-proof and can be completely inverted. If neither is
possible, then the tank must be gently shaken to and fro.
Whichever form of agitation is used, it should be carried out
at regular intervals throughout development.

There exists apparatus which automatically agitates the
spool, either by means of a small water turbine or a tiny
electric motor driving a small pulley on the spool, the
connection being made by a rubber band. The cost of such
a device is, however, somewhat high and, as a result, such
mechanical agitation has not been widely adopted.

Page 147: DEVELOPING TANK, APRON OR BAND TYPE.
Left top: the complete apparatus— thermometer, knob for agitating film
during development, cover, spool and tank. Left bottom: method of
spooling with film and apron, the backing paper being previously re-
moved. Right from top to bottom: processes of development: (1) The
spool is placed in the tank in the dark-room. (2) When the developer
has been added and the cover closed, the tank can be brought into bright
light and development proceeded with. (3) The developer is poured away
and a short rinse given. (4) The fixing bath is introduced and 10 minutes
fixing given. (5) Washing for 30 minutes follows the fixing.

Page 148: DEVELOPING TANK, SPIRAL GUIDE TYPE. Left
top: the assembling of the tank. Left bottom: spool with spiral guide for the
film. The film is wound on to the spool after the backing paper has been
removed. Right from top to bottom: steps in the process: (1) Placing the
film in the tank in the dark-room. (2) Development. (3) Rinse between
development and fixation. (4) Fixation. (5) Washing. The last three pro-
cesses can be carried out in daylight.

Page 149: DAYLIGHT-LOADING DEVELOPING TANK. This
particular model is designed for daylight processing of 35 mm. black-and-
white film when it is in standard 35 mm. cassettes. To use the tank, the
film leader must extend outside the film cassette. The film can then be
loaded, developed, rinsed, fixed and washed in the tank in daylight.
The tank has two chambers, into one of which the cassette of film to be
developed is wound before development. To load the tank, the cover is
raised as shown in the top drawing on the left. The film cassette is inserted
into the cassette chamber and the film leader threaded into the spiral as
shown in the bottom drawing on the left. The cover is replaced on the
tank and the film wound from the cassette on to the tank reel by turning
the reel collar. Now the cassette collar is rotated (first drawing on the
right) to cut ofi' the film from the spool by means of a stationary knife
located within the tank. By lifting out the cassette knob the empty cassette
can be removed (second drawing on the right). The developer is poured
into the opening at the top of the cassette chamber and the film agitated
during development by rotating the reel collar (fourth drawing). The

151

temperature can be measured during development by Inserting a thermo-
meter into the magazine ctiamber. After development is complete, the
developer is poured out, the tank filled with water for rinsing and then with
fixing bath. To dry the film, fasten the end, while it is still on the reel, with
a film clip suspended from the ceiling or a shelf and unwind the film as
shown in the last drawing on the right.

RAPID DAYLIGHT PROCESSING OF 35 mm. FILM

A very simple procedure for the rapid processing of 35 mm.
film in the cassette has been described by Kodak Ltd. The
procedure requires that a twenty exposure 35 mm. film be
given only sixteen exposures: two extra blank exposures
should be made at the beginning of the film and two more at
the end. It is also important to ensure that after the sixteen
exposures have been made the film leader is not re-wound into
the cassette, this can best be achieved by taping the leader
to the take-up spool when loading the film into the camera.

The apparatus required is a small beaker or measure, an
agitation rod approximately six inches long that fits tightly
into the cassette spool and a monobath solution (see page 153).

Processing is as follows :

(1) Cut the leader from the film leaving approximately
one inch of film protruding from the cassette as
shown in the top diagram on page 153.

(2) Wrap the protruding film back around the cassette
and secure with a rubber band as shown in the
bottom diagrams on page 153.

(3) Insert an agitation rod into the cassette and rotate
gently to tighten the film on the cassette spool.

(4) Slowly unwind the film by rotating the agitation
rod anti-clockwise counting the number of turns
until resistance is felt.

(5) Slowly lower the cassette into a measure or beaker
containing sufficient monobath solution (see page
153) to cover the cassette whilst winding and un-
winding the film by the number of turns determined
in step (4). Carry out this winding and unwinding
procedure twice whilst lowering the cassette into
the monobath.

(6) When the cassette is fully immersed wind the film
by half the number of turns originally determined
in step (4) and during the recommended processing

152

RAPID DAYLIGHT PROCESSING OF
35 mm. FILM

oDoioanoaaaa oaaoDDoanoDODD

Preparing a 35 mm., 20-exposure film for development within the cassette.
Top: Removal of the film loader. Bottom, left to right: Wrapping the film
around the cassette, securing the film with a rubber band, and insertion
of the agitation rod.

153

time (about 3-8 minutes depending on the film and
monobath used) rotate the rod to and fro through
about one and a half turns.
(7) After processing lift the cassette and allow the
monobath solution to drain, discard the monobath
solution and immerse the cassette in water of
approximately the same temperature as the mono-
bath. Remove the film from the cassette and wash
and dry the film in the normal manner.
The winding and unwinding operations should be carried
out gently, making sure that the film is not wound too tightly
on the spool; otherwise, scratches may result. It is quite
normal for air bubbles to be released from the cassette during
processing.

Generally too much rotation of the agitation rod during
processing causes dark bands to be formed across the width of
the film, while light bands across the width of the film are
caused by insufficient agitation during processing.

LARGE TANK DEVELOPMENT

Tank development renders possible the development of a
large number of films simultaneously. It is therefore essential
for the mass handling of negative material and is of particular
importance for the photo-finisher.

An intermediate step between the small spiral tank and
the large photo-finisher tank is supplied by tanks with a
capacity of about three gallons. Spirals are used too but they
are placed in baskets (see page 157) making it possible to
develop 18-24 films at the same time. To keep the processing
solution at the correct temperature these tanks can be placed
in a water bath as shown on page 156. Instead of moving
the films manually from tank to tank there are processors
available where the timing, transporting, agitation and
washing is carried out automatically (see page 163). The
processing cycle can be programmed and it is thus possible to
use the same machine for different processes.

TYPES OF TANKS

For large scale production deep tanks are used, big enough
to accommodate all sizes of roll films fully extended. There
are three different types:

154

(1) Developer tanks equipped with a circulating pump
unit which includes motor and pump as well as the heating
and cooling arrangements, this is mounted at the side
of the tank (see page 158). In this way, the space in the tank
itself is reserved entirely for the films and the temperature of
the solution can be controlled during development without
sacrificing tank capacity.

The heating element and the cooling coil are located
in the path of the circulating developer so that an even
temperature is maintained throughout the tank. For smaller
tanks and lower output an immersion heater can be used.

(2) Chemical tanks for the processing solutions in
which agitation and temperature control are not so important.
All the tanks have grooves on top for supporting the
frames and an outlet for emptying the tanks quickly and
completely.

(3) Washing tanks used for rinsing the film thoroughly
between the individual baths and at the end of development.
Fresh water enters through a jet at the bottom of the tank
and causes a turbulence in the tank. The used water flows
off over the top of the tank.

The actual routine of development is as follows :
The films are loaded into frames (see page 158) which
grip them firmly, preventing touching or movement, and
facilitate quick handling. Cut films or plates are inserted into
special frames. The frames are then lowered into the tank
and given one or two sharp up and down movements in
order to displace any air bubbles which may have formed
on the film surface. The negatives must not be left motionless
in any processing solution for the whole of the time. In the
case of developing tanks provided with a circulating pump
the solution is constantly agitated.

AUTOMATIC PROCESSING MACHINES

For large scale production the movement of the frames from
tank to tank by hand would be much too slow a procedure.
Film processing machines do this job automatically and there
are two types in use in which the films are processed either
vertically or horizontally. Timing, temperature control,
agitation and developer circulation, and in most cases also
filtration, are carried out automatically. The films are put

155

PROCESSING BENCH

The tanks are placed in a water bath which keeps them at the correct
temperature. The bench is also equipped with a unit for nitrogen burst
agitation. These processing benches are useful for small scale production
in tanks of 3 gallons capacity.

156

ACCESSORIES FOR TANK DEVELOPER

To accommodate films and sheet films in small and large tanks, some
special accessories are necessary such as baskets for spirals (top right),
sheet film holders (left), clips for roll films (bottom right).

157

PROCESSING TANKS

For large scale production, deep tanks are used, big enough to accom-
modate all sizes of roll films fully extended. There are different types
of tanks as shown in the illustration. Bottom, from left to right: developer
tank with temperature control unit, chemical tank, washing tank. Top,
from left to right: Temperature control unit for developer tanks showing
thermometer circulator, thermostat and immersion heater and cooling
tube: cut film frame: roll film frame.

158

into clips and hung on bars, or into carriers, and then are
passed through the machine automatically. The bars holding
the films (see page 156) are moved up and down and the
films move forward in each tank by a rack. After washing
they pass through a drying tunnel and are taken out ready
for printing.

The level and the working strength of all processing solu-
tions are maintained automatically by a replenishing unit
such as the one shown on page 162. This unit is made of
plastic and has a total capacity of If gallons, enough to
maintain constant level in a 48 gallon developer tank for
about three hours continuous working. The container is fed
through a f in. diameter pipe into a cup connected indepen-
dently by rubber tubing to the bottom of the developer tank.
The cup is set vertically Ln a position coinciding with the
correct level required in the developer tank. The pipe through
which the developer passes into the cup is fitted with a non-
return ball valve to prevent the developer in the tank from
rising into the container. When the level in the developer
tank drops the ball falls away and allows sufiBcient developer
to flow into the cup and from there into the developer
tank.

Besides the straight-line type of processor there is also
available a circular version. The processor consists of a
tubular framework in the form of a circle around which are
arranged a series of deep tanks. The films, fixed to hangers,
are transported from tank to tank by small carriages which
rim round the framework. Each carriage has two motors,
one to drive it from tank to tank, the other to raise and lower
the films.

The tanks are circular, the chemical tanks being water
jacketed. A small pump circulates water from a temperature
control xmit through the jackets. To ensure good heat con-
duction the developing tank is made of stainless steel, the
remainder of rigid P.V.C. Movement of the carriages is
controlled by an ingenious system. Above the tanks are
mounted small coils energized with low voltage A.C. Each
carriage has a pick-up coil which receives a signal as soon
as the carriage is above one of the tanks. This signal operates
a relay which stops the carriage and lowers the films into the
tank. At the end of the processing time a further signal causes
the carriage to lift the film and move on towards the next

159

AUTOMATIC PROCESSING

For large scale production, the movement of the frames from tank to
tank by hand would be much too slow a procedure and therefore film pro-
cessing machines are used. Film processing machines do this job auto-
matically. The films are put into clips and hung on bars and are then
passed through the machine automatically. The bars holding the films
are moved up and down by a chain drive and the films moved forward
in each tank by a rack. After washing, they pass through a drying tunnel
and are taken out ready for printing.

160

MACHINE FOR ROLL FILMS

161

REPLENISHING UNIT

These units are used to replenish automatically the processing solution in
film processors. When the level in the developer tank drops, the ball of
the non-return valve falls away, allowing sufficient developer to flow.

162

AUTOMATIC PROCESSOR FOR SHEET FILM

Instead of moving sheet tilm from tank to tank by hand, these machines
do this job automatically.

(a) Track for automatic carriages, (b) Tubular support for overhead track,
(c) Stainless steel tanks with water jacket, (d) External control panel for
programming the machine, (e) Stainless steel basket or rack for film.

163

tank. A simple timing unit controls the processing time in
each tank.

The main feature of this film processor is its flexibility.
Machines can be supplied for any process merely by provid-
ing the appropriate number of tanks and setting the timing
unit. Should the machine be required for another process this
can be done by re-arranging the tanks and modifying the
timing unit. It is even possible to use one machine for several
different processes, by providing some extra tanks and
programming it to miss those not required. Machines can be
supplied for different outputs. For negative developing the
hangers normally take 12 films. With three carriages fitted
the machines have an output of 30-40 films per hour. By
adding extra tanks and carriages this can be increased to
about 150 films per hour.

Temperature Control. It is of the utmost importance for
large-scale processing that the temperature of the solutions,
especially the developer, is carefully controlled. This can be
achieved either by using a water bath or water jacket for the
solution tanks or by controlling the solution temperature
itself. When only small quantities of photographic materials
have to be processed, manual adjustment of temperature
is practicable. An immersion heater either in the water bath
or in the solution itself may be sufficient but for more accurate
requirements it should be connected with a simple thermostat.

When appreciable quantities of films must be handled on a
production basis a more accurate and dependable tempera-
ture control system is necessary. Thermostatically-controlled
mixing valves provide a compact and economical system for
the control of water temperatures. These valves operate by
mixing warm and cold water to obtain the desired tempera-
ture within about ±i°F. The temperature of the cold water
supplied must of course be lower than the temperature required
for the mixture. In areas where the cold water during summer
months is warmer than the desired temperature, an auxihary
cooling system is necessary.

The water bath or jacket system is usually used for
smaller tanks. Larger developer tanks (see page 158) are
usually connected with a second tank as shown in the drawing.
This tank contains the immersion heater and sometimes a
cooling coil and thermostat. The developer solution is
circulated by a pump and is thus kept at the correct tempera-

164

tiire. At the same time this system provides the necessary
agitation for the solution.

Agitation by Nitrogen. Agitation of developer solution can
be provided either by mechanical devices such as pumps and
propeller stirrers or by gaseous bursts of nitrogen. The
nitrogen gas is released very near the bottom of the tank
intermittently and provides a consistent and reliable agitation
of processing solution. To provide automatic control of the
flow of nitrogen to the processing tank, an electrically oper-
ated solenoid valve is required in the line between the gas
pressure reducing valve and the point of release in the tank.
The burst valve works usually in conjunction with the burst
valve control unit which enables both the duration of the gas
flow and the interval between each burst to be regulated
within wide limits.

To ensure that all parts of the solution receive equal
agitation and that the processing will be consistent, a uniform
pattern of nitrogen bubbles is necessary. A special gas
distributor is therefore used. It consists of a rectangular grid
of plastic tube which is perforated with evenly spaced holes
and is connected to the outlet side of the burst valve. The
grid rests on the bottom of the processing tank and the tank is
carefully levelled so that the pattern of bubbles rises uni-
formly through the solution and is not concentrated to one
side of the tank only. Where the volume of work is large a
separate gas distributor for each processing solution is
desirable. Each distributor is then connected up to a multiple-
outlet manifold at the outlet side of the burst valve. The use
of agitation by nitrogen gas is essential for colour develop-
ment where manual systems of agitation are time-consuming
and wasteful of manpower.

SELF-THREADING ROLLER-PROCESSORS

In these machines the film is transported through the various
stages of processing and drying by powered transport rollers.
A commercially available sheet film processor of this type is
shown on page 166 (Versamat type).

The part of this machine to the left of the panel is the film-
feed section normally located in a photographic darkroom.
The rest of the machine, consisting of the processing section
and the dryer, is located in fully illuminated space on the

11 165

SELF THREADING ROLLER PROCESSOR

The film is transported through the various stages of processing and
drying by powered transporting rollers. This system differs radically from
conventional hand or machine processing methods. Film hangers are
eliminated. The exposed sheet or roll films are hand fed, one at a time,
into the feeding tray. The films are then transported by a system of rollers
through the processing tanks and drying compartment to the deUvery bin.
The temperature of the developer is controlled by circulating the solution
through a heat exchanger and filter, and by a thermostatically controlled
immersion heater in the developing tank. The temperature of the wash
water is regulated by a thermostatically controlled mixing valve. The
machine also incorporates an automatic replenishing system.

166

opposite side of the darkroom wall. To prevent light fog, the
developer and the stopbath sections of the processor are
shielded by a protective cover.

In normal operation, individual sheets of exposed film
are fed singly through a narrow slot in the housing of the feed
section. The film is picked up by rollers and delivered to the
processing section of the machine where it is accepted by a
special grouping of rollers which directs the leading edge
vertically downward. The film is then transported vertically
in this case at the rate of 5 feet per minute, between driven
rollers arranged in staggered positions. Each side of the film
thereby receives identical processing treatment. The Versamat
type processor can process film at rates up to 25 ft. per minute.

On reaching the bottom of the developer rack, the film
is caused to reverse its direction by an arrangement of rollers
which has become known as a "turn-around". This device
consists of a large driven roller around which are positioned
three smaller rollers and two guide shoes. The shoes and the
small rollers, known as "cluster rollers", cause the film to
turn 180° around the large or "master" roller, after which it
continues vertically upward between the staggered rollers
which form the opposite side of the rack.

On reaching the top of the rack, the film enters an arrange-
ment of rollers and shoes very similar to that used in the
"turn-around" just described, but inverted to cause the film
to leave in a downward direction, and offset, with regard to
the developer rack, to cause the film to pass on to the stop-
bath rack. When so used, these rollers make up what is
known as a "cross-over".

The processing section has four stages: developer, stop
bath, fixer, and wash. The processing racks and cross-
overs used in each of these positions are substantially identi-
cal. In each case, the solution on the film surface is displaced
by the action of the rollers in contact with the film and is
replaced by relatively fresh solution from the larger volume
in the tank. This action provides substantial agitation at the
film surface, resulting in uniformity of development and per-
mitting rapid completion of the action of each of the solutions
in this case, 60 sec. in each solution.

Control of temperature and uniformity of chemical com-
position throughout the system are maintained by recirculat-
ing each of the processing solutions continuously through a

167

system of heat exchangers in which the water used for temper-
ing purposes is finally delivered to the wash tank. In the
developer recirculation system, a thermostatically controlled
electrical heater is provided to increase the flexibility of the
system. In addition, the developer is filtered continuously
by being recirculated through a replaceable cartridge-type
filter.

Replenisher solution is delivered to each of the processing
systems by means of a pump which operates only while film
is being fed into the machine. Thus, by controlling the rate
of flow through the pump, the solutions are replenished at a
rate that is directly proportional to the film load.

After being transported through the wash rack, the film
enters a special "exit cross-over", which causes it to turn
90° and delivers it horizontally to the dryer.

On entering the dryer, the film first passes through a pair
of powered, soft-rubber wringer rollers which effectively
remove all remaining surface water. It then passes on to
powered transport rollers which carry the film through the
remainder of the dryer.

Between each pair of transport rollers and located above
and below the film plane are the air-distributor tubes with
slit orifices through which high-velocity hot air is directed
at both sides of the film.

The commonly used roller processors described above, all
use a vertical up and down means of transporting the material
through the various processing baths. However, a novel
horizontal transport of the material is used in the Itek Transflo
system (Rolor Co., Syosset, New York). In this "straight-fine"
transport of the film, deep vertical tanks and large numbers of
rollers are eliminated.

The processing solutions are applied to the material by
pumping into shaped applicators placed between rollers, as
shown in the diagram on page 169. The applicators are
designed so that the solution flows across the width of the
film and assists the travel of the material. Solutions are
returned by gravity flow to the tanks where they are filtered,
replenished and maintained at the correct temperature.

It is claimed that this type of processor eliminates pheno-
mena such as "bromide drag" and adjacency effects because
of the efficient agitation by pumping of solutions through the
apphcators. Also the air-exposed "turn-around" rollers are

168

PROCESSORS

t::^

Top: ITEK TRANSFLO SYSTEM. Film is transported horizontally
by rollers through the applicators into which the processing solutions
are pumped. Slits in the applicators direct a uniform liquid cushion
across the film so assisting its passage tlirough the applicator.

The film is dried by a high velocity warm air dryer before collection
at the end of the process.

Centre: MERZ-TYPE TUBE PROCESSOR. The diagram shows the
tubes, drive rollers and constant temperature cabinet.
Bottom: COLENTA-TYPE PROCESSOR. On the left-hand side cut
film holders are shown and on the right-hand side roll film holders are
shown.

169

eliminated (a possible source of contamination in the pre-
viously described self-threading roller processors). The rollers
in these processors operate under compression and act as
solution barriers and squeegees as well as transporting the
film.

TUBE AND DRUM PROCESSORS

These processors use the "one-shot" system. Small quantities
of fresh processing solutions are used for each batch of
material and then discarded. This method of processing gives
uniform results because fresh solutions are used and no
complicated replenishing systems are required. It is especially
suitable for photographers who wish to process a large variety
of materials as tube processors are suitable for processing
most types of colour or black and white positives, negatives
or papers.

The operation of the processors is simple and only the
loading of the tube requires to be carried out in the dark.
The tubes are surrounded by a light-tight box containing air
thermostatted at the required temperature and agitation is
accomplished by rotation of the tubes.

The (Merz-type) processor consists of two horizontal tubes
in which films or papers are placed. Small quantities of pro-
cessing solutions or water are then introduced by the inlet
funnel and at the end of each stage the tubes are tilted to
discard the chemicals (see centre diagram page 169).

Tube processors are available in varying degrees of sophi-
stication from the very simple Merz S30 which has a single
tube into which solutions are introduced by pouring into the
inlet funnel, to more sophisticated systems which use a pump
for introduction of solutions and programming of the pro-
cessing sequence by a timing clock (such as the "Atmac"
processors, Atlas Photography Ltd., London) or even by a
punched card (such as the "Atmac" processors or "Colenta"
processors, Huss Labortechnik, Weiskirchen). The "Colenta"
system uses a drum around which the material is placed
emulsion side outwards and processing solutions are pumped
into a trough in which the drum rotates (see bottom diagram
page 169).

170

A large variety of drums or processing reels are available
for these types of processors for processing most sizes of sheet
films, roll films and papers.

171

Developer Formulae

There are so many developer formulae that it is no easy
matter to survey them clearly or to reduce the host of recipes
and processes to a definite order. They are, therefore,
organized here according to the purpose for which they are
designed. The largest group includes the general purpose
M.Q. developers designed for universal use. There is then a
group of special M.Q. developers to which belong tank, fine
grain, high contrast, rapid, tropical and other more specialised
formulae.

By far the largest number of modern developer formulae
are based on the use of metol and hydroquinone, in some cases
replaced by the combination Phenidone-hydroquinone.
However, for some purposes, special developing agents are still
being used and they are classified here in a separate group.

When interpreting a formula, or designing a new one, or
adapting an existing one to a new purpose, we have to
consider the photographic effect of the components in the
light of the knowledge we have gained from pages 80-105.
The main points to keep in mind are these:

(1) The developing agent, its natiu-e, concentration
and, in cases where several are used, the ratio
between them.

(2) The alkali or accelerator, its nature and con-
centration.

(3) The preservative, which has, however, only a
limited eifect on the result.

(4) The restrainer, its choice and quantity.

(5) The total concentration of all components.

In tables of developer formulae in which no units are stated,
the quantities given are proportions which should be construed
as grams for solids and millilitres (ml.) for liquids.

172

GENERAL PURPOSE DEVELOPERS

The developer formulae classified in this group, are based on
the use of metol and hydroquinone. The main characteristics of
these two agents are, as we already know: Metol— soft and
rapid working. Hydroquinone — contrasty and slow working.

By mixing these two ingredients in different ratios and
concentrations it is possible to design formulae for nearly
any purpose. The other components of the developer,
especially its alkali contents must be adjusted accordingly.

The general purpose developers are very versatile and of
universal application and by the simple method of diluting
a stock solution in different degrees the result can be altered
to quite an extent. Even so, it is not possible to alter the
contrast of the negative in a degree sufficient for all purposes.
There are, therefore, three different types of general-purpose
developer, namely:

Group I. Soft Working Developers (Table XVIII).
Group II. Normal Developers (Table XIX).
Group III. Contrast Developers (Table XX).

XVIII.— GENERAL PURPOSE M.Q. DEVELOPERS
Croup I — Soft

DI65

ID3

3
G2I5

4
G2I2

AN40

Metol

0.8

Sodium sulphite anhyd.

Hydroquinone

—

1.5

1.2

Sodium carbonate anhyd.

Potassium bromide

0.5

1.5

Special additions

—

^—

—

Pot.
metabi-
sulphite

Water to

1000

Dilution

1 :3

I :3

none

Development Time (min)

5-8}

173

XIX.— GENERAL PURPOSE M.Q. DEVELOPERS
Group II — Normal

D6la

G2I4

8
AN47

9
AG46

10
AN6I

Metol

3.1

1.5

I.I

Sodium sulphite anhyd.

21.5

Hydroquinone

5.9

1.6

Sodium carbonate anhyd.

11.5

Potassium bromide

1.7

0.8

0.4

Special additions

— Sod. Pot. —

metabi- metabi-

sulphite sulphite

I 0.4

Water to

1000

Dilution

1 :2
1 :3

none

none
1 : 1

none

Development Time

(min.)

7
14

4-8

5-7
12-16

8-10

4-6

XX.— ^

GENERAL PURPOSE M.Q.
Group III — Contrasty

DEVELOPERS

II
DM

12
iD2

13
AN30

14
G20I

D72

Focal

Universal

Metol

3.5

1.5

3.1

Sodium

sulphite anhyd.

Hydroquinone

Sodium

carbonate anhyd

37.5

67.5

Potassium bromide

1.9

Water to

1000

Dilution

none

1 :2
1 :5

none

none
1 :3

1 :l-2(:

seep, 141)

Development Time
(min.)

5
9

5
10

4 (seep. 141)

174

XXI.— GENERAL PURPOSE M.Q. DEVELOPERS
Two Solution Formulae

M.Q. 1

M.Q. ;/

Metol

20
Hydro-
quinone

Solution A

Metol

3.5

—

Sodium sulphite anhyd.

100

Hydroquinone

—

6.5

—

Potassium bromide

—

2.5

—

Potassium carbonate

—

Water to

1000

Solution

Sodium sulphite anhyd.

—

Hydroquinone

—

Potassium carbonate

125

Potassium bromide

—

Water to

1000

Working Solution I part A + 3 parts A + I part A + I part A +

0-5 parts B I part B + I part B 5 parts B

4- water to 4-6 parts

make 6-12

parts

Development Time (min.) 3-5

water

3-5

5-7

Let US look first at Group I — Soft Working Developers,
represented by Formulae 1-5, in Table XVIII.

These formulae make use of the soft working characteris-
tics of metol and, as a matter of fact. Formulae 1-3 contains
metol only and no hydroquinone at all. Formulae 4, 5 do
contain some hydroquinone — about the same amount as or
a httle more than the metol. The sulphite content of all these
formulae is practically the same and is so chosen that the
solution has good keeping properties. As alkali, sodium
carbonate is used in an average quantity. The alkali content

175

of the developer must naturally not be too high or it would
interfere with its soft-working characteristics.

The next large group (II) contains the normal developers.
Their main characteristic is that they use, of course, both
developing agents but more hydroquinone than metol. As
far as the contents of preservative and alkali is concerned,
the same is true as for Group I.

For Group III (Contrasty developers) still more use has
been made of the contrasty working characteristics of hydro-
quinone. In these developers the metol content has been
reduced and that of hydroquinone considerably increased.
They contain 3, 4 and in one case even 9 times more hydro-
quinone than metol. The percentage of alkali is normal and
in some cases rather high and the sodium sulphite concen-
tration has been increased accordingly to achieve better
keeping properties. In general they are also used at less
dilution than the developers of the other two groups to get
more contrasty results. It should also be noticed that the
potassium bromide content is, on average, higher so the
developer is more energetic and has therefore a higher
tendency to fog.

As these formulae show, the photographic result can be
controlled to a wide degree by the ratio of metol and hydro-
quinone. It naturally occxurs to us, therefore, to make up
such developers in the form of two stock solutions, one
containing metol and the other hydroquinone and to mix
these two solutions in the required ratio (Formxilae 17-20).

There are other variations of such two-solution formulae.
The developers are made up in two solutions, one containing
the developing agent or agents and the other the alkali. By
increasing the quantity of the second solution higher contrast
and rapidity can be obtained (Formulae 131-134).

An example of a developer which can be adapted to a lot
of uses simply by dilution, is the Focal Universal Developer
(Formula 16).

(1) Undiluted, it is rapid working and contrasty and can
be used for technical photography, X-ray films and process
work where the highest contrast is not required. Development
time 3-5 minutes.

(2) For dish development of plates and films dilute accord-
ing to the contrast required with from three to seven volumes
of water. The more concentrated the developer the higher

176

the contrast and more rapid the development. With a dilution
of 1 part stock solution to 5 parts water, development time
is 5-7 minutes.

(3) For tank development, including daylight developing
tanks take one part stock solution to 10-15 parts water.
Development time 10-15 minutes.

(4) For chloride (contact) papers dilute one volume with
two volumes water. Development time 45-60 seconds.

(5) For bromide and chloro-bromide prints and enlarge-
ments. One part stock solution to 5-7 parts water. Develop-
ment time 1^2 minutes.

HIGH CONTRAST DEVELOPERS

WhUe the formulae already given for contrast developers may
be contrasty enough for general purpose there are cases
where still higher contrast is wanted. High-contrast developers
are needed not only for special purposes, such as process
work, but in many cases for general commercial work as well,
particularly in industrial and press photography. They also
find wide applications for the development of X-ray and
aerial film.

There is, however, a basic difference between these two
main applications for contrast developers. While for process
work the highest possible contrast is usually required, com-
mercial and industrial work calls for developers which still
give a good reproduction of half tones.

In this latter case, developers based on a high concen-
tration of sodium carbonate are contrasty enough. The
general concentration of the developer should also be high
and the hydroquinone content should exceed the metol to
quite a considerable extent (see Formulae 11-16, Table XX).

Where maximum contrast is required, the formula has to
be based on the use of sodium hydroxide (see Formulae
21-29). The use of this alkali certainly leads to the desired
result but off'ers a number of other inconveniences. Devel-
opers containing caustic alkalies have limited keeping
properties and one will therefore, in many cases, prefer to
make the developer up in two stock solutions of good keeping
properties (see Formulae 30-34).

Hydroxides are not pleasant to handle, owing to their
caustic properties, so formulae have been devised using

177

XXII.— SPECIAL DEVELOPERS
High Contrast (X-Ray, Aerial Film)

21
DI9b

22 23 24
DI9bR ;DI9 /DI9R

25 26 27
AN 30 G209O AG 30

28
D82

29
DI78

Metol

2.2

3.5

■4

3.5

I4»

—

Hydro-
quinone

8.8

Sodium sul-
phite anhyd.

52.5

Sodium carbon
ate anhyd.

—

Potassium
bromide

—

3.5

8.8

Sodium
hydroxide

—

7.5

—

8.8

Water to 1000

1000

1000 1000

1000

Dilution

—

2:1

Development
lime (min.)

—

6-8

5-8

4-8

3-4

* Add 48 ml. alcohol to the Limltial water volume.

XXIII.— SPECIAL DEVELOPERS
High Contrast (Two Solutions)

30
DI53

;di3

32
AN 70

33
G220

34
AG 70a

Hydroquinone

Solution A
25

Potassium metabisulphite

Potassium bromide

Water to

1000

Solution B

Potassium hydroxide

—

Sodium hydroxide

—

or 36

—

Water to

1000

Working Solution
Equal parts A and B, 3-5 mIn.

178

XXIV.— SPECIAL DEVELOPERS
Extreme Contrast (for Process Materials)

35
AN79b

36
D85
AN79

37
DP7d

Solution 1

Single

Solution

Sodium sulphite anhyd.

Paraformaldehyde

7.5

Potassium metabisulphite

10.5

2.6

Water to

1000

—

Solution 2

Sodium sulphite anhyd.

120

—

Boric acid cryst.

7.5

Hydroquinone

22.5

Potassium bromide

1.6

Water to

3000

1000

Dilution

1 part
sol. 1
3 parts
sol. 2

1:1

Development Time (min.)

paraformaldehyde which, as we already know (page 87),
forms hydroxide with sulphites or bisulphites in solution.
Several such formulae are given in Table XXIV. Again it is
possible to make these up in two solutions for better keeping
properties. The developing agent used for these high contrast
developers is hydroquinone.

The addition of formaldehyde causes caustic alkali to be
generated in the developer and formalin bi-sulphite com-
pounds are formed. These keep the sulphite concentration at
a low and constant level. The keeping qualities of the
developer are not seriously affected, but the hydroquinone is
more easily oxidised to quinone and semi-quinone. The
latter acts as an accelerator causing rapid development of the
silver halide grains and also a reduction of grains adjacent to

179

those already developed. This process of "infectious" develop-
ment gives gradation curves with very high gamma and short
toe as required for lith materials.

LOW CONTRAST DEVELOPERS

It was mentioned on page 66 that optimum exposure of a
negative required that the shadows be recorded on the toe
region of the characteristic curve. Average scenes, i.e. those
with a subject brightness range of about 160:1 (log scale 2.2),
can be accommodated on normal negative materials as shown
in the characteristic curve on page 193. Also it can be seen
that these materials can accommodate at best a scene with a
brightness range of approximately 1000:1. However for
certain special purposes such as photographing an eclipse of
the sun, a lamp filament when lit etc., it may be necessary to
record scenes with brightness ranges that may be as high as
1,000,000:1.

If the scene has a higher brightness range than 1000:1
considerable highlight detail would be lost as the highlights
would be recorded on or beyond the shoulder of the curve
where the density of the negative is approximately constant.
It is possible to record subjects of extended brightness ranges
by developing to a lower contrast value than normal. This
could be achieved by diluting a conventional developer and or
developing for a shorter time but this procedure would result
in loss of emulsion speed and exposure latitude. With specially
formulated low contrast developers (Table XXV) it is possible
to record subjects of extended brightness range without loss of
emulsion speed in the toe region and, because the characteristic
curve is very flat (gamma 0.12-0.25), a tremendous increase in
exposure latitude results.

The formulae of Table XXV contain a low concentration
of developing agents and moderate concentration of sulphite
as the main ingredients. Agitation must be efficient and uniform
with these developers because density differences are small.

The contrast obtained with these developers varies with
the nature of the emulsion used. As a general rule, thick
emulsions afford a lower contrast than thin emulsions. The
photographer must, therefore, alter the developing time to
suit the subject brightness range and the negative material
being used.

180

CORRECT DEVELOPMENT— PERFECT GRADATION.

The obtaining of a picture that, from the deepest shadows right
through to the highlights, reproduces a correct and natural scale
of contrast is in the first case a question of the right choice of
sensitive material (see page 30). The correct choice of negative
material can, however, be completely nullified by inappropriate
development and in this connection the formula used and the
method of development can exercise a tremendous influence on
the result. Only when negative material and development are
perfectly suited to one another can a correctly-developed picture
with perfect contrast, such as is shown in our illustration, be
produced. — Hugo van Wadenoyen.

181

182

DIFFERENT PICTURES— SAME DEVELOPMENT
PROBLEM. The appeal of the picture on the left hes in the
brilhant lighting and the contrast between light and shade,
whereas, in the picture above it is the delicate tone values which
provide the attraction and reproduce the atmosphere of a rainy
morning in early spring. In both cases the production of too hard
a negative had to be avoided.

In the picture opposite, taken against the light, a contrasty
developer would have produced deep shadows devoid of detail
and chalky highlights. A soft-working compensating fine-grain
developer (see page 210) is the correct formula to use in such a
case. Such a developer is also suitable for the picture above so
long as the negative material permits it and the necessary
adjustment in exposure has been made. Otherwise a somewhat
more energetic but still soft-working developer such as M-Q
(see page 206) should be used or a diluted para-aminophenol
(see page 197) developer. — B. Pratchett and G. Schuh.

183

AVOIDING EXCESSIVE CONTRAST. This has been
achieved in the pictures above and opposite by the use of an
appropriate developer. A briUiant-working developer (page 174)
would here have been a mistake, for it would probably have
resulted in loss of detail in the distance and in the snow appearing
like marble instead of appearing translucent. Developers which
obviate both these possibilities are fine grain or high definition
developers (see pages 202 and 214).

184

AVOIDING HALATION. As explained on page 69, the
avoidance of halation is not merely a question of sensitive
materia], but also a matter of correct development. One must
choose a surface developer, for example a fine-grain compen-
sating developer (see page 203) or a tanning developer (see
page 222). In the picture on page 186 halation is hardly percep-
tible, but in that on page 187 very characteristic and marked
halation is seen in the street lamps. In neither of these cases was
the development exactly right, but in neither case is the result
unnatural. — P. C. Poynter and P. Damm.

185

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186

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THE DEVELOPMENT OF PORTRAITS. Portrait negatives
require very special care in development if tlie fine shadoivs and
details in the flesh tones are not to be lost. Moreover, thai
possibility is often increased by the photographer choosing somv
what strong lighting in order to obtain increased effect (opposite).
Hence in developing portrait negatives the whole endeavour must
be directed towards obviating contrast and obtaining modelling
and detail as well in the deepest shadows as in the highlights.
Many professionals hold the view that this can only be obtained
by the use of a Pyro developer (see page 196), while others favour
a diluted para-aminophenol (see page 197). Fine-grain developers
are obviously applicable, but choice should be made of a formula
which is not too soft-working, such as the borax M-Q developers
(see page 206). — Ralph Ballon and Leslie Turtle.

188

AGAINST THE LIGHT. The development of examples such
as that above, where very strong light effects are present, is the
same as for night photographs (page 185). In such a case as that
above a tanning developer (page 222) is particularly suitable.
Silhouettes {opposite) call for a pronouncedly contrasty or hard-
working developer such as an M-Q contrasty developer (page
174). — J. Dulovits and Hugo van Wadenoyen.

190

COMMERCIAL PHOTOGRAPHS. With pictures as that on
the next page it is essential that the subject be shown in good
contrast with every detail clear and unmistakable and that the
nature of the material composing the articles should be revealed.
For this a brilliant working developer must be chosen such as
the Focal Universal M-Q 16 (page 174), used at a dilution of 1 : 3
to 1 : 5.—H. Gorny.

191

192

CHARACTERISTIC CURVES AND LOW
CONTRAST DEVELOPMENT

D 30

10 2 30

Log rel E

40 50 60 70

D 3-0

10 20 30 40 50

Log rel E

60 70 80

D 3-0

Top: Normal development (D76 undiluted, 9 min.). The negative can

only accommodate a subject brightness range of 1000:1.

Centre: Development in D76 diluted 1 :1, 5 min. The negative can record

a subject brightness range of approximately 10,000:1.

Bottom: Low contrast development (POTA, formula 39). The negative

is able to accommodate a subject brightness range of 1,000,000:1 or

greater.

u 193

XXV.— SPECIAL DEVELOPERS
Low Contrast (for Recording Scenes of Extended Brightness Range)

38
TIO
XDR-4*

39
POTA**

Potassium sulphite

—

Sodium sulpiiite

—

Phenidone

—

1.5

Metol

—

Hydroquinone

—

Potassium bicarbonate

—

Water to

1000

Development Time

(min.)

2-7

* Phot. Sci. Eng., 14, 363 (1967) ** Phot. Sci. Eng., 11, 46 (1967).

OTHER DEVELOPING AGENTS

Metol and hydroquinone are the developing agents most
frequently used but there are others that can be used for
special purposes. Some well-known formulae and their
important characteristics are listed in this section.

Pyrocatechin
Important characteristics: similar properties to hydroquinone.
Special applications see page 222.

40.— SINGLE-SOLUTION PYROCATECHIN DEVELOPER
Pyrocatechin J ounce 20 grams

Sodium sulphite, anhyd. 2 ounces 50 grams

Caustic soda 320 grains 16 grams

Potassium bromide 40 grains 2 grams

Water to make 16 ounces 400 ml.

To use, dilute 1 part with 10-15 parts of water. Develop-
ment time 5 minutes.

Caution: The pyrocatechin must be dissolved only when all
the other constituents are in complete solution. Does not
keep well; should be made up immediately before use.

194

41.— TWO-SOLUTION PYROCATECHIN DEVELOPER

A. Pyrocatechin 200 grains 10 grams
Sodium sulphite, anh/d. } ounce 20 grams
Water to make 20 ounces 500 grams

B. Potassium carbonate 2i ounces 60 grams
Water to make 20 ounces 500 ml.

Caution: Dissolve the pyrocatechin after the sulphite.

For use take equal volumes of A and B. Time 7 minutes.

Chlorquinol

Important characteristics: Similar in properties to hydro-
quinone but more rapid working.

XXVI.— CHLORQUINOL DEVELOPERS

Solution 1

Single

Solution

Metol

—

Chlorquinol

Sodium sulphite anhyd.

100

Water to

1500

—

Solution 1

Potassium carbonate

—

300

250

Sodium carbonate anhyd.

120

—

Potassium bromide

2.5

Water to

1000

Dilution

3 parts
sol. 1

1:3-5

1:5
1:10

2 parts
sol. 2

Development Time (min.]

5-7

2-3
5

Caution In the metol-chlorquinol developer (Formula 44) both the metol
and the chlorquinol must be completely dissolved before adding the
sulphite.

195

Pyrogallol

Important characteristics: gives negatives with delicate grada-
tion and good detail. Owing to the ease with which pyro is
oxidised in alkaline solution, single-solution developers are
impracticable as they do not keep.

45.— TWO-SOLUTION PYRO DEVELOPER

For use take 1 part A, 1 part B and 4 parts water. Develop-
ment time 6-7 minutes.

Glycin

Important characteristic: Slow and clean working, giving low
contrast and has good keeping properties.

XXVII.— GLYCIN DEVELOPERS

Pyrogallol

2 ounces

50 grams

Potassium metabisulphlte

88 grains

5 grams

Sodium sulphite, anhyd.

5 ounces

1 25 rams

V^ater to make

40 ounces

1000 ml.

Sodium carbonate, anhyd.

3 ounces

75 grams

Water to make

40 ounces

1000 ml.

46
AN72

/D60

48
AGS

49
G204

Sodium sulphite anhyd.

125

12.5

Potassium carbonate anhyd.

250

Glycin

Methyl alcohol

—

Water to

1000

Dilution

1:4
1:15

1:7

—

1:3i

Development Time (min.)

5-10
20-25

12-15

10-12

9
30

p-Aminophenol hydrochloride

Important characteristics: rapid fog-free developer, not much
affected by variations of temperature. Permits preparation
of concentrated stock solutions.

196

XXVIII.— P-AMINOPHENOL DEVELOPERS

Solution 1

Single

Solution

p-Aminophenol hydrochloride

100

7.3

Potassium metabisulphite

—

300

—

Water to

1000

—

Solution 2

Sodium sulphite anhyd.

—

Potassium carbonate

150

—

Sodium carbonate anhyd.

—

Water to

2000

1000

Sodium hydroxide (50% solution)*

—

qs**

—

Dilution

1 part
sol. 1

2 parts

sol. 2 1 :20-25 —

Development Time (min.)

5-6

4-5

8-15

*Caution When making up 50 per cent sodium hydroxide heat is
generated and the solution must be cooled before adding to the developer.

**Add the 50 per cent sodium hydroxide solution dropwise until the
precipitate which forms just redissolves.

More contrasty results can be obtained with Formula 51 by diluting the
developer with only 10 parts of water.

53._p.AMINOPHENOL-HYDROQUINONE DEVELOPER

Working Solution Replenisher

Kodelon (p-aminophenol oxalate)

1.5

Hydroquinone

Sodium sulphite anhyd.

Sodium hydroxide

Potassium bromide

2.5

—

Water to

1000

Caution: Dissolve the sodium hydroxide separately in a small
quantity of water, then add to the solution containing the
other constituents already dissolved.
Development time 12-15 minutes.

197

Important characteristics: this developer has similar pro-
perties to a metol-hydroquinone tank developer, it does
not keep quite so well and is perhaps not so energetic but its
particular value lies in its usefulness in all cases where
protection against metol poisoning is essential, although
Phenidone-hydroquinone developer may serve equally well
(see page 199).

Amidol

Important characteristic: provides a rapid alkali-free devel-
oper.

54.— AMIDOL STOCK SOLUTION
Sodium sulphite anh/d. 1 ounce 25 grams

Water to make 40 ounces 1000 ml.

To 4 ounces of this solution (100 ml.) 10 grains (0.5 gram) of amidol
is added just before use.

Development time 3-5 minutes.
Caution: The developer does not keep and should be dis-
carded after use.

Phenidone

Important characteristics: in combination with hydro-
quinone similar to M.Q. developers.

Phenidone has replaced metol in many formulae for
general use as well as special purposes. It produces with
hydroquinone a superadditive mixture in the same way as
metol but is much more efficient in this respect. A given
weight of hydroquinone requires about one quarter of its
weight of metol to form an active mixture but only one
fortieth part of its weight of Phenidone. This makes possible
the formulation of highly concentrated developers with no
tendency for he developing agents to crystallise out. The
working solution of a P.Q. developer is, at the same pH, only
slightly more active than a similar M.Q. developer. An
increased quantity of Phenidone, however, produces the
highly active type of developer required, for instance, for
monobaths (see page 278).

Phenidone-based developers keep better than those based
on metol. The reason is, as we have already seen in
the paragraph on superadditivity (page 101), that the oxidation
product of Phenidone is regenerated by hydroquinone in a
much more efficient way than the regeneration of metol by
hydroquinone. Furthermore, while the first oxidation

198

product of hydroqiiinone, namely its monosulphonate,
forms an almost inert system with metol, it has with Pheni-
done a superadditive effect increasing developing power.
It is thus obvious that Phenidone forms with hydroquinone
very efficient developers of good keeping and exhaustion
properties which are also easy to replenish. A number of
such formula are recorded in Table XXIX. There are general
purpose developers containing sodium carbonate as alkali.

XXIX.— PHENIDONE-HYDROQUINONE (P.Q.) DEVELOPERS

General Fine- High- Concentrated

Purbose Grain Contrast Tonk Sol.

55 56 57 58 59 60 61 62

/D62 ;D67 /D68 /D68 ;D72 /D72 Nor- Con-

R R mal* trast*

Sodium sulphite anh)

,'d.50

100

100 72

125

120

Hydroquinone

8 8.8

12.5

Sodium carbonate
anhyd.

37.5

—

— 48

— •* 60

100

Borax

—

9 —

—

Boric acid

—

1 —

—

Phenidone

0.5

0.25 0.2

0.25 0.22

0.25 1

1.5

Potassium bromide

— 4

—

Benzotriazole 1%

—

— 10

300

—

Water to

1000

1000 1000 1000 1000

1000

Dilution

1 :3
1 :7

1 :2
1 :3

none

— none

—

1 :20
1 :50

1 :9

Development Time
(min.)

3-4
6-7

— 5

—

11
15

* A. Wiedermann, Sc.et
** Sodium hydroxide 7.5

.Ind.Phot.. Vol

. 32, 97-128.

Phenidone formulae require a rather high restrainer
content; benzotriazole has to be used in addition to potassium
bromide. With borax, fine grain developers can be prepared
similar to their M.Q. counterparts. Highly concentrated P.Q.
developers can be prepared by formula number 61, giving
efficient developers even at a concentration of one part in
50 parts of water.

199

When making up these developers the constituents must
be dissolved in the order given, as Phenidone is not soluble
in water.

TANK DEVELOPERS

Tank developers intended to handle large numbers of plates
or films must satisfy quite a number of conditions. As
development is by time and a variety of films are developed
together, the developer must possess such properties that its
results are neither too hard nor too soft. The ratio of metol
to hydroquinone, the quantity of these developing agents
and that of the alkali must therefore be carefully adjusted to
achieve the best compromise.

As tank developers are in use for weeks or even months
they must have good keeping properties and not be easily
exhausted. The sodium sulphite content should therefore be on
the high side and the exhaustion taken care of by regular ad-
dition of a replenisher solution (see "R" in Table XXIX). Dur-
ing use the developer loses strength by chemical reaction and
at the same time the level of the solution drops. Every film
which passes through the tank removes a small quantity of
solution and this loss must be made good by the addition of
a solution of a composition very similar to that of the
original developer. This is the strengthener or replenisher and
it is added at suitable intervals and its concentration is so
adjusted that it maintains the level of the liquid in the tank
and at the same time the energy of the developer. As can be
seen from Table XXX the composition of the replenisher is
very similar to that of the original developer but it is usually
a little more concentrated. It does not usually contain
potassium bromide.

As mentioned above and on pages 74-76, developers
require replenishment because their activities change during
use. These changes in development activity may be summarised
as follows :

(1) The developing agent is used up by aerial oxidation
and by oxidation during the development process
(reduction of the silver haUde to silver involves
oxidation of the developing agent). The former
causes the pH of the developer to rise and the
latter causes the pH to drop. Thus the development

200

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activity is altered both by diminution of the
concentration of the developing agent and by
changes in pH although this effect is reduced by
the inclusion of buffers in developer formulations
(page 89).

(2) Loss in developer due to carry over of the solution
by the film.

(3) The sulphite is used up by reaction with oxidised
developing agent (page 81), which may result in
stain and also affect the grain size (page 194).

(4) The bromide content of the developer increases
because bromide ions are released in the develop-
ment reaction. This results in a slowing down of
the development reaction (page 91).

In order to overcome these effects, which generally result
in a decrease in developer activity, the developer must be
replenished. The control of developer activity for the large
scale user is given in the chapter on Quahty Control.

FINE GRAIN DEVELOPERS

Fine grain development has played an important part in the
history of modern negative technique. There was a time when
it was considered as absolutely essential to reduce the size of
the silver grain by fine grain development and numerous
formulae were published to get this result. However, the
importance of fine grain development has receded since. The
main reason is that the granularity of the emulsion has itself
been made so much finer that it is no longer so important to
rely on the development process.

This does not mean that fine grain developers are com-
pletely obsolete. They are still essential for the production of
a good negative — but in a different context. Modern emul-
sions still need fine grain development in the sense that a
developer must be chosen which is suitable for these fine
grain emulsions, in the following respect:

(1) The developer must give the correct gamma and
have no tendency to produce excessive contrast.

(2) The developer must preserve the original fine
grain of the emulsion and have no tendency to
cause "clumping" of the grain.

(3) If, in addition, the developer even reduces the

202

granularity, it is certainly a useful feature as long

as it can be achieved without other important

factors suffering.

We can thus define the fine grain developer as a developer

which gives a low contrast without any, or at least any serious,

loss of speed and without "clumping" of the grains. The

developer may or may not actually improve the definition.

We have therefore to deal with three types of developers

specially suitable for fine grain materials:

(1) Medium fine grain developers of the "retarded
development" type (Table XXXI).

(2) True fine grain developers, also called super or
ultra fine grain developers (Table XXXII).

(3) High definition developers (Table XXXIV).

All these developers act as "compensating" developers,
i.e. they prevent the formation of heavy, imprintable deposits
in highlight areas.

PRINCIPLES OF FINE GRAIN DEVELOPMENT

The question as to which factors have the main influence in
fine grain development has attracted considerable research.
From the many theories, the following two conclusions are
generally admitted to be well founded.

(1) The first condition which a fine grain developer
must fulfil is that it shall be capable of dissolving
the silver halide of the emulsion.

(2) The second condition is that its energy of develop-
ment shall be low so that its slow working
will give a negative of medium contrast and
density.

These two characteristics are found as we shall see in all
fine grain developers and we are therefore dealing with them
in greater detail.

A. Solvent for a silver bromide. If in any developer the
sodium sulphite content is raised to about 100 grams of the
anhydrous salt in one litre of water, the developer has
solvent properties for silver halide. To enhance this further
other solvents for silver halide have been suggested such as
ammonium chloride, hypo, or thiocyanate. Their true value

203

is however doubtful as they tend to cause fog and have the
tendency to reduce the speed of the emulsion.

The favourable action of p-phenylenediamine, the classical
fine grain developer, can be explained too as being due to the
fact that it is not only acting as a developer substance, but
also as a solvent for silver halide. This developing agent has
unfortunately a number of very unpleasant properties: it is
poisonous, has very strong dyeing properties, and stains
fingers and photographic utensils.

Hence it is important to have a developer which has the
good without the bad properties of p-phenylenediamine. This
has been achieved by combining p-phenylenediamine with
other developing agents forming new compounds which have
less objectionable properties (page 100). p-Phenylenediamine
has also been successfully replaced by other organic solvents
for silver hahde which may not be useful developing agents
themselves. A substance of this type is o-phenylenediamine,
which is used in combination with metol. This developer gives
excellent fine grain, has good keeping properties and shows
no tendency to fog or stain (Formula number 98).

B. Low developing energy. When a film is fully developed
the exposed grains are completely converted to metallic silver.
When, however, the film receives only partial development
to a lower contrast, most of the exposed grains are only
partially developed and give therefore smaller particles of
metallic silver (page 52). To obtain such an effect of re-
tarded development the alkahnity of the developer has to be
reduced. This can be done simply by having a very low alkaU
content in the formula. Some fine grain developers contain
therefore sodium carbonate only at a fraction of the normal
amount. An alternative method is to replace this alkali by
weaker substances such as borax or Kodalk. This, of course
leads to developers with lower pH and a glance at Table
XXXI will show us which level we have to take. We might
also use one of the buffer mixtures which help to maintain
the pH value of the developer solution and to achieve
consistent results.

MEDIUM FINE GRAIN DEVELOPERS

The more well-known metol-hydroquinone formulae of this
type are summarised in Table XXXT. It will be seen that all

204

are characterised by high sulphite content and either low
or weak alkali content. The sulphite content is aroimd 100
grams per Utre to give the developer good solvent properties
for silver halide.

The column "Alkali" of this table reveals a number
of interesting facts. In Formula 88 sodium carbonate is
used at the comparatively low concentration of 5-6 grams
per litre. In Formula 80 which represents Kodak D76, one
of the most popular fine grain developers of this type, borax
is added as an alkaU. Wherever borax is used in any developer,
the granular or crystallised quality should be used as these
are more easily soluble than the powder form which has the
tendency to float on the surface of the solution and is only
very slowly dissolved. If, in Formula 80 or similar formulae,
the borax is replaced by an equal weight of Kodalk, a some-
what more energetic developer is obtained allowing somewhat
shorter developing times. At the same developing time a little
higher contrast would be obtained while the grain size is
not noticeably aifected. All these developers lend themselves
excellently to tank development but for large-scale use a
replenisher solution is required, for reasons which are dis-
cussed on page 76. Replenishers for some of the fine grain
developers are listed in Table XXXI under Reference "R".

As we already know, the use of an alkahne buffer mixture
ofi'ers advantages as far as the exhaustion properties of the
solution are concerned. Such a formula is No. 85. It must
be noted that developers of this type are, in general, somewhat
softer-working and give lower e8"ective film speed than the
standard D76 formula.

An interesting fact is that Formulae 82, 83 do not contain
any added alkali. These developers rely on the alkalinity of
the sodium sulphite itself which has a pH value of 8-9. In this
way excellent but somewhat slow-working fine-grain devel-
opers can be obtained. There is no point in using hydro-
quinone in these developers: it would not contribute to the
developing properties under these conditions.

Formulae of type 83 go a step further in this direc-
tion. The alkalinity of the sodium sulphite is still further
reduced by the addition of sodium metabisulphite. These
developers have the lowest activity of all developers in this
group and give the finest grain and also the lowest contrast.

Going too far in this direction would be fatal: the speed

205

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206

of the film would suffer to a very considerable degree. All
true fine grain developers reduce the speed of the emulsion
to some degree compared with that obtainable by full develop-
ment in a normal developer. However, in most cases the loss
of speed is negligible and within the latitude of the emulsion.
Nevertheless, when using fine-grain developers of the lowest
activity such as Formula 83 it is advisable to give ample
exposure.

Phenidone (page 101), has been used in combination
with hydroquinone to make up "medium fine grain devel-
opers". Formulae for a developer Uke that together with the
necessary replenishers have been published by A. J. Axford
and J. D. Kendall. As shown in Formula 94 they recom-
mend two types of replenisher, one for the topping-up method
of replenishing, and another for the bleed system. The
differences between these methods are as follows :—

In the topping-up method (page 159), the developing
solution is maintained at a constant level by adding from
time to time a certain quantity of the replenisher so that the
loss of solution by developer carried over in the gelatine or
on the sm-face of the material, is replaced. In the bleed
system which is normally only used in large-scale proces-
sing, used developer is run off and replenisher fed in
continuously so that the level of the developer and its
photographic characteristics remain fairly constant. The
bleed system has the advantage over the topping-up method
that a very high degree of constancy can be maintained,
provided of course that the replenishing is controlled
properly.

94.— PHENIDONE-HYDROQUINONE FINE GRAIN DEVELOPER

Ref>lenisher
Working Topping-up bleed

Solution Method System

Sodium sulphite anh/d.

Hydroquinone

Borax

Boric acid

Potassium bromide

Phenidone

Water to make

Developing time

100
5
3

3.5
I

0.2
1000
8.95

100
8
9
I

0.24
1000
9.28

100
6.25
4
2.5

0.22
1000
9.09

10 minutes at 68°F. 20°C

207

EMULSION SPEED AND FINE GRAIN DEVELOPMENT

When comparing the graininess characteristics of developers
it is important to consider the relative emulsion speeds. A
proper comparison can only be carried out if the negatives
are developed to the same gamma. In fine grain work this
should be 0.6-0.7. Under these conditions the emulsion-speed
ratio of the four classes of developers is as follows :

(a) To achieve low contrast with a normal M.Q.
developer (page 174), the negative has to be under
developed, with a consequent loss of speed that
might amount to 50%. If— on the other hand—
we develop the negative completely out, without
any regard to contrast, we would make full use
of the maximum speed of the emulsion, but the
negatives might show a very coarse grain.

(b) With fine-grain developers (Table XXXI) we can
obtain low contrast without noticeable loss of
emulsion speed as compared with the manu-
facturer's speed figiu-e and without interfering
with the original fine-grain characteristics of the
emulsion.

(c) With super-fine grain developers (Table XXXII)
the same result is obtained, possibly with improved
granularity. Emulsion speed, however, is reduced
to about 60-70 % of that given by ordinary fine-
grain developers.

(d) High-definition developers (Table XXXIV) give
good negative quahty, i.e. correct low contrast
without efi"ect on the grain, and also improve
definition. There may even be a gain of speed
compared with ordinary fine-grain developer.

SUPER-FINE GRAIN DEVELOPERS

The classical super-fine grain developer is p-phenylene-
diamine which is capable of giving an exceedingly fine grain,
but requires strong over exposure and a very long developing
time and even then the contrast of the negatives is rather low.
In addition, as we already know, this developing substance
has a number of rather unpleasant properties. This naturally
led to research for other additions which would have the

208

effect of shortening the developing time, increasing contrast,
and if possible avoid the disagreeable properties of para-
phenylene diamine.

The first step in this direction was the Sease formula
(Formula 95) which contains glycin. The mixture of the two
developing agents gives a fine-grain developer with improved
photographic properties as far as emulsion speed and rate of
development is concerned, but the solution has still the
unpleasant properties of p-phenylenediamine. An improve-
ment in this respect is the developing agent Meritol, a com-
pound of p-phenylenediamine with pyrocatechin. Two
developers of this type are Formula 97 of Table XXXII and
Formula 104. Of these two, Formula 97 leads to a finer
grain but requires longer development. A further application
of Meritol is given at the end of this section.

There are now available quite a number of derivatives of
p-phenylenediamine (see page 366) as these have found wide
application in colour developers. These substances are much
superior in many ways to p-phenylenediamine itself but they
are not capable of producing quite such a fine grain. Formulae
of this type are Nos. 99-100. In Formula 95 use has again been
made of the accelerating effect of glycin. In Formula 100
hydroquinone is used for the same purpose.

There have been efforts to replace p-phenylenediamine by
other agents. A successful result is the Windisch formula
(No. 98) which makes use of o-phenylenediamine. This agent
has only weak developing properties but is a good solvent for
silver halide. As the actual developing agent, the Windisch
formula contains metol.

The attempt to find suitable fine grain developers in other
chemical groups has not been very successful. An exception is
the M & B formulae (Nos. 102-103) based on the use of
hydroxethyl-o-aminophenol. It is interesting to note that
glycin has an accelerating effect on this developing agent, too.

As far as the general composition of these super-fine
grain developers is concerned, a glance at Table XXXII shows
that nearly all of them make use of the effect of a high sodium
sulphite content. As alkali they are using either small quanti-
ties of sodium carbonate or borax. There is also one formula
containing the buffer mkture borax — boric acid (Formula
100), while, in the Windisch formula No. 98 the pH of the
sodium sulphite is reduced by the addition of sodium meta-

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bisulphite to decrease the activity of the developer and to
produce a finer grain.

SPECIAL TECHNIQUES WITH MERITOL

Amongst these fine grain developing agents Meritol lends
itself to the use of some special techniques, which have proved
successful in practice.

By using after any Meritol developer a solution of caustic
soda as an after-bath, F. H. Lawrence succeeded in obtaining
an increase in film speed without much loss in fine grain.

The principle is similar to that of two-bath developers
(page 234). The film is first soaked in a solution containing
Meritol. No development takes place, but the gelatine
emulsion absorbs a quantity of the solution. Without rinsing,
the film is transferred to a dilute solution of caustic soda
which, together with the Meritol held in the emulsion of the
film, causes rapid development to take place.

The advantages of the method are: (1) rapid processing
little affected by temperature, (2) excellent gradation and
resolution, (3) automatic compensation of very strong
contrasts, (4) automatic "forcing" of under-exposed negatives
and (5) very fine grain with maximum emulsion speed.

Meritol-caustic deals well with under-exposure; it gives
fine-grain negatives of good printing quality in normally
hopeless circumstances.

In normal conditions with good light, about half the
exposure indicated by a reliable meter gives the best results.
Over-exposure should be avoided — it will give flat negatives
and increased grain.

104.— MERITOL-CAUSTIC FINE GRAIN DEVELOPER

Warm water at I25°F. (52°C.)

ounces

400 ml.

Sodium sulphite, anhyd.

ounces

45 grams

Meritol

140

grains

8 grams

Cold water to make

ounces

500 ml.

Cold water

ounces

200 ml.

Caustic soda

ounce

25 grams

Cold water to make

ounces

250 ml.

Both these are stock solutions.

Stock solution 1. is the Johnson Super Fine Grain Meritol
developer, and is obtainable in tins to make 20 ounces of
solution. For use it is diluted according to Table XXXIII
on page 213.

211

Stock solution 2 will Iceep well in a rubber stoppered
bottle. It is corrosive, and hands contaminated with it should
be well rinsed in running water. For use one part is diluted
with water to make 15 parts of solution.

Tank development for films. The steps are as follows.

(1) Load film into developing tank.

(2) Pour in the necessary quantity of the working
strength solution 1.

(3) Agitate the film for three minutes.

(4) Poiur out the solution 1 and, without rinsing,
poiu* in the right quantity of the working strength
solution 2.

(5) Agitate thoroughly for three minutes.

(6) Poiir away the caustic solution (now a bright
purple).

(7) Fix in an acid hardening fixer, wash and dry.

An acid hardening fixing bath must be used. All processing
solutions must be kept at the same temperature (best 60° to
70°F.), variations may cause reticulation.

The treatment for plates is similar to that given for 35 mm ,
film. Convenient quantities of the 1 and 2 working strength
solutions may be poured into dishes and the plate first soaked
in the 1 bath and then transferred to the dish containing the 2
(caustic) solution.

The coloured backings of most roll films have a restraining
effect on Meritol, and these backings should be removed
before development.

This is best achieved by soaking the film before develop-
ment in a fresh solution of sodium sulphite made by
dissolving 200 grains (10 grams) of the crystals in 20 ounces
(500 ml.) of water. Alternatively 100 grains (5 grams) of the
anhydrous salt may be taken.

It will take some time for the Meritol solution (No. 1
bath) to replace the sulphite solution absorbed by the
emulsion of the film or plate, and the latter should therefore
be left in this bath for six minutes with continuous agitation.
The procedure for the second bath and following treatment is
then the same as for 35 mm. film which has no special
backing and therefore does not need this fore-bath.

The working strength Meritol solution (1) can be used
several times when processing 35 mm. film or plates. As this

212

is a two-bath method (see page 234) hardly any development
takes place in the first bath, though the dilute solution
deteriorates slowly, and therefore should not be kept for
more than three or four weeks. It should be filtered occasion-
ally. On the other hand, a solution in which roll films with
soluble backings have been processed, and where these
backings have an adverse eff"ect on the solution, should be
discarded after use.

The workmg strength caustic solution (2) must only be
made up in its diluted form just before use, and must only
be used once.

Contrast control by composition of the first bath. The
contrast of negatives produced by the Meritol-Caustic
developer depends on the type of film, and on the amount
of Meritol stock solution used in the first bath. The com-
position of the latter for any particular type of film may be
determined from the following table:

XXXSII.— QUANTITIES OF MERITOL STOCK IN THE
WORKING DEVELOPER

Soft negs. Normal negs.
Film Group ounces ml. ounces ml.

Hard negs.
ounces ml.

To make 16 ounces (450 ml.) of working strength No.
A 4i 125 6 170
B Si ISO 7 200
C 6 170 8 225

1 solution.
9 255
lOJ 300
12 335

To make 10 ounces (285 ml.) of working strength No. I solution.
A 2* 80 3J 105 5J 155

B 3i 95 4J 125 6i 190

C 3i 105 5 140 7i 210

The film groups referred to are those given on page 38.

The addition of a developer improver such as Kodak Anti-
Fog or Johnson's 142 to the working strength Meritol bath
(about 40 minims to 20 ounces, or 2 ml. to 500 ml.) will
greatly reduce any tendency of the film to fog. There is, how-
ever, a slight apparent loss of emulsion speed, and exposures
should preferably be not less than those indicated by a
reliable meter.

With pronounced fog, as with stale film, the developer
improver may be increased up to 200 minims in 20 ounces

213

(10 ml. in 500 ml.) of the working bath. Exposures should be
doubled.

The addition of the developer improvers will give bright
negatives of good printing quality, and is recommended
where maximum emulsion speed is not essential. They are
also useful for known over-exposure.

There have been numerous other formulae put forward as
fine-grain developers, about some of which the most extra-
vagant claims have been made. In quite a number of cases
upwards of a dozen constituents are included, and it is not
infrequently found that some of them are incompatible with
the other constituents, or merely perform the same function.
Such formulae, better called recipes, are like some old
remedies into which all kinds of weird ingredients were
added in the hope that even if they did no good they could
do no harm.

HIGH-DEFINITION (HIGH ACUTANCE) DEVELOPERS

This group has become one of the most important because the
developers it includes lead to negatives of enhanced acutance
and prints of good image sharpness (see page 58).

To make full use of the advantages of this type of
developer it is, of course, advisable, as we have already seen
on page 62, to choose a fine-grain, thin-emulsion film of low
or medium speed. It is doubtful whether, for these films, fine
grain developers are the best to use. Modern films of this
type are already so fine in grain that there is reaUy no need
for further improvement. Nevertheless, it is important to get
the best possible result as far as negative quality and emulsion
speed is concerned.

To get the optimum negative quality with these thin
emulsion films the problem must therefore be approached
in a quite different way. Let us consider the various properties
a developer should have to give the best results with fine
grain films. These films tend to yield excessive contrast and
one of the properties of the developer should therefore be the
reduction of contrast. However, while the contrast should be
reduced the gradation must not suffer i.e. the tone scale must
not get too restricted. We, therefore, need basically a soft-
working developing agent such as metol. It should also be a
compensating developer (see page 139) i.e. the concentration

214

XXXIV.— SPECIAL DEVELOPERS
High Definition

105

106

107 108

FXI FX2

W. G. W. G. W.

Beut/er Windisch Crawley Crawley
{&rit. /ourn.)

109
FXI 3
G. W.
Crawley

Metol 5

—

0.5

0.25

0.5

Glycin —

—

0.75

—

Pyrocatechin —

12.5

—

Sodium sulphite anhyd. 25

3.5

Sodiumcarbonateanliyd.25

—

2.5

—

2.5

Potassium carbonate —

—

7.5

—

Special additions

Pot. Iodide llford Pot. Iodide

0.001% Desensitol 0.001%

5 ml. Yellow 5 ml.

Sol.

3.5 ml.

Water to

1000 1000

1000

Dilution

25 ml. +
15 ml.
Pot. Hy-
droxide

10% +
960 ml.

water

Development Time(min.) 7-10 15-20

of the developer should be comparatively low so that it
exhausts rapidly in the highlight areas. But a diluted developer
may not develop shadow details adequately, which amounts
to a loss of emulsion speed, so the alkali content should be
relatively high.

Such a developer, having a low concentration of develop-
ing agent, the activity of which is maintained by high alkali
content, has at the same time a tendency to produce the
border effects which we have mentioned before (page 77).
The diluted compensating developer becomes quickly
exhausted over the dark areas where a lot of silver halide has
to be developed. The exhausted developer meets active

215

ADJACENCY EFFECTS IN DEVELOPMENT

The active developer of light areas cairies over and continues to develop
the edge of the dark area while the exhausted developer of the dark area
migrates to the light area and retards development there. The result is that
the "sharpness" is increasedduetothehigher edge contrast. High definition
developers are based on this effect.

216

developer at the border of the dark area and the action of
both naturally spreads somewhat in the neighbouring areas.
The result is that the active developer of the light area carries
over and continues to develop the edge of the dark area. On
the other side the exhausted developer of the dark area
niigrates to the light area and retards development there.
The result is that the "sharpness" of the outUne is increased
due to the higher edge-contrast (page 216).

Table XXXIV gives formulae for a number of such high-
definition developers. They are all characterised by the fact
that the concentration of developing agent is very low,
approximately in the region of only .5 grams per 1 litre.
However, the activity of the developers is maintained by a
comparatively high alkali content. In Formula 106 the
compensating effect has been increased by the choice of
pyrocatechin as a developing agent which has a selective
imagewise tanning effect on the gelatine of the emulsion
(page 222).

These developers are also characterised by the absence of
bromide which enhances local developer exhaustion at the
boundary between high and low density areas. Agitation of
these developers must be carefully controlled because too
vigorous agitation neutrahses the adjacency effect and too
Uttle causes streamers.

All these high-definition developers can only be used
once. It is, therefore, advisable to make them up either in the
form of a concentrated stock solution or in the form of two
solutions, of which one contains the developing agent and
sulphite in 500 ml. of water, and the other the sodium
carbonate in the remaining 500 ml.

INVERSION AGITATION

It has already been mentioned (page 78) how important it
is to agitate the film in the tank properly, especially when
spiral tanks are used for development. In these tanks the
coils of the film are quite close together and unless the
solution is kept on the move, the negatives may not be evenly
developed. Rotating the spiral with a stirring rod is not a
fool-proof method as agitation may not be quite even.

Inversion agitation eliminates the danger of uneven
development. Many modern tanks are provided with a plastic
cap which fits over the pouring opening of the tank lid. With

217

the cap in position the tank is water-tight and can be turned
upside down. Sufficient space is provided in the tank above
the normal level of the solution so that when inverted a
substantial portion of the solution flows across the film coils.
To obtain the full benefit of this method, the tank must not be
filled beyond the volume of solution prescribed by the
manufacturer.

For inversion agitation the tank is turned upside down
and held in this position until the developer has stopped
running into the lid. Then the tank is turned back again. At
the beginning of the development, repeat this half a dozen
times or give the spiral a few twists with the stirring rod to
dislodge any air bubbles. Then invert the tank for about
10 seconds (4 inversions) at 1 minute intervals throughout
development.

PHYSICAL DEVELOPMENT

Physical developers, which differ from chemical developers
in that they contain silver salts, were originally used almost
exclusively for special purposes in scientific and technical
photography. Later, they were found of particular interest in
general photographic work, owing to their property of devel-
oping a fine grain. Today they are of academic interest only.

Formulae for physical fine grain developers specially
devised for sensitive materials of that time were put forward
by Odell and improved formulae were put forward by Turner.

The process consists of the following steps.

(1) Treatment in a forebath.

(2) Development in the silver-containing solution.

(3) Fixing in an acid hardening-fixing bath.

(4) Washing and drying.

Development can be carried out in a dish, but a tank is
preferable. It is, of course, essential that the material of the
vessel, whether dish or tank, should not be such as to pre-
cipitate the silver from the bath. Glass, porcelain, hard
rubber or plastic can be used, but metals are not permissible,
with the exception of certain types of stainless steel. Vessels
and solutions used for the preparation of the developer and
the development tank or dish must be scrupulously clean.
Undissolved chemicals or dust particles etc. can act as nuclei
for the precipitation of silver.

218

110.— FOREBATH FOR PHYSICAL DEVELOPMENT
Potassium iodide 100 grains 5 grams

Sodium sulphite, aniiyd. J ounce 12.5 grams

Water to make 20 ounces 500 ml.

The film is placed in the dish or tank dry and the forebath
is then poured upon it and allowed to act for 3-4 minutes.
The forebath is then poured off and can be used again and
again, usually serving for at least eight treatments. The film
is then rinsed well in two changes of water. Panchromatic
films may be desensitised in the usual manner before being
placed in the forebath (see page 251).

For development a concentrated silver-stock solution is
prepared. It is of the utmost importance that the directions
for making this solution be carefully and accurately followed.

111.— PHYSICAL DEVELOPER

C.
D.

Solutions A and B are prepared warm (about 120°F.,
50°C.) and allowed to cool to about 75°F. (24°C.). The solution
A is poured slowly with constant stirring into solution B.
Stirring must be continued until the white precipitate which
forms initially is completely dissolved. When this is accomp-
lished solution C is added to the mixture of solutions A and B
to give the silver stock solution which has good keeping
properties.

When the film has been treated in the forebath and received
its two good rinsings it is placed in the physical developer
solution consisting of 1 part of the silver stock solution
(A + B + C), 1 part of the exciter solution (solution D) and
3 parts of distilled water.

XXXV.— APPROXIMATE TIME OF PHYSICAL DEVELOPMENT

Silver nitrate

1 ounce

12.5 grams

Distilled water

8 ounces

200

ml.

Sodium sulphite anh/d.

2 ounces

grams

Distilled water

20 ounces

500

Hypo crystals

6 ounces

150

grams

Distilled water to

40 ounces

1000

ml.

Metol

40 grains

grams

Hydroquinone

80 grains

grams

Sodium sulphite anhyd.

If ounces

grams

Tribasic sodium phosphate

l| ounces

grams

Distilled water to

40 ounces

1000

ml.

Film Speed

ASA

50-125
160-320
400-800

Deve/opment Time at 65°F.

29 min.
34 „
36 „

219

When development is complete the film is given a good
rinse and is then fixed in a normal acid hardening and fixing
bath. (See page 273.)

As the silver bromide in the emulsion will have been
partially converted into iodide in the forebath, a much
longer fixing time will be necessary than that required for a
normally developed negative, certainly not less than about
20 minutes: after that the film should be well washed and,
before drying, the developed surface should be gently wiped
over with a wad of cotton wool to remove any loose deposit
of reduced silver.

Further formulae for physical development have been
devised as a result of the careful investigations of F. R.
McQuown. It is claimed that by this method the over-
exposure usually called for is not necessary.

112.— FOREBATH FOR PHYSICAL DEVELOPMENT
(F. R. McQUOWN)
Potassium iodide 120 grains 6 grams

Sodium sulphite, anhyd. 280 grains 14 grams

Borax powdered 50 grains 2.5 grams

Water to make 20 ounces 500 ml.

All the chemicals can be dissolved together. The borax
may be omitted if the bath is to be used up within a week or
so. The bath can be used repeatedly. The film is immersed,
without previous wetting, for 40 seconds in the forebath with
vigorous agitation. After the forebath treatment rinse the
film in water for 20 seconds and proceed to develop in the
working physical developer solution.

113.— PHYSICAL DEVELOPER (F. R. McQUOWN)

Sodium sulphite, anhyd.

ounces

grams

Silver nitrate, cryst.
Borax, powdered
Hypo (Sodium thiosulphate)
Water to make

130
130

24
20

grains
grains
ounces
ounces

6.5
6.5
60
500

grams
grams
grams
ml.

The sulphite should be dissolved in about 14 ounces (350
ml.) of water at about 120°F. (50°C.). The silver nitrate is
dissolved in about 4 ounces (100 ml.) of water and slowly
added to the sulphite solution which is vigorously stirred.
The other chemicals are then dissolved in the order named
and the volume made up to 20 ounces (500 ml.).

The plate or film is immersed in the following working
solution:

220

1 ounce

25 ml.

4 ounces

100 ml.

6 grains

0.35 grams

Developer stock solution
Water to make
Amidol

The working solution should be used within about ten
nainutes of making up.

Average times of development: 16 minutes at 60°F.
(15°C.), 11 minutes at 65°F. (18°C.), 7 minutes at 70°F.
(2rC.).

Tap water is satisfactory for all solutions. The stock
solution can be filtered if desired. Allow to stand for about
12 hours and then filter through a Whatman No. 2 filter paper.

When development is complete a short wash is given
before fixing in an acid hardening and fixing bath (page 273).

All the physical developer formulae mentioned above
suffer from two major disadvantages: they are extremely
unstable and spontaneous precipitation of silver may occur
immediately after mixing or at some time during the develop-
ment process. Also, physical developers are very slow acting
(see Table XXXV) and result in considerable loss in emulsion
speed.

Recently, research workers at the Philips Research Labor-
atories in The Netherlands have discovered that the inclusion
of two wetting agents (surfactants) in a physical developer
greatly increases its stabihty to spontaneous precipitation of
silver and also makes it possible to prepare more concentrated
physical developers of higher activity than was previously
possible.

114._STABILIZED PHYSICAL DEVELOPER
(H. Jonker, A. Molenaar and C. Dippel)

Metol 8.6 grams

Silver nitrate 1.7 grams

Citric acid, crystalline 21 grams

Armac 12D, 10% solution* 2 ml.

Lissapol N, 10% solution** 2 ml.

Distilled water to 1000 ml.
♦Surfactant, Dodecylamine acetate, Armour Industrial Chemical Co.
♦♦Surfactant, I.C.I. Ltd.

The silver nitrate content of the above developer can be
increased by a factor of five with some loss in stability but a
corresponding decrease in development time.

Formula 1 14 has a half life (the time after which the initial
development rate is reduced by one half) of five hours, whereas

221

a developer containing no surfactants has a half life of twelve
minutes.

TANNING DEVELOPERS

It has already been mentioned elsewhere that in the process of
development oxidation products are formed from the
developing agents or substances, and these products have
certain properties of varied interest and application in photo-
graphy. We already know that they can affect the colour of
the negative and stain fingers. They can also bring about the
tanning of the gelatine of the emulsion — a process favoured
by a low concentration of sulphite in the developer or, better
still, by its complete absence. Under these conditions the
tanning of the gelatine is proportional to the quantity of
silver reduced. Hence the tanning is greatest in the most
strongly blackened parts of the negative.

This property has been made use of in a number of ways
in photography. In the preparation of tanned relief pictures
for example the untanned gelatine, that is the gelatine
existing in the unexposed parts of the picture, is dissolved
away by warm water. In certain processes of colour photo-
graphy and in particular in the making of colour prints this
process is of great importance.

In ordinary black-and-white photography the tanning
effect on gelatine can be made use of in the following way.
Wherever the gelatine has been tanned by the developer,
the access of further developing solution to the film is
rendered difficult and development slowed down. This
braking effect on development is strongest in those parts of
the negative which have received the heaviest exposure, that
is in the highlights. Hence the further development of the
highlights is held back, and a certain degree of compensation
or equalising of contrast is attained; another point is that as
the action of the developer is almost wholly on the surface of
the emulsion, halation is not shown because the effects of
halation occur in the depths of the emulsion to a very much
greater extent than on the surface. Furthermore, such a
developer tends to improve the acutance of the negative for
the reasons explained on page 215.

The following formula are examples of tanning developers
having properties such as have just been described.

222

IIS.— TANNING DEVELOPER.

Pyrocatechin 40 grains 2 grams

Sodium sulphite anhyd. solution 5% 2 drams 5 ml.

Caustic soda solution 5% 4 drams 10 ml.

Water to make 40 ounces 1000 ml.

Development time is 15-20 minutes.

116.— TANNING DEVELOPER DI75

Solution A.

Pyrogallol 4 grams

Sodium sulphite anhyd. 5 grams

V\/ater to make 1000 ml.

Solution B.

Sodium carbonate anhyd. 28 grams

Water to make 1 000 ml.

Mix equal parts solutions A and B immediately before use.

With the exception of glycin most of the usual developing
agents will produce a tanned image when used with a similar
bath to the above, but pyrocatechin and pyrogallol are the
most powerful tanning agents among them.

CHROMOGENIC DEVELOPERS

The word chromogenic is applied to materials which when
oxidised produce colours: its use in photography is com-
paratively recent, but is of material significance in the
development of modern colour photography.

We have already seen that the oxidation products of
developing substances have dyeing properties and can colour
the silver image and stain gelatine, etc. Until recently this
property was not utilised in practice to any great extent.
Some small use was made of a brown-tone developer foi
lantern slides, still more rarely for papers, generally a
pyrocatechin sulphite-free developer of the type described
above.

Today this dye- or colour-producing property of develop-
ers assumes great importance, for the Kodachrome, Koda-
color, Agfacolor and other processes use this principle. The
oldest example of the formation of a dye image by the
development process is pyro, which in an alkali-rich formula
does not produce a black silver image but one which is more
or less brown or even yellow. If such a negative be treated with
Farmer's reducer so that the whole of the silver image is
removed, there still remains a clearly perceptible dye image
of yellow-brown colour.

223

Starting from this point, Homolka sought materials
which could act not only as developers but also as stepping-
stones to dye products, and he found such compounds in
indoxyl and thioindoxyl, which are capable of developing the
latent image in exposed photographic materials and are
oxidised by the development process to the deeply-coloured
indigo dyestuffs.

The next step in the process was supplied by the researches
of Fischer and Siegrist who discovered that many usable
developers had the property of forming dyestuffs under the
influence of the developed image. p-Phenylenediamine,
p-aminophenol and allied compounds possess this property
to a remarkable degree, and are able through simple oxidation
with phenols and amines to produce a whole range of dyestuffs
which are known as indophenols, indoanilines and indamines.

The oxidation which brings about the formation of these
dyestuffs can be easily effected by the exposed silver bromide
in the photographic film. Hence it is possible by direct
development to obtain a reduction of silver and a proportional
formation of dyestuff, given, of coiu-se, that the dyestuff is
insoluble in water and remains precipitated where it is
formed, thus producing a dye image.

The phenols and amines used with the developers are
called couplers because they couple with the oxidised
developer to give dyestuffs. By the choice of suitable and
specific couplers a very big range of compoimds has been
produced, many of them the subject of patents, but the work
of the researchers already named has provided quite a
number of valuable and useful couplers.

The origin and character of the colour depends in large
degree on the developer and by the introduction of colour-
deepening groups it is possible to produce a range of shades.
For example, using dichloronaphthol as coupler and varying
the developer from paraphenylenediamine to some of its
derivatives one can obtain the shades in Table XXXVI. Of
these three developers the third is perhaps the most easily
obtainable and finds a place in many chromogenic developers.
The diethyl compound of p-phenylenediamine is similar in its
action.

The wide variety of colour tones obtainable through the
particular choice of developer and coupling body is of great
importance in the application of the method for colour

224

photography, particularly in the preparation of separation
pictures in the correct basic colours.

The great importance of such developers and couplers in
colour photography will be obvious. There is also an interest-
ing and fascinating field in the development of lantern slides
and of positives on paper, for not only can one obtain a big
range of colours by the choice of developer and coupler, but
one can also remove the silver image in part or entirely by
the use of Farmer's reducer.

XXXVI.— CHROMOGENIC DEVELOPER SUBSTANCES AND
COUPLERS

p-Phenylenediamine Blue-red or violet

o-Methyl-p-phenylenediamine Blue

N,N-Diethyl-p-phenylenediamine Blue-green

Further changes in colour can be obtained by the choice of different
couplers.

Alpha naphthol Blue

2:4-Dichloro-alpha-naphthol Blue-green

Pentabromnaphthol Green

p-Nitrobenzylcyanlde Yellow

1 -Phenyl — 3-Methyl — 5-pyrazolone Red

Colour developers can be used on most, but not all,
lantern plates and papers. Chlorobromide papers are suitable,
but bromide papers may not give very satisfactory image
tones and chloride papers tend to show stained whites. In
general it is more satisfactory to develop, fix and wash in the
usual way, and then to bleach with a ferricyanide- bromide
bleach and re-develop with the colour developer. This method
is, of course, apphcable to any type of paper.

117.— FOCAL COLOUR DEVELOPER
N,N-Diethyl-p-phenylenediamine
-hydrochloride or -sulphate or
-bisulphite
Sodium carbonate, anhydrous
Sodium sulphite, anhydrous
Potassium bromide
Hydroxylamine hydrochloride
Water to make

It is advisable to prepare this developer from 10% stock
solutions of the various ingredients before use. The colour
formers are added immediately before use.

MAGENTA COLOUR FORMER

grains

grams

ounces

grams

grains

gram

grams

gram

grams

gram

ounces

1000

ml.

p-nitrophenyl acetonitrile

10 grains

0.5 gram

Acetone

i ounce

12 ml.

Methylated spirit (colourless industrial)

4 ounces

100 ml.

225

BftOWN COLOUR F'ORMEfi

2.S-dichloro acetoacetanilide 10 grains 0.5 gram

p-nitrophenyl acetonitrile 10 grains 0.5 gram

Acetone J ounce 12 ml.

Methylated spirit (colourless industrial) 4 ounces 100 ml.

BLUE COLOUR FORMER
Alpha-naphthol 14 grains 0.7 gram

Methylated spirit (colourless industrial) 4 ounces 100 ml.

BLUE-GREEN COLOUR FORMER
2:4-Dichloro-alpha-naphthol 20 grains 1 gram

Methylated spirit (colourless industrial) 4 ounces 100 ml.

GREEN COLOUR FORMER

2.4-dichloro-alpha-naphthol 10 grains 0.5 gram

2.5-dichloro acetoacetanilide 10 grains 0.5 gram

Methylated spirit (colourless industrial) 4 ounces 100 ml.

YELLOW COLOUR FORMER
o-Chloro acetoacetanilide or

2.S-dichloro acetoacetanilide 20 grains I gram

Methylated spirit (colourless industrial) 4 ounces 100 ml.

For use take about 2 drams (10 ml.) of the colour former
solution as detailed above for each 4 ounces (100 ml.) of
developer solution. By mixing the colour former solutions
nearly any shade of colour can be obtained. When once used,
the developer must be thrown away and a fresh portion used
for each separate development.

TROPICAL DEVELOPERS

With any normal developer, increase of temperature means
increased rate of development and increased danger of
fogging, but the greatest danger is that at high temperature
the gelatine of the emulsion swells excessively and becomes
very weak and may even melt entirely. The name "Tropical
Developer" is given to those formulae in which provision has
been made to avoid dangerous swelling, either by the addition
of a substance which reduces the swelling of the gelatine or
by balancing the ingredients, eliminating those which cause
swelling to excess. In general, the more alkaline the developer
the more the gelatine swells and the more rapidly develop-
ment takes place. Alkali free developers of the amidol type
or one of the mildly alkaline fine grain developers are basic-
ally preferable to those with normal alkali content when

226

working at high temperatures. The choice of a suitable
developer formula is not, however, the only means of coping
with high temperatures. There are a number of other tech-
niques which can be used alone or in combination with a
special formula.

PRE-HARDENER

A very efficient method to prevent excessive swelling of the
gelatine in a developer is the use of a pre-hardener solution.

118.— PRE-HARDENER

Solution

■A'

Formaldehyde, about 37% solution by weight

ml.

Solution

•B'

Water

900

ml.

*0.5% solution of Anti-Fog No. 2

(6-Nitrobenzimidazole nitrate)

40.0

ml.

Sodium sulphate, desiccated

SCO

grams

Sodium carbonate, monohydrated

12.0

grams

Water to make

1000

ml.

*To prepare a 0.5% solution, dissolve I gm. of Kodal< Anti-Fog No. 2 in
200 ml. of distilled water.

The working solution should be prepared just before
using by adding 5 ml. of Solution A to 1 litre of Solution B
and mixing thoroughly.

Immerse the exposed film in the Pre-hardener for 10
minutes with moderate agitation. Then remove the film from
the solution, drain for a few seconds, immerse in water for 30
seconds, drain thoroughly and immerse in the developer.
The selection of the proper developer will depend upon the
contrast and the time of development desired. In general, up
to 90°F. (32°C.), conventional developers such as Formula
6, may be used without modification.

Times of development will be about as follows:

At 75°F. (24°C.) — use the normal development time re-
commended at 68°F. (20°C.) without pre-
hardening

At 80°F. (27°C.)— 85 % of normal time

At 85°F. (39°C.)— 70% of normal time

At 90°F. (32°C.)— 60% of normal time

At 95°F. (35°C.)— 50% of normal time.

Following development, rinse, fix in an acid hardening
fixing bath, wash, and dry in the usual way.

227

At HIGHER TEMPBRAtURES

At temperatures above 95°F. (35°C.), increase the concen-
tration of Anti-Fog No. 2 in the prehardener up to double
the normal formula concentration, if necessary, to control
fog. Process as before, using a low-activity developer, such
as a fine grain formula, to avoid excessively short develop-
ment times. The average development time at 110°F. (43°C.)
after prehardening is about one-quarter of the time at 68°F.
In case the development time at elevated temperatures is
too short for practical use, sodium sulphate can be added to
the developer to extend the time of development. The keeping
properties are adequate for ordinary tray and tank practice.
Gradual deterioration does occur on standing, but the bath
will keep satisfactorily (without use) in a closed bottle for 3
or 4 weeks at 95°F. (35°C.). For most applications, the useful
life without replenishment is more than forty 8 x 10-inch
films per gallon without serious change in properties.

ADDITION OF SODIUM SULPHATE

The substance usually added to developers to reduce the
swelling of gelatine is sodium sulphate (Glauber salt). It is
essential that it should be present in high concentration.
Most normal developers may be made suitable for tropical
processing by the addition of 8 ozs. (105 gms.) of sodium
sulphate cryst. to each 80 ozs. (1000 ml.) of the working
solution. The time known to produce a certain gamma value
at 68°F. (20°C.) or 65°F. (18°C.) in a normal non-sulphated
developer, should be referred to in columns 1 or 2 in Table
XXXVII and the required development time will be found in
the appropriate temperature column for the same developer
after the addition of the sulphate.

SPECIAL TROPICAL DEVELOPER FORMULAE

Several special formulae for tropical developers are given in
Table XXXVIII. Most of these formulae contain sodium
sulphate while the alkali content is kept low or a milder alkali
is used. Approximate developing times for the formulae are
5-7 min. at 24°C., 4-6 min. at 27°C., 3-4 min. at 29°C. and
2-3 min. at 32°C. These times are for tank development; for
tray development, they have to be reduced by about one-fifth.

228

XXXVII.— DEVELOPMENT TIMES IN NON-SULPHATED
AND SULPHATED DEVELOPER

Normal Development

Time (minutes)

Calculated Development Time (minutes)

in non-sulphated

/n sulphated developer

develop:

er at: —

65°F.

68°F.

75°F.

80° F.

85''F.

90°F.

(I8°C.)

(20°C.)

{24°C.)

(27°C.)

(29X.)

(32X.)

XXXVIII.

.—SPECIAL DEVELOPERS
Tropical

119
DI3

120
DKI5

121
DKISo

122
AN64

123
G222

Metol

—

5.7

2.5

Sodium sulphite anhyd.

52.5

Hydroquinone

10.5

—

6.5

Para-aminophenol
hydrochloride

5.2

—

Sodium carbonate anhyd.

—

13.5

—

Potassium carbonate

—

Kodalk

—

22.5

—

Sodium sulphate

—

Potassium bromide

—

1.9

1.5

Special addition

Pot.

iodide

2.1

—

Water to

1000

Development time (min.)

6-7
29°C.

2-3
32°C.

2-3

29°C.

2
29°C.

229

Where still higher temperatures have to be dealt with the
use of the above pre-hardener, in conjunction with a tropical
developer, is necessary. By this method developing can be
carried out up to temperatures of 105'F. (4FC.)-

After development a stop-bath of the type given in
Formula 180 should be used. This has a hardening and anti-
swelling effect. For fixing, too, a special tropical formula,
such as Formula 187, is recommended.

LOW-TEMPERATURE DEVELOPMENT

It is generally assumed that most developing agents become
inactive below a temperature of about 12°C. (55°F.).
It is certainly advisable to avoid processing at such
a low temperature but there may be cases where it is
not possible to warm solutions to the normal working
temperature.

The feasibihty of processing at very low temperatures has
been investigated by R. W. Henn and J. I. Crabtree of the
Kodak Research Laboratories (Communication No. 1019)
who have shown that it is indeed possible to develop films at
low temperatures with modifications of standard formulae
and even at very low temperatures with special developers
of exceedingly high energy.

The main problem is, of course, the loss of activity of the

developer. It is advisable therefore to start with a developer

which at normal temperature is very active. For instance, a

caustic hydroquinone developer (Table XXIII) or a still more

alkaline variation of a caustic M.Q. developer (Formula 124),

such as the following:

124.— HIGH ENERGY DEVELOPER
for low temperature processing

Water(l2S°F. or52''C.) 500 ml.

Metol 14 grams

Hydroquinone 14 grams

Sodium sulphite anhyd. 52.5 grams

Sodium hydroxide 17.6 grams

Potassium bromide 8.8 grams

Benzotriazole 0.2 grams

Add cold water to make 1000 ml.

For use down to + 30°F. (1°C.) : Use above formula undiluted.
For use down to + 5°F. (-15°C.): Take 3 parts stock solu-
tion, 1 part ethylene glycol.

230

The ethylene glycol should be added prior to storage at low
temperatures.

For very low temperature processing a caustic solution
of two powerful developing agents has been designed, namely
Amidol and Pyrocatechine.

1 25.— AMI DOL-PYROCATECH I N DEVELOPER
for very \ow temperature processing

Solution A

Water (I25°F. or S2°C.)

500

ml.

Sodium bisulphite

100

grams

Amidol (2, 4 diaminophenol hydorchloride)

grams

Pyrocatechin

grams

Benzotriazole

grams

Add cold water to make

1000

ml.

Solution 6

Cold water

500

ml.

Sodium hydroxide

120

grams

Potassium bromide

grams

Potassium iodide

grams

Add cold water to make

1000

ml.

For use down to +30°F. (rC): Solution A, 1 part; Solution
B, 1 part; Water, 2 parts.

For use down to +5°F. (-15°C.): Solution A, 1 part; Solu-
tion B, 1 part; Water, 1 part; ethylene glycol, 1 part.
For use down to -40°F. (-40°C.): Solution A, 1 part; Solu-
tion B, 1 part; ethylene glycol, 2 parts.

The glycol may be divided and added to each of these
solutions previous to storage at low temperatures. Combine
Solutions A and B only immediately before use, since the
mixed developer oxidises rapidly. Solution A may also
deteriorate on keeping, and should be kept well-stoppered
and as cool as possible.

FACTORIAL DEVELOPMENT

Alfred Watkins' factorial system of development played a
valuable part in photography for many years. Today it is but
Uttle used, largely because development by inspection has
been superseded by more modern methods.

In 1893 Watkins discovered that there was a definite
relation for almost every developer between the time of
appearance of the first trace of developed image and the time

231

that would be required for the full development of the image.
This was the foundation of his factorial development.

The "time of appearance" is the exact time elapsing
between the pouring on of the developer and the first appear-
ance of any trace of image. This "time of appearance" is
multiplied by a factor for each particular developer.

The factors for the more important developing agents are
as follows:

XXXIX.— WATKINS- FACTORS

Chlorquinol

Factor 5

Amidol (concentration 4 parts per 1 ,000)

„ 18

Pyrocatechin

Glycin

Hydroquinone

Metol

, 30

Metol-h/droquinone (normal formulae)

Pyrogallo!

Pyrogallol and amidol do not obey the rule strictly, as
with these two substances the concentration of developing
agent can vary he factor, and in some other cases excessive
dilution and wide variations in temperature may also
influence the results.

In the case of combined developers such as metol-
hydroquinone the factor is the average of the factors of the
two constituents if they are present in equal proportions.
Thus with equal parts of metol and hydroquinone the factor
would be 5 + 30 = 35 divided by two = 17|. If, however,
there were 2 parts of metol and 3 of hydroquinone, then the
factor would be 30 + 30 + 5 + 5 + 5 = 75 divided by five
= 15. Using this method it is a simple matter to estimate the
factor for the most generally used developers.

The fact that the factor failed when the temperature varied
notably from the normal, induced Andresen to produce a
formula that could be varied to suit varying temperatures:

126.— TIME-TEMPERATURE DEVELOPER

A. Metol
Sodium sulphite, anhyd.
Water to

B. Potassium carbonate
Potassium bromide
Water to

232

200

grains

10 grams

ounces

SO grams

ounces

1000 ml.

,'*

ounces

40 grams

grains

0.5 gram

ounces

400 ml.

This developer is so compounded that, by varying the
proportions of the two solutions, development time can be
kept constant over a wide range of solution temperatures.
The proportions recommended for temperatures from 59-
86°F. (15-30°C.) are as follows:

Temperature 59° F. = 1 5°C. take of A 50 ml. of B 39 ml.

60.8°F. = 16X. „ 50 „ 30

62.6°F. = 17°C. „ 50 „ 23

64.4°F. = 18°C. „ 50 „ 18

66.2°F. = 19°C. „ 50 „ 14

68° F. =20°C. „ 50 „ 11

70° F. =2rC. „ 50 „ 9

71.6°F. =22°C. „ 50 „ 7

73.4°F. = 23°C. „ 50 „ 5

75° F. = 24°C. „ 50 „ 4

77° F. =25°C. „ 50 „ 3

79° F. = 26°C. „ 50 „ 2

82° F. =28°C. „ 50 „ 1

86° F. = 30°C. „ 50 „

The solutions are kept in the room in which development
is to take place. It is then only necessary to note the tempera-
ture of the room and to use the above proportions of
the solutions to obtain constant development time.

Development time is from 5-7 minutes. The method is of
interest for tropical development as sodium sulphate can be
added to the solutions to prevent excessive swelling of the
gelatine (see page 228).

QUICK-FINISH (rapid ACCESS) DEVELOPERS

There are numerous applications of photographic methods
where it is important that development shall be as rapid as
possible. The normal cycle of processing, even if it is reduced
to a few minutes only, is too long for many purposes. This is
for instance the case in one of the most important applica-
tions of high speed processing, namely the recording of
cathode ray tube traces, particularly in radar work. When an
aeroplane is detected by the radar devices, it may be essential
that the information should be passed with the minimum of
delay to the control station. Seconds or even fractions of
seconds can be of highest importance.

233

Another valuable use of high speed processing is in the
recording of instrument dials, to enable the inspecting
personnel to examine the exposed film or paper as soon as
possible after recording. A well-known application of high
speed processing is the photo finish method which takes a
photograph at the end of a race and supplies a print within
about 1 minute.

In all these cases highly active developers are required
and the formulae such as those in Table XL make full use
of all means to accelerate the developing process, such as
high general concentration, strongest alkai (sodium hydroxide)
at maximum content and also high temperature. In cases
where temperatures are employed considerably exceeding
normal working temperatures special "Quick-Finish" (rapid
access) films have to be used which stand temperatures up to
nearly 200°F. (93°C.). The emulsions of these films are
specially hardened and also thinly coated. It is in fact
possible to develop these films in the short period of one-fifth
of one second, but this requires, of course, the use of special
high speed processing machines in which the developing,
fixing and washing solutions are pumped on to the film,
picture by picture, and are almost instantly blown away
again by a jet of compressed air so that the next stage of
processing can be applied.

In normal photographic practice one will be satisfied with
the developing times of a few seconds. Using a developer
such as Formula 128 in Table XL, for instance, a normal
film would require a developing time of 20-30 seconds at
70°F. (2rC.), while a "Quick-Finish" film requires only 15
seconds under the same conditions. For the processing of
this special film higher temperatures can be applied and the
developing time can thus be reduced to, for instance, 4
seconds at 110°F. (43°C.).

TWO-BATH DEVELOPMENT

In the ordinary process of development the developing agent
becomes used up and various reaction products, particularly
bromides, slow the action of the bath. To meet these condi-
tions it is necessary to increase time of development or to
add a replenishing solution. There exists another method of
overcoming these difficulties, and that is the use of separate

234

baths for the developing agent and the alkali, or, as it is
generally called, two-bath development.

The first bath contains only the developing agent and the
preservative, and therefore no, or only incomplete, develop-
ment takes place in it. What happens is that the exposed film
or plate becomes saturated with the solution. As no chemical
action takes place, the properties of the bath do not alter; all
that happens is that each plate or film treated in it removes a
small quantity of the solution when taken out. Hence such a
bath, being constant in properties, allows very constant
results to be obtained. As the concentration of such a bath
can be altered at will, so can the desired grade of contrast in
the negative be influenced within comparatively wide limits
and where one type of material is being used the optimum
conditions can be obtained and maintained.

XL.— SPECIAL DEVELOPERS
Quick-Finish

127 128 129 130

L S. Fon-
C. Orlando miller and G. E. Duffy
Phot. Sc. co-operators Phot.
Eng. 2, 144 Phot. Eng. 7, 17 Eng. 6, 127 D8

Alcohol

—

Metol

—

Sodium sulphite anhyd.

Hydroquinone

Sodium hydroxide

37.5

Potassium bromide

—

8.8

Benzotriazole 1%

200

—

Water to

1000

Dilution

—

2:1

Development time (sec.)

0.2
I85°F.

1
I40=F.

0.2
I70°F.

2 min.

The actual development takes place in the second bath
which contains the alkali: here chemical action takes place
but not in quite the same degree as in a normal developer.
The film is already swollen and saturated with fresh developer

235

solution and the process of development is therefore speedy
and complete. Moreover, as the bath only contains alkali it
is cheap and can be renewed at frequent intervals.

The two-bath method has other advantages, one of which
is that a large tank can be used for the developing agent
solution, but a small one for the alkali. The method is worthy
of more attention than it has hitherto received.

131.— TWO-BATH DEVELOPER

Metol

100 grains

Hydroquinone

40 grains

Sodium sulphite, anhyd.

4 ounces

Sugar (cane)

4 ounces

Sodium bisulphite

100 grains

Water to make

40 ounces

Sodium sulphite, anhyd.

4 ounces

Sodium carbonate, anhyd.

200 grains

Water to make

40 ounces

5 grams

2 grams

100 grams

5 grams

1000 ml.

100 grams

10 grams

1000 ml.

The addition of sugar and bisulphite to the first bath has
the effect of retarding the action of the bath and at the same
time preventing the appearance of any image due to the slight
alkalinity of the sulphite.

The negative material should have about 5 minutes in
solution 1, and 4-6 minutes to develop in solution 2.

VELOPER (H. ST

OECKLER)

100 grains

5 grams

4 ounces

100 grams

40 ounces

1000 ml.

200 grains

10 grams

40 ounces

1000 ml.

132.— TWO-BATH FINE

Metol

Sodium sulphite, anhyd.

Water

Borax

Water

The time that films should remain in solution 1 varies
with different makes of film; the times for the film groups as
given on page 38 are as follows (at a temperature of about
65°F. or 18°C.):

Group A 3 mins.

Group B 4 „

Group C 6 „

The development time for all the films in bath 2 is about
3 minutes.

H. Stoeckler sets out the advantages of the two-bath fine-
grain developer method as follows: (1) Harmonious com-

236

pensation for great contrasts when used for the new and
harder films, soft negatives of a gradation which allows
easy enlarging. (2) The effective sensitivity of the film is not
materially reduced. If it is imperative not to lose any sen-
sitivity, only the first bath should be used and the develop-
ment carried out for sixteen minutes. (3) As it is development
at the surface, there is less halation and irradiation, and the
best possible rendering of sharpness. (4) Great economy and
cheapness of the solutions, which last longer and can be used
many times.

133.— TWO-BATH KODAK DK20 SUPER-FINE GRAIN DEVELOPER

Water distilled at I25°F.

(52°C.)

IS ounces

750

ml.

Metol

45 grains

grams

Sodium sulphite, anhyd.

2 ounces

100

grams

Potassium thiocyanate

8 grains

gram

Potassium bromide

4 grains

0.5

gram

Distilled water to

20 ounces

1000

ml.

Kodalk

175 grains

grams

Water (distilled)

20 ounces

1000

ml.

Water distilled (about 125"^)

15 ounces

750

ml.

Metol

65 grains

7.5

'i grams

Sodium sulphite, anhyd.

2 ounces

100

grams

Potassium thiocyanate

44 grains

grams

Distilled water to

20 ounces

1000

ml.

For use the solution 2 is diluted 10 times (50 ml. made up
to 500 ml. with water). This is thrown away after using for
the development of one film. The total bulk of solution
1 is kept at 1000 ml. by filtering back into the bottle after
use. 20 ml. of Replenisher (solution 3) is added to the amount
required for the tank for each film after the first. Develop-
ment time is thus kept constant.

The following development times in minutes are correct
for a gamma of 0.7 at 65°F. (See also page 38 for Film
Groups :) Group A films : 6 J mins. in Bath 1, 3| mins. in Bath 2 ;
Group B films: 10 mins in Bath 1, 3| mins. in Bath 2;
Group C films: 15 mins. in Bath 1, 3^ mins. in Bath 2.

As already noted on page 235 the principle of two-bath
development may be usefully combined with high speed
development. The high speed two-bath developer meets the
requirements of those who must complete the processing
of exposed films in the shortest possible time, e.g., in news
photography. The following method permits complete
processing within fifteen minutes.

237

134.— HIGH SPEED TWO-BATH DEVELOPER

Hot water (IIS^F. or 52°C.)

30 ounces

750 ml.

Metol

100 grains

5 grams

Sodium sulphite, anhyd.

1^ ounces

30 grams

Hydroquinone

200 grains

10 grams

Water to make

40 ounces

1000 ml.

Hot water (125°^ or 52°C.)

30 ounces

750 ml.

Sodium carbonate

5 ounces

125 grams

Water to make

40 ounces

1000 ml.

Solutions 1 and 2 are stored separately and used separ-
ately. Solution 2 must be replaced when it becomes badly
discoloured. Both solutions are used at full strength.

For development immerse films for one minute in solution
1, agitating the whole time, then transfer film to solution 2
for one minute. The solutions should be used at a temperature
of 70°F. (2rC.). If bath temperature be 75°F. (24°C.) then
only 45 seconds should be given in each bath, but should bath
temperature fall to 65°F. (18°C.) then development time in
each bath must be 1 minute 1 5 seconds.

Contrast can be controlled by varying the time of
immersion in solution 2 as contrast increases with increas-
ing time of immersion in this solution.

As soon as development is judged complete plunge
film into a stopbath consisting of a 1 % solution of acetic
acid.

MULTI-SOLUTION TECHNIQUE

Multi-solution developer is made up of a range of concen-
trated stock solutions of good keeping quality, so that by
simple measurement and without weighing, a whole selection
of developers can be prepared easily and rapidly. This method
has the advantage that when a particular developer is only
wanted occasionally, or when one uses a range of developers
such as a normal negative developer, a fine grain or a paper
developer, one can prepare any or all such developers quickly
and safely from the same stock solutions. If one has a normal
developer in frequent use it will be necessary to keep it ready
made up, but even then it is an advantage to have a multi-
solution set at hand, either to allow rapid preparation
economically and quickly of a special developer, or to use
the stock solutions to modify the normal developer in some
desired manner.

238

135.— METOL-HYDROQUINONE MULTI-SOLUTION
DEVELOPER

(A) Metol Stock Solution
Sodium sulphite, anhyd.
Metol

Water to make

(B) Hydroquinone Stock Solution
Sodium sulphite, anh/d.
Hydroquinone

Water to make

(D) Sodiunri Carbonate Stock Solution
Sodium carbonate

Water to make

(E) Potassium Bromide Stock Solution
Potassium bromide

Water to make

(F) Borax Stock Solution
Borax

Water to make

grains

2 grams

40
4

grains
ounces

2 grams
100 ml.

grains

2 grams

40
4

grains
ounces

2 grams
100 ml.

ounce
ounces

20 grams
100 ml.

400
4

grains
ounces

20 grams
100 ml.

200
4

grains
ounces

10 grams
100 ml.

100
4

grains
ounces

5 grams
100 ml.

The preparation of a developer with the aid of these stock
solutions is shown by an example using the Focal Universal
M-Q developer No. 16. To produce a dish developer with
a dilution of 1 : 5 we shall require the following quantities
taken in the order given.

Focal Universal M-Q

Original

Stock Solutions

Quantity

No. 16

Formula

for 600 ml.

Metol

3 grams

150 ml. (A)

15 ml.

Sodium sulphite

75 grams

375 ml. (C)

37.5 ml.

Hydroquinone

11 grams

550 ml. (B)

55 ml.

Sodium carbonate

75 grams

375 ml. (D)

37.5 ml.

Potassium bromide

1 gram

10 ml. (E)

1 ml.

Water to make

6000 ml.

600 ml.

Note that in each case the total volume of water is given
and not the amount which must be added to reach the requir-
ed volume. In the case of the third column of figures, for
example, the total volume of the necessary stock solutions
is 146 ml. We shall therefore require to add a further 454 ml.
of water to bring the volume to 600 ml.

It will be seen that the developer compounded from the
stock solutions is not quite identical with the original formula
inasmuch as the stock solutions A and B each contain
a certain amount of sodium sulphite as preservative.
The increase in the total sulphite content is not sufficient

239

to call for any adjustment when the stock solution C is
added.

From the example given it will prove a simple matter to
make up other developer combinations using the multi-
solution technique. There is just one precaution to bear in
mind and that is not to overstep the saturation limit with the
stock solution of any one constituent. (The saturation limit
of all the chemicals can be obtained under the heading of
"solubility" in the list on pages 401-406.)

INORGANIC DEVELOPERS

Inorganic developing agents such as ferrous oxalate had been
used in the early days of photography but were then com-
pletely superseded by the organic developers. However,
recent inorganic developers employing a metal ion, such as
iron or titanium, and a modern chelating (sequestering)
agent give results comparable to conventional developers.
As a matter of fact, they have many features of special
interest.

Iron developers can be prepared by replacing the complex
oxalate ion by more modem complexing agents, such as
ethylenediaminetetraacetic acid (EDTA). The compound
formed by mixing ferrous sulphate and EDTA is com-
mercially available; in a 5 per cent solution it gives a developer
which is an improvement on the old iron developers as it is
faster working.

Still more promising results are obtained with titanium
developers as they show a greater activity. To prepare these
developers, titanium trichloride is used in the form of the com-
mercial 20 % solution. By combining this solution with EDTA
as the chelating agent, a purple solution is formed which
is a very active developer. As with the usual organic de-
velopers, it is necessary to adjust the pH value and to add
anti-fogging agents. A formula of this type has been pub-
lished by G. M. Haist, J. R. King, A. A. Rash and J. I.
Crabtree:

136.— TITANIUM DEVELOPER

Titanium trichloride solution 20% 3 ounces 75 ml.

EDTA (tetra-sodium salt) 4 ounces 100 grams

Sodium acetate 350 grains 20 grams

Potassium bromide 70 grains 4 grams

Water to make 40 ounces 1000 ml.

240

The pH of the mixed solution must be adjusted to 4.0
with hydrochloric acid. The sodium acetate is added as a
buffer and has no photographic effect. The developer has
given good results with cine positive film at 5 minutes
development (68°F.). It gives higher speed at shorter de-
velopment time than conventional developers. For the devel-
opment of negative films it may be advisable to dilute the
developer and to increase the concentration of potassium
bromide.

Inorganic developers offer the interesting possibility of
regeneration by electrolytic methods. The above titanium
developer can be regenerated by electrolysing at a cm-rent
density of 250 amps per square metre in a cell having a lead
cathode with a graphite anode enclosed in a porous cup. The
exhausted developer is used as the catholyte and a dilute
sulphuric acid solution as the anolyte.

RESTRAINED DEVELOPMENT

We have seen (page 77) that in addition to the chemical
reaction involved in the reduction of the silver bromide there
are other processes taking place during development which
can notably influence the result. The process of image
formation is considerably affected by the fact that in the
heavily exposed areas the bromide set free during develop-
ment acts as a strongly retarding agent on the growth of the
image at those points. This naturally suggests that if we could
control this particular process it could be used to modify the
contrast of the negative. Actually such methods were pub-
lished about 1900 and in recent years they have again been
brought forward sometimes with somewhat extravagant
claims as to their advantages.

One of the oldest of such processes by which the bromide
effect is utilised is that which the Germans called "PlanUege"
development, literally "flat lying development". This consists
in having the carefully levelled negative lying sensitive face up
in developer which is completely undisturbed. The perfectly
horizontal position of the plate inhibits the diffusion or flow
of the exhausted developer from the heavily exposed parts
of the negative with the natural effect that development slows
down in the highlights but proceeds normally in the shadows.
This never was a popular process with amateurs because of

241

the trouble involved in the careful levelling of the plate but
it still finds applications in the graphic arts.

A simpler method makes use of the principle of inter-
mittent development and was introduced about the year
1911. If a negative is plunged into developer and then with-
drawn, the adsorbed developer continues to work but in the
highlight areas its energy is soon spent. In the shadows or
lightly exposed areas the developer retains sufficient strength
to continue development for a longer period. The result is
that development of the highlights is held back but the
shadow areas go on developing. This can be of real advantage
in the case of underexposed negatives or those of very
contrasty subjects.

This principle can be applied in various ways. One of the
oldest methods is to place the negative in developer until
reasonably saturated with the developer solution, then with-
draw it and place in water, repeating the process mitil the
desired effect or degree of development has been attained.
In later years this process had been investigated by A. Knapp
who suggested the following formula.

137.— AMIDOL DEVELOPER FOR INTERMITTENT DEVELOPMENT

Amidol 10 grains 0.5 gram

Sodium sulphite, anhyd. 40 grains 2 grams

Water to make 4 ounces 100 ml.

The negative is given three soakings in the developer for
40 then 50 and finally 90 seconds respectively and after each
immersion in the developer is allowed to lie in water for two
minutes without being disturbed.

More energetic and more concentrated developers may
be successfully used but no hydroquinone developer is
suitable.

H. C. McKay has proposed the following metol formula:

138.— METOL DEVELOPER FOR INTERMITTENT DEVELOPMENT

Metol Jounce IS grams

Sodium sulphite, anhyd. 2 ounces 60 grams

Caustic soda 90 grains 6 grams

Sodium carbonate 90 grains 6 grams

Borax I ounce 30 grams

Water to make 32 ounces 1000 ml.

Another method of intermittent development consists in
taking the developer-saturated negative and pressing the
gelatine face into close contact with a glass plate and then

242

leaving the two plates in water at a temperature of 70°F.
(24-25°C.) until development is complete. This process was
re-introduced luider the name P. & H. process and a special
film ribbon was provided to allow the development of roll
films by the process.

The metol developer, Formula 138, is suitable for this P.
& H. process, the negative being given an immersion ranging
from 70 to 140 seconds according to the contrast of the
subject and the properties of the film used. The greater the
contrast the shorter the time the film should remain in the
developer. Allow the film 15 minutes in the water.

Whilst intermittent development can provide the desired
adjustment of contrast it would be quite wrong to think that
there are no other methods of attaining a similar result. The
method makes use of concentrated developer and hence
there is a notable difference as compared to the result obtain-
able with normal developers. If one uses a soft compensating
fine-grain developer almost the same result can be obtained
as by the intermittent method, with the added advantage of
consistent fine grain. Hence the practical value of intermittent
development is open to doubt.

REVERSAL DEVELOPMENT

The purpose of reversal development is the opposite of that
of normal development in which from an exposed plate or
film we obtain a negative, or if we are printing from a
negative we get a positive. With reversal development there
are two stages which result in our obtaining a positive direct
from an exposed plate or film, or a negative from a negative
and a positive from a positive by contact or enlarging
methods of reproduction.

The process is of particular importance in the handling
of cine-film and 35 mm. film for miniature cameras and finds
wide application in many processes of colour photography.
In cases where the amateur requires only a single copy of an
exposure, reversal development will supply him with a trans-
parency which can be visually examined or projected in a small
projector. The process is also useful in the preparation of
duplicate negatives.

Reversal development is not a simple process and does
not permit any universally applicable formula being used,

243

as its successful application depends to so large an extent on
the nature of the sensitive emulsion being used.

The difficulties that may arise can best be dealt with by
making a detailed study of the processes which comprise re-
versal development of black-and-white materials (see page 245) :

(1) The exposed material, plate or film, is first
developed with a developer which will ensure that
every exposed grain in the emulsion is developed.
This is the primary development.

(2) The image so developed is next dissolved com-
pletely away with a suitable silver solvent.

(3) The silver bromide remaining, that is the silver
bromide not affected by the first exposure, is now
fully exposed and developed and so provides the
final image; this is the secondary development.

It will be clear that the nature and quality of this final
image will be determined by the quantity and structure of the
silver bromide left behind after the removal of the primary
silver image.

If that primary image was a dense one, extending well into
the emulsion layer, then the silver bromide remaining after
its removal would be comparatively thin, and the secondary
image produced by its exposure and the secondary develop-
ment would naturally be thin also.

If, on the contrary, the primary image was thin, then a
large quantity of silver bromide would remain and would
produce a dense and probably clogged-up image on secondary
development.

If a successful result is to be obtained by the reversal
process, it is obvious that a nice balance must be observed
between the image produced by the first exposure and the
quantity of silver bromide which will remain when the
primary image is removed.

It must be noted therefore:

(1) That the primary exposure will largely determine
the density and the proportion of the emtilsion
forming the first image, and therefore the density
and quality of the second or final image. Thus
there is no room for either over or under-
exposure and latitude in exposure when using the
reversal process is small.

244

THE PROCESS OF REVERSAL DEVELOPMENT

^T^

Reversal development involves three distinct stages. A. Primary
development in which the exposed material is developed with an energetic
developer to a normal negative. The diagram shows a section through
the three parts of the negative, shadows, middle tones and highlights.
B. The dissolving of the primarily-developed silver. This is effected
by a suitable silver solvent, leaving behind the unexposed silver bromide,
which will go to form the positive image. C. This unexposed silver bromide
is now exposed to light and developed to form the actual positive.

Column 1, on the left, shows the reversal development of a well
exposed picture. Column 2, in the centre, shows the reversal of an over-
exposed picture, the highlights of which are being lost. Column 3, on the
right, shows the reversal of an under-exposed picture. The highlights of
this imder-exposed pictiu'e will remain partly undeveloped in stage A,
leaving too much silver bromide undissolved in stage B, which exposed
in stage C leads to much density in the highlights.

245

(2) The development of the primary image will have
a great influence on the result. Such development
must be complete, and so a strong-working,
energetic developer is used and development time
is such that there shall be no doubt that full
development has been attained. To further this
end it is usual to employ a silver bromide solvent
in the primary developer, such as ammonia or
potassium thiocyanate which assists in the
development and helps to reduce the silver
bromide left for the secondary image.

(3) When the primary development is complete the
image so developed is dissolved away in what is
usually called the bleach bath. After a wash the
remaining silver bromide is fully exposed to white
light and completely developed in a normal
developer.

Any sensitive material can be reversal processed but
those intended for it are specially coated for the purpose,
and the emulsion is usually thinner than with ordinary films.

In the various formulae which follow, examples of most
of the practical variations in reversal procedure will be given,
but it must be emphasised that for any particular reversal
film the maker's instructions should be adhered to, as they
have been carefully worked out for that particular film.

XLI.— FIRST DEVELOPERS FOR REVERSAL PROCESSING

139
D168

140
D1 9+ thiocyanate

141
ID36+hypo

Metol

Sodium sulphite anhyd.

Hydroquinone

Sodium carbonate aniiyd.

44.5

Potassium bromide

—

Potassium tliiocyanate

—

Water to

1000

Dilution

1:1

246

Formula 139 (Kodak D168) is suitable for all Kodak
continuous tone materials and formula 140 is suitable for
Kodak Panatomic X film, whereas formula 141 requires
different quantities of crystalline sodium thiosulphate (from
4-12 grams per litre) to be added to the diluted developer
depending on the particular Ilford film being processed. Thus
Fine Grain Safety Positive film requires the addition of 4
grams per litre, HP3 and HP4 requires 8 grams per litre and
FP4 requires 12 grams per litre.

It is recommended that the user finds for himself the
optimum quantity of thiosulphate to suit the particular film
being processed. As a general guideline increasing the thio-
sulphate reduces the maximum and minimum densities that
are obtained on reversal, i.e. the positive characteristic curve
is displaced downwards to lower densities, whereas reducing
the thiosulphate concentration has the opposite effect. Increas-
ing the time of the first development has a similar effect to
increasing the thiosulphate concentration.

XLII.— BLEACH BATHS FOR REVERSAL PROCESSING

142

143
KodakRllA

Potassium permanganate

—

Potassium dichromate

—

Water to

1000

Sulphuric acid cone.

Dilution

—

1:9

Caution Add the concentrated sulphuric acid slowly with constant stirring
to the cold solution of the permanganate or dichromate.

XLIII.— CLEARING BATHS FOR REVERSAL PROCESSING

144

145
KodokR216

Sodium or potassium metabisulphite

—

Sodium sulphite anhyd.

—

Sodium hydroxide

—

Water to

1000

247

XLIV.— SECOND DEVELOPERS FOR REVERSAL PROCESSING

146
D158

147
D8

Metol

3.2

—

Sodium sulphite anhyd.

Hydroquinone

13.3

Sodium carbonate anhyd.

—

Sodium hydroxide

—

37.5

Potassium bromide

0.9

Water to

1000

Dilution

1:1

—

XLV.— REVERSAL PROCESSING
Processing Steps and Formulae

Kodak

llford

1. First developer

D168 (No. 139)
5-10 min.
Undiluted or
1:1, 20X.
Or No. 140
6 min. 20X.

ID36 (No. 141)
12 min. 20°C.
1:1 + Hypo

Wash

5 min.

3 min.

Bleach

R21A (No. 143)
3-5 min.

No. 142
3-5 min.

Wash

2-5 min.

Clear

R21B (No. 145)
or 144
2 min.

Nos. 144
or 145
2 min.

Wash

i min.

2 min.

Re-expose

2J min.

1-2 min.

8. Second Developer

D158 (No. 146)
2-5 min. 1:1, 20°C.
Or No. 140
4 min. 20°C.

Same as first
developer,
6 min. lO'C.

9. Wash

Rinse

10. Fix

Acid hardening
fix

11. Wash

15-30 min.

30 min.

248

REVERSAL OF PROCESS MATERIALS BY THE
ETCH-BLEACH PROCESS

The etch-bleach process of reversal processing provides a
simple and rapid method of preparation of reversals for
positive working lithographic plates, photo-engraving, etc. In
this process the silver image formed in the first developer is
removed, together with the gelatine, by an etch-bleach bath
(formula 148) to leave a positive relief image which can be
developed or dyed to a particular colour.

148.— ETCH-BLEACH-BATH (Kodak £8-3)

A. V\/ater, 86-9S''F. (30-35°C.) 750 ml.
Cupric chloride 10 grams
Citric acid 10 grams
Water to 1000 ml.

B. Hydrogen peroxide 10 volume solution.

For use mix equal volumes of solutions A and B.
Notes: Hydrogen peroxide solutions tend to decompose on
storage and this may result in incomplete removal of the
gelatine although the silver image bleaches. If this occurs it is
reconunended that the proportion of hydrogen peroxide be
increased.

XLVI.— ETCH-BLEACH REVERSAL PROCESSING
for Process Materials such as Kodalith, Steps and Formulae

First Developer

D8 (No. 147) + 4g./1 of potassium
thiocyanate, 2J-3 min. 20°C.

Stop-bath

5% acetic acid, IS seconds

Etch-bleach

EB-3 (No. 148)

Wash

IS seconds

Re-expose

Second Developer

D158(No. 146)orD8(No. 147).
5-6 min. 20°C.

Hardener

see Tables Llll and LIV

Wash

5 min.

ELECTROLYTIC DEVELOPMENT

The idea that electrolytic processes, which play so large a
part in technology today might be of service in photography

249

IS not new, yet so far no really practical method has been
evolved although some interesting investigations have been
carried out.

J. Rzymkowski has pubhshed a reproduction of an
electrically-developed portrait, but did not disclose the com-
position of the developer solution. He used a cylindrical
battery jar with a resistance between it and the electric light
supply. In the battery jar a porous cell separated the anode
from the cathode. The anode consisted of a metal plate, while
the cathode was of cylindrical form and of punched metal.
The film was placed round the wall of the battery jar. The
time of development was given as 15 minutes with a current
strength of J-ampere.

Another method which dispenses with electric current,
but may be claimed as electrolytic, is that of R. S. Morse, who
bathes the exposed material in the following bath and then
places it in intimate contact with a copper plate.

149.— BATH FOR ELECTROLYTIC DEVELOPMENT

Ammonia IJ ounces 40 m\.

Formaldehyde 85 minims 5 mL

Mercuric chloride 10 grains 0.5 gram

V/ater 8 ounces 200 ml.

BASIC FORMULAE

The photographer can choose from a truly formidable
collection of developer formulae. We have made every effort
to arrange them in groups according to their properties and
their modes of application. It should therefore not be undtily
difficult to choose the right developer for any job. However
in addition to the developers hsted here the photographer is
confronted by a host of formulae pubhshed elsewhere.

Through the publication of curves and data for every
single recipe or formulae the impression is strengthened that
essential differences do exist between all of them and that
the results published in such detail are really a scientific
contribution and that the photographer is expected to keep
strictly to all these recommendations.

In fact, on more close scrutiny we find, behind the over-
whelming variation of formulae, repetition of the same basic
concepts; in many cases old formulae are named and coded

250

in a manner which can suggest a new formula and the claim
for original authorship. This situation leads to the question
whether such a vast variety of formulae is really necessary.

When analysing in detail the formulae as grouped in the
various tables of this book it soon becomes obvious that
those in each of the groups are in fact very closely related.

It seems therefore to be quite feasible to devise in most
cases a formula which represents all the main features of the
group in question. An attempt to devise such basic formulae
has been made in Table XL VII. These formulae are not merely
of academic interest but they are quite practical.

Formulae published by various manufacturers of sensitive
material are certainly primarily designed for their own
makes. However, this does not mean that these formulae are
not interchangeable. Only highly specialised formulae must be
restricted to the use of the product for which they have been
originally evolved.

DESENSITISING

Desensitising is a process which reduces the light sensitivity
of emulsions to such a degree that they can be developed in
comparatively bright light. The process was discovered by
Dr. Luppo Cramer and is no doubt one of the most interest-
ing photochemical effects from the theoretical point of view.
For some time it was of great practical importance too as it
allowed panchromatic and other high speed materials to be
handled under conditions which permitted closest possible
control.

Today, however, the process is only of very limited
practical importance, because development is generally
carried out by the time-temperatiire method.

The main present-day use of desensitisers is in developing
high speed emulsions by direct inspection, as by the inter-
mittent development method described on page 239. In cases
where special effects are required, direct control of the
negative image in the developer can be advantageous too.
Yet again, close inspection of the image during development
might help to save negatives where there are serious doubts
as to the correctness of exposure and it may be necessary to

251

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252

modify development or even the developer itself to a large
extent.

Desentisers also prevent chemical fog caused by atmo-
spheric action when films soaked with developer are exposed
to air, which can happen m some types of developing
machines. In this case the desensitiser acts as an anti-fogging
agent.

Desensitising agents must be able not only to reduce
considerably the light sensitivity of the silver halide but must
do so without in any way aifecting the latent image and with-
out exerting any adverse effect on the developer and the
developing process. Many such substances have been dis-
covered but only a few have received practical apphcation.

Phenosafranine

This was the first densitiser to be used to any great extent,
and appeared on the market under the names Pinasafrol and
Desensitol. It is a useful desensitiser but has one drawback :
it stains films and fingers. Nevertheless it is cheap, works well
and is compatible with most developers.

An exception is hydroquinone, the action of which is
accelerated. With normal M-Q developers there is little
perceptible effect so long as the concentration of pheno-
safranin is low.

Desensitisers can be used in two ways, either as a fore-
bath or added to the actual developer. Of these two methods
the fore-bath is always preferable for a number of reasons,
and should be employed whenever possible. Some of the
desensitisers are precipitated by certain constituents in
developers and can cause troublesome flecks and spots of
colour on negatives and thus should not be used in the
developer.

Desensitisers are best kept in the form of a stock solution
which can be diluted when required to prepare the fore-bath.

1S8.— PHENOSAFRANINE DESENSITISER
Phenosafranine 1 part

Water 1000 parts

When the fore-bath is required, one part of the stock
solution is diluted with 10 parts of water, thus giving a bath
of 1 : 10,000.

253

The bath can be used for several negatives, but should
not be kept too long as moulds tend to grow on it.

When used in the developer the desensitiser should have
approximately the same strength as in the fore-bath, hence
for each 40 ounces of developer (1000 ml.), 4 ounces (100 ml.)
of the stock solution will be used.

When the plate or film has been about one minute in the
fore-bath or the developer, the yellow safelight can be turned
on in the dark-room. This should be safe for all sensitive
material, but if very highly-red-sensitive panchromatic
material is being developed, then a somewhat darker yellow-
green safelight may be preferable.

Basic scarlet N is another desensitiser, consisting of a
mixture of phenosafranin and chrysoidine, the latter being a
brown dyestuflf. Its properties are similar to those of pheno-
safranin, except that it must only be used as a fore-bath. The
following formula, devised by B. T. Denne, reproduces the
properties of basic scarlet.

159.— DESENSITISER (B. T. DENNE)

Chr/soidine 20 grains I gram

Phenosafranine 20 grains I gram

Distilled water 4 ounces 200 ml.

Alcohol 1^ drams 5 ml.

For use, one part of the stock solution is diluted with 50
parts of water.

When dissolved the solution is allowed to cool and is
then sufficient to add to 20 ounces (500 ml.) of developer.

Johnson's Yellow Desensitiser is a non-staining desen-
sitiser supplied in powder form. Contents of tube are dis-
solved in 20 oimces warm water and upon cooling may be
used as a fore-bath without further dilution. Keeps well if
stored in a brown bottle, away from bright light.
Caution: Many fine-grain developers will not work well with
densitisers, which, therefore, should not be used with them.

Pinacryptol

The disadvantage of the strong staining properties of pheno-
safranin and its allied compounds soon led to the discovery
of other desensitisers which did not stain to the same extent.
Pinacryptol green was the first to receive wide application,
In solution it has a dark-green colour, but its staining

254

properties are weak and the slight coloration of the film
resulting from its use disappears entirely on washing.

Pinacryptol yellow has only a pale yellow colour in
solution and does not stain at all. For use, it is dissolved
1 : 2000 in water.

Both these desensitisers must be used as a fore-bath and
not in the developer solution. Pinacryptol green is pre-
cipitated by many developers and pinacryptol yellow is
decomposed by sulphites. Their use may slightly lengthen
development time, but in general this is not noticeable.

160.— PINACRYPTOL DESENSITISER
Pinacryptol green 20 grains I gram

Water 20 ounces 500 ml.

To prepare the bath, 1 part of the above stock solution
is diluted with 9 parts of water, giving a bath of 1 : 5000 of
the actual desensitiser.

The material to be desensitised is given two minutes in
the fore-bath, then the light safelight can be turned on, the
plate or film quickly rinsed and placed in the developer.

Finally, pinacryptol white was added to this series of
desensitisers. It is colourless and has the advantage that it
can be used in any developer if so desired, as no precipitation
occurs nor is it decomposed by the solutions. It appears on
the market in the form of small tablets.

A stock solution is made by dissolving one tablet in about
1 ounce (25 ml.) of warm water.

255

Increasing Film Speed

There are various means of increasing the speed of sensitive
materials when extra sensitivity is required for special
purposes. These methods can be classified as follows:

(1) Treatment before exposure. This is known as
hypersensitising, and increases the apparent speed
of the material.

(2) Treatment after exposiire, but before develop-
ment. This is known as latent image intensifica-
tion, or latensification. It increases the sensitivity
of the latent image to development, usually by
increasing the size of the sensitivity specks by
chemical or light treatment similar to hyper-
sensitising.

(3) Development with special high-energy developers.

(4) Intensification of the developed negative. This is
dealt with on page 347.

HYPERSENSITISING

Hypersensitising was very useful when emulsions were
generally considerably slower than they are now, but it is
of little value with modern fast materials. These have already
been hypersensitised during manufacture, and further hyper-
sensitising by the amateur before exposure does not give
good results. With careless handling it may even give rise to
a great deal of fog and other troubles.

Nevertheless, materials cannot be hypersensitised suffici-
ently during manufacture to obtain the utmost sensitivity,
because films and plates treated in the ways described below
have rather poor keeping qualities. If these methods are
employed, the material should be used within a few days of
treatment.

The effect of hypersensitising is usually fairly uniform

256

over the range of colours to which orthochromatic films are
sensitive, but it increases with the longer wave-lengths
(redder colours of light) and is particularly pronounced in
the infra-red region. Hypersensitising therefore affects pan
films and plates more than others, and has special use in
work with infra-red sensitive materials.

BATHING

The commonest method of hypersensitising consists of
bathing the film or plate in a dilute alkaline solution such as
ammonia, borax, triethanolamine, or other amines. Alter-
natively a very dilute solution of silver nitrate or even plain
distilled water may be used.

One of the effects of this treatment is that it dissolves out
the sUght excess of potassium bromide usually present in
most emulsions. This potassium bromide increases the
keeping qualities of the emidsion and keeps down fog, but
it also decreases the speed, and this state of affairs is reversed
by bathing. If silver nitrate solution is used, which not only
dissolves out potassium bromide, but also provides free
silver, the effect is even greater, but so is the fog.

When using the alkali solution which can be 1 part of
0.880 ammonia diluted with 30 parts of water, or a 0.5%
solution of triethanolamine, the film is immersed in the
solution in total darkness before exposure for two minutes
at 55°F. (13°C.). The low temperature helps to minimise
swelling of the gelatine. The excess liquid is then wiped off
carefully, and the film dried as quickly as possible. The whole
process is, of course, carried out in complete darkness. An
anti-fogging agent such as a 1 : 30,000 solution of benzotriazole
should be added to the developer during subsequent processing,
to keep down fog.

VAPOUR TREATMENT

In a second method of hypersensitising by chemical
means the material is exposed to the vapour of such liquids
as mercury. While the results are somewhat uncertain and
inconsistent, this method does not require removal of the
film from its wrapping as long as this does not contain metal.
There is no wetting (and therefore no drying) of the film or

18 257

plate, and the colour sensitivity and curve of the material
are unaffected.

Vapour treatment is best carried out by placing the film
(which may be wrapped up with its backing paper, but
removed from any metal reel or holder) in a non-metallic
container which is tightly sealed. Alongside in the container,
in a small dish, is put a drop of mercury. To observe and
test the effect the material can be treated for a range of times
of up to two days. As the container is sealed, it is soon filled
with mercury vapour. Although the vapour pressure of
mercury is very low at the temperature of this treatment,
there is enough mercury vapour present to have an appreci-
able effect during the 24 to 48 hours for which the material
is exposed to the vapour. It is believed that the vapour
deposits mercury on the sensitivity specks in the emulsion,
and increases the sensitivity of the film in this way.

FOGGING BY LIGHT

Apart from the chemical methods of hypersensitising,
increased emulsion speed can be obtained by exposing the
material to light for a very short time before the proper
exposure. This increases the fog density and thus lowers the
contrast of the image, which should just be apparent on
development. The image density is, however, increased rather
more than the fog density, residting in an increased effective
speed. Pre-flashing effectively extends the toe of the char-
acteristic curve and gives a real speed increase. It also over-
comes reciprocity failure if main exposure is long.

The procedure consists of pointing the camera, loaded
with the films, at an evenly illuminated white card, and
exposing with the smallest aperture and fastest shutter speed.
The image of the card should completely fill the negative
area, and it must be out of focus to avoid any image of the
card texture. A certain amount of experiment will soon
show the best conditions for any plate or film.

LATENT IMAGE INTENSIFICATION

This process, also known as latensification, is very similar to
hypersensitising, except that it takes place after the exposure
of the negative.

258

Bathing the material will give good results after exposure
as well as before with the same solutions of alkalies, Uke
ammonia, triethanolamine, etc. In addition, various oxidising
agents can be used such as potassium permanganate, dilute
nitric acid, and peroxide solutions. Aqueous sulphur dioxide
solution has also been used quite successfully.

One such bath may be a 0.5% solution of potassium
metabisulphite containing 0.85% of anhydrous sodium
sulphite. This has a pH value (see page 88) of about 6. If
the pH value is raised (the solution made more alkaline by
decreasing the metabisulphite relative to sodium sulphite)
the speed increase is greater, but so is the fog produced. If
there is already too much fog, the bath must be made more
acid by increasing the metabisulphite concentration, or some
1 : 30,000 solution of benzotriazole may be added.

The film is bathed, after exposure, in the solution for
about five minutes at 65°F. (18°C.), well drained, and wiped
carefully. To get the best speed increase out of the material,
the film should not be developed immediately, but should be
dried first (in the dark-room) before any processing is started.

This treatment after exposure instead of before has the
advantage that there is no need to rewrap the material, and
further, the loss of the anti-halo dye in the solution does not
matter at this stage.

VAPOUR LATENSIFICATION

Mercury vapour can be used as for hypersensitising. The
result is similar and just as uncertain. If anything, the speed
increase is slightly greater with mercury vapour treatment
after exposure in the camera than before.

Other vapours, such as those of formic and acetic acid,
can also be used. They tend to soften the film base, so films
should not be exposed to the vapour for too long.

Sulphur dioxide gas is also effective and can be used either
in solution, as described above, or in the following way:

A dish or jar containing 1 ounce (25 ml.) of 10% acetic
acid and 1 ounce (25 ml.) of 10% sodium sulphite (anhydrous)
is placed in a light-tight tin. The exposed film is wound into a
developing tank spiral, which is suspended above the dish
in the tin. This is left for 24 hours and the film then developed
as usual.

259

POST-EXPOSURE FOGGING

Fogging by light after exposure can also increase the effective
film speed. While with hypersensitising a very short exposure
to a comparatively strong light is given, fogging after the
camera exposxire yields the best results with long treatment
by a very dim hght. Light of very weak intensity is much
more effective in increasing an existing latent image than in
starting a new one. Consequently the increase in the image
density will be greater than in the fog density, and the
shadows will be strengthened, but overall contrast decreased.

The film is exposed to a very weak dark-room light for
about 30-60 minutes. For supersensitive panchromatic
materials a dark green (Wratten Series 3) safe-hght with a
10-watt bulb and a working distance of about 12 feet is best.

The speed increase obtainable by fogging after exposure
is usually somewhat greater than by pre-exposure treatment
(about 100%, as compared with 50-75%).

HIGH-ENERGY DEVELOPMENT

This is perhaps the simplest and most convenient method
for obtaining maximum emulsion speed. It does not need
special apparatus or extensive modifications in processing
technique. Its chief drawback, however, is rather coarse
grain, since the characteristics of high-energy development
formulae are the exact opposite of fine-grain developers.

Research by Kodak has shown that imder certain condi-
tions the addition of hydrazine salts or hydrazine derivatives
such as semicarbazide hydrochloride results in greatly
increased contrast and film speed. Such compounds can be
added to a normal M.Q. developer like D72 or D19, in fact
the SD19a formula given below is obtained by adding a small
quantity of hydrazine dihydrochloride and an anti-fogging
agent to the normal D19 developer.

The speed increase in this type of developer has been
shown to be due to chemical fogging of silver halide grains.
Only those silver halide grains adjacent to exposed grains are
affected and not the under-exposed latent image, nor the
other unexposed silver salts. The resultant disadvantage of
this is, in addition to the graininess already mentioned,
appreciable loss of definition in the developed silver image,

260

as the image is spread beyond what is recorded on the films
by the camera lens. Mechanical defects such as finger marks,
abrasion marks, and emulsion or agitation irregularities are
also considerably magnified. Handle the film with care.

161.— KODAK SDI9a HIGH-ENERGY DEVELOPER
A. 6-nitrobenzimidazole nitrate,

0.2% solution 385 minims 20 ml.

Hydrazine dihydrochloride 30 grains 1.6 grams

Water to make I ounce 100 minims 30 ml.

Water (I25°F.,S2X.)

30 ounces

750 ml.

Metol

39 grains

2.2 grams

Sodium sulphite, anh/d.

3 ounces 368 grains

96 grams

Hydroquinone

168 grains

8.8 grams

Sodium carbonate, anhyd.

1 ounce 400 grains

48 grams

Potassium bromide

90 grains

5 grams

Water to make

40 ounces

1000 ml.

Hydrazine dihydrochloride is also sold as Eastman
Organic Chemical No. 1117. 6-nitrobenzimidazole nitrate is
Kodak Anti-Fog No. 2; 36 grains (2.0 grams) of the solid are
dissolved in 40 ounces (1000 ml.) of hot distilled water to
make the 0.2% solution.

The chemicals are dissolved in the above order. Just before
use a working solution is prepared by mixing 1 part of
solution A with 32 parts of solution B (which is the ordinary
Kodak D19 formula). The working solution does not keep.

The developer is used like a normal dish or tank
developer.

The approximate time of development at 68°F. (20°C.)
with intermittent agitation is about 16 minutes for normal
films in Group B (see page 38).

The best useful speed increase is obtained by development
to a fog density of 0.4, though fog densities of up to 0.6
can be tolerated. This will give rather dense and flat negatives
which will need long printing times. They can, however, be
reduced as described on page 344ff"., to remove this fog.
The best reducer for this is Farmer's reducer (No. 220 on
page 342).

Exact development times can be foxmd by cutting up a
trial under-exposed negative into several strips, and develop-
ing these for a range of times from 10 to 20 minutes. The
strip showing the best compromise of a low fog density with
a satisfactory speed increase can then be taken as standard
and its time of development as the standard time for that

261

material. It must, however, be remembered that even then
much depends on how badly the negatives were under-
exposed. With only slight under-exposure it is not necessary
to develop to as high a fog density, nor will the gain in
emulsion speed be as apparent.

DEVELOPMENT TO COMPLETION

We have seen that the time of development is of great
practical importance (page 38) and has a real influence on
the practical sensitivity of our material. To utilise fixlly the
whole sensitivity of our material we must develop it
"completely".

If we say "completely" we do not necessarily mean
development to maximum gamma (page 35), i.e., develop-
ment to finality. This would lead to very contrasty negatives
giving poor photographic results. It is obviously not wise
to over-develop but the development must be kept within
such limits that a gamma value is reached which still gives
an acceptable print. This is the reason why the British and
American standard specifications for the measurement of
film speed give a definite development time in a standard
M.Q. developer. The speed figure of the product is based on
such a procedure even if the material gives a higher speed
figure at longer development.

The photographer might therefore, much to his surprise,
find in practice that he can get higher speed by over-
developing his film. In cases of emergency this can be useful
and the result may be quite acceptable under certain con-
ditions, especially if the original subject is flat.

As longer development leads to increased contrast it is
advisable to use a soft working developer, for instance, the
fine grain developers Nos. 80-93 or the high-definition devel-
oper Nos. 105-109. In some cases it may be more convenient
instead to raise the temperature to about 77°F. (25°C.).

The gain in speed depends on the type of emulsion —
some films are more suitable for this method than others.
But in the most favourable circumstances the increase in
speed is not likely to be more than two or three times. If
speed tests are not carried out under controlled conditions
results can easily be very misleading and this explains
probably the exaggerated claims advanced from time to time.

262

Fixing

WHAT THE PROCESS IS AND HOW n WORKS

When we expose and develop a plate or film, only about
25% of the silver bromide in the emulsion is used up in
forming the negative image. The balance, which has not
undergone any change in the developer, must be removed in
the fixer if the negative is to be clear and permanent.

As a fixing agent hypo is used almost exclusively. To the
chemist hypo is sodium thiosulphate, but the photographic
world always calls it hypo. Other silver halide solvents are:
alkali thiocyanates, cyanides, sodium sulphite, ammonia,
thiourea, thiosinamine, concentrated solution of potassium
iodide. Some of these fixing agents are used for special
purposes.

Fixing is no simple process of solution hke the dissolving
of a lump of sugar in water; it involves a series of reactions
in which the silver bromide is converted into a series of
complex argentothiosulphates containing varying ratios of
silver to thiosulphate (H. Baines 1929). The first reaction
between a silver halide and hypo forms a rather insoluble
and not stable compound. If at this stage the fixing process
is stopped, the negative will not be permanent and will have
a milky appearance. The intermediate compound reacts
with more hypo to form finally very soluble complex com-
poxmds of sodium argentothiosulphate, which can be easily
removed.

This short summary of the fixing process shows how
necessary it is to allow sufficient time for proper fixation if
we are to obtain permanent negatives. A useful rough rule
is to allow at least double the time that is required for the
clearing of all trace of milkiness from the film. Only by so
doing can one ensure that no deleterious residue is left behind
which will affect the permanence of the negative.

263

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Two points emerge from the consideration of the nature
of the fixing process, first that a sufficient excess of hypo
must be present in the bath in order to form the easily
soluble double salt, and also that it is not good policy to use
too strong a bath. From what has been said it will be clear
that the disappearance of the milky silver bromide from the
film is not necessarily evidence that the bath is working
normally. Unless the necessary excess of hypo is there the
soluble double salt cannot be formed and cannot therefore
be dissolved out.

It may also just be mentioned that economy in fixing baths
does not pay with hypo being as cheap as it is.

RATE OF FIXATION

The clearing time or the practical rate of fixation is, according
to C. E. K. Mees, affected mainly by the following factors:

(1) Nature of emulsion. The clearing time varies with
the silver halide content of the emulsion, the
composition of the silver halides and, to quite a
considerable degree, on the grain size.

It is much shorter for fine-grain than for
coarse-grain emulsions because of the much
greater total area of the finer grains. It is also
apparent that the clearing time will vary with the
path of diffusion of the fixing solution in the
emulsion and is thus longer for thick emulsion
ayers than for thin ones. Sheppard and Mees
found that, rather unexpectedly, the hardness of
the gelatine has practically no effect.

(2) Concentration of thiosulphate. As one would
expect, the fixing time decreases with increase of
thiosulphate concentration, but only up to a
certain maximum. The optimum concentration
is between 30 and 40%.

(3) Nature of the thiosulphate compound. The fact that
ammonium thiosulphate is more rapid than the
sodium compoimd has been known for a long time
but it is only comparatively recently that fixing
preparations containing ammonium thiosulphate
have found wide apphcation in practice. Such

265

preparations had gained a reputation for pro-
ducing less stable images than plain hypo and
only recently have investigations proved that
that this is not the case. Another reason why the
more rapid fixing action of ammonium thio-
sulphate was not made wider use of before is
the fact that this fixing agent was not available
in the stable pure form in which it is now
produced. It was therefore the usual practice to
produce ammonium thiosulphate in the solution
itself by adding ammonium chloride to the hypo
bath. Table XLIX shows that the clearing time can
be considerably shortened and that the optimum
is reached at a concentration of 20 % hypo and
4% ammonium chloride. However, still better
results can be obtained by using ammonium
thiosulphate which has about 50% more rapid
action than the mixture of hypo and ammonium
chloride.

XLIX.— EFFECT OF AMMONIUM-CHLORIDE ON CLEARING TIMES
(C. W. Piper)

Ammonium

ch/or/de

10%

(Ci

Sodium thiosulphate
'earing times in minutes)
20%

40%

over IS'

266

-CLEARING TIME IN SODIUM THIOSULPHATE
(C. E. K. Mees)

Sodium
thiosulphate

I3°C.

55°F.

Time

: in Minutes
I8°C.
65°F.

24° C.
75°F.

longer than
10

(4) Temperature. Higher temperature accelerates the
fixing process as shown by Table L. The effect
is more pronounced at lower concentrations of
hypo than at higher ones. The best practical
working temperature is between 65 and 75°F.
(18 to 24°C.). Below this range the action may be
too slow while above it the gelatine may become
too soft.

(5) Agitation. Agitation increases the rate of fixation
by supplying fresh solution to the emulsion and
removing reaction products from the emulsion
surface. However, in practice the effect is not
very pronounced because the differences be-
tween the specific gravities of the fresh solution
and the reaction products leads to convection
currents which "agitate" the solution to some
degree.

(6) Exhaustion. A number of changes take place in
the composition of the fixing bath while it is used.
Reaction products accumulate and the solution
becomes also more and more diluted as a certain
volume of water or developer is carried in by
each film. The degree of exhaustion of the fixing
bath must therefore be carefully watched.

267

LI.— CLEARING TIME IN SODIUM AND AMMONIUM

THIOSULPHATE (at lO'C.)

(C £. K. Mees)

Concentration

Sodium

Thiosulphate

Time in Minutes

Ammonium

Thiosulphate

Time in minutes

10%

20%

30%

40%

50%

—

60%

—

70%

—

LIFE AND CAPACITY OF FIXING BATHS

If permanent negatives are desired, it is very important that
the fixing bath should not be overworked. It is impossible
to control the condition of the jfixLng bath by mere visual
examination. A fixing bath near exhaustion will still appar-
ently clear the negative but the not easily soluble silver salts
will remain in the film. It should, therefore, be a rule to
discard the fixing bath when it takes twice as long to clear
the film as it did when the bath was fresh. The exhaustion
figures of Table LII should be taken as a safe maximum.

Lir.— CAPACITY OF A FIXING BATH

Number per
Size of Film I litre

Sheets 8 x 10 in. 25

Roll film 120 or 620 2S

Roll film 127 50

35 mm. film (36 expos.) 25

Sheets 6^ x 8|^ in. or 18 x 24 cm. 40

Sheets 4} x 6| in. or 13 x 18 cm. 60

Sheets 4 x 5 in. 100

Sheets 3i x 4J in. or 9 x 12 cm ISO

268

All fixing solutions have good keeping properties. In an
open tank they can be kept for at least one month; in a well
stoppered bottle they will last for three months or longer.

A simple method to determine the degree of exhaustion
is the use of indicator papers:

(1) Test for Silver. As we already know, overworked
fixing baths contain complex silver thiosulphate
compoimds which are retained by the film and
caimot be completely removed by washing. The
silver contents of used fixers of all types can
easily be estimated with Johnson or similar
"Silver Estimating Papers".

A piece of test paper is quickly dipped in the
fixer, shaken to remove excess liquid and laid on
a clean white card. After about 15 seconds the
coloiu: of the test paper is compared with the
colour patches of the chart supplied with the test
paper. The nearest match indicates the silver
content in grams per litre. For normal work in
dishes or small tanks 3.5 gm. /litre is a safe
maximum. In large tanks silver contents of 10
gm. /litre or more are sometimes reached, but 7
gm. /litre is best regarded as the limit.

The degree of exhaustion of the fixing bath
can also be tested with a 5 % solution of potas-
sium iodide. Add about 2 drops of this solution
to 10 ml. fixer in a test tube. If no cloudiness
appears, the bath is still fit for use. If there is
cloudy precipitate which, however disappears on
shaking, the bath is becoming used up, but if a
permanent precipitate (silver iodide) is formed,
the bath is exhausted.

(2) Test for acidity. The acidity can be checked with
indicator paper. The pH of working strength
fixer should be between 4.2-4.5. The use of litmus
paper is not recommended, it is better to deter-
mine the pH with a "Narrow Range" Indicator
paper such as B.D.H. 4055. If the pH is close to 5,
more acid must be added to the fixer, either a
50% acetic acid solution or a further quantity
of the acid hardener stock solution.

269

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RINSE AND STOP-BATHS

Developers and fixing baths do not agree with one
another, hence it is necessary to remove as much as possible
of the developer from the negative before it is placed in the
fixing bath. If this is not done, developer in the fixing bath
can affect its working, shorten its life and give rise to a
number of troubles. (See page 396.) In certain cases develop-
ment may even continue in the fixmg bath.

Hence the rinse between developing and fixing is not so
unimportant as some people think. It should be short but
thorough, and preferably in running water, or at least in water
that is frequently renewed. There is no point in rinsing the
negative in a bath which contains nearly as much developer
as the developer bath itself.

It is better and safer to use a stop bath instead or as an
auxihary to the rinse. This is a weak acid solution containing
usually about 2 % of glacial acetic acid. The same purpose is
fulfilled by a 3-5 % solution of potassium metabisulphite or
sodium metabisulphite. Such a stop-bath interrupts the
action of the developer more or less immediately while in a
water rinse the development can still carry on often to quite
an extent until the developer is completely washed out. It is,
of course, essential that the stop-bath is really acid and if it is
continuously used it may be necessary to test it with an
indicator as suggested for the fixing solution (page 277). It
is often desirable to stop and harden the film at the same time,
and if the processing has to be carried out at raised tempera-
ture this is absolutely imperative. The simplest stop-hardening

LIV.— STOP AND HARDENING BATHS

178

179

SB3

AN2I6

180
SS4

181

182
OP207

183
D2S

184
G357

Acetic acid (glacial)

—

6.5

—

Chrome alum

—

Sodium sulphate

—

Potassium metabisu

Iphlte

—

Water to

1000

271

bath is about a 3 % solution of potassium or chrome alum.
To this solution acetic acid can be added. If sodium sulphate
is added as an anti-swelling agent, the temperature has still
less effect.

A number of formulae for these various types of stop-
bath are to be found in (Table LIV).

PLAIN OR NEUTRAL FIXING BATH

Fixing baths consisting only of a solution of hypo in water
are suitable for the fixation of negatives, but they are used
in practice only on very rare occasions. It is vital, then, that
no developer is carried over to the fixing bath. As we have
already seen, the speed of fixation rises with the content
of hypo up to a certain point.

The useful limit lies at about 40 % of hypo and in practice
the most generally useful concentration is in the region of
25-30%.

ACID FIXING BATHS

The acid fixing bath is the most widely used in practice. It
promptly neutralises any trace of alkali brought over from
the developer and prevents stains and other troubles that
might otherwise arise from this source. Developing agent
transferred into the fixing bath would oxidise pretty rapidly
in a neutral solution, discolouring the bath and ultimately
causing stains in the film.

Acidification of the bath cannot simply be achieved by
the addition of any acid as many of them would decompose
hypo and set free sulphur. Siilphurous acid does not de-
compose thiosulphate but as this acid itself is not stable, its
salts are used, such as potassium metabisulphite or sodium
metabisulphite.

Certain weak organic acids like acetic acid can also
be used, but only together with sodium sulphite to produce
sulphurous acid in solution.

A number of such acid fixing baths are listed in Table
XLVIII. In the usual type of acid fixing bath, bisulphites are
used and ammonium chloride can be added to speed up the
fixing process (see page 266). It is also possible to replace
hypo by ammonium thiosulphate to produce an acid rapid

272

fixing bath. In making up fixing bath solutions the following
points have to be observed.

It must be noted that hypo, when dissolving in water,
produces a noticeable lowering of temperature. It is, there-
fore, advisable to use warm water to accelerate the process
of solution. However, after hypo is dissolved the solution
should regain approximately room temperature before the
acid component is added.

It is also recommended practice to dissolve the acid ingred-
ient separately in a small volume of water, especially
when the mixture of sodium sulphite and acetic acid is
appUed.

HARDENING AND FIXING BATHS

The advantages of the hardening-fixing bath are not confined
to working at higher temperatures, they materially reduce
risk of injury to the gelatine layer of the film at any tem-
perature.

The actual hardening agent is usually chrome alum or
potassium alum. Of these two agents chrome alum exerts the
greater hardening effect, but chrome alum baths have poorer
keeping properties than those using potassium alum. Usually,
potassium alum is therefore used.

All hardening and fixing baths must contain a definite
proportion of acid. Otherwise, alkah from the developer
might precipitate the hardening agent. Normally, acetic acid
is used, of course, in the presence of sodium sulphite for the
reasons stated above. It has been found that acetic acid may
be supplemented, with advantage, by boric acid, which
increases the hardening, lengthens the life of the bath, and
notably inhibits the formation of a precipitate even under
adverse conditions.

To make up a hardening-fixing bath the various ingredi-
ents should be dissolved in the order given in Table LV. In
the case of hardening-fixing baths with chrome alum the
preferred method is usually to make up two stock solutions
A and B as shown in Table LVI. Solution B, containing the
chrome alum, has better keeping properties than the mixed
working solution. It is also often found convenient to make
up the fixer containing potassium alum from a stock solution,
as given in Table LVII. To make up the working solution the

273

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LVI.— ACID HARDENING BATHS
(With Chrome Alum)*

195

FI6

AN202

196
AG306

197
/G308

Solution A

Sodium thiosulphate

960

280

340

Sodium sulphite anhyd.

Sulphuric acid cone.

—

1.5

—

Sodium metablsulphite

—

37.5

Water to

3000

500

Solution B

Potassium chrome alum

Sulphuric acid cone.

—

Water to

1000

500

Working solution

Add B to A

♦Chrome alum is a very poor fixer-hardener in practice. Potassium alum
is to be preferred (see Table LV).

LVII.— ACID HARDENING STOCK SOLUTION

198
FSa

199
F6a

200

201
D2FH

Sodium sulphite anhyd.

Acetic acid*

235

190

Boric acid cryst.

37.5

—

Sodium metaborate

—

Potassium alum

100

Water to

1000

Working solution

1
four

part stock solution to
parts 30% hypo solution

'Glacial acetic acid 3 parts, water 8 parts.

275

acid hardening stock solution is simply diluted with a 30%
solution of plain hypo.

RAPID FIXING BATHS

In all these fixing solutions ammonium thiosulphate can be
used instead of the sodium compound or a mixture of hypo
with ammonium chloride.

When fixation has to be completed in 20 seconds or less,
sodium or ammonium thiosulphate is not suitable. Satis-
factory fixing agents for this purpose are potassium cyanide
or ammonium thiocyanate. As the former is highly poisonous,
ammonium thiocyanate is usually used.

Ammonium thiocyanate has its quickest fixing action at
a concentration of 40-50 %. If fixing has to be carried out in
a matter of a few seconds, the temperature of the solution
can be taken up to about 50°C. (122°F.). As solutions of
ammonium thiocyanate have a Uquefying effect on gelatine,
5% formalin might have to be added, even if fixing is carried
out at normal temperature, in case the emulsion is not
sufficiently hardened. Fixing with ammonium thiocyanate is
especially suitable for high speed processing materials having
thin and highly hardened emulsion coatings.

Solutions of ammonium thiocyanate are also suitable
when the fixing process has to be carried out at a very low
temperature, as they do not freeze above— 18°C. At— 7°C.
for instance, fixing takes only about 4 minutes, whereas it
would take 1 hour in ordinary hypo.

Another formula for a rapid fixing bath of this type is
the following:

202.-

-RAPID THIOCYANATE FIXER

Potassium thiocyanate
Potassium alum
Water to make

Acetic acid

Dissolve and add

100 grams
50 grams
1000 ml.

35 ml.

FIXING BATH MAINTENANCE AND REGENERATION

The composition of a fixing bath, like that of a developer,
changes with use. As the bath is used, more and more of the
alkaline developer is carried over and the acid in the fixing

276

solution becomes exhausted. If an acid hardener fixing bath
becomes neutral or alkaUne, sludge may form and deposit
on the negatives in the form of scum, which is very difficult
to remove once the negatives are dry. Not only does the
acidity decrease as the bath is used, but the clearing action
itself becomes slower, due to overall dilution of the fixer. In
addition, by-products are formed which increase fixing time
and can also have an effect on the permanence of the nega-
tives. To maintain the efficiency of the fixing solution, the
following measures have to be taken: —

1 . Control of Hypo-concentration

The drop in hypo-concentration can be overcome simply
by maintaining the specific gravity, which should be measured
with a hydrometer. There are hydrometers available which
are scaled directly in grams of hypo per htre.

2. Check of Acidity

The acidity can be simply checked by the use of an
indicator, either in the form of indicator solution or indicator
paper. For use with acid hardening fixing solutions containing
potassium alum, Bromo-cresol green is recommended as an
indicator. A sample of the fixing solution is taken in a test
tube and a few drops of the indicator are added. If a bluish-
green colour instead of a green colour is obtained, a 50%
solution of acetic acid is added to the fixing solution in the
tank until a further indicator test gives the correct green
colour. A yellow-green colour indicates that the solution is
too acid, which might lead to decomposition of the solution
by sulphurisation. In this case, small quantities of a 10%
solution of sodium hydroxide should be added until a green
colour is obtained. For testing the acidity of non-hardening
fixing solutions or those containing chrome alum, the
indicator Bromo-cresol purple should be used. If the colour
of the test is purple, it indicates that the fixing solution needs
more acid until a yellowish-green colour is obtained with the
indicator test.

3. Exhaustion of Fixers

The degree of exhaustion of fixers can easily be deter-
mined with the Johnson Silver Estimating Papers (see page
269). For normal work in dishes and small tanks 3.5 grams
per litre is a safe maximum. In large tanks silver contents of
10 grams per litre or more are sometimes reached, but 7
grams per litre is best regarded as the limit.

277

Print fixers should be discarded when silver contents
reach 1.75 grams per litre. For maximum print stability, 1
gram per litre should not be exceeded.

Even if the fixing solution is regularly replenished, the
bath must be renewed from time to time as the clearing time
will eventually become excessive. This is due to the build-up
in the bath of alkali halides which slow down the fixing
action and cannot be removed from the fixing solution. With
silver recovery, the adding of replenisher can be continued
for a considerably longer time than normally. However,
when the clearing time is doubled, the fixing bath should be
discarded.

Fixing bath regeneration is more reliable when electrolytic
methods of silver recovery are being used. Of the chemical
methods, the sodium-hydrosulphite process is in this respect
the best one.

MONOBATHS

The combination of developing and fixing in one operation
and in one and the same bath is an old problem in photo-
graphy to which a satisfactory solution has only been found
quite recently. The idea of such a monobath is rather ap-
pealing as it eliminates separate stop and fixing and even
hardening solutions. Moreover it requires no precise
timing of development and it decreases the effect of
variations in agitation, temperature and other processing
conditions.

In view of these advantages it may seem remarkable that
combined development and fixing, first suggested in 1889,
has taken such a long time to become practicable. The
answer lies in the fact that, in spite of the efforts of a great
number of investigators, monobath formulae had a number
of serious shortcomings. As a matter of fact, most of them
were considered as inherent characteristics of the method.
It seemed to be impossible to avoid loss of speed, the grada-
tion and maximum density was unsatisfactory and there was
pronounced tendency to produce fog. Keeping and exhaus-
tion properties tended to be poorer than with conventional
developers of similar type.

These drawbacks were overcome as a result of more
recent research work, helped by the fact that modern films

278

are basically more suitable for the method than those avail-
able hitherto. Formulae, especially those based on the use
of Phenidone, have been devised which produce results that
are practically identical with those obtainable by conven-
tional processmg. The problem consists of combining a
developer which acts so quickly that the development is
finished before the fixation starts. But even while fixing has
already started, development is probably helped by a process
of physical development.

Many monobath formulae are based on M.Q. with a
high proportion of sodium hydroxide as accelerator, (see
Table LVIII.

Another point to be considered is the concentration of
the monobath developer. When the usual concentration of
conventional developing solutions aie mixed with the usual
concentration of hypo baths to form a monobath, no satis-
factory result is obtained. For acceptable results the developer
concentration has to be increased on an average by 5 times.
At the same time the pH has to be raised to pH 11-12 while
the hypo content has to be reduced.

To increase the stability and exhaustion properties until
they are equal to those of conventional developers, potassium
alum is added in Formula 203. Such a developer keeps a
pH of 11.5 throughout its useful life. This buffer also helps
to prevent excessive swelling of the gelatine and reticulation.
Monobaths can be of very quick action, processing the film
in approximately 3 minutes at 75°F. Where rapid processing
is of importance, a monobath can be used at this or even
higher temperature.

A number of published monobath formulae are based on
the use of Phenidone and it is claimed that this leads to higher
speed contrast and maximum density (Formulae 204, 206-208).
In place of alum Formula 204 contains formahn which is a
still more effective hardener, especially in alkaline solution
and in the presence of sulphite.

The gamma value of a monobath is fixed by its composi-
tion and cannot be varied by change in dilution, time or
temperature of development. It is, however, possible to obtain
a wide gamma range without loss of film speed by the simple
method of varying the hypo content. With Formula 204, for
instance, a gamma range of 0.65-1.05 is obtained by varying
the hypo content between 150 and 250 grams per litre.

279

C .

toil

0(0
CN O -^
>0 <

CO
O

0:3
5

(~4

•^

I/)

_c
c

-C
Q-

= I

s-<=*

4->

-0

«->

«t

280

Using the same expedient, monobath formulae can be
adapted to various types of films. They are basically not as
universal as conventional developers and it may be necessary
to alter the ratio between speed of developing and fixing to
fit different emulsions. The speed of development can usually
be controlled by the alkali content (pH value) while the
course of fixation can be influenced by the amount of hypo.

G. Haist has summarised the variations in monobath
formulation and processing conditions which may be used to
modify the results obtained :

To increase contrast and emulsion speed

(1) Raise the pH.

(2) Increase the concentration or activity of the
developing agents.

(3) Reduce the concentration of the fixing agent.

(4) Raise the processing temperature.

(5) For more contrast increase the concentration of
hydroquinone and for more speed increase the
concentration of Phenidone or metol.

To reduce contrast or emulsion speed

(1) Lower the pH.

(2) Increase the concentration or activity of the
fixing agent.

(3) Increase the salt content or viscosity.

(4) Use more vigorous agitation.

Although monobath formulae of Table LVIII have all used
hypo a recent development* has been the use of a-thioglycerol
as the fixing agent. This monobath formula (209) uses
antimony potassium tartrate as a stabiHsng agent and it has
been claimed that high-speed film such as Kodak plus-X

209.— ULTRA RAPID MONOBATH
(pH 12.65 by addition of potassium hydroxide)

Potassium sulphite 20 grams

Antimony potassium tartrate** 40 grams

Phenidone 3 grams

Hydroquinone 60 grams

a-Thioglycerol ISO ml.

Water to 1,000 ml.

**toxic substance
*L. Corben, C. Bloom, D. Willoughby and A. Shepp, J. Phot. Sci., 14,
297 (1966).

281

Reversal SO-273 can be processed in 2.5 seconds at 120°F.
(48°C.) to yield results comparable with those of the film
normally processed in D-19 developer.

FIXING AT LOW TEMPERATURES

Fixation, like development (see page 230), is less rapid at
lower temperatures and it is therefore advisable to employ
a bath of high activity i.e. fixing solutions based on the use of
ammonium thiosulphate (Formulae 193, 194). The optimum
concentration of ammonium thiosulphate fixers varies with
the temperature and it may in fact be better to dilute solutions
when the temperature is lowered. At a working temperature
of 20-40°F. (minus 6 to + 4°C.) the standard fixing solution
should be diluted with 3 parts of water and at the very low
temperature 1 part of ethylene glycol has to be added to
prevent freezing.

Much more rapid fixing can be obtained by the use
of a thiocyanate bath (Formulae 202). A concentration
of 40% potassium thiocyanate has been found about
optimum for temperatures ranging from 20-70°F. (minus
6 to 21 °C.). At 20°F. for instance the bath will clear the
developed film in 3-4 minutes, whereas an ammonium thio-
sulphate bath would take over 1 hour. Since the freezing
point of this thiocyanate bath is about 0°F. (minus 18°C.) no
anti-freeze has to be added when working within this range.
Thiocyanate fixing bath has the tendency to soften gelatine
and may cause difficulties in washing and drying. This may
be largely overcome by adding about 5% formalin as a
hardener and makmg the fixing solution slightly alkaline by
the addition of sodium carbonate.

If washing under these conditions offers difficulties, there
are no objections to adding ethylene glycol to the wash
water as an anti-freeze. The film can for instance be washed
in 4 successive baths of a 25 % solution (by volume) of ethy-
lene glycol, 10 minutes in each change.

At very low temperatures it may be necessary to accelerate
drying by the use of alcohol (see page 296).

THE RECOVERY OF SILVER

Silver is a rather costly material and its recovery is, therefore,
worthwhile when it occurs in appreciable quantities in fixing

282

baths. Usually, only about 25 % of the silver in sensitive
materials is used up in the developed image: the balance finds
its way into the fixing solution. When large quantities of
photographic materials are used, the amount of silver so
accumulated is appreciable. On average, 1 oz. of silver can
be recovered from:

300 films 120 size, or
1000 ft. of 35 mm. cine film, or
100 sq.ft. of X-ray film, or
300-400 sq. ft. of printing paper.

Recovery of the silver is often worthwhile.

DETERMINING THE AMOUNT OF SILVER IN FIXING BATHS

The amount of silver which a fixing bath contains depends
naturally on the extent to which the bath has been used. On
average, a silver content of 2-3 parts per 1000 parts of fixing
solution can be expected, but it may go as high as 1 part per
100.

In most cases, it is not necessary to calculate the probable
silver content of the fixing bath; it is sufficient to recover it.
If determination is required, the usual analytical methods
can be used, but they are normally beyond the capacity of
the darkroom staff.

Kodak have produced an "Argentometer" which is very
simple to operate, but rather expensive to purchase. It
measures a depth of colour of a colloidal solution of silver
sulphide by means of a photocell and so determines the
amount of silver in the bath. Ilford can supply a simpler
"Silver Estimator" based on a visual colour test. To estimate
the silver concentration, a sample of the fixer is compared
with the test solution through a comparator which, when
adjusted, indicates the concentration of silver in the fijcing
bath in grams per litre.

The simplest means of determining the silver content of
used photographic fixers is the Johnson or Agfa Silver Esti-
mating Papers. A piece of test paper is dipped in the fixer, the
excess liquid removed and the paper laid on a clean white card.
After 15 seconds, its colour is compared with that of the
chart supplied with the estimating papers. One compares it
with the nearest two adjacent colour patches and takes the

283

40 ounces

1000

ml.

4 ounces

100

grams

54 grains

2.6 grams

80 grains

grams

4 ounces

100

grams

40 ounces

1000

ml.

80 grains

grams

40 ounces

1000

ml.

i ounce

grams

J ounce

grams

4 ounces

100

ml.

nearest match. One can then read on the scale the silver
content in grams per litre.

The following method uses a similar principle of colour
comparison. It requires two solutions:

2f0.— TEST SOLUTION FOR DETERMINING SILVER

1 . Water
Hypo cryst.
Silver chloride

2. Citric acid
Sodium citrate
Water to make

3. Gelatine
Water

Add a few drops of clove oil to solution No. 3 as preservative.

The gelatine is first swollen in cold water, then heated on
the water bath with stirring until completely dissolved, and
finally made up to the correct volume.

4. Sodium sulphide
Sodium sulphite
Water to

The Standard solution for comparison is made by taking
4 ml. of solution 1 and adding 6 ml. of solution 2 followed by
10 ml. of solution 3. After diluting to nearly 100 ml., 2 ml. of
solution 4 are added to the mixture which is then made up to
exactly 100 ml. This provides a brown colloidal suspension of
silver sulphide which keeps reasonably well in a stoppered
vessel.

The standard solution gives a brown colouration resulting
from 2 grams of silver per litre contained in solution 1 which
can be compared with the colouration obtained by preparing
a similar mixture using 4 ml. of the fixing bath in place of
solution 1 and the same amounts of solutions 2, 3 and 4 and
making up to 100 ml as before.

If now equal volumes of these two solutions contained in
vessels of equal size (e.g. test tubes), that is, the standard and
the one made from the fixing bath, are compared and are
found to have identical shades of brown, they must contain
the same quantity of silver, namely 2 grams per htre. If the
solution from the fixing bath is a deeper brown, it contains
more silver.

Then take half the volume, add an equal volume of water

284

and shake well and compare again. If now the colour is equal,
then the fixing bath contains twice as much silver as the
standard, namely 4 grams per Htre.

One or two trials will be sufficient to determine fairly
exactly how much silver the bath does contain.

Naturally such a method is not necessary for the smgle
worker, but it is useful in the small business where it is useful
to know how much silver baths contain and therefore the
amount which can be recovered from them.

ELECTROLYTIC RECOVERY OF SILVER

Where large volumes of fixing bath have to be dealt with,
this is the ideal method of silver recovery. It is clean-working
and produces a very pure silver. It also offers the advantage
that the fixing bath is regenerated and can be used again.

Various types of unit for the electrolytic recovery of silver
are commercially available, such as the Ilford Silver Recovery
Unit, the Argelec Unit, the Baker Unit and the John Betts
Unit. The equipment consists basically of a power unit,
designed to hang on the wall, controlling the plating current.
It is connected to the immersion unit which is suspended in
the fixing bath. This immersion unit contains the electrodes
and is capable of holding a large quantity of reclaimed silver.
It may be left undisturbed in the solution for a period of
between six and 12 months.

For small users, self generating units are sufficient. They
require no connection to an electric supply. A unit of this
type is the "Argeco" which consists of a 7 in. x 9| in.
collector plate to which two small cells are attached, the unit
lying flat or hanging upright in the hypo bath. A cell con-
sisting of a white plastic case with perforated hd and con-
taining a sink element with filters is fitted to the collector
plate. The element is consumed in proportion to the deposi-
tion of the metallic silver on the plate and requires replace-
ment when it is completely used up. The deposited silver can
easily be removed from the plate.

In the Purhypo Process the silver automatically plates
out on the stainless-steel cathode, which, together with the
anode, is immersed in the fixing tank or in a separate tank
to which the used fixer is transferred or continuously cir-
culated. The fixing solution is regenerated by this process and

285

requires Only the addition of hypo or fixer powder and other
additives— acid hardener, etc. — to maintain its strength. The
"Purhypo" process is suitable for the larger-sized establish-
ments, such as X-ray departments processing at least fifty
14 X 17 in. double-coated X-ray films per day, or the
equivalent in area in single-coated negative materials. (An
average-size roll film — 120 or 620 — has an area of approxi-
mately 80 sq. in.) When only paper is used, the consumption
shoidd be at least 60,000 sq. ft. per annum to justify an
installation of this type.

These silver recovery units do not require much attention
in use. It is however necessary to test periodically the pH
value of the hypo solution and to adjust it to the pH recom-
mended by the manufacturers from whom the necessary test
solutions can usually be obtained. It is also advisable to
maintain the specific gravity of the hypo strength (see page
277).

PRECIPITATION OF SILVER BY OTHER METALS

Many metallic powders will precipitate silver from its
solutions; the best results so far having been obtained by
using zinc dust. It requires 3 parts of zinc dust to precipi-
tate 1 part of silver; hence it is important to have some
idea of the amoimt of silver present so as not to waste
zinc.

The silver is precipitated in the form of a black mud
which contains about 50 % metallic silver. Under no circum-
stances should the precipitation be carried out in the vessel
used as a fixing bath. The best way is to accumulate sufficient
spent fixing bath liquor and precipitate a large volume at a
time. A simple test to determine if the silver is completely
precipitated consists in placing or hanging in the bath a small
freshly-cleaned strip of copper or brass. If after a time the
strip shows any trace of a white deposit of silver the pre-
cipitation has been incomplete.

When all the silver is thrown down it is allowed to settle,
the supernatant Uquor syphoned or poured off and the residue
collected and dried.

A more recent adaption of this principle is by the use of

steel wool.* Theoretically one part by weight of iron (steel

*May & Baker, Dagenham, Essex. Leaflet "Silver Recovery from

Amfix, Perfix and hyper Amflx High Speed Fixers, Use of Steel Wool".

286

wool) should displace approximately four parts by weight of
silver from used fixer solutions, but in practice only two to two
and one half parts by weight are displaced.

In this method used fixer solution is slowly passed upwards
through a column of steel wool where iron passes into the
solution and displaces the silver which is then held in the steel
wool. Only exhausted fixer can be employed in this method; the
effluent from the column cannot be used as a fixer because it is
contaminated with iron.

The apparatus required is extremely simple and is illustrated
in the diagram on page 288. It may be connected to the outlet
of an automatic processor. The size of the vessel is limited by
the rate of fixer usage, May & Baker recommend that fixer
should pass through the apparatus in twenty-four hours to
allow sufficient time for the exchange to take place. Thus if
fixer is used at the rate of twelve gallons per day the vessel
should be of twelve gallons capacity and the rate of flow should
be one half gallon per hour. If less fixer than this is used per day
it may be collected in a header tank until twelve gallons have
been collected, or a smaller vessel could be used.

The exhaustion of the steel wool is readily determined by
measuring the (high) silver content of the effluent or more
simply by the visual appearance of grey flecks of silver in the
upper layers of the steel wool. When this point has been
reached the steel wool is removed from the apparatus and left
to dry before sending to the refiners. The apparatus is then
re-charged with steel wool and silver recovery may once again
be started. This principle is also used in silver recovery
cartridge assemblies which can be attached directly to auto-
matic processing machines.

PRECIPITATION OF THE SILVER BY SULPHIDE

This is the oldest and the cheapest method of recovering
silver. It is obtained as a silver sulphide mud containing from
40-70% of silver.

Sodium sulphide is usually used, although the potassium
salt, liver of sulphur can be used but is more expensive.
The great disadvantage of the method is the evolution of
hydrogen sulphide gas which occurs. On this account the
operation must always be carried out in the open air and as
far away from the dark-room as possible, as sulphuretted

287

SILVER RECOVERY UNIT

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A typical steel wool silver recovery unit consisting of a tank of wood
or plastic (b). Used fixer is run into the vessel (b) through (a) and passes
upwards through the steel wool (d) supported on a perforated platform
of wooden slats for example (c). Finally the fixer from which the silver has
been removed, is run to waste via the exit tube (e) or into a second recovery
vessel for more efiicient removal of silver.

288

hydrogen is fatal to sensitive photographic materials. The
amount of hydrogen sulphide produced can be greatly
reduced by neutralising the fixing bath with soda before the
sodium sulphide is added. The bath can be tested with
litmus paper to make sure that it is alkaline. In general, about
one ounce of a 20 % solution of sodium sulphide is required
for each 10 ounces of bath.

When the precipitate has settled the overlying solution is
tested with a few drops of sodium sulphide solution. If no
brown cloudiness is produced precipitation is complete; if
not, then more sodium sulphide must be added. The residue
is treated in the same way as if it had been precipitated by
metal powder.

PRECIPITATION WITH SODIUM HYDROSULPHITE

A somewhat expensive method, but one producing a clean
and pure silver. Each part of silver in the bath requires 3 parts
of hydrosulphite. (NaaSaOj.) Precipitation is facilitated by
warming the bath to about 120°F.

The required quantity of hydrosulphite is added, along
with five times that quantity of anhydrous sodium carbonate.

REGENERATION OF THE FIXING BATH

Many attempts have been made to find methods of pre-
cipitating the silver in such a way that the fixing bath would
be regenerated and so could be used again. The only fool-
proof method which allows of this is electrolysis, for all
the other methods result in the accumulation of much
unwanted material in the bath and in most cases result in the
decomposition of some or all of the hypo.

289

Washing and Drying

Fixation of a negative is always followed by a thorough
washing, for in addition to correct fixing the permanence
and good keeping properties of the negative are entirely
dependent on the efficiency and completeness of the final
wash which must remove every trace of fixing bath and all
other soluble salts from the film.

TECHNIQUE OF WASHING

Washing must never be attempted in a perfunctory manner.
Its purpose will not be fulfilled unless the water is frequently
replaced by a fresh supply, or else the washing is carried out
in a stream of running water.

To attempt washing in a dish, or the arrangement shown
on page 129, No. 1, is to risk failure because here the water
is not efficiently renewed. A distinct improvement is to lead
the water by means of a rubber tube so that it enters at the
bottom of the dish. In this way the incoming stream of water
catches up and mixes with the hypo solution dissolved out
of the film and so removes it. Many of the washers on the
market are provided with a syphon which empties them from
the bottom of the washer, and so provides a practical solution
to the problem.

The time required for washing naturally depends in some
measure on the quantity of water available and the number
of the negatives. With a good supply of running water 30
minutes should suffice, but if there are many negatives being
washed this time may be increased to 40 minutes.

If running water is not available, then the water in which
the negatives are washing must be changed at intervals of not
more than 5 minutes, and 5-6 such changes are essential.

As to the quantity of water to use, use as large a volume

290

as possible but not less than about 8 ounces for each negative
2i X 2J ins. or pro rata. (200 ml. per square decimetre of
surface.)

WASHING IN SEA WATER

The use of sea water for washing photographic materials is
practical only when a final wash of about five minutes in
fresh water is used. This final wash removes, as tests of the
Kodak Research Laboratories have shown, the residual salts
from the material and thus prevents rapid fading of the image
caused by these salts in the presence of hypo, and absorption
of moisture by the hygroscopic sea salts.

The removal of hypo is greatly accelerated during washing
in sea water as compared with fresh water. As a result, it is
recommended that films and prints be washed in sea water
for about one-half of the usually recommended times, and
finally for about 5 minutes in fresh water.

An increase of 20 to 40 degrees in the temperature of sea
water increases the rate of washing by 25 to 50 %, but washing
at as low a temperature as 50°F. (10°C.) removes the
hypo more rapidly than at 70°F. (21°C.) in fresh water.
The total time involved in washing in sea water followed by
fresh water is therefore less than required in fresh water
alone.

CONTROL OF WASHING

The occasion may arise when it is necessary to test the
efficiency of washing or to discover how long it takes. It must
be remembered that washing must remove not only every
trace of hypo but also any soluble silver salts in the film.
Two tests serve to find out whether washing has been com-
plete. The first is for the hypo.

211.— HYPO TEST SOLUTION

Distilled water 6 ounces ISO ml.

Potassium permanganate 6 grains 0.3 gram

Caustic soda 12 grains 0.6 gram

Distilled water to make 10 ounces 250 ml.

To make the test, pour about 8 ounces (200 ml.) of
water into a glass, add about 20 minims (1 ml.) of the

291

above solution, and allow some of the water to drain from
the plate or film being washed into the test glass.

If there is still hypo present the violet colour of the
permanganate will be discharged in a few seconds, and the
test solution will take on a yellow colour.

To test for silver a filter paper can be impregnated with a

212.— SILVER TEST SOLUTION
2% solution of sodium sulphide

This should be done away from the dark-room. The paper
can be dried and when used for the test one or two drops
of water are allowed to drain from the plate or film on to
the impregnated filter paper. If silver salts are present there
is a brown or yellowish -brown colour where the drops have
soaked into and spread in the filter paper.

Another test is to take a strip of unexposed film which
has not been developed and fix and wash it simultaneously
with other material. When washing is considered complete,
this strip is immersed in the above silver test solution. Any
trace of silver salts in the film will give rise to a brown
coloration.

This test is also useful in that it can indicate that the fixing
bath is exhausted, and that insoluble silver salts are remaining
in the film. In this case the strip of fixed and washed film is
divided into two. One part is tested when washing should be
complete. If discoloration occurs the washing is continued
for another 15 minutes and the second strip is tested. If this
still shows the discoloration then the fixing bath is not work-
ing properly and must be replaced by a fresh one, and the
whole of the material washing must be re-fixed and washed
agam.

SHORTENING WASHING BY CHEMICAL MEANS

The fact that washing is normally a long operation has led
many people to attempt to shorten it by chemical means.
A number of substances have been used, all of which are
oxidising substances which destroy or decompose hypo.

It must be admitted that the value of such methods is
very doubtful. Unless they are used in very dilute solution,
there is real danger of their attacking the image. There is also

292

the possibility that the products of the reaction will remain
in the film and have a bad influence on its keeping proper-
ties. Hence even when they are used a short wash must
follow.

A better method is to use:

213.— HYPO REMOVER
5-10% solution of sodium carbonate or bicarbonate

in which the negative is bathed for 5 minutes. A short wash
will then remove every trace of hypo.

A new hypo-eliminator, recommended by J. L. Crabtree,
C. T. Eaton and L. E. Muehler consists of two volatile
chemicals, hydrogen peroxide and ammonia. This combina-
ation oxidises hypo to sulphate which is inert and excess
eliminator, being volatile, evaporates. The new ehminator is
intended for use with paper positives or negatives. It is
difficult, if not impossible, to remove the last traces of hypo
from paper and, as a result, the sulphur in the residual hypo
sooner or later attacks any silver image forming a yellowish-
brown silver sulphide.

214.— HYPO ELIMINATOR FOR PAPER MATERIALS

Water 20 ounces 500 ml.

Hydrogen peroxide 3% solution 5 ounces 125 ml.

Ammonia 3% solution 4 ounces 100 ml.

Water to make 40 ounces 1000 ml.

To make 3 % ammonia dilute one part of .880 ammonia
with 9 parts of water.

Paper prints or negatives should be given as thorough a
wash as possible, about 30 minutes at 65-70°F. (18-2rC.) in
running water. At lower temperatures the washing time
should be increased and for double weight prints or X-ray
paper negatives the time should be doubled. Then immerse
each print in the hypo-eliminator for about 6 minutes at
WF., irC.) and finally wash for 10 minutes. About 50
prints 10 X 8 or equivalent can be treated in one gallon of
the solution.

With negatives or transparencies on glass or film hypo
can usually be removed completely by water alone without
the use of a hypo eliminator. If the washing process has to
be speeded up then a supplementary alkaline bath can be

293

used. The negatives, etc., can be washed in running water for
ten minutes and then treated in the following bath.

215.— HYPO ELIMINATOR FOR NEGATIVES
Ammonia .880 4 ounces 100 ml.

Water to make 40 ounces 1000 ml.

The negatives are bathed in this solution for 3 minutes
and then washed for 2-3 minutes.

This formula is preferable to No. 213 as being volatile
there is no solid residue left in the gelatine film of the
negative.

DRYING

When washed, negatives should be dried in a dust-free place.
Film can be hung free with a fairly heavy clip below to
prevent air currents blowing it about too freely. Plates should
be in a drying rack.

Before being put to dry, both sides of negatives, whether
plates or films, should be gently but firmly wiped with a piece
of viscose sponge or similar material, to remove all super-
fluous water.

Not only does this accelerate the drying, but it removes
any spots or flecks of gelatine which may have settled on the
film, and it removes the possibility of small areas of irregular
density due to drops of water on the film.

Drying can be accelerated by using warm air propelled
by a fan. The temperature should not exceed 85-88°F.
(30°C.), otherwise melting of the gelatine may occur. In the
larger drying cupboards used in the photographic business
the heating unit is part of the whole installation (see page
297).

Small blower dryers are available that dry the film without
removing it from the spiral. In these dryers (see page 295)
air is blown upwards through the film on the reel and drying
may be accelerated by warming the air. It is claimed that in
this method there is less risk of dust settling on the film than
when the film is hung up to dry in an ordinary room.

Where very rapid drying is necessary an alcohol bath may
be used.

294

FILM DRYER

Film dryer: (a) the film on its spiral, (b) fan blades, (c) electric motor,
and (d) heating element.

295

216.— BATH FOR RAPID DRYING
Dilute the spirit with 10-20% water

Dilution of the spirit is necessary to prevent attack on
the celluloid of the film. The bathing should last 3-4 minutes
and the film can then be rapidly dried in a current of air.
With methylated spirits there usually occurs a more or less
milky turbidity in the film, but this does not usually interfere
with the printing from it.

Another method of quick drying depends on the use of
a concentrated solution of a salt:

217.— ALTERNATIVE BATH FOR RAPID DRYING
Saturated solution of potassium carbonate

In this the film is immersed for a minute and then wiped dry
with chamois leather.

218.— ALTERNATIVE BATH FOR RAPID DRYING
Saturated solution of magnesium sulphate (Epsom salts)

may be used for a like purpose; in this case the film is given
half a minute in the salt solution, then squeegeed free from
excess solution, given a spirit bath for a second or two and
then dried in a few seconds in the stream of air from a fan.
These methods of very rapid drying are used in press
work where often every second is of importance. Negatives
dried by such means are usually used to produce enlarge-
ments. If they are to be preserved they should receive a
thorough washing as soon as they have provided the necessary
enlargements, otherwise the presence of salts in the film will
lead to damage and disintegration.

STABILIZATION

In cases where it is important to save time and the perman-
ence of the print is of secondary importance, the developed
image can be treated with a stabilizing agent without washing
afterwards. The purpose of this stabilizing agent is to make
the undeveloped silver halide substantially light fast and
give it a certain amount of stability.

According to W. L. Brice, H. D. Russell and E. C. Yackel
the stabilizing agent must be a compound which does not

296

DRYING CUPBOARD

Heated air is blown down through the cabinet and out through the grilled
floor. A filter is fitted in the air inlet to the cabinet. Interlocking double
doors give easy access to the interior.

297

react with metallic silver but forms a light-inert silver com-
pound by reaction with the undeveloped silver halide. The
resulting silver compound should be hght-coloured or trans-
parent, so that it does not interfere with the viewing or
printing of the final image.

Stabilizing agents which may be employed are organic
compounds containing double-bonded sulphur or an SH
linkage, and include alkali metal and ammonium thio-
sulphates and thiocyanates, thioureas, and thioglycoUic acid.
Compounds containing a quaternary nitrogen atom, such as
a-picoIinium-)ff-phenylethobromide, may also be employed.
The agents are generally used in lower concentration than
they would be in normal fixing procedures, where the
emulsion is washed after fixing.

Specific stabilizing agents which may be used, together
with the useful concentrations (by weight) in aqueous
solutions, are as follows:

Potassium thiocyanate 10%

Ammonium thiocyanate 5%

Sodium thiosulphate (crystalline) 10%

Potassium thiosulphate 10%

Ammonium thiosulphate 10 %

Thiourea 2%

Ethylene thiourea 2 %

Propylene thiourea 2 %

ThioglycoUic acid (Na salt) 10%

a-picolinium-/5-phenylethobromide 10 %

Other stabilizing compounds which may be used in
various concentrations are the following:

Thiobarbituric acid
Ammonium dithiocarbamate
2-Mercapto-4-methyl-5-nitro-thiazole
2 Mercapto-4-methyl-tliiazole
Dithio biurea

4-Aminometliyl-2-mercapto imidazole
5-Amino-2-mercapto-l, 3, 4-thiodiazole
2-Mercapto-5-amino-benzimidazole
6-Amino-2-thio-4-hydroxy-pyrimidine
Dithio oxamide

298

Thio trimethyl acetamide
Cysteine hydrochloride
Thioacetamide
Thiopropionamide
Thioglycollic hydrazide

FORMULATION OF STABILIZERS

The concentrations given above are based on a treatment or
immersion time of about 30 seconds. Lower concentrations
might be used with longer application or immersion times.
The upper limit of concentration is defined by the solubility
of the reagent and the general tendency toward crystaUisation
in the photographic material when very high concentrations
are used.

The time of treatment will vary with the nature of the
film (that is, the grain size and chemical composition), the
temperature of treatment and the manner of apphcation of
the stabilizing solution. The time necessary for the application
of a given stabilizing solution may be readily judged by
inspection of the emulsion layer. It is necessary that the
silver hahde shall have disappeared from the emulsion and
the disappearance of the halide, which indicates the forma-
tion of a complex with the stabilising compound, may be
determined by inspection of the emulsion layer. When the
silver halide has just disappeared from the emulsion, stabiliza-
tion is complete.

The thiosulphates and thioureas are used in acid solution,
the thioglycollic acid in alkaline solution, and the thio-
cyanates in either acid or alkaline solution.

According to D. J. Norman and P. G. Lungley,* experi-
ence has shown that prints stabilized with ammonium thio-
cyanate are permanent in an atmosphere of low humidity,
but that under conditions of high humidity the silver image
is attacked and may eventually become bleached out. It is
therefore desirable to apply the minimum quantity of
ammonium thiocyanate to the print.

IMPROVEMENT OF STABILITY

The stabihty can be further improved by using a solution
containing both ammonium thiocyanate and ammonium
•British Patent No. 876,497 (1961).

299

chloride. In general, the best results are obtained when the
said stabilizing solution is prepared by saturating ammonium
thiocyanate solution with ammonium chloride at room
temperature. The concentration of ammonium chloride in
this saturated solution will vary with the concentration of
ammonium thiocyanate. A very satisfactory stabilizing
solution for use in the case when the stabilizing solution is
applied in the form of a film to the developed emulsion layer
contains 180 grams per litre of ammonium thiocyanate and
180 grams per litre of ammonium chloride.

John Wilham Glassett and Frank Shirley Sutton* have
disclosed a photographic process utilising an ascorbic acid
or a salt for the purpose of reducing the adverse effect of
excessive humidity on the developed image. The ascorbic
acid or salt is added to a stabilizing solution containing
ammonium thiocyanate and the ammonium chloride. Suit-
able ascorbic acids or salts which may be included in this
stabilising solution are 1 -ascorbic acid (commonly known
as "Ascorbic acid") iso-ascorbic acid (also known as "Ery-
thorbic acid" or "D-araboascorbic acid"), or a salt of either
of these acids. If desired, a mixture of 1-ascorbic acid and iso-
ascorbic acid may be used in the said stabilising solution.

The invention is illustrated by the following example: A
silver chloride emulsion containing hydroquinone is de-
veloped by the application of 5 % caustic soda solution. The
excess alkali is removed by a squeegee, and immediately after-
wards there is applied to the material, by means of a roller,
a film of stabilising solution made up according to the
following formula:

219.— STABILIZING SOLUTION

Ammonium thiocyanate 180 grams

Ammonium chloride 180 grams
Ascorbic acid 20 grams

Water to 1000 ml.
Ammonia (S.G. 0.910) 6 ml.

The quantity of ammonia is sufficient to raise the pH of the
stabiliser to about 4.5. The excess stabilising solution is
afterwards removed from the surface of the material.

•British Patent No. 875,878 (1961).
300

Rapid Access Processes

Rapid access processing can be defined as a technique that
produces a usable picture in much less time than is pos-
sible by conventional processing methods, usually in the
order of a few seconds and in some cases even in fractions
of a second. In contrast to normal processing, in rapid
access processing the solutions are apphed by special
applicators.

CELL AND CHAMBER PROCESSORS

Cell and chamber processors permit the contact of small
amounts of processing liquids with the emulsion and the film.
A narrow space is provided between the film emulsion and the
processing device. In a processor of this type, designed by
K. H. Lohse and M. B. Skolnik* the film is first located over
a sealing frame, and then held tightly against the seal by
means of a pressure plate. Through the centre bore of the
processing platen, metered volumes of processing solutions
are brought into the capillary chamber. The liquid could
freely overflow the platen but is held within the chamber by
capillary forces.

The chamber dimensions are critical and must be optim-
ised. Good processing results have been obtained using a
chamber depth from 0.010 to 0.030 in. A nearly square frame
of 1.16 by 1.06 in. is preferred; however, equal success has
been attained with a more rectangular frame of 1.16 by
0.92 in.

The volume of processing liquid required to fill the

chamber ranges from 0.3 to 0.5 ml., depending on the

frame size. The figures given apply to the processing of a

35 mm. double frame. Since the processing solutions contact

*Phot Sci. and Eng. 5: 149 (1961).

301

the emulsion side of the film only, this process is well suited
to ultra rapid processing.

After development is complete, the fixing solution is
introduced into the capillary chamber through the centre
bore. This pushes the developer into the overflow and then
into the waste container. Any intermixture of the two liquids
is counteracted by the strength of the fixing solution, which
not only rapidly stops the development but also completes
the fixation of the image in the presence of traces of the
developing solution. A wash solution follows the fixing
solution after fixation is completed. Four to eight times the
chamber volume will yield sufficient washing. The processing
cycle is completed by drying the emulsion with a hot, high-
velocity airstream which enters the chamber from the side
and is directed evenly over the film surface. The drying air,
which escapes through the waste spacing into the vented
waste container, cleans and dries the chamber as well as the
film.

The emulsion of the film and the desired image character-
istics determine the selection of processing solutions. The
capillary chamber process permits great flexibihty in this
area, for any wet process can be used with this technique.
Monobath processing yields acceptable results, although in
certain apphcations, such as the one mentioned above where
image requirements of high contrast combined with low fog
level are desired, better results are attainable if development
and fixation are separated.

While this processing technique is not limited to the use
of certain types of emulsions, it has been noted that for ultra
rapid processing those emulsions especially designed by the
manufacturers for rapid processing applications give superior
results.

Processing cycle: The capability of the capillary chamber
process may be illustrated by the following typical processing
cycle :

Development for 1.5 seconds, followed by
Fixation for 0.5 second, and
Washing for 1 second.

The film is then dried in 2 seconds, giving a total process-
ing time of only 5 seconds.

302

■fhe processing platen, which is part of the heater block
contains heating elements and a temperature sensing probe.
The preselected processing temperature is automatically
controlled and is maintained within ± 0.5°F. The processing
temperature can be set for any point from ambient to 130°F.
Although high-temperature processing is not necessarily
needed for ultra rapid processing, it has been foimd that, at
varying ambient conditions, elevated processing temperatures
can be maintained more easily.

Using a developing chamber with a cavity of approxi-
mately 0.005", C. Orlando* has developed a method for the
production of photographic data recording 1 /5 second after
exposure. The 35 mm. film used for taking the photograph
makes a seal with the lips of the chamber during the process-
ing operation. The developing solution, which is preheated
to 170^F., is sprayed on the film through a narrow slit
located on the upper section of the chamber. The developer
is withdrawn from a slit on the lower end by means of a
vacuum produced by a self-contained pump. After develop-
ment, which normally takes 0.6 second, the film is kept in
this chamber and hot air saturated with acetic acid vapour
is drawn through the liquid ports. The hot air dries the film
and the acetic acid vapour neutralises the alkaline developing
solution and stabilises the image. The stabilisation, however,
is not complete and a yellow light is used for projection
to prevent fading of the image. The drying and stabilis-
ing operation takes a little less than 1 second so that the
image can be projected approximately 1.5 seconds after
exposure.

For processing, the monobath (Formula 205) gave
excellent photographic results at 140°F. and 1.3 second
processing time. However, a serious difficulty was en-
countered which made the technique impractical. The mono-
bath solution forms a silver compound which precipitates
and adheres to the surface of the developing chamber and its
liquid ports. Since these ports are very narrow— approxi-
mately 0.005 in. wide — any foreign deposition causes restric-
tion to the liquid flow sufficient to make the equipment
inoperative after a very short time. A two-bath system is more
reliable but involves the use of two chambers, one to develop
the film, the other to clear it. For development. Formula
•Phot. Sci. & Eng. 2: 142/147 (1958).

303

127 is used at 185°F., and for fixing a 50% hypo solution
at 205°F. Each step requires only 0.2 second.

VISCOUS LAYER APPLICATORS

In selecting a processing method for a machine to be designed
for both rapid and simplified processing, the viscous technique
has found commercial application on a large scale.

P. A. Hermle and H. D. Lowry* have described a machine
which processes 16 mm. black and white positive films at
36 ft./min., with a dry-to-dry time of one minute. The
developer and fixing solutions are each coated on the emul-
sion surface as a viscous layer in an atmosphere saturated
with water vapour at 125°F. The viscous processing solutions
are packaged in one-gallon disposable collapsible poly-
ethylene bags which can be changed without interrupting
the processing operation.

The film enters the processing chamber from the feed
chamber and passes round the coating roller. At this point
viscous developer is applied to the emulsion surface by the
coating hopper in a layer approximately 0.008 in, thick. The
reaction loop of the developer is adjustable by raising
or lowering the roller to provide developing times of 2^
to 7 seconds. By this means a specified contrast may be
selected.

The developer coating is removed by a high-velocity
water spray jet. The surface water on the film is removed by
a Venturi-type air squeegee. The film then passes round a
second coating roller where the viscous fix is apphed by
another coating hopper. Two hehcal loops are required for
the fixing time of 12 seconds.

The coating of viscous fix is removed by a second spray
jet at the bottom of the second loop. The film then passes
beneath a partition and into the wash compartment. Three
helical loops are formed in the wash stage with the film
emulsion toward three spray nozzles having a hollow, conical
spray pattern. The bottom rollers are adjustable to give
washing times of 13 to 17 seconds. After passing through a
second Venturi squeegee, the film goes into the impingement
air dryer. The bottom roller assembly for the three loops in
the dryer is adjustable to give times of 15 to 21 seconds. In

•S.M.P.T.E. 70, 875-877 (1961),

304

summary, the processing sequence includes: viscous devel-
oper, spray cut-off, air squeegee, viscous fix, spray cut-off,
wash, air squeegee, and dry.

The hoppers of the coating mechanism are made of two
wedge-shaped stainless steel elements separated by a U-
shaped plastic shim 0.008 in. thick. With the two halves in
place, the shim forms a channel as wide as the film and 0.008
in. thick. The solution in flowing through this channel forms
a smooth ribbon, which is apphed to the emulsion. Both
coating hoppers are hinged to permit the passing of splices.

POROUS PLATE AND ROLLER APPLICATORS

Rapid access processes based on the application of thin
layers of solution to the emulsion surface by means of porous
rollers or plates provide another technique.

A porous applicator processor, was described by R. P.
Mason.* The figure on page 310 illustrates its main features.
A J in. thick porous plate, made from sintered stainless steel
granules, is cut to the width of the exposed area on the film
and to a length generally determined by the required film
rate. It has been found desirable to limit the processing head
to approximately 1 in. in length, and build up as many 1 in.
modules as required for a particular length. In this case, a
single head was utilised for each of the two processing
solutions. The stainless steel plates are fastened to a manifold
block which contains a feed pipe and a cavity containing a
Dacron wick material. This aids in dispersing the solution
flow imiformly through the porous material.

A pump rate is maintained which slightly exceeds the
rate of solution carry-off, thereby forcing the meniscus to
bulge shghtly on all four free boundaries. The excess solution
flows down the edge of the porous shoe from the boundaries
of the meniscus, and is collected in a moat around the shoe.
From there, it is drained by gravity or pumped into the waste
tank. By means of cartridge heaters, the thermostatically
controlled manifolding block is heated to the temperature
desired in the process. The solution flow rate is slow enough
to permit the solutions to reach the temperature of the block
before coming in contact with the film. In a simpler head
design, the chamber containing the wick is eliminated and
•Phot. Sci. & Eng. 5: 79/86 (1961).

1, 305

the porous plate accomplishes the dispersion of the solution
flow.

An applicator relying on a meniscus of solution formed
between a porous roller and the film emulsion was described
by E. D. Seymour.* The applicator roller is a hollow stainless
steel tube plugged at both ends with small holes drilled
radially through the roll and with die-cut Dacron felt washers
slipped on the tube and retained by axial pressure of a collar.
The processing solution, preferably a monobath, is brought
first to the required temperature and then forced under
pressure into the applicator tube through small holes in the
bearings that coincide with similar holes in the applicator
tube. From there it flows out through the Dacron felt washers
to contact the emulsion.

JET SPRAY AND SLIT PROCESSORS

For the Kelvin Hughes system of rapid processing the
Venturi-type jet spray system was adopted. This is operated
by compressed air.f Atomised droplets of the various
solutions are sprayed onto the emulsion at high velocity and
at an economical rate. As this is a "total loss system", results
are constant and no replenisher system is required. For
reasons of economy the jet profile is eUiptical instead of
round and this has been achieved by the use of twin air jets.
Jet spray techniques were considered unsuitable for the
airborne processor because of the problems associated with
condensation of spray mist and the question of successfully
sealing a continuously moving film. Thus a processing "slot"
was devised} and this is a unit made in Inconel or Hastelloy
"C", consisting of a bar of material with three slots accurately
machined therein. Two of these slots carry the processing
fluids and, thus, have an inlet and outlet feed and return, but
the centre slot is not so provided since its function is to
separate the developing slot from the fixing slot by ensuring
an area of ambient pressure between these. Each slot may be
regarded in itself as an open weir, which, when placed close
to the emulsion surface of the film, forms a closed channel
through which the processing fluid is drawn in contact with

♦Edgar D. Seymour, Phot. Sci. & Eng. 2: 91 (1958).

fR. C. M. Smith and E. R. Townley, J. Phot. Sci., 7, 55 (1959).

IE. R. Townley, Phot. Sci. & Eng., 6: 26 (1962).

306

the emxilsion surface. Since this fluid is drawn through the
channel by negative pressure, it becomes a leak-proof
system, which is consistent with airborne requirements of
altitude and attitude.

The film is transported past the slot where it is fully
developed at a temperature of 40°C. in a time of 2 seconds;
it then passes a narrow ambient air channel after which it is
fixed via a slot similar to the developer channel in a similar
time. Thus, the record is available with an access time of
only 5 seconds. It should be appreciated that this applicator
is arranged transversely to the film motion and is so aligned
that there is a small air cushion between the emulsion and
slot surfaces, ensuring turbulent Hquid flow in the slot
channel and at the same time preventing damage to the
emulsion surface. Further, the emulsion is effectively squee-
geed as it leaves the slot glands.

ROLLER APPLICATORS

Processing solutions can also be apphed to the emulsion
surface by non-porous rollers or wheels. Such a processor is
the U.S. Signal Corps wheel processor which has three roller
applicators for continuous rapid processing at an approxi-
mate rate of 100 ft. per minute.* Normally this machine
works with three tanks, but its principle is adaptable to
various processing techniques. It is claimed that this process-
ing technique can halve the processing time in comparison
with immersion processing under the same temperature and
bath conditions. The three applicator wheels are so arranged
that they are sequentially contacted along a portion of their
periphery by the emulsion side of the film. The rollers are
driven in a contrary direction to the motion of the film.

A similar device was constructed by J. C. Barnes and
L. J. Fortmiller.f The lower portion of the rotating drum is
suspended in the solution and the drum rotates at the rate
of 300 r.p.m., in this case, however, in the direction of film
travel. A comparatively thick layer of solution is carried
round the upper circumference of the drum over which the
film is positioned by two small guide rollers. Normally two
drums are used. The first drum applies the developer, the

*S. L. Hersh and F. Smith, Phot. Sci. & Eng. 5: 52 (1961).
jPhot. Sci. & Eng. 7: 269 (1963).

307

RAPID ACCESS PROCESSING

a *

The elements of the viscous solution applicator (above) are:

a. Solution reservoir, b. Gear pumps, c. Coating hopper, d. Back-up

roller, e. Film. f. Temperature control jacket.

i ^ >|r ^ ^

©TrnY

In the capillary chamber processor the film is pressed against an opening
of a narrow chamber into which the processing solutions are introduced
in sequence.

a. Capillary chamber, b. Sealing frame, c. Heater block, d. Pressure
plate, e. Film. f. Film emulsion, g. Overflow well. h. Opening through
which solutions are introduced.

At the start of the processing cycle the film moves into position I and is
pressed against the sealing frame. Then follows II, development; III,
fixing; IV, washing; V, drying by air blown into the chamber; VI, re-
moval or advancement of the film for the next cycle.

308

RAPID ACCESS PROCESSING

In viscous processing, the film passes through a processing chamber 'A'
where the viscous solution is applied to the film surface by a coating
hopper and from there into the wash compartment 'B' and the drying
chamber 'C. This scheme applies to a monobath solution ; with two-bath
(development and fixation) processing the wash chamber is followed by
a second processing chamber for the fixer and another wash chamber.

a. Adjustable roller to lengthen or shorten the film path (for longer or
shorter development) after the developer is applied, b. Coating hopper,
c. Coating roller, d Entry of film from camera spool, e. Cut-off spray to
stop development, f. Drain, g. Air squeegee, h. Spray washing nozzles,
i. Warm air stream, j. Exit of film to spooling.

309

RAPID ACCESS PROCESSING

S::ltf5^»

In the porous plate applicator the
solutions are appUed through porous
plates in contact with the film surface
which moves past the plates,
a. Film. b. Back-up plate, c. Solution
meniscus, d. Porous plate, e. Wick,
f. Solution, g. Thermostatic heater
block, h. Drain.

The unit shown has two applicators
for development and fixing respect-
ively.

The porous plate applicator is here part of a complete camera and viewing
system. The film from the supply roll c travels past the lens which projects
the image on it and past the porous plates, running in front of a lamphouse
where it can be observed immediately.

a. Film drive, b. Drive motor, c. Film supply, d. Solution meniscus,
e. Waste tank. f. Processed film. g. Lamphouse. h. Solution supply tank,
i. Pump.

'D' is the developer tank and stage, 'F* the fixing tank and applicator.
310

RAPID ACCESS PROCESSING

The jet spray processor is again a chamber system where the chemicals
are sprayed on to the film surface held against a spray chamber.
a. Pressure plate, b. Film. c. Jet. d. Jet chamber, e. Waste outlet.

In the negative-positive rapid access system, the film, after exposure in
the camera unit (shown shaded), passes a viscous solution applicator. A
positive film is then pressed into contact, emulsion to emulsion with the
negative, and this sandwich runs in front of a printing light which prints
the negative on to the positive where it is immediately developed,

a. Solution applicator, b. Negative supply in camera, c. Camera lens in
exposure station, d. Printing light, e. Negative after separation of sand-
wich, f. Processing solution layer, g. Positive film. h. Viewer, i. Positive
film supply.

311

RAPID ACCESS PROCESSING

With non-porous roller applica-
tors the film 'a' is stretched over
the top of a fast-rotating drum
'b' which dips into a solution tray
'c' to carry the solutions to the
film surface. Each processing
station has a similar applicator.
The film travels at ten feet per
minute.

Saturated web processing involves the use of a suitable absorbent material
acting as the intermediate carrier for the processing solution. Equipment
utilising the saturated web is leakproof, requires no pumps, valves, meter-
ing devices or complex machinery. In operation, the web is pre-saturated
with aqueous processing solution such as a monobath and then brought
into intimate contact with the emulsion surface of the film

a. Motor, b. Film in camera, c. Take-up spool for web. d. Web. e.
Supply of saturated web. f. Processed film. g. Sandwiching rollers,
h. Camera lens recordmg image.

312

RAPID ACCESS PROCESSING

This apparatus takes a photograph from a cathode ray presentation,
processes it automatically and then projects it immediately. The machine
is designed for two solution processing and the drawing shows the relative
position of the developing chamber and the transparent fixing chamber.

a. Transport sprockets, b. Transparent fixing chamber, c. Screen, d.
Projection lens. e. Cathode ray tube. f. Camera lens. g. Developing
chamber.

313

second one the fixer. The film then passes over a spacer roller
into a washing tank and finally past a squeegee into a simple
drier. The speed of the operation is variable so that various
times of treatment from 1-10 seconds can be produced.

SATURATED WEB APPLICATORS

Saturated web processing involves the use of a suitable
absorbent material acting as the intermediate carrier for the
processing solution. For this system, a number of advantages
are claimed.* The volume of solution used is very small,
approximately equal to the volume of the material to be
processed. Each area of emulsion is processed with fresh
solution. Undesirable by-products of the reaction are
removed with the web upon its separation from the processed
film. The web is adaptable to various processing formulations,
i.e. monobath as well as standard 2 stage processing. Equip-
ment utilising the saturated web is leakproof, requires no
pumps, valves, metering devices or complex machinery.
However, the selection of a suitable web material offers a
number of problems. If paper is used, fibre markings appear
in the negative. For the RaproroU system a special paper is
used made of fine fibres in a sheet of high porosity permitting
uniform compression. Paper alone has insuflBcient web
strength and it is therefore used bonded to a non-porous
plastic film. This laminated backing gives it not only high
tensile strength, but decreases also the chance of entrapping air
and makes the processing solution available from one side
only. It also serves as an evaporation and oxidation barrier.
In operation the web, pre- saturated with an aqueous
processing solution such as a monobath, is brought into
intimate contact with the emulsion surface of the film.
Contact between the web and the emulsion is accomplished
by winding the surfaces together under tension around a
portion of the periphery of a drum. After processing is
complete, the web is stripped away from the developed film.

"dry" development

Rapid dry development of oscillograph traces in a silver-
sensitised recording paper has been achieved by P. H.
♦Seymour Schreck, Phot. Sci. & Eng. 4: 298 (1960).

314

Stewart, W. Bornemann and W. B. Kendall* using a pro-
cessor of simple design. The paper contains all the necessary
developer chemicals incorporated in the emulsion. The
processor is a heating chamber entirely enclosed, except for
slits at the front and back for exposed material to enter and
leave. Processing is initiated by moisture driven from the
emulsion and base which condenses on the cool surface of
the entering emulsion. The combination of increased moist-
ure and rapid application of heat causes development to
occur within a few seconds.

The machine is built to develop 12 in. wide rolls of paper
and consists essentially, of a chamber completely enclosed,
except for provision for the paper to enter and leave. The
curved bottom plate is of smooth metal and is equipped
with four 350-w. heaters along its 21 in. length. The roof is
another metal sheet, spaced just 0.5 in. above the bottom
plate, and is equipped with four 160-w. heaters. A pair of
drive rolls is located just below the exit to pull the paper
through the processor. When the machine is operating at
the rate of 25 ft./min. or less, the temperature of the bottom
plate is usually adjusted to about 240°F. At higher speeds,
however, bottom plate temperatures as high as 300°F. may
be required to ensure sufficiently rapid transfer of heat
from the plate to the emulsion layer through the paper
base.

Prints prepared according to the methods outlined are, of
course, unfixed. Furthermore, the developer remaining in the
background areas is still essentially as active as it was befoie
the paper was processed. Consequently, if the prints are
fogged by exposure to ambient light, the background tends
to darken because of developing and printing out. Neverthe-
less, these unfixed prints may have considerable utility, for
instance for recording oscillographic traces.

A processing technique similar to the above is flash
processing, described by J. H. Jacobs. j The developer is
applied in a very thin layei to the emulsion side only of the
recording medium which is then run over a hot surface. The
heat applied through the back causes rapid development and
drying. The record can then be viewed in daylight or subse-
quently be stabilised or fixed if required.

*Phot. Sci. & Eng. 5: 113/114 (1961).
tPhot. Sci. & Eng. 1: 156 (1958).

315

PHOTO DEVELOPMENT

The need in modern engineering developments for materials
to record data at very high speeds and the need to obtain
access to such data in a minimum of time and with a minimum
of chemical processing has led to the development of a new
class of direct-writing recording materials. H. D. Hunt*
reported on these new products which have the unique ability
of being processed entirely by radiant energy with no liquid
or chemical steps. The developed image can be viewed within
1 second of recording when the proper energy sequence is
followed.

The rapid writing speed of these new materials is obtained
by enhancing the ability of the silver halide crystals to form
internal latent images at high intensity in extremely short
exposure times, for it is the internal latent image, rather than
the surface latent image, that is intensified subsequently by
absorbed radiant energy.

In the amplification or development of the latent image
to a visible form, also called "post-exposure intensification"
or "photo" development, the energy used is the light absorbed
by the silver hahde in a second exposure rather than energy
released by the reducing agents in normal chemical develop-
ment. This light is ultraviolet and blue light, but must be of
lower intensity than the exposing light. However, the energy
absorbed — that is the intensity multiplied by the time — in
this step is much greater than that used in forming the latent
image. The intensity and time of exposure are in the region
where little or no new internal latent image will be formed.
This low-intensity amplification exposure, in addition, forms
surface latent images on the non-image grains, i.e. on those
which did not receive the high-intensity initial exposure.
These surface latent images apparently inhibit or prevent the
formation of internal latent images. As a result the back-
groimd is desensitised and is not easily darkened by further
exposure to either high- or low- intensity radiation.

To review the sequence of events that occur when this
emulsion is used: first, the initial exposure is made with a
high-intensity (usually UV) light source to form an internal
latent image. Following this the paper is given an exposure
to light at a lower intensity for a longer period such as

*Phot. Sci. &. Eng. 5: 104/8 (1961).

316

normal room light. During this second step, only the grains
which were originally exposed become blackened while the
remaining grains are desensitised by the low-intensity
exposure.

DRY SILVER PROCESS

Another process that leads to the formation of an image
without any wet chemical processing stages is the 3M Dry
Silver Process described by B. R. Harriman.* This process
uses a heat development stage for forming the visible image in
a specially designed hght sensitive material. The material
consists of a silver halide as the light sensitive element, a
source of silver in the form of a silver soap or behenate, a
developer or reducing agent all contained in a film-forming
binder and coated on an inert support. It can be seen that this
process is similar in principle to conventional photographic
materials except that all the chemicals required for image
formation are contained in the material itself and after
exposure, development or amphfication of the latent image is
brought about by heat and no fixing stage is required.

The thermal development of this dry silver material
generally is carried out at relatively high temperatures (80-
120°C. for 5-20 seconds) and so yields an image within a very
short period of time. A further fixing stage is not required
because development is unlikely to continue at normal
temperatures although there may be some additional latent
image formed. At the present time the fastest dry silver
material commercially available is a green sensitive material
with an ASA speed of 0.1 coated on a paper base which is
used for recording cathode ray tube images.

The heat development of coatings of a silver soap forms
the basis of the 3M Dry Copiers. A separate foil containing
the reducing agent is used for the exposing step in contact
with the original in which the reducing agent is destroyed by
the action of light in areas where there is no image. Heating
this foil in contact with a paper coated with the silver soap
causes reduction of the silver soap to silver to form a positive
copy of the original.

•Unconventional Photographic Systems. S.P.S.E. Symposium (1967).

317

CHEMICAL TRANSFER PROCESSING

The chemical transfer process makes it possible to produce
negatives and prints in a matter of seconds either direct in
the camera or in special machines for document reproduction.

The emulsion layer of the material used for this process
is similar to that of a normal photographic emulsion. The
positive paper has a gelatine layer, but instead of the silver
halides it contains so-called "nucleating" agents which are
capable of converting dissolved silver halide into metallic
silver grains. The process depends therefore on the presence
of sodium thiosulphate as a silver halide solvent. When the
developed negative is squeegeed into contact with this
positive paper, the hypo dissolves the unchanged silver halide
in the un-exposed image areas, but no such action takes place
in areas where the silver halides have been developed to
silver grains. When the developer-hypo solution diffuses from
the negative emulsion layer into the gelatine layer of the
positive paper, it encounters the nucleating agents which can
be formed by colloidal silver. The dissolved silver haUdes
are precipitated in the form of black metallic silver thus
forming a black positive image on the positive paper. The
gelatine layers of the negative and positive materials are so
thin and the distances travelled by the solution so small that
no significant sideways diffusion takes place. A sharp well-
defined reproduction is obtained when the sheets are stripped
apart.

This principle has been developed by E. H. Land for the
one-minute Polaroid camera and by Rott and Weyde for
document reproduction. In the Polaroid camera a finished
positive print is directly produced in the camera itself
immediately after exposure. The roll film consists of two
paper strips, one with a negative type emulsion, the other
with a fast light sensitive layer containing nuclei for pre-
cipitating silver during simultaneous development of the
negative and positive images. The two paper strips travel
through the camera independently at first but are brought in
contact after exposure of the negative layer. Pods of develop-
ing agent attached at proper intervals along the positive
paper strip are ruptured when the two strips are pressed into
contact between metal rollers and form a very thin layer of
developer between the two strips. After a processing period

318

of 10 seconds (originally, it was about 60 seconds), a door is
opened at the back of the camera and the positive print, and
in some of the systems also the negative, can be pulled out.

For document reproduction the material is used in the
form of sheets and the negative material and positive material
is handled separately. The negative paper is first exposed and
then inserted together with the positive paper into two
closely spaced slots of the developing machine. The two
sheets of paper pass through a container of developer
solution being held apart by a series of guides or channels.
On emerging from the developer, the sheets pass between a
pair of revolvmg rollers which complete the transport of the
paper through the developer, squeegee the sheets into contact
with one another and eject them from a single exit slot. The
sheets are then stripped apart by hand to separate the copy
from the negative paper.

The principle is also used in the Kodak Bimat* system
which employs a transfer film pre-soaked by the manufacturer
or bought dry and soaked by the user in the solution provided.
Fairly simple apparatus yields both a negative and a positive
by the mechanism described previously.

It is a semi-wet process and no additional solutions are
required by the user unless stable images are required, in which
case the films should be washed and dried in the normal
manner. Even without washing it is claimed that these films
are stable for several months if stored dry.

The pre-soaked transfer film and the exposed negative may
be wound on to a roller where the transfer and development
takes place as shown in the diagram on page 320. After the
recommended time (90 seconds to 20 minutes at 60°-100°F.)
the tacky films are unwound, stripped apart and dried. The
process is self-limiting so that these times represent minimum
times but the exposed and transfer films must not be allowed
to dry in contact with each other or stripping apart becomes
impossible.

Access times as low as ten seconds are claimed for cathode
ray recording film using a continuous process but the negative
is normally discarded. This system has obvious advantages for
aerial reconnaissance work where solutions would be im-
possible to use or in places where water is unavailable.

"An Introduction to Kodak Bimat Transfer Processing System, Kodak
Pamphlet No. P-65, R. P. Mason, S.P.S.E. News, 9 (2) 8, (1966).

319

KODAK BIMAT SYSTEM

The elements of the Bimat system are: a. Reel of Bimat film. b. Reel
of negative film. c. Pressure roller, d. Wind-up spindle.

320

FINE-GRAIN DEVELOPMENT. The developer has a very
important influence on the grain of the negative. The naked eye
may fail to detect grain or graininess, but enlarging will reveal it.
A section of a negative was here developed 1. (top) in ordinary
developer (p. 174), 2. (centre) normal fine-grain developer
(p. 206), and 3. (bottom) a super-fine grain developer (p. 210).

321

INTENSIFICATION. The negative was badly under-
developed but still showed all the essential detail ; the density was,
however, so low that even an extra-hard paper failed to produce
a satisfactory print (top). By intensification (see page 347),
however, a reasonably normal result (bottom) was obtained. —
H. Gornv.

322

PROPORTIONAL REDUCTION. The negative was dense
and contrasty, so that even when a soft paper was used the result
was too hard (left). By the use of proportional reduction (see
page 343) the negative was notably improved and {right) a good
print obtained on a soft paper. — H. Corny.

323

SUBTRACTIVE REDUCTION. The negative as a whole
was somewhat too dense and was rather strongly fogged in the
shadows {left). By the use of Farmer's reducer (see page 34'') the
fog was removed and the whole negative brightened up (rieht) —
H. Gorny.

324

SUPER-PROPORTIONAL REDUCTION. The fault in the
negative was mainly too dense highlights, whereas the rendering
of the shadows was approximately correct {left). The treatment
called for was the reduction of the highlights and so a super-
proportional reducer, ammonium persulphate (see page 344), was
chosen. — H. Corny.

325

PARTIAL REDUCTION. The sky in the negative appeared
ahnost opaque and would therefore print as a white expanse.
As the negative was not suitable for treatment with the ammon-
ium persulphate reducer, the process of partial reduction
described on page 355 was used because in this case one had a
single well-defined area which was comparatively simple to
operate upon. — Alexander.

326

PARTIAL INTENSIFICATION. The highlights of the
negative were well defined and the shadows had detail, but
insufficient to provide a really good print or enlargement. An
all-over intensification of the negative would have emphasised
the highlights too much, so a partial intensification (see page 355)
of the shadow areas was carried out. — Alexander.

327

, iSi.' f '.I' „, ff ■• ?

■I»^J

BLOCKING OUT. This process, which is described on page
356, can be used particularly for emphasising the more important
parts of a subject. It may be employed to hold back or to sup-
press entirely some unwanted portion of the background by
blacking it out as seen in the lower picture. — Polytechnic oj
Central London.

328

RIGHT AND WRONG METHODS IN RETOUCHING.

Left top. The right attitude and arrangement when retouching.
The retouching desk is so arranged that it is evenly illuminated
by light reflected from the mirror behind it, while the eyes of the
operator are protected by the shade projecting from the frame of
the desk.

329

TWO IMPORTANT OPERATIONS IN RETOUCHING.

Left. Applying the varnish (see page 361) with the aid of a linen
swab before proceeding to retouch with a pencil. The varnish is
essential if the pencil is to take on the negative surface.

Right: Rubbing down the graphite powder which is to be used
in local intensification or retouching. The negative must be treated
with a matt varnish before the graphite is applied. — W. Nurnberg.

Continued from page 329.

The illustration top right shows none of these conditions ful-
filled; the angle of the desk is wrong, the position cramped and
the eyes subjected to a glaring light.

Left bottom. The correct method of holding the retouching
pencil. It is held lightly and not too near the point; hence the
danger of too heavy a stroke is obviated.

Right bottom. The wrong way to hold the pencil; it is held too
tightly and too near the point. Control is difficult and the strokes
will be too heavy. — W. Nurnberg.

330

DEFECTS IN NEGATIVES. Lejt. 1. Correct exposure. 2.
Under-exposure (p. 394—1). 3. Over-exposure (p. 395—5). Right.
1. Correct development. 2. Under-development (p. 394—2).
3. Over-development (p. 394 — 4).

331

7. Grey fog all over (p. 395—6). 8. Reversal of the negative
(p. 400—38). 9. Fogging through backing (p. 395— 6b). 10. Black
fog on edge of plate (p. 395—7). 11. Reticulation (p. 399—30).
12. Reticulation magnified.

332

13. Melting due to hot water. 14. Melting (p. 400—39).
15. Frilling (p. 400—36). 16. Finger marking (p. 400). 17. Marks
caused by dust brush. 18. Contact during development (p. 400).

333

19. Irregular density (p. 399—27). 20. Streaks on the negative
(p. 398—15). 21. Area of higher density (p. 398—21). 22. Areas
of lower density due to adding potassium bromide (p. 398 — 21).
23. Irregular development (p. 398 — 18). 24. Stop bath too strong.

334

25. Air bell marks (p. 399—28). 26. Air bells magnified. 27. Small
blisters (p. 400—35). 28. Streaks fp. 398—15). 29. Small flecks
(p. 399—26). Dark flecks (p. 400—32).

335

31. Dust (p. 400—31). 32. Chemical dust (p. 400—31). 33.
Drying marks (p. 400—34). 34. Water splashes (p. 400—34). 35.
Water splashes (p. 400—34). 36. Holes in the film (p. 400—33).

336

COMBINED CAMERA-PROCESSORS-VIEWERS

In many cases it is important to shorten the time between
photographic recording of information and its presentation
for visual inspection either in a permanent or temporary
form. This can be achieved with combined camera-proces-
sors-viewers or -projectors.

A system for projection of the photographic data record-
ing within a fraction of a second after exposure has been
developed by C. Orlando.* The equipment (page 313) takes
a photograph from a cathode-ray presentation, processes it
automatically and then projects it immediately. The machine
is designed to use two solution processing which in this case
gives results superior to those obtainable with monobath
processing. It is possible to process a film within 0.2 seconds
at 185°F. and to fix it in approximately 0.2 to 0.3 seconds at
205°F. The schematic drawing on page 313 shows the
relative position of the developing chamber and the trans-
parent fixing chamber. A similar device was described by
R. P. Mason.f His radar recording equipment employs a
porous apphcator which is inserted in a narrow space
between a camera portion and the viewing station (page 310)
using a U-shaped film path in a relatively small piece of
equipment. A machine has also been designed which provides
both negative and positive in a rapid processing operation.
A sandwich is formed between the exposed negative and a
positive film with a processing solution in between. The
processing solution is a monobath. It develops the negative
which is immediately printed on the positive material and
thus developed by the same monobath. The processing
solution develops and fixes the positive image almost
immediately. The positive and negative films are then
separated and either of them can be used in the usual way.J

FORMULAE FOR RAPID PROCESSING

Rapid access processing requires highly active developers
which make full use of all means to accelerate the developing
process, such as high general concentration, pH and tempera-
ture. In cases where temperatures considerably exceeding

•Phot. Sci. and Eng, 2: 142 (1958). U.S. Patent 2856829.

tPhot. Sci. and Eng. 5: 79 (1961).

JFairchild Camera & Instrument Corp., Brit. Pat. No. 884.391 (1961).

20 337

normal working temperatures are employed, special "quick-
finish" (rapid access) films have to be used which stand
temperatures up to say approximately 200°F. (93°C.).

Some of the machines described in the foregoing use
"monobaths", i.e. Table LVIII.

In cases where the two solution technique is used, a
fixing formula based on ammonium thiosulphate should be
chosen. For certain specific uses, however, where permanence
of the photographic record is of less importance and where
it is desirable to produce it in the least possible time, the so-
called "stabilisation technique" is applied. This is based on
the use of a stabiliser which renders the imdeveloped silver
halide relatively inert to the effects of heat, light and moisture.
The main stabilising agents used for this purpose are:
Ammonium thiocyanate and thiourea ammonium thio-
cyanate approximately 20% solution, thioiirea in about
3 % solution. Prints stabilised in this way are not to be washed
(see page 296).

338

After Treatment of the Negative

The correcting of negatives by after treatment, in particular
by reducing or by intensification, has lost much of its former
importance. This is mainly because a satisfactory print can
be made from almost any negative on one or other of the
many grades of paper now available. Moreover, the very
notable latitude in exposure and in manipulation of modern
negative material makes the really poor negative a com-
parative rarity.

Hence the correction of a negative by chemical treatment
is called for only in exceptional cases, or when the negative
has to be suited to some special positive material which is
only available in a restricted range of contrasts. A particular
case which may arise is the preparation of lantern slides or
diapositives, for here the material available does not appear
in a wide range of contrasts.

REDUCTION

All reducers are oxidising solutions, they either oxidise the
silver to a soluble salt or contain a solvent for the silver salts
if these are insoluble in water. The permanganate, dichro-
mate, ferric ammonium sulphate, eerie and persulphate
reducers are used in the presence of sulphuric acid, forming
silver sulphate which is soluble in water. Ferricyanide is used
with hypo or thiocyanate to dissolve the silver ferrocyanide
which is formed but not soluble in water.

The object of reduction is, as its name implies, the
reducing of the density of a negative; it may be the correcting
of over-exposure or over-development. Errors in exposure
or development may display themselves in various ways in
the negative and variously aifect its character. The choice of
the right reducing agent to use in any particular case will go

339

far to bring about the necessary correction. The way in which
various reducers act is shown on page 341, where the grada-
tion of various negatives is shown diagrammatically in the
form of a stairway of densities. They give a section through
the film of the negative showing the three steps of varying
heights representing shadows, middle tones and highUghts.
The various reducers can act in three different ways which
we will now describe.

(1) The reducer removes the same quantity of deposit
from shadows, middle tones and highlights. It
planes down the surface of the negative deposit
evenly (page 341), and to this type of reducer we
give the name subtractive. As the diagram shows
the greatest effect is in the shadows, less in the
middle tones and least of all in the highlights.
Hence the general effect is to increase the general
contrast of the negative. Reducers of this type are
Farmer's (see page 342) and Belitzki's (see page
343). They are particularly adapted for reducing
negatives where the shadows want clearing and
where a general increase in contrast is desirable,
as is particularly the case with over-exposed
negatives.

(2) The reducer acts proportionally to the amount
of silver present, that is it removes but little from
the thin parts, more from the middle tones and
most in the heavy densities (see page 341). From
the diagram it will be seen that the action results
in a notable reduction in the density of the whole
negative, the total density of which may be
reduced to about one half. It might be said to
represent the opposite of over-exposure where, as
we have seen (see page 34), increasing length of
development gives increased density without
notably increasing the contrast of the negative.
Reducers of this type are called proportional, and
the best known examples are potassium perman-
ganate (see page 343), and mixtures of per-
manganate and ammonium persulphate (see page
343). These proportional reducers are used to
correct over-developed negatives, or all those in
which the densities are too heavy.

340

REDUCTION

Log E

Reduction consists of reducing the density of the negative. Reducers
can act in several ways, as the diagram shows. The middle series shows
the effect of three types of reducer on the sensitometric curves. The solid
lines represent the negative before reduction and the dotted lines represent
the negative after reduction. The diagrammatic representation of the house
shows the effect of reduction. On the left, the negative before treatment
and on the right, after reduction. From top to bottom: First, subtractive
reduction. Second, proportional reduction. Third, super-proportional
reduction.

341

(3) The reducer attacks the heavy parts of the
negative more strongly than the middle tones and
lighter parts (see page 341). It is called super-
proportional for it tends towards a reduction of
the general contrast and so is suitable for im-
proving negatives which are too contrasty. That
applies particularly to those which have had a
short exposure and been over-developed. In such
cases it is important that the details in the
shadows are not attacked because, by reason of
the under-exposure, they are already very thin
and weak. Reducers of this type comprise:
Ammonium persulphate (see page 344). Benzo-
quinone (see page 345). Re-development (see
page 345). Bleaching processes (see page 346).

SUBTRACTIVE REDUCERS

The best known and most widely used subtractive reducer is
Farmer's solution. It is almost always kept in the form of
two stock solutions.

220.— FARMER'S REDUCER

A.
B.

Hypo cryst. 1 ounce
Water up to 10 ounces
Potassium ferricyanide ^ ounce
Water up to 5 ounces

25 grams
250 ml.

12.5 grams
125 ml.

Immediately before use take 4 ounces (100 ml.) water,
4 ounces (100 ml.) of solution A and 2 drams (6 ml.) solution
B and mix well. The action of the reducer depends upon the
proportion of solution B, the more B is present the more
rapid the action, but the strength given above is convenient
for good control of the process.

Caution: The stock solutions keep indefinitely, the mixed
solution has very little keeping power.

The reducing should be watched carefully. It is best to
treat the negative for about 20 seconds in the reducer, then
rinse well and examine, repeating the operation until the
required reduction has been reached. Reduction can be
imdertaken immediately after the negative has been fixed,

342

only a short wash being necessary before placing the negative
in the reducing bath. When reduction is complete the
negative is well washed and dried. Such reduced negatives
always show a shiny surface due to the silver having been
removed from the outside layer of gelatine.

Belitzki's reducer works in a similar manner to Farmer's.

221.— BELITZKI'S REDUCER

Ferric chloride cryst. i ounce 6.5 grams

Potassium or sodium oxalate I ounce 12.5 grams

Sodium sulphite anhyd. 160' grains 8 grams

Water to make 8 ounces 200 ml.

Before use add 60 grains (3 grams) oxalic acid crystals,
shake well imtil the solution turns green, allow to settle,
pour off the supernatant hquor from the crystals and add
2 ounces (50 grams) hypo crystals. For use take one part of
this solution and dilute with 11 parts of water.

PROPORTIONAL REDUCERS

The following formula is midway in properties between
subtractive and a true proportional reducer.

222.— PERMANGANATE REDUCER

A. Potassium permanganate 40 grains 2 grams
Water to make 20 ounces 500 ml.

B. Water 20 ounces 500 ml.
Sulphuric acid cone. 20 minims I ml.

Immediately before use take 4 ounces (100 ml.) of water
and add 2 drams (7 ml.) each of A and B.

To produce a correctly proportional reducer potassium
permanganate is combined with ammonium persulphate as
follows:

223.— PERMANGANATE-PERSULPHATE REDUCER

A. Potassium permanganate, 1% solution
Sulphuric acid, 10% solution
Water to make

B. Ammonium persulphate
Water to make

For use take 1 part A, 1 part B and 4 parts of water.

If in either of the above cases the negative shows a brown
stain after reduction, this can be removed by immersion in
the following:

343

i ounce

12.5 ml.

J ounce

6.5 ml.

20 ounces

500 ml.

i ounce

12.5 grams

20 ounces

500 ml.

224.-

-STAIN REMOVER

Sodium sulphite anh/d.
Oxalic acid
Water to make

6 ounces

1 ounce

40 ounces

1 50 grams
25 grams
1000 ml.

SUPER-PROPORTIONAL REDUCERS

The property of reducing the denser parts of the negative in
preference to the middle tones and shadows is possessed in
an unusual degree by the ammonium persulphate reducer.
Ammonium persulphate is, however, notably subject to
deterioration on keeping and is also easily affected by other
substances; hence successful control of reduction when using
it requires special precautions. The usual solution used
consists of:

225.— AMMONIUM PERSULPHATE REDUCER
Ammonium persulphate 50 grains 2.5 gram

Sulphuric acid, 10% solution 20 minims I ml.

Water 4 ounces 100 ml.

If the tap water contains chloride or lime salts distilled
water should be used. Also when fresh the crystals of per-
sulphate crackle as they dissolve; if this does not occur the
freshness of the persulphate is suspect and the action of the
reducer will be lessened or may be absent.

Some workers prefer as an alternative solution the
following:

226.— ALTERNATIVE AMMONIUM PERSULPHATE REDUCER
Distilled water 4 ounces 100 ml.

Ammonium persulphate 50 grains 2.5 grams

Ammonia 0.910 40 minims 2 ml.

Hypo 50 grains 2.5 grams

All negatives that are to be reduced with persulphate
must be very thoroughly washed. The negative must be care-
fully watched during the process of reduction, preferably at
intervals of not more than 1 5 seconds. The rate of reduction
varies with different materials; with some it is slow, with
others very rapid. As soon as the desired degree of reduction
is approached the process should be stopped. This can best
be done by using a stop-bath consisting of a 12% solution
of sodium sulphite-

344

The negative is given a rinse and placed in this bath for a
minute or so and then given a thorough final wash.

Most of the earlier failures with persulphate reducers can
be traced to the use of old and partially decomposed, or to
impure persulphate. They had the effect, however, of inducing
workers to use other methods which were less imreliable. Of
these one well used formula is that using benzoquinone.

227.— BENZOQUINONE REDUCER

Water 4 ounces 1000 ml.

Sulphuric acid cone. 60 minims 3 ml.

Benzoquinone 20 grains I gram

The well washed negative is treated for 4-5 minutes in
this solution.

RE-DEVELOPMENT

A useful and controllable method of reducing the contrast
of a hard negative is the so-called re-development method in
which the negative is just bleached in a suitable bleaching
bath and is then re-developed to the desired contrast and
density. This is sometimes called harmonising.

What actually happens is that during the so-called bleach-
ing process the developed silver image of the negative is
re-converted into chloride or bromide and so can be developed
again to the desired gradation and density. For this purpose
it is preferable to use a somewhat slow working fine-grain
developer; as soon as the required density and gradation are
reached the re-developed negative is thoroughly fixed out.

A useful bleaching solution is:

228.— BLEACH BATH FOR RE-DEVELOPMENT

Water 40 ounces 1000 ml.

Copper sulphate 4 ounces 100 grams

Sodium chloride (common salt) 4 ounces 100 grams

Sulphuric acid cone. I ounce 25 ml.

Bleaching must be thorough and no trace of the original
reduced silver image must remain. When this is accomplished,
wash for a few minutes until the image is pure white and
re-develop with the following developer.

229.— FINE-GRAIN RE-DEVELOPER

Water 40 ounces 1000 ml.

p-Phenylenediamine 60 grains 3 grams

Sodium sulphite anhyd. 1 ounce 25 grams

345

Development must be carried out until the image is plainly
seen through the back of the negative otherwise the grada-
tion will suffer and the negative be too thin. Another devel-
oper, somewhat more energetic, which can be used for this
purpose is the metol single solution (Nos. 1-3) used well
diluted. As a general guide the re-developed negative should
appear not very different to the original negative be-
fore bleaching. If it is now rinsed and thoroughly fixed it
will be foimd to have distinctly less density and a less steep
gradation.

Another interesting method of varying and reducing the
contrast makes use of the idea of protecting the silver in the
shadows or thin densities of the negative either by depositing
there a substance not attacked by the reducer or by converting
the silver into a compound which equally is not attacked. To
do this the negative is given a superficial bleach in the follow-
ing bath:

230.— BLEACH BATH FOR SUPER-PROPORTIONAL REDUCING
Water 4 ounces 100 mL

Mercuric chloride 40 grains 2 grams

Potassium bromide 40 grains 2 grams

The time of the bleaching is so arranged that only in the
shadows and the thinner middle tones does bleaching take
place. Hence when seen through the back of the negative all
the parts that are to be reduced must remain black.

Then the negative is washed well and treated in a

231.— GOLD CHLORIDE BATH
Solution of gold chloride I : 500

This will have the effect of darkening all the bleached
parts and as soon as this happens the bathing is stopped.
The negative is now washed and treated with Farmer's
reducer imtil the heavy densities are reduced as required.

With experience this is a very practical and useful method
and can provide almost any desired alteration of contrast.

Variations of the method consist in the use of gold or
selenium toning of the image, omitting the bleaching bath;
in this way the toned parts are protected from the action of
the reducer. The bleaching method is, however, safer and
allows of better control as the observation of the image during

346

the bleaching is a certain guide to the progress of the opera-
tion. In the gold and selenium toning there is no alteration in
image colour, hence there is no observable change to act as a
guide to the completeness or otherwise of the reaction.

INTENSIFICATION

Negatives which are too soft and thin, either through over-
exposure, too short development or other mistakes can be
improved by intensification. This is called for when it is not
possible to produce a satisfactory print by the choice of a
suitable hard gradation paper.

There are physical, chemical and optical intensifiers.
Chemical intensification is effected by adding something to
the silver image — either silver or other compotmds. If, for
instance, the image is bleached i.e. converted into silver
chloride with a solution of ferricyanide and sodium chloride
and then redeveloped in a non-staining developer, a moderate
iacrease in density can be achieved. If we use a staining
developer, such as pyrogallol, a brown-black image is
obtained which has a higher printing density than a neutral
black image, provided the positive material is not colour
sensitive. This process is called optical intensification, as it
depends on the colour of the transmitted light rather than on
its intensity. We talk of physical intensification if metallic
silver or mercury is deposited on the silver image with the
help of a reducing agent in the solution, the silver grains
acting as neutral nuclei for this reaction. A suitable solution
consists for instance, of silver nitrate, pyrogallol and citric
acid, or a mercury salt, metol and citric acid.

Intensifying consists in depositing either metal or a
metallic compound of black or dark colour on the silver
forming the negative image and so increasing its printing
density.

There is one reservation to be made here, and that is the
fact that some enlarging papers today are orthochromatic
and some panchromatic* With such papers a negative
having a yellow-brown image such as results from uranium
intensification will not give the same result as on a normal,
not colour sensitised bromide paper. Hence care should be
used in the choice of the method of intensification.
*See Enlarging, by C. I. Jacobson and L. A. Mannheim, Focal Press.

347

In the following formulae the different types of intensifier
are separated according to the degree of density and contrast
they can confer on the negative. With the range of printing
and enlarging papers available today it will generally be
found convenient to use an intensifier of medium type, e.g.,
mercury, chromium or dyestuff.

It must be emphasised that one can only intensify when
there is some image to work on. If under-exposure has been
so gross that no image has been developed in the shadows
and only clear film exists, then there is nothing to intensify
and no use in attempting it.

The action of intensifiers on the negative image is shown
on page 349. It will be seen that with almost all intensifiers
the denser parts of the image are more strongly intensified
than the shadow details, hence the contrast is increased.
These are just the properties required, for in the majority of
cases our reason for intensifying a negative is to increase
density and also to obtain greater contrast.

MERCURY INTENSIFIER

This is the most widely used method. The negative must be
thoroughly fixed and washed before intensification is
attempted. Any trace of hypo left in the negative will cause
indelible stains to appear.

The negative is first bleached in the following solution:

232.— BLEACH BATH FOR MERCURY INTENSIFICATION
Mercuric chloride 40 grains 2 grams

Ammonium chloride 40 grains 2 grams

Water 4 ounces 100 ml.

Bleaching must be carried on until all trace of the black
silver image has been replaced by a grey-white image.

Blackening is carried out after the bleached negative has
been given a short wash and may be done with:

233.— BLACKENING BATH FOR MERCURY INTENSIFICATION
(\) A 10% solution of sodium sulphite or

(2) A 5% solution of ammonia or

(3) By using any normal (not fme-grain) developer

Of the three the first gives the least effect and the third
348

INTENSIFICATION

Density

Log Exposure

1^'— H— 1

H-

Intensification of a weak negative consists in increasing its density by
the addition of a black or a dark-coloured layer through chemical
action. The additional density is proportionate to the densities already
existing in the weak negative. The deep shadows remain virtually un
altered as almost clear emulsion while the highlights attract the greatest
proportion of the additional intensity. In this way the contrast of the
negative can be increased. The upper part of the diagram shows the
effect of intensification on the characteristic curve (full line before in-
tensification and dotted line after intensification). The lower stylised
picture shows the effect of the increased contrast.

349

the most. The second gives an image which does not with-
stand prolonged light action.

After blackening the negative should be well washed.

A single solution mercury intensifier can be made up:

234.— SINGLE-SOLUTION MERCURY INTENSIFIER

Mercuric chloride 200 grains 10 grams

Ammonium thiocyanate 120 grains 6 grams

Water 4 ounces 100 ml.

Dilute one part with 9 parts of water for use. Maximum
intensification requires about 10 minutes. If longer treatment
is given the image begins to lose density.

MERCURIC IODIDE INTENSIFIER

The following is a simplified method of mercury intensi-
fication.

235.— MERCURIC IODIDE INTENSIFIER
To a solution of 120 grains (6 grams) mercuric chloride in 20 ounces
(500 ml. ) of water add a 10% solution of potassium iodide until the
voluminous red precipitate which forms is just re-dissolved. This will
require about 3 ounces (75 ml.) of the iodide solution. To the mixture
add the following solution:

Sodium sulphite, anhyd. 4 ounces 100 grams

Water to make 20 ounces 500 ml.

If the above intensifier be used alone, the intensified
negative has poor keeping properties, it is therefore usual to
blacken the image by usiag any normal developer.

URANIUM INTENSIFIER

This method gives strong intensification but the image colour
is yellow brown and the keeping properties of the intensified
image are not good.

236.— URANIUM INTENSIFIER

A. Water 4 ounces 100 ml.
Uranium nitrate 20 grains I gram
Acetic acid glacial jounce 12.5 ml.

B. Water 4 ounces 100 ml.
Potassium ferrlcyanide 20 grains 1 gram

For use take one part of A and two parts of B, mix, and
then intensify to the required degree. Care must be exercised

350

in washing the intensified negative, using running water and
wash until the water runs smoothly over the intensified
surface. If washing be prolonged the density tends to regress.
If the yellowish colour of the highlights is objectionable, it
can be reduced by treating with a 5 % solution of common
salt (sodium chloride) in water.

CHROMIUM INTENSIFICATION

This is a simple, easily controlled, and very satisfactory
method which has largely supplanted mercury intensification.
A stock solution of potassium dichromate, 10% in strength
is used to make up the following baths:

237.— CHROMIUM INTENSIFIER

Stock potassium dichromate 10% sol. i ounce 12.5 ml.

Hydrochloric acid cone. 5 minims 0.3 ml.

Water up to 4 ounces 100 ml.

238.— ALTERNATIVE CHROMIUM INTENSIFIER

Stock potassium dichromate 10% sol. J ounce 12.5 ml.

Hydrochloric acid cone. 25 minims 1.2 ml.

Water up to 4 ounces 100 ml.

No. 237 gives more intensification than No. 238.

The well washed negative is immersed in the bath until
completely bleached; this converts the silver image into a
combination of chloride and chromium compound. The
negative is now washed vmtil completely free from yellow
stain, and developed in daylight, or after exposure to day-
light, with a normal developer.

A notable advantage of the method is that if sufficient
intensification is not attained in the first attempt the whole
treatment can be repeated.

COPPER-SILVER INTENSIFIER

For very weak negatives M. G. Zelger recommends the

following formula:

239.— COPPER-SILVER INTENSIFIER

A Water 2" ounces 500 ml.

Copper sulphate 100 grains 5 grams

Acetic acid glacial ' ounce 25 ml.

B Water 10 ounces 250 ml.

Potassium iodide 100 grains 5 grams

Ammonia .880 2 ounces 50 ml.

351

Two parts of A and one part of B are mixed to form the
bleach bath; the negative after bleaching is washed for 15
minutes and blackened in

240.— BLACKENING BATH FOR COPPER-SILVER INTENSIFIER
Water 10 ounces 250 ml.

Silver nitrate 20 grains I gram

Sodium acetate 80 grains 4 grams

If desired the film may be hardened after the bleach bath
in saturated solution of potash alum.

QUINONE-THIOSULPHATE INTENSIFIER

In many cases with high speed photography it is impossible
to give adequate exposure. In such cases considerable inten-
sification is the only solution of the problem of getting a
printable negative. Sports photographers in particular are
always faced with difficulties of this kind, and similar prob-
lems are also found in stage and circus photography where
the light is poor but reasonably fast shutter speeds are still
needed.

Good results are being obtained with the Kodak IN6
quinone-thiosulphate intensifier formula. This is of special
value when used on high-speed material, producing a greater
effect than any single-solution intensifier.

The intensified image is brownish, and is not indefinitely
permanent, being similar in this respect to uranium-toned
images. Negatives must be well washed and free from finger
marks, and require a preliminary treatment in alkaline
formaldehyde hardener, such as Formula 307 on page 396.

241.— KODAK IN6 QUINONE-THIOSULPHATE INTENSIFIER

A. Warm distilled water
Sulphuric acid cone.
Potassium dichromate
Distilled water to make

B. Warm distilled water
Sodium bisulphite
Hydroquinone
Kodak Wetting Agent,

10% solution
Distilled water to make

C. Warm distilled water
Sodium thiosulphate cryst.
Distilled water to make

60 ounces

2 ounces 96 minims

I ounce 350 grains

80 ounces

60 ounces

133 grains

I ounce 88 grains

I ounce 270 minims
80 ounces
60 ounces

I ounce 350 grains
80 ounces

750 ml.
30 ml.
22.5 grams
1000 ml.
750 ml.
3.8 grams
1 5 grams

20 ml.
1000 ml.
750 ml.

22.5 grams
1000 ml.

352

The sulphuric acid must be slowly stirred in.

Distilled water should be used, as a trace of chlorides in
the water will greatly reduce the degree of intensification,
and may bleach the image.

For use one part of solution A is taken, and two parts of
B stirred in, followed by two parts of C. The mixture is well
stirred, and another part of solution A is then added. This
order of mixing is important, and should not be changed.

After a five minute wash the negatives are hardened by
immersing them for about five minutes in the alkaline
formaldehyde hardener (No. 307, page 396), and washed
again for five minutes in running water. They are then treated
in the working solution, made up as described above, for up
to ten minutes with continuous agitation. Negatives are
best treated singly. They are then well washed, and dried.
The working solution should only be made up immediately
before it is needed and must be discarded after use.

The brown colour of the image is really an intentional
developer stain and is of the same nature as the stain
produced on prints when they are put into a fixing bath
after development without an intermediate rinse.

The intensified image is destroyed by acid hypo, so
intensified negatives must not be placed in fixing solutions,
or in washing water contaminated by fixing baths.

The aiustrations of defects in negatives on pages 321-336 have been
contributed by the Eastman Kodak Company, Rochester (U.S.A.), the
Gevaert Factories, Antwerp (Belgium) and Ilford Limited, London.

21 353

Retouching

The retouching of negatives today is usually confined to
deahng with actual imperfections in the negative or to
modifying some excess or want which detracts from the
quality of the picture. In eariier days retouching reached
such proportions that it was not uncommon to find the
finished picture bearing but Uttle resemblance to the original.
Such "beautifying" is not the true object of retouching.

PLAN OF WORK

If retouching is undertaken it should always be carried out
in a definite order and according to a deliberate plan.

(1) The first stage is the wet retouch sometimes called
chemical retouching. This comprises the local or
partial reduction or intensification of any areas
requiring such treatment.

(2) The treatment of the dried negative comprises
dealing with those portions which are too thin
and which require blocking out or treating in such
a manner as to reduce the amount of Ught which
they can pass.

(3) If any slip be made in carrying out No. 2, then
the matter can usually be remedied by treatment
or washing of the negative.

(4) The next process will be the mechanical reduction
of any part of the negative which is too dense,
i.e., rubbing down.

(5) Then will follow, if required, any knife-work,
which is used to reduce small local densities, to
remove black spots and the like.

(6) The last retouching to be undertaken is that

354

carried out with the pencil, and then it is usual
to varnish the negative.

This long list does not mean that all or even any of these
stages are necessary for every negative. It does mean that
if more than one of the operations is required they should
follow one another in an ordered sequence so that they do
not interfere with one another.

PARTIAL REDUCTION OR INTENSIFICATION

In normal reduction and intensification the whole of the
negative image is treated, whereas in chemical retouching
only certain parts of the image are singled out, as for example
in a landscape it may be found that the sky is too dense and
hence would print too light.

To partially reduce this portion of the negative the
procedure is as follows.

Soak the negative for about 10 minutes to swell the
gelatine, and then place it on a white tile, or in a white dish.
Take a paint brush, not too full, of Farmer's reducer (see
page 342), and distribute the Farmer's reducer carefully over
the sky to be reduced. The line where the sky meets the rest
of the picture must be carefully traced and not overstepped.
Care must be taken not to flood the reducer over the negative.
After a fewmoments the negative should be well rinsed and
examined to ensure that action is equal over the desired area.
This should be repeated until the necessary amount of
reduction has been achieved.

Where very small areas in the negative call for reduction
the same procedure can be followed, but a fine camel hair
brush should be used to apply the reducing solution. A useful
tip is to thicken the reducer with glycerine so that it does
not flow so easily and can be more easily confined to the
necessary limits.

In special cases those parts of the negative which are not
to be reduced may be protected by painting with a waterproof
varnish such as shellac. This should be applied, of course, to
the dry negative. When the varnish is dry the negative can be
treated after swelling in a reducer bath, washed and dried and
the protective varnish then removed with benzol or alcohol.

Partial intensification can be carried out by similar means.

355

using the various intensifiers that are normally used (see
page 347).

SHADING AND BLOCKING OUT

This is used for those parts of a negative where the image is
so thin that it will print too dark, and where local intensifica-
tion is not possible, or unlikely to give the desired result.

Solutions of red or yellow dyestuffs are used which tint
the gelatine of the negative and so retard the passage of light.
Such substances are Neo-Coccin, Vanguard yellow, etc.

The art consists in tinting the required part of the negative
perfectly evenly. To this end a very pale solution is used to
begin with; the brush is well filled and applied firmly and
evenly to the negative so that the whole area to be treated
is flooded evenly with the dye solution.

With films the dye may be apphed to the back of the film,
when as in many cases, this carries a gelatine coat. It is not
possible to use this method with unbacked 35 mm. (miniature)
film for miniature cameras. With glass plates the dye is
sometimes apphed to the back but causes trouble when
enlargements have to be made. When it is desired to use the
back of the plate it must first be given a coat of varnish which
can be prepared as follows:

242.

-MATT VARNISH

Ether

Gum sandarac
Gum mastic
Benzol

7 ounces
J ounce
80 grains
3 ounces

175 ml.
18 grams
4 grams
75 ml.

If the ether is quite water free, about 20 minims (1.5 ml.)
of water should be added so as to ensure that the varnish
will dry with a matt surface.

For dealing with quite small areas which require darken-
ing, fine graphite powder can be used, rubbing it into the
matt varnish coating with a leather stumping pencil.

Where there are parts that require a little lightening in
cases where the plate has been given a matt- varnished back,
the varnish can be removed by a knife or by an alcohol
damped stump.

In some cases it is necessary to cut out portions of a
negative so that they do not print at all. This is usually the

356

case with unwanted backgrounds, and the usual method is
to use an opaque medium, such as Photopake, which is
painted either on the face, or more usually on the back of the
negative and so cuts out that part of the negative it covers.
Another method is to use the matt varnish and tint it
strongly with a red, yellow or other dye so that no actmic
light can pass. Such dyes as congo red, quinoline yellow,
malachite green, etc., are used for this purpose, but the
process is only suitable for use with glass negatives from
which contact copies are required.

SPOTTING

Spotting is the name given to the operation of removing or
filling in small spots, flecks or pin holes in the negative. The
procedure naturally depends on the nature of the spot.

Whatever the type of spot the aim is to treat it so that it
is hidden, hence if it be a pin hole in a light part of the
negative, it is spotted out by using special water-colour paint
and a very fine pointed brush. The first step is to ensure that
the tint used is the same shade as that part of the negative
where the spot occurs. This is achieved by a trial or two on
a piece of white paper. Then the spot or pin hole is carefully
touched with the point of the brush, laden with the retouch-
ing medium, until the required density is built up. Photopake
is sometimes used, but the water colour retouching medium
is preferable as Photopake on a thinly covered part of
the negative tends to give a hght coloured spot or area on
prints.

Some workers prefer to do their retouching on the print
and not on the negative, but it is obvious that if many prints
are to be made the retouching should take place on the
negative before printing.

DRY REDUCTION

Reducing normally depends upon chemical action, that is
the solution of part of the silver image, but local reduction
can be carried out by mechanical means, that is by rubbing
down or abrading the heavier parts of the image. Globe
metal pohsh has long been used for this purpose, but if
unobtainable a substitute may be prepared as follows:

357

243.— DRY REDUCER

Paraffin wax I ounce 25 grams

Tallow I i ounces 36 grams

Vaseline 4 ounces 100 grams

Oleic acid 2^ ounces 65 grams

Nitrobenzene 15 minims I ml.

This mixture is melted at as low a temperature as possible
and stirred until thoroughly mixed. Then there is added with
careful stirring and mixing while warm,

Tripoli (Finest Kieselguhr) 10 ounces 250 grams

The tripoli may be replaced by very finely powdered
pumice which has been sifted through fine silk bolting cloth.
Or the pumice powder may be used dry or with the following
medium:

244.— ALTERNATIVE DRY REDUCER MEDIUM
Oil of turpentine 2 ounces 50 grams

Benzene or carbon tetrachloride 2 ounces 50 grams

The application of the abrasive may be made with the aid
of artist's stumps, either of leather or paper, or by using a
pen holder, the rounded end of which has been covered with
linen or wash leather, or for very small areas chisel shaped,
pear or other similar wood tools.

When the reduction is complete every trace of the
abrasive material must be carefully removed with brush and
alcohol or benzol.

KNIFING

This is normally a more drastic method of retouching than
the use of abrasive, for it allows of the complete removal of
part of the image if desired. The retouching knife must have
a razor edge and the edge must be constantly renewed by
the proper use of an oilstone.

Knifing is carried out by making parallel strokes one after
the other until the whole area to be reduced has been covered.
The process is now repeated with the direction of the strokes
at a decided angle to the first set and so on. In this way if the
work is carefully done the individual strokes are quite
imperceptible.

With negatives which have already been reduced with

358

Farmer's reducer the knife sometimes takes badly; in such a
case the area can be lightly rubbed down with Globe metal
polish or similar very lightly abrasive pastes.

PENCIL RETOUCHING

The art of pencil retouching can easily be abused, and its
excessive use has brought discredit on certain branches of
photography in past times. Used with discretion, that is not
for the beautification of a picture but for the correction of
blemishes or errors, it can perform valuable service.

In order that the negative will take the pencil properly,
it is usually necessary to treat it with a varnish. Certain
portrait plates and films are actually supplied with a matt
surface to facilitate retouching, but in the absence of this a
matt varnish must be used.

VARNISHING

One of the most useful is the water varnish made up as
follows:

245.

—WATER VARNISH

Orange shellac

1 J ounces

36 grams

Borax

200 grains

10 grams

Carbonate of soda

40 grains

2 grams

Glycerine

40 minims

2 ml.

Water

16 ounces

400 ml.

The borax and soda are dissolved first in about half the
water, the solution warmed and the shellac added and stirred
until dissolved, which will probably require gentle heating.
Then filter through clean linen and make up to the full
quantity after adding the glycerine.

The negative can be bathed in this varnish and so given
a matt coat, both back and front, which will easily take
retouching.

Some workers prefer a warm alcohol varnish and a useful

one is:

246.— ALCOHOL VARNISH

Bleached shellac (powdered) 8 ounces 200 grams

Gum sandarac 2 ounces SO grams

Gum mastic i ounce 6 grams

Gum dammar Jounce 6 grams

Castor oil 5 drops 5 drops

95% alcohol 80 ounces 2000 ml.

359

When the shellac and the gums are completely dissolved
the varnish must be filtered. Before it is used the plate must
be warmed and sufficient of the varnish poured on to flow
evenly over the surface to be matted, the excess being allowed
to flow back into the varnish bottle from a corner of the plate.

This matt coating can be removed, if necessary, by dis-
solving off with alcohol.

A cold varnish can also be used, namely:

247.— COLD VARNISH

Gum dammar J ounce
Carbon tetrachloride 4 ounces
When dissolved add manilla copal J ounce

6 grams
100 ml.
6 grams

Solution takes some time and is best helped by heating
the mixture in a water bath. The varnish should be filtered
hot. Note that it is not inflammable.

Another cold varnish is prepared by taking:

248.-

-ALTERNATIVE COLD VARNISH

Gum sandarac

2 ounces

SO grams

Benzene

8 ounces

200 ml.

Acetone

10 ounces

250 ml.

Alcohol 95%

4 ounces

100 ml.

Solution can be aided by careful warming in a water bath
and the varnish must be filtered warm. The cold varnishes can
be applied to well dried negatives without their being warmed.

The cold varnishes give a somewhat thinner film than the
warm varnish, but permit of an even heavier retouching being
carried out.

Another type of matting is that which is applied with a
wad of linen and not poured over the negative. These
varnishes have the advantage that they dry very rapidly but
are not particularly suitable for use on negatives which are
to be enlarged.

•49.— NORMAL MATTING VARNISH

Gum dammar
Oil of turpentine

1 ounce
5 ounces

250.— RAPID MATTING VARNISH

25 grams
125 ml.

Gum dammar
Oil of turpentine
Petrol-ether
Oil of lavender

i ounce

3 ounces

30 minims

12 grams

75 grams

2 grams

360

These two varnishes give a very thin matt coating which
will only take very Ught retouching.

When negatives are intended for enlarging the varnish
must be apphed equally over the whole of the negative
surface but, for contact prints only, the varnish can be applied
just where retouching is required.

In addition to providmg a surface which takes retouching
in a satisfactory manner, these varnishes also act as a
protective coating to the negative and preserve it from
scratches or other change.

A simple protective varnish can be prepared from waste
film which has been cleansed free from all gelatine coating
and carefully dried.

2S1.

—CELLULOID VARNISH

Celluloid
Amyl acetate
Acetone

J ounce
4 ounces
4 ounces

6 grams
100 ml.
100 ml.

APPLYING THE VARNISH

For good results to be obtained it is important that varnish
be applied so that an even coat covers the whole of the
negative. The negative is first dusted carefully with a soft
brush, and a small pool of the varnish poured on to the
centre of the plate. By tilting the plate carefully, first one
way and then another, the varnish is caused to flow evenly
over the whole surface. Finally, the plate is tilted so that the
excess varnish flows back into the varnish bottle from the
right lower corner.

To varnish film negative they are first fastened down to a
glass plate with a suitable cement and the process then carried
out as for a glass plate. Note that shellac or gum dammar
varnishes may be used with films, but the celluloid varnish
must not be used as it would attack the film base.

PENCILS FOR RETOUCHING

Pencils of varying hardness are used in retouching. Soft
pencils give dark marking and density, while harder pencils
give lighter eS"ects. As a general rule the pencil chosen for a
particular piece of work should need to go over the area 4-5
times in order to build up the necessary density. The pencil

361

is used to give a stippling effect on the film, £ind both practice
and good judgment are required for success.

If, by chance, too heavy a retouch has been given,
correction can be achieved by removing the blackening with
benzine or turpentine and the area dealt with again.

All retouching work should be carried out on some form
of retouching desk. This consists essentially of a frame (page
329), which encloses a ground glass sheet upon which the
negative is laid. The frame can be set at any convenient angle
and light from a window or other light source is reflected by
a mirror through the ground glass screen. If artificial light is
used, the mirror should be covered by a white card or sheet
of paper to diffuse the Ught.

362

Processing Colour Films

Practically all modern colour films rely on the formation of
dye images in three separate emulsion layers by a process of
chromogenic development similar to that described on page
223. Before giving details of processing procedures for colour
films it is advantageous to outline the basic principles upon
which modern colour films are based.

Modern colour materials utilise the subtractive principle of
colour reproduction which is the reproduction of colours by
the formation of various amounts of cyan, magenta, and
yellow dyes in three separate red, green and blue sensitive
emulsion layers. Cyan, magenta and yellow are the subtractive
primaries and are equivalent to minus red minus green, and
minus blue respectively:

Minus red = cyan (blue + green)
Minus green = magenta (blue + red)
Minus blue = yellow (green + red)

The diagrams on page 365 show these subtractive primaries
together with the composition of white light and the additive
primaries (red, green and blue).

The subtractive primaries are used in modern colour
material because they possess the property that they can be
superimposed in all possible combinations to form an infinite
range of colours, whereas the additive primaries do not have
this property (see page 366). Thus :

Red = magenta + yellow (white minus green and minus blue)
Green = cyan + yellow (white minus red and minus blue)
Blue = cyan + magenta (white minus red and minus green)

Most modern colour photographic materials are in the
form of an integral tripack (see diagram on page 367) which
consists of a blue sensitive layer that records the blue portions
of the original scene as a yellow image, a green sensitive layer
that records the green portions of the original scene as a

363

magenta image, and a red sensitive layer that records the red
portions of the original scene as a cyan image. Integral tripacks
also contain a yellow filter layer immediately below the top
blue sensitive layer to filter out blue light to which the green
and red sensitive layers are also slightly sensitive. The procedure
described above and illustrated on page 367 results in the
formation of a colour negative, because the colours in the
negative are complementary to those of the original scene. It
can be worked out from the various colour equations given
previously that if a colour negative is printed on to a similar
tripack material coated on paper a positive print will be
formed : e.g. consider the reproduction of a red : this will be
recorded in the negative as a cyan (blue + green) image which
on printing will expose the blue and green sensitive layers of
the paper to form yellow and magenta images (minus blue
and minus green, i.e. red).

Reversal processing, however leads directly to a positive
transparency as shown in the diagram on page 368.

With negative colour films, the processing is comparatively
simple and can be carried out with the same equipment as for
black and white materials. Colour processing, however,
requires much stricter control of processing conditions than
black and white processing. Development temperature must
be maintained within very close limits (±i°C.), pH values of
the processing solutions must be kept within the specified
values and development times must not be altered from those
recommended by the manufacturer.

The processing of reversal colour film requires more steps
leading to a positive transparency. The procedure is straight-
forward and can also be carried out with the same equipment
as used for black-and-white material. The main points to
watch are also temperatures and times, and the instructions
given by the manufacturers must be carefully followed.

"official" and "substitute" formulae

Amateurs who prefer to make up their own solutions will find
this a straightforward job in black-and-white photography.
There is no doubt as to the choice of the formula as all manu-
facturers have published the most suitable formulae for their
products. Besides, in nearly all cases it is possible to use
universal formulae suitable for a wide range of makes of film.

364

WHITE LIGHT, THE ADDITIVE AND
SUBTRACTIVE PRIMARIES

500

600 700

Wavelength(n.m.)

^^^1

V= Violet B=Blue G=Green Y-- Yellow 0=Orange
R=Red

1 : The approximate distribution of colours in the visible spectrum.

2: The visible spectrum can be divided into three equal regions of blue,

green and red known as the additive primaries.

3-5: Subtracting each additive primary colour in turn from the visible

spectrum gives the subtractive primaries. Thus: minus blue appears

yellow (3), minus green appears magenta (4), and minus red appears

cyan (5).

365

SUBTRACTIVE COLOUR SYNTHESIS

The above diagram shows that superimposition of the subtractive pri-
maries) yellow, magenta, and cyan) can form red, green, blue, and black.

366

FORMATION AND APPEARANCE OF A
COLOUR NEGATIVE

BL R G

C M Y W

i i ^ ^

i i i ^'

Yellow

Magenta

^^S^

Cyan

1 : The original, consisting of areas of black (BL), red (R), green (G),

blue (B), cyan (C), magenta (M), yellow (Y), and white (W)-

2: The integral tripack negative material consisting of: a blue sensitive

layer (a) containing a yellow coupler, a yellow filter layer (b), a green

sensitive layer (e) containing a magenta coupler, and a red sensitive

layer (d) containing a cyan coupler, coated on a film base (e).

The yellow filter layer (b) is present to filter out blue light to which the red

and green layers (c and d) are also slightly sensitive.

The shaded portions represent the formation of dyes in the appropriate

layers after exposure, colour development and removal of the silver images.

3 : The appearance of the negative which is complementary in both hue

and tone to the original. Colour negatives generally have an orange cast

which is the colour of the mask used to correct for dye imperfections and

ultimately lead to more faithful colour reproduction at the printing stage.

367

FORMATION AND APPEARANCE OF A
COLOUR POSITIVE TRANSPARENCY

BL R G B C IVI Y W

WKK^^M WH

—■^—^^^8

I i iTT'i 1 1

BL R G B C M Y W

Yellow

Magenta

[, ,s,>\-$<; Cyan
■.\\\\\\]

1 : The original.

2: The integral tripack after exposure and the first black and white

development stage.

3 : The integral tripack after the colour development stage and removal

of the silver image.

4 : The appearance of the colour transparency.

Explanations of the symbols used in the above diagram can be found on p.367.

368

In colour photography, the situation is rather different.
First, only a few manufacturers have pubhshed processing
formulae; most recommend the use of the chemicals packed
by them or the return of the films to them or other processing
stations. Secondly, colour materials of various makes are so
different in their characteristics that universal formulae can
be used only to a very limited extent.

These facts have to be borne in mind when using the
information published in this chapter. Formulae which have
been officially published by the manufacturer are marked as
such. In most cases, however, the reader will have to make
use of "substitute" formulae as published by various experts
or by the author.

Colour processing with independent formulae is thus
more in the nature of an experiment than a standardised
technique. Excellent results can be obtained provided that the
job is tackled systematically and adjustments to the suggested
procedure are made when necessary. For this reason, we have
endeavoured to give some idea of the action of the various
components in the more important formulae and of the effect
of variations in composition and processing times.

COLOUR NEGATIVE FILM

The first step in processing colour negative film is colour
development. This produces a dyestufiF image together with a
silver image in each layer.

Then follows an intermediate step to stop development
and remove developer and by-products. This can be done
simply by prolonged washing, but a definite after-development
effect takes place during washing. In some processes this effect
is made use of to complete development, mainly in the bottom
layers of the film, and to get a good colour balance. If a stop-
bath is used, the development is interrupted immediately, and
the removal of certain by-products becomes easier. The washing
time can therefore be reduced. In other processes a combined
stop-fix bath is used, usually with a hardening agent.

The first cumulative stage of the processing procedure,
i.e. the production of the colour "picture" by the developer
and subsequent operation — stop bath and/or wash — must be
considered as a sequence specific to individual makes and
cannot be replaced by any sort of universal treatment.

369

The next operation is the removal of the unwanted silver
image (and the unchanged silver halide, if no fixing agent has
been used in the stop-bath). The traditional method is to use
a potassium ferricyanide bleach bath followed by a fixing
bath. An alternative is a combined bleach-fix solution in
which the ferricyanide is replaced by organic iron com-
pounds. Bleach-fix solutions of this type have good keeping
properties and less tendency to stain than ferricyanide
solutions. They are very useful for processing colour paper
but not recommended for film. The processing is finished as
usual by a thorough wash.

It is not possible to use one and the same formula for all
types and makes of colour film. Better results can be obtained
by adapting the formula to the film as suggested later on. The
other stages of the process are less critical and it is possible to
use universal formulae for different makes of colour film.

COLOUR DEVELOPMENT

The most usual developing agents are salts of diethyl-p-
phenylenediamine (4-amino-N,N-diethylanline) or derivatives.
There is quite a choice of agents of these types :

LIX.— COLOUR DEVELOPING AGENTS

Chemical Names

Trade Names

Diethyl-p-phenylenediamine sulphite
N,N-Diethyl-p-phenylenedlamine sulphite
p-Diethylamlnoaniline sulphite
4-Amino-N,N-diethylaniline sulphite

Genochrome
(May & Baker)

Activol No. 1
(Johnsons)

Names as above but hydrochloride or sulphate

Activol No. 6 or
Activol No. 7
(Johnsons)

Ethylhydroxyethyl-p-phenylenediamine sulphate Droxychrome

N-Ethyl-N-hydroxyethyl-p-phenylenediamine sulphate (May & Baker)

p-Ethylhydroxyethylaminoaniline sulphate Activol No. 8

4-Amino-N-ethyl-N-(^-hydroxyethyl)aniline sulphate (Johnsons)

N,N-Diethyl-3-methyl-p-phenylenediamine Tolochrome

hydrochloride (May & Baker)

2-Amino-5-diethylaminotoluene hydrochloride Activol No. 2

4-Diethylamino-o-tolurdine hydrochloride (Johnsons)

4-Amino-N,N-diethyl-3-methylaniline hydrochloride CD2 (Kodak)

N-Ethyl-3-methyl-N-(j3-methylsulphonamidoethyl)-p- Mydochrome

phenylenediamine, sesquisulphate (May & Baker)

4-Amino-N-ethyl-N-(j3-methylsulphonamldoethyl)-m- Activol No. 3

toluidlne, sesquisulphate (Johnsons)

4-Amlno-N-ethyl-3-methyl-N-(;3-methylsulphonamido- CD3 (Kodak)
ethyl)aniline sesquisulphate

370

To simplify things we shall refer in all formulae not to the
chemical name but to the trade names.

In addition to one of these agents the colour developer
contains a large amount of alkali, such as potassium carbonate
sodium metaborate, or trisodium phosphate and usually a
small amount of sodium sulphite to improve keeping properties.
Further ingredients are hydroxylamine hydrochloride as an
anti-stain agent, potassium bromide or iodide as an anti-
fogging agent, and calgon as water softener.

LX.— COLOUR NEGATIVE DEVELOPERS*

252

253

254

Kodak

Agfa

3A1(Ferronio)

Benzyl alcohol

8.5

1S*»

Calgon, sodiunn hexameta-

phosphate or tripolyphosphate

—

Sodium metaborate, cryst. or

Kodalk

—

Trisodium phosphate, cryst.

—

Hydroxylamine hydrochloride

—

1.4

—

Sodium sulphite, anhyd.

2.5

Potassium carbonate

—

Potassium bromide

1.5

2.5

1.5

Potassium iodide, 1% solution

—

CD3, Mydochrome or Activol

No. 3

7.8

—

7.8

Activol No. 7

—

Water to

1000

10.5-10.6

11.0-11.3

10.5-10.7

♦These substitute formulae are suitable for colour negative films of th
manufacturer indicated under the formula number and are those published
in The British Journal of Photography Annual (1971).

**3S% solution: 35 grams benzyl alcohol, 45 ml. diethylene glycol
made up to 100 ml. v/ith v^ater.

Notes: It is best to make up the stock solution containing all
the ingredients, except the developing agent, in slightly less
than 1000 ml. and shortly before use add the developing
agent and make up to 1000 ml. The developing agent of
Formula 253 tends to form oily droplets when added to the
remainder of the developer. It is recommended that this
developing agent be dissolved in 20 ml. of water prior to its
addition to the developer with constant stirring .

STOP-BATH

As in black-and-white processing the stop-bath for negative
colour film is a weakly acid solution, but the pH value must

371

be more carefully adjusted and controlled. The acid is usually
acetic acid sometimes with addition of sodium acetate to
increase the pH value to between pH 5.0 and 6.0. As mentioned
above, in some cases an addition of fixing and hardening
agents is reconmiended and Tables LIII and LXV list a number
of such variations of stop-bath formulae. Formula 255 is a
typical stop-bath recommended by E. Gehret for Kodak and
3M colour negative films.

255.— STOP-BATH FOR COLOUR NEGATIVE FILMS (E. GEHRET)
Glacial acetic acid 20 ml.

Sodium sulphite, anhyd. 10 grams

Water to 1000 ml.

pH 4.3-4.7

256.— INTERMEDIATE BATH FOR AGFACOLOR CNS
AND CN17 FILMS
Magnesium sulphate, cryst. 30 grams

Colour developer (Formula 253) 30 ml.

Water to 1000 ml.

pH 10.2-10.5

HARDENING-BATH

After development has been stopped it is normal procedure to
use a hardening-bath to reduce the possibility of damage to
the emulsion during subsequent processing stages. A typical
hardening-bath based on formalin is as follows :

257.— HARDENER FOR COLOUR NEGATIVE FILMS (E. GEHRET)

Formalin 20 ml.

Sodium carbonate, anhyd. 10 grams

Water to 1000 ml.

pH 10.4-10.8

BLEACH- AND FIXING-BATHS

Generally potassium ferricyanide is used together with
bromide and various pFI controlling agents as a bleach-bath
(see Table LXI) followed by fixing in sodium or ammonium
thiosulphate (Table LXII). The main function of the ferri-
cyanide-bromide bleach is to convert the silver image, formed
together with the dye image in colour development, to silver
bromide which can be removed by fixing.

372

LXI.— BLEACH-BATHS FOR COLOUR NEGATIVE FILMS*

258

259

260

Kodak

Agfa

3M(Ferrania)

Potassium nitrate, cryst.

Potassium ferrocyanide

Potassium ferricyanide

112

Potassium bromide

Monosodium phosphate,

hyd.

—

Boric acid

—

Disodium phosphate, cryst.

—

Borax, cryst.

—

Sodium thiocyanate

—

Water to

1000

6.6-7.0

5.8-6.2

6.6-6.8

♦Substitute formulae: British Journal of Photography Annual (1971).
LXII.— FIXING BATHS FOR COLOUR NEGATIVE FILMS*

261

262

263

Kodak

Agfa

3M{Ferrania)

Ammonium thiosulphate

120

—

100

Sodium thiosulphate, cryst.

—

200

—

Potassium metablsulphite

—

Sodium sulphite, anhyd.

—

Water to

1000

4.4-4.6

8.0-9.0

4.4-4.8

♦British Journal of Photography Annual (1971).

The pH value of the bleach-bath is critical for Agfacolor
CNS films because mask formation for the cyan layer occurs
in this bath unlike Kodak and 3M colour negative materials
in which masking occurs in the development stage. Kodak
and 3M materials use coloured couplers, i.e. the mask is
already present and is destroyed where colour development
takes place.

Combined bleach-fix solutions simplify the process but
such solutions prepared by mixing hypo with ferricyanide
(Farmer's reducer, Formula 220) have very limited keeping
properties. One method of making up a bleach-fix solution is
based on the use of iron-EDTA (ethylenediaminetetracetic
acid) complex with hypo. These solutions are however slower
working than those based on ferricyanide and it is difficult to
estimate the progress of bleaching by visual inspection. The
average time of treatment is 10 minutes but they are recom-
mended for prints while for negatives the formulae based on

373

ferricyanide (Table LXI) are preferable. Two typical bleach-fix
formulae are:

264.— BLEACH-FIX BATH (G. THEILGAARD)

Sodium hydroxide

Etiiylenediaminetetraacetic acid

Ferric chloride, cryst.

Hypo cryst.

Sodium sulphate, anhyd.

Water to make

410 grains
730 grains
455 grains
6^ ounces
260 grains
43 ounces

23.5 grams
42 grams
26 grams
160 grams
15 grams
1000 ml.

This solution should have a pH of 7.0.

265.— BLEACH-FIX BATH (H. GORDON)
Ferric salt of ethylenediaminetetra

acetic acid ("Iron-Sequestrene") 2i ounces 60 grams

Sodium carbonate, anhyd. 88 grains 5 grams

Potassium bromide I jounces 30 grams

Sodium thiosulphate (hypo) anhyd. 5| ounces 140 grams

Potassium thiocyanate 175 grains 10 grams

Water to make 40 ounces 1000 ml.

After the bleach-fix process follows a thorough washing.
When no hardening agents have been used in the processing
solutions, it may be advisable to apply a hardening solution
containing 2% formahn and 0.3% sodium carbonate
(anhydrous) for about 5 minutes, followed by a short wash.

COLOUR REVERSAL PROCESSING

The steps in processing a reversal colour film are :

The film is first developed in a black/white negative
developer producing a negative silver image. After several
intermediate steps such as treatment in stop and hardening
solutions, the unaffected silver salts are re-exposed to a strong
light source. Then follows colour development where the re-
exposed silver salts are reduced to silver, and dyes are simul-
taneously produced in the three layers. There may again follow
intermediate treatment in hardening and stop solutions, and
in the next step all the silver is removed, leaving only the dyes
and silver halide which is dissolved in the usual way with a
hypo solution. The majority of the formulae in this section are
those devised by E. Gehret and are given in the British Journal
of Photography Annual 1971.

374

LXIII.— COLOUR NEGATIVE PROCESSING PROCEDURES
Processing Steps and Formulae (firit. J. Phot. Annual 1971)

Kodak

Agfa

3A1 (Ferronia)

Kodacolor X,

Agfacolor CNS.

Color

Ektacolor

CN17

Colour Developer

No. 252,

No. 253,

No. 254,

14 min.,

8 min.,

14 min.,

24 + 0.3X.

20 + 0.2°C.

24 + 0.25X.

Intermediate or

No. 255,

No. 256,

No. 255,

Stop-Bath

4 min..

4 min.,

4 min..

20-24X.

20±0.2°C.

22-26° C.

Hardener

No. 257,
4 min.,
20-24°C.

No. 257,
4 min.,
22-26°C.

Wash

4 min.,

15 min..

4 min.,

20-24°C.

14-20°C.

18-24°C.

Bleach

No. 258,

No. 259,

No. 260,

6 min..

5 min..

6 min..

20-24X.

20 + 0.5°C.

22-26°C.

Wash

4 min..

5 min..

4 min..

20-24X.

14-20°C.

18-24X.

Fix

No. 261,

No. 262.

No. 263,

8 min..

5 min..

4-8 min..

20-24°C.

18-20°C.

22-26°C.

Final Wash

8 min..

10 min..

8 min..

20-24°C.

14-20°C.

18-24X.

Wetting Agent

1 min..

i min..

1 min..

20-24°C.

14-20°C.

18-24X.

10.

Drying

Max. 49°C.

Max. 35X.

Notes: Continuous agitation for the first 15 seconds, followed
by agitation for 5 seconds every minute is recommended in
the colour developer and in the other solutions.

Processing may be continued in room light after step 3 for
the Kodak and 3M processes and after step 5 for the Agfa
process.

FIRST DEVELOPMENT

The choice of the first developer for reversal films depends
on the make of the film: there is no universal formula.
Certain features are, however, common to these developers.
First, they all possess a very high development energy and are
used more concentrated than for normal black-and-white
development. They also contain more alkali.

Secondly, the M.Q. types contain a low concentration of
thiocyanate which dissolves silver hahde and it therefore
helps to produce transparencies with clear whites by removing

375

any excess of silver halide. Most of these developers are of
the M.Q. type.

The M.Q. developers require either an efficient stop or a
combined stop-hardening bath (Table LXV) after development
and then a short wash.

LXIV.— FIRST DEVELOPERS FOR COLOUR REVERSAL PROCESSES*

266

267

268

269

270

Kodak

Agfa

Ansco

£3

£4

RC131

Calgon, sodium

hexametaphosphate or

tripolyphosphate

—

Metol

3.5

—

2.8

Sodium sulphite, anhyd.

Phenldone

—

0.8*

Hydroquinone

Borax, cryst.

—

Sodium metaborate.

cryst.

—

Sodium carbonate, anhyd.

Trisodium phosphate.

cryst.

—

Potassium bromide

2.5

Sodium thiocyanate

1.3

1.8

0.7

Sodium hydroxide

—

0.8

—

Potassium iodide.

1% solution

6-Nitrobenzimldazole

nitrate 0.2% solution

—

Water to

1000

9.9-10.0

10.1-10.3

9.4-9.6

10.1-10.3

♦British Journal of Photography Annual (1971).
**Dlssolve in 50 ml. of warm water (80°C.) then add to the solution.

Phenidone (0.5 grams) may be used in place of metol in the
Kodak E3 Formula 266.

Because of the high temperatures (29°C.) and high pH
values used in the Kodak Ektachrome E4 process (Formula
267) a pre-hardening bath is required together with a neutraliser
before the first development is started :

271.— PRE-HARDENER FOR EKTACHROME E4 PROCESS

(E. GEHRET)

Sodium or potassium bisulphate 0.8 gram

2,5-Dlmethoxytetrahydrofuran 5 ml.

Sodium sulphate, anhyd. 136 grams

Formalin 35 nil.

Potassium bromide 16 grams

Water to 1000 ml.

pH 4.9-5.0

376

Note: 2,5-Dimethoxytetrahydrofuran is readily absorbed by
the skin and has a harmful vapour. This compound should be
used in a well-ventilated room and contact with the liquid
should be avoided.

272.— NEUTRALISER FOR EKTACHROME E4 PROCESS

(E. GEHRET)

Glacial acetic acid 1.5

ml.

Sodium acetate, cryst. 24

grams

Potassium bromide 17

grams

Sodium sulphate, anhyd. 25

grams

Potassium metabisulphite 30

grams

Water to 1000

ml.

5.1-5.2

LXV.— STOP AND HARDENING BATHS FOR COLOUR
REVERSAL PROCESSES*

273

274

275

276

277

Kodak

Agfa

Ansco

£3

£4

VC233

Sodium acetate, cryst.

5.3

Glacial acetic acid

—

Potassium alum

—

Chrome alum

—

Sodium or potassium

bisulphate

—

— ■

—

Potassium metabisulphite

—

Boric acid

— .

—

Water to

1000

3.3-3.7

3.4-3.6

5.0-5.4

4.0-4.5

4.0-4.4

♦British Journal of Photography (1971).

COLOUR DEVELOPMENT

Before the film can be colour developed, it has to be re-
exposed. This is usually carried out at a distance of about
3 feet from a Photoflood lamp for 3 minutes, \\ minutes on
each side. The film must be completely re-exposed.

The Kodak E4 process uses a colour developer that con-
tains a chemical fogging agent (t-butylaminoborane) and
requires no re-exposing. This compound is, however, extremely
toxic and all contact and inhalation of the vapour must be
avoided. In the substitute formulae given here (No. 279)
t-butylaminoborane may be omitted provided that the film is
re-exposed to white hght in the normal manner.

The composition of the colour re-developer is similar to

377

the formulae for negative film (pages 223-226), but in most
cases a colour developer of higher energy is used, i.e. devel-
opers containing an alkaU hydroxide or a tri-alkali phosphate
or a so-called "accelerator". Some of the colour developer
formulae given (Table LXVI) also contain: citrazinic acid

LXVI.— COLOUR DEVELOPERS FOR REVERSAL PROCESSING*

278

279

280

281

282

Kodak

Agfa

Ansco

£3

£4

RC125

Sodium sulphate.

—

100

anhyd.

Sodium metaborate,

cryst.

—

Calgon, sodium

hexametaphosphate

or trlpolyphosphate

—

Trisodlum phosphate,

cryst.

—

Sodium carbonate.

anhyd.

—

Sodium hydroxide

5.6

0.2-2t

Potassium carbonate.

anhyd.

—

Ethylenediamine

sulphate

7.6

Benzyl alcohol

10**

t-butylaminoborane

0.1

Citrazinic acid

1.3

Hydroxylamine

hydrochloride

—

2.2

EDTA tetrasodium

—

^-Phenylethylamine

—

Sodium sulphite.

anhyd.

—

2.5

Potassium bromide

—

0.2

1.2

Potassium iodide.

0.1% solution

CD3, Mydochrome or

Activol No. 3

—

Droxychrome or

Activol No. 8

—

Dlethyl-p-phenylene-

dlamlne sulphate

—

2.8

Water to

1000

11.4-11.6

11.8-12.0

10.7-10.9

11.0-11.2

10.7-10.9

•British Journal of Photography Annual (1971).
**35% solution see Table LX.
fAdd to adjust pH to the required value.

Notes: Extreme caution should be exercised in the preparation
and use of the solutions. All contact with skin by the processing
solutions and the individual ingredients should be avoided.

387

(2,5-dihydroxy-wo-nicotimc acid) to prevent excessive contrast
of the dye image, EDTA (ethylenediaminetetracetic acid) as an
accelerator, benzyl alcohol to aid diffusion of the developing
agent or its oxidation products to the site of couphng, and the
usual restrainers and antifoggants. The time of colour develop-
ment is generally 10-20 minutes.

In all cases it is necessary to put the film after development
through stop and hardening baths or combined solutions
(Table LXV) and it must then be thoroughly washed.

The removal of silver is carried out in bleaching solutions
containing potassium ferricyanide, in most cases in mixture
with potassium bromide (Table LXVII). These solutions
convert the black metallic silver produced in the first developer
as well as in the colour developer into silver bromide which is
then removed by a 20% solution of hypo (see Table LXVIII).
A final wash of about 20 minutes finishes the process.

LXVII.— BLEACH-BATHS FOR COLOUR REVERSAL PROCESSING*

283

284

285

286

287

Kodak

Agfa

Ansco

£3

£4

VC212

Potassium ferricyanide

112

Potassium ferrocyanide

—

Potassium bromide

Disodium phosphate, cryst.

—

Monosodium phosphate,

anhyd.

—

Sodium acetate, cryst.

—

Boric acid

—

Potassium alum

—

Sodium or potassium

bisulphate

—

Sodium thiocyanate

—

Sodium carbonate, anhyd.

—

Water to

1000

—

6.6-6.7

5.0-5.4

—

5.1-5.2

♦British Journal of Photography (1971).

All these bleach-baths are based on ferricyanide-bromide
and vary only in buffering salts and hardeners.

The formulae for bleach- and fixing-baths given in Tables
LXVII and LXVIII are those that have been found to work
best for the particular type of film being processed. For reversal
processing the steps following colour development are less

379

LXVIII.— FIXERS FOR COLOUR REVERSAL PROCESSING*

288

Kodak

£3

289

Kodak
£4

290
Agfa

291

FC200

292

Ansco

Sodium thiosulphate, cryst. 160 — 200 200 150

Ammonium thiosulphate — 120 — — —

Formalin — — — — 25

Potassium metabisulphate 10 20 — — —

Sodium sulphite, anhyd. — — 10 — 10

Boric acid — — — — 10
Monosodium phosphate,

anhyd. 4.5 — — — —

Water to 1000 1000 1000 1000 1000

pH 4.4-4.8 4.5-4.9 6.0-7.0 7.0-8.0 9.3-9.7

* British Journal of Photography Annual (1971).

critical than those in colour negative processing and some
interchangeability of these solutions is possible as the main
requirement is that the removal of silver and unchanged
silver halides is complete. Care should be exercised in inter-
changing solutions because some contain hardening agents
and others do not and different types of films may require
different bleach and fixer formulations to ensure that these
processes go to completion.

Table LXIX summarises the processing steps and formulae
recommended for various types of reversal films.

After the final wash a stabilizer-wetting agent solution
(Formula 293) is generally used which contains formaldehyde
as the stabilizing and hardening agent and a 10% solution of
any of the following wetting agents to speed drying and to
avoid drying marks:

Aerosol OT (Cyanamid)
Tergitol 7 (Union Carbide)
Tergitol NPX (Union Carbide)
Invitol (Ciba)

293.— STABILIZER BATH (E. GEHRET)

Wetting agent, 10% solution 5-10 ml.

Formalin 5.10 ml.

Water to 1000 ml.

GENERAL SUMMARY OF OPERATIONS FOR COLOUR
PROCESSING

In colour processing the essential steps are those connected
with the actual production of the picture, i.e. the colour

380

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381

development itself and also the black-and-white (first) develop-
ment for reversal materials. As indicated before, there are no
universal formulae for these steps, and it is imperative to use
the formulae recommended for the make of film in question.

The subsequent operations — stop-bath and/or wash — are
also a sequence specific to individual makes and should not
be altered, either. They are especially critical in processing
negative colour films where the step after development is
either a stop-bath or an extended wash, and one cannot
replace the other. The purpose of a wash of 15 minutes or so
is not only to remove developer and by-products from the
film, but at the same time to allow a considerable degree of
after-development to take place. This is essential to achieve
the colour balance of the negative. On the other hand, in cases
where a stop-bath is stipulated, one would again seriously
interfere with the colour balance of the negative by omitting
it and just carrying on with a wash.

As was mentioned earlier the steps after that are critical
for some types of colour negative film (especially Agfa) as
the mask is formed in the bleach-bath. Otherwise, the main
function of the processing steps following colour development
is to remove the "unwanted" products — silver and unchanged
silver hahde.

Here then is a summarised sequence of operations for
colour negative films and the approximate times for each
step:

(1) Colour development (see Table LX) as recom-
mended for the individual material.

(2a) Rinse, stop-bath or stop-fix bath (see Formula 255)
for 5 minutes and a 5-minute wash; or

(2b) Extended wash as recommended for the film used.

(3) Bleach or bleach-hardener (Table LXI) for 5-10
minutes.

(4) Wash for 5 minutes.

(5) Fix in 20% hypo cryst. (see Table LXII) for 5-10
minutes.

(6) Final wash for 10 minutes.

For colour papers the procedure is basically the same
with the main diff"erence that steps 3, 4, and 5 can be replaced
by a combined bleach-fix (see page 374).

382

This is the sequence for colour reversal films:

(1) First development (see Table LXIV) as recom-
mended for the individual film.

(2a) Rinse, stop-bath and hardener (see Table LXV) for
5 minutes, wash of 5 minutes, or

(2b) Extended wash.

(3) Re-exposure.

(4) Colour re-development (see Table LXVI) as recom-
mended for the film used.

(5) Rinse, stop-bath (see Table LXV), and wash for 5
minutes.

(6) Bleach or bleach-hardener (Table LXVII) for 8-10
minutes.

(7) Wash for 5 minutes.

(8) Fix in 20% hypo cryst. (see Table LXVIII) for 5
minutes.

(9) Final wash for 15 minutes.
(10) Stabilizer for 1 minute.

In reversal processing the steps following the colour
development are less critical than in the processing of
negative colour films.

383

Quality Control

For the photofinisher it is of primary importance that negatives
are uniformly and correctly processed. Unless film development
is controlled within carefully defined limits, consistent print
quality is not possible. Moreover, uniform negative develop-
ment is important to operating costs ; it reduces the number of
reprints and economises on the usage of chemicals. Correct
development also helps to retain the usefulness of many
underexposed or overexposed negatives, resulting in a greater
number of acceptable prints.

Control of development involves time, temperature,
agitation and development activity. All of these effect, as we
know from previous chapters, the overall density and contrast
of the negatives. Although the average degree of replenishment
recommended for tank development (see page 76) keeps the
activity of the solution reasonably constant, variable factors
such as considerably different carry-over rates from plant to
plant make it necessary to test the activity of the developer at
regular intervals throughout its life. For this purpose, test
strips are supplied. These are pre-exposed strips of film with
either two control spots or a number of density steps. They are
developed at regular intervals together with negatives and then
measured with a densitometer. The result gives a numerical
measure of the activity of the developer from which the
necessary degree of replenishing can be deduced.

PROCESS CONTROL CHART

The test strips should be processed in the middle of a batch of
films, if possible in the same position in the tank each time, as
this represents the average development conditions for the
films. After processing of the strip the densities of the low
density spot and the high density spot are measured with a
densitometer. Subtraction of the low density value from the

384

PROCESS CONTROL CHART

09-
3-

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is.

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13 16 19 22 25 28 31

DATE
(Month:

The broken horizontal lines U.C.L. and L.C.L. represent the upper
control limit of 0-85 and the lower control limit of 0-70.

The centre broken line shows the acceptable scatter of a process under
control and no action is necessary.

The top full line shows that development activity is increasing and on
the 13th of the month remedial action must be taken. The replenisher was
therefore diluted and thereafter the process shows an acceptable random
scatter. Conversely the bottom full line illustrates a decreasing developer
activity which on the 10th day the replenisher was made more concentrated
and thereafter the process is once more showing the normal scatter.

It is generally recommended that the developer activity is adjusted by
varying the replenisher dilution rather than by adjustment of time or
temperature of development as trends are cumulative.

385

high density value gives a figure which must be within the range
defined by the manufacturer (0.70-0.85 for the Kodak DN-13
system). This gives an approximate measure of the contrast.
The figures obtained from control strips processed at various
intervals of time (such as twice a week) are plotted against
time to give a process control chart. It is of the utmost im-
portance to take remedial action as soon as a discernible
upward or downward trend is shown in the process control
chart. If the process exceeds the control Umits (set by the
manufacturers) it is too late to take action and the process has
got out of control with the result that many negatives are
ruined. The accompanying process control chart shows when
and where action should be taken (page 387).

COLOUR PROCESS CONTROL

The control of colour negative processing is much more com-
plicated since there are at least six stages (see page 375) as
opposed to three for black and white processing. Also a colour
negative has three colour images containing magenta, cyan and
yellow dyestuff"s requiring measurements of densities through
green, red and blue filters of the densitometer. For quality
control of a colour negative process (e.g. Kodak C-22) three
density patches are generally used each read through the three
filters of the densitometer (nine readings). These three density
patches correspond to a high density (HD) a low density (LD)
and a minimum density (D-min.). HD minus LD gives an
approximate measure of the contrast, LD gives an approximate
measure of the speed and D-min. gives an approximate mea-
sure of the fog for each of the three layers. In practice
these readings obtained from the control strip, developed
with the films, are subtracted from HD minus LD, LD and
D-min. values obtained from a control strip processed by the
manufacturer and supplied with the un-processed control
strips. This gives either positive or negative values which are
then plotted against the date on the process control chart.

The action required to be taken by the process controller
when the control is about to be (or is) exceeded is very complex
because of the number of solutions and variables. The reader
is therefore recommended to consult the manufacturer's
booklet on process control for the particular film types being
processed (Kodak C-22, Ferrania NM-64, etc.).

386

COLOUR PROCESS CONTROL CHART

CONTROL NUMBER 1

CONTRAST
(HD Minus LD)

RED-oeol

GREEN- O60I

BLUE-O60J

SPEED
(LD)

RED- 0-60

GREEN- 0-95

BLUE- 131

FOG
(D-Min)

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The above diagram represents a typical colour process control chart
(Kodak C-22 process).

23* 387

Preserving the Negative

Negatives are valuable. They are originals and frequently
irreplaceable. As they also tend to be fragile and easily
marked, they must be stored in a maimer that protects them
from physical, chemical and atmospheric damage.

PLATE AND FLAT-FILM NEGATIVES

These are best stored in transparent envelopes of parchment
or Cellophane, upon which a consecutive number is marked
or sufficient detail to identify the negative by. The envelopes
with their negatives can be kept in plate or film boxes which
bear on their cover details of the contents, or the boxes may
be stacked in book-form on shelves and have labels on their
ends. The orderly and precise worker will have a catalogue
of his negatives which will contain their consecutive number
and description.

A much more costly method is to keep the negatives
in racked wooden boxes, but this usually involves more
room, as well as expense, than the average photographer
desires to afford.

ROLL-FILM NEGATIVES

In roll form, films are almost certain to suffer damage and
they may also collect dust and grit. They should therefore
always be preserved flat — cut either into single negatives or,
in the case of 35 mm. films, into five or six negatives at most.

Here again parchment or Cellophane envelopes should be
used, marked with the negative number or detail and pre-
served in larger envelopes or in boxes.

All negatives should be kept in suitable conditions. That
is in a dry, cool place not subject to any wide variations of

388

temperature and well clear of any fumes from fireplaces, gas
fires or the like.

CLEANING FILM

Dirty and dusty or greasy film can be cleaned:

294.— FILM CLEANER

Acetic acid I njrt

Vaseline 5 parts

Carbon tetrachloride 100 parts

The solution is applied either with chamois leather or
viscose sponge. Shake the solution well before using it. The
film is lightly rubbed with the solution, being careful not to
exert any serious pressure. After about 10 minutes the film
is then dried with a soft clean chamois leather xmtil every
perceptible trace of the cleaner is removed, and the film
appears quite dry.

DEALING WITH SCRATCHES AND ABRASIONS ON FILM

The trouble can be overcome comparatively simply so that
the scratches are rendered imperceptible. The method con-
sists in coating the film with a thin solution of gelatine which
fills in the scratches and renders them incapable of affecting
the optical properties of the film during printing.

295.

-ANTI-SCRATCH SOLUTION

Water

Chloral hydrate
Gelatin

20 ounces

2 ounces

i ounce

500 ml.
50 grams
12.5 grams

The chloral hydrate is dissolved first, then the gelatin, in
small pieces, is allowed to swell in the cold and when swollen
the whole is warmed on a water bath and stirred until
solution is complete.

The temperature should not exceed 140°F. (60°C.).

The solution, which has reasonably good keeping pro-
perties, should be used at about room temperature.

389

Dark-Room Hints

ANTIDOTES FOR POISONS

Against Acids: Alkaline drinks, i.e., sodium bicarbonate,
magnesium carbonate or a suspension of magnesium oxide.
If these are not available, then quantities of warm water to
induce vomiting. Milk and oil may also be used.

Acid splashes in the eyes: Wash with warm water or with
very dilute sodium bicarbonate solution.

Against Caustic Alkalies: Drink strongly diluted vinegar
of citric acid or apple juice. Suck pieces of ice. Milk or oil
may be drunk.

Alkali splashes in the eyes: Wash with water or very dilute
boric acid.

Gas Poisoning: Fresh air, remove constricting clothing,
artificial respiration.

Mercury Poisoning: Milk and white of egg.

PREVENTION OF DERMATITIS

As a preventive against dermatitis caused by metol to
especially sensitive persons, the fingers may be rinsed both
before and during development in:

296.— PREVENTIVE AGAINST METOL DERMATITIS
Hydrochloric acid I part

Water 500 parts

It is always better to avoid dermatitis either by wearing
protective gloves or by using solutions that do not contain the
particular chemical to which one is allergic.

REMOVING DEVELOPER STAIN FROM THE HANDS

Rub the hands well with a

297.— STAIN REMOVER
1% solution of potassium permanganate

390

until they have taken on an overall brown colour, then wash
well in the ordinary way and finally rinse in a

298.— CLEANSER
Strong solution of sodium bisulpliite

which will completely remove the brown colour.

REMOVING DEVELOPER SPLASHES FROM CLOTHES

Damp the spots or splashes with

299.— STAIN REMOVER
5% solution of potassium permanganate

Allow to remain for a few moments and then decolorise
with

300.— CLEANSER
10% solution sodium bisulphite

In the case of coloured cloth or fabric, care must be
exercised, otherwise the treatment may cause the appearance
of a bleached area.

CLEANING SOLUTION FOR ALL NON-METAL VESSELS

301.— VESSEL CLEANSER

Water 40 ounces 1000 ml.

Potassium dichromate 4 ounces 100 grams

Sulphuric acid cone. 4 ounces 100 ml.

Dissolve the dichromate first and then add the acid
slowly and with constant stirring as great heat will be evolved.
When this solution has been used the vessels must be well
washed with plenty of water.

RELEASING JAMMED GLASS STOPPERS

Quickly but carefully v/arm the neck of the bottle with a gas
or spirit lamp flame. Then tap the stopper with a piece of
wood until loosened. Where the jamming of the stopper is
due to crystallising of salts out of solution a drop or two of
water is a help, or the bottle may be inverted and placed in
warm water up to the neck of the bottle.

391

DISINFECTING OF WOOD AND COMPOSITION TANKS

Large tanks often develop a black deposit after some time
in use, which harbours bacteria and causes evil smelling gas
to be given off. Such tanks can be disinfected as follows.

302.— DISINFECTANT
Remove all metal parts such as hangers, rods and the like, then fill
the tank with water, add a quart (I litre) of commercial hydrochloric
acid, stir in about 4 ounces (100 grams) chloride of lime.

Put the lid on the tank and leave it over night, preferably
out of doors. Next day empty the tank and wash out well
with plenty of water.

SAVING CRACKED OR BROKEN PLATES

(1) The Film is Undamaged: It should be separated from the
glass as follows. Harden the film for 15 minutes in

303.— HARDENING BATH
10% solution of formalin in water

Then with a sharp knife cut round the edge of the film about
l/16th-inch (2 mm.) inside the edge of the plate, wash the
plate free from formahn solution and place in a dish with
the following:

304.— PLATE STRIPPING SOLUTION

Water 4 ounces 100 ml.

Ammonium bifluoride 40 grains 2 grams

Sulphuric acid, 10% solution S drops S drops

After about two minutes the film can usually be stripped off
the glass. It is washed carefully in water and floated on to
another plate. If preferred, this can be a normal plate, fixed
but undeveloped, in which case the gelatine film holds the
stripped film firmly.

(2) The Film is Damaged: In this case the broken pieces
must be cemented together:

305.— CEMENT
Water glass or Canada balsam thinned down with benzol

The broken pieces of glass have their edges painted with
the cement and are then carefully fitted together on a glass
plate and allowed to dry.

392

GIVING GREATER TRANSPARENCY TO PAPER NEGATIVES

The back of the negatives should be well rubbed with a very
thin clear machine oil of the kind used for typewriters or
sewing machines. If necessary the oil can be thinned with a
little clear parafiBn oil. Care should be taken not to use any
excess of oil beyond that required to render the negative
transparent. Warming helps.

WRITING ON NEGATIVES

(1) To Reproduce Clear Writing on Dark Ground: On a
well-gelatined strip of paper write the necessary text with a

306.— WRITING SOLUTION
Concentrated solution of potassium ferrlcyanlde

and allow it to dry. Then damp the negative surface by
soaking, remove all superfluous moisture and lay the gelatined
paper on the negative with the writing against the negative
film; leave for one minute and then remove and wash.

(2) To Reproduce Black Lettering on the Negative: The
necessary text is written in waterproof ink on thin Cellophane
or celluloid which is then cemented on to the negative with
the written side in contact with the negative film.

393

Defects in Negatives

FAULTS IN THE GRADATION OF THE NEGATIVE

(7) The negative lacks detail in the shadows and density in the
highlights.

The usual cause is under-exposure (page 34).

If there is perceptible detail in the shadows, then some
improvement may be effected by intensification (page 347).
(2) The negative is thin and flat, but there is reasonable detail
in the shadows.

The negative has been correctly exposed but has been
under-developed.

(a) Development was too short (page 38).

(b) The developer was exhausted or too heavily
diluted (page 140).

Intensification or the choice of a hard gradation paper, or
both, should produce reasonably satisfactory pictures (page
347).

(5) The gradation of the negatives is flat and the shadows fogged.
The parts of the plate or film protected from light, particularly
the edges, are however clear.

The negative has been over-exposed. A somewhat similar
fault develops in negatives of subjects taken against the light
when parts of the subject have been too biilliantly lighted
(page 34).

The best remedy is the choice of a hard printing paper
(page 339). Where a shorter exposure, either for printing or
enlarging is desired, the use of Farmer's reducer for clearing
the shadows will also help by increasing the general contrast
(page 342).
{4) The negative is hard and has heavy, dense highlights.

It has been over-developed.

394

(a) Development was carried on for too long.

(b) The developer was too strong or contained too
much alkah.

Choose a soft paper (page 339) or use a superproportional
reducer, i.e., ammonium persulphate, or both (page 344).
(5) The negative is hard as in {4) and the shadows are fogged.

The negative has been over-exposed (page 34) and also
over-developed (page 38).

A soft paper should be used, but the shadows should first
be cleared with Farmer's reducer (page 342) and then the
whole negative reduced with persulphate (page 344).

THE NEGATIVE IS FOGGED

(5) The negative shows grey fog all over, including those parts
protected from light by the rebate of camera or dark-slide.

(a) Development is too long or too warm developer
or lack of bromide (page 91).

(b) Unsafe dark-room light, or stray white light in
darkroom (page 122).

Test safelight to ensure that it is suitable for the
negative material being used.

(d) Aerial fog due to too much exposure to air during
development; this can occur particularly in drum-
development and when dish-development is
used.

Desensitisation helps to reduce this possibility (page 251).

Use of a hard printing paper (page 339) may help, also
clearing the fog with Farmer's reducer (page 342) followed
later by intensification (page 347).

(7) The edge of the plate or film shows a black fog which tails
off towards the inside of the plate or film.

(a) Manufacturing fault or stale material, more
common in plates than film.

(b) In roll-film can occur through a loosely-wound
spool being exposed to daylight during charging
or emptying the camera.

395

(5) Dichroic fog, appears red or violet by transmitted light and
bluish or green by reflected light.

(a) Spent developer or developer contaminated with
hypo (page 271).

(b) Unsuitable developer (i.e. containing silver sol-
vent such as potassium thiocyanate).

(c) Developer too warm (page 107) or development
too protracted. With fine-grain developers too
high a sixlphite content can cause the trouble
(page 203).

(d) Exhausted fixing bath, or fixing bath too v/arm
and spent (page 268).

(e) Fixing bath contains too much carried over
developer (page 271).

(f) Insufficient rinse between development and fixing,
or exhausted stop-bath (page 271).

(g) Negative exposed to white light before fixing was
complete.

(9) The negative shows yellow fog when examined by trans-
mitted light.

Causes similar to those detailed under dichroic fog.

Removal of yellow and dichroic fog.

1st Method: Harden the emulsion film in the following:

307.— HARDENING BATH
Formalin

Sodium carbonate, anhyd.
Water np to

Then wash for a moment or two and treat for 5 minutes in a
J % solution of potassium permanganate, wash, fix in 30 %
plain hypo, clear in 10% bisulphite and wash finally.

2nd Method: Bathe the negative in the following solution.

i ounce

12 ml.

J ounce
40 ounces

6 grams
1000 ml.

308.-

-FOG REMOVER

Thiourae
Citric acid
Water to mai<e

28 grains

5 ounces

1 .4 grams
1.4 grams
125 ml.

(70) Yellow fog which merges into brown.

Caused by oxidation products in the developer, usually
due to too low sulphite content (page 81). It may also occur
when a fixing bath is exhausted and contaminated with
developer (page 268).

396

To remove the fog harden the negative in the formahn bath
given above, wash, bleach in the permanganate bleach made
up as follows. Make up a solution containing:

309.— FOG REMOVER

Sodium chloride (common salt) J ounce
Sulphuric acid cone. 20 minims
Water 4 ounces

7 grams
1.5 ml.
100 ml.

30 ounces

750 ml.

1 ounce

i ounce

40 ounces

25 grams
6.5 grams
1000 ml.

Add to this just before use 4 ounces (100 ml.) of i% solution
of permanganate. Bleach for 3-4 minutes: the film will
become covered with brown manganese dioxide which, after
a good rinse, is removed by sodium bisulphite solution. Now
wash the negative well and place in full daylight until it
assumes a reddish colour and then re-develop it, using the
amidol developer recommended by Kodak.

310.— AMIDOL RE-DEVELOPER
Water at I25°F. (52°C.)
Sodium sulphite, anhyd.
Amidol
Cold water to make

(77) The negative shows a red, blue or greenish coloration.

Usually caused by the anti-halo layer (page 61).

The colouring can easily be removed by a weak alkaline
solution, e.g., a diluted developer or water containing a few
drops of ammonia.

V/HITE DEPOSIT ON OR IN THE FILM OF THE NEGATIVE

(72) Fine-grained white deposit.

Chalky residue from very hard water (page 92).

To prevent, use Calgon or similar compound in developer.
To remove deposit, bathe negative in 2% acetic acid, then
wash well. If this treatment causes a coloration of the nega-
tive, add a few drops of ammonia to the wash water.
{13) Whitish deposit on the dried negative, which has a shiny
appearance when wet.

The deposit consists of aluminium sulphite derived from
a hardening and fixing bath into which too much developer
has been carried over.

24 397

The use of an acid stop bath helps here and lengthens the
hfe of the hardening fixing bath (page 271). To remove the
deposit, harden the film in alkaline formalin solution (page
377), and then treat the film m a 5 % solution of sodium
carbonate, then wash well.
(14) Pale yellowish-white appearance of negative. Opalescence.

Due to decomposition of fixing bath and setting free of
sulphur. The fixing bath contains too much acid, too little
sulphite or is too warm (page 272).

To remove the opalescence harden the film in alkaline
formalin solution (page 396), wash well and treat with a 10%
solution of sodium sulphite at a temperature of about 100°F.
(38°C.).

DARK OR LIGHT STREAKS OR BLOTCHES ON THE NEGATIVE

(75) Light or dark parallel streaks appearing, light streaks on
dark parts and dark streaks on light parts of negative.

Due to insuflicient movement of developer during
development, allowing local concentration of used-up
developer (page 78).

(76) Dark or light streaks originating where the plate or film
holder touched the negative material.

Dirty plate or film holder.
See page 391 for cleaning.

(77) Scum markings.

Dirty developer due to dust, etc.
{18) Large irregular light areas with sharp edges.

Unequal initial flow of developer over negative so that
development was uneven.
(79) Regular wave-like markings on negatives dish developed.

Insufficient rocking of dish during development.
(20) Sharply-defined areas of varying density.

Too small an amount of developer in dish, also see {18).
{21) Irregular areas of higher density.

Variations in concentration of developer can be caused
by adding concentrated or warm developer to tank or dish
during development. This should never be done.
{22) Irregularly-defined light areas, often contaminated with
scum.

Due to developer standing in tank improtected from dust

398

and air. The surface becomes covered with a scum of oxida-
tion products which gets on to the surface of the negative
and locally hinders development.

If such scum is seen on the surface of the developer, the
developer should be filtered or discarded.

SPOTS, FLECKS AND LINEAR MARKINGS

(25) Thin black or light straight lines.

Scratches due to abrasion. Often caused on roll film by
dust or grit getting into the camera, or by careless loading
of spools causing the film to jam when being wound through
the camera. If the scratches are made before exposure they
usually appear light; if after exposure they are darker than
their surroundings.

(24) Black irregular forked or branched wavy lines.

Static markings caused by an electric charge bemg
developed on the film. Usually caused in manufacture, but
can occur in very cold and dry areas, if the film is carelessly
handled and roughly wound up.

(25) Strong black lines usually radiating from a corner or
side of negative.

Light leaks either in the front or the bellows of the
camera.

(26) Small, light, undefined brownish flecks.

Over-used and insufficiently agitated tank developer.

(27) Marbling-like or honeycomb markings on the film.
Exhausted, insufficiently mixed or unstirred developer.

(28) Clear, well-defined light round spots, sometimes with
comet-like tail.

Air bells on the film during the early stages of develop-
ment.

(29) Honeycomb markings with dark surrounds.

Scum on the developer which has collected on the face of
the negative.

(30) Wrinkled film or reticulation.

Too great a variation in temperature between baths,
possibly too high a developer temperature followed by a cold
fixing bath.

399

(5/) Small light or dark spots usually well defined.

Ordinary or chemical dust which has settled on the
negative before development.
{32) Small dark or light flecks of irregular form.

Particles of undissolved chemicals in the developer.
(5i) Holes in the film or hollows.

A fault caused by bacteria or moulds, most common in
summer when plates or films have been too long drying in
a warm, moist atmosphere.
{34) Light or dark drop-like markings on the film.

(a) Spots of water which have fallen on a partially
dry negative.

(b) Drops of water left on a negative when put to dry.

LESS COMMON NEGATIVE FAULTS

{35) Small blisters covering the negative.

Usually caused by carbon dioxide gas set free when the
negative is transferred from the developer to a too-acid stop
bath or an acid fixing bath.
{36) Wrinkled emulsion at edges of film floating off support.

Too high temperature developer or wide differences
in the temperature of the different baths.
{37) The numbers and other indications from the red or green-
black paper of the roll-film appear as developed image on
the film.

Badly stored or stale film.
{38) Partial or complete reversal of the negative into a positive
image.

Use of unsafe dark-room lighting (page 122) or accidental
fogging with white hght before exposure.
{39) Partial melting of film during drying.

Too high a drying temperature (page 294) and not
sufficient air current.

400

Photographic Chemicals

In the following pages, details are given of the more import-
ant photographic chemicals, arranged as follows.

(1) The common name of the chemical, other names
in use, chemical formula and British and American
standards (BS and AS respectively).

(2) Appearance, method of preserving, special pro-
perties, i.e., poisonous, corrosive or inflammable.
Solubility in water at normal temperature (in
case of developing agents in parts per 100=WS.).
In the case of developing agents there is also given
(a) Solubility in 100 parts 10% sodium sulphite
solution S.S.S. and (b) SolubiUty in 100 parts of a
mixture of equal volumes of sodium sulphite
J% and sodium carbonate 1% solutions, S.S.C,
all at normal temperature, i.e., 65°F. (18°C.).

(3) Use for photographic purposes, usually with page
references.

ACETIC ACID GLACIAL. CH3COOH. BS 576: 1950; AS PH4. 100 (1958).

Water clear fluid with stinging smell. Solidifies at temperatures below
62°F. I7°C. Corrosive action.

Mixes in all proportions with water.

Used for stop bath (pps. 270-71), addition to fixing baths (page 274) and
in uranium intensifrer (page 350).
ALUM, POTASH. Aluminium potassium sulphate. Rock alum.

K^k\^(SO,)i.l4H^O. BS 3312: 1961 ; AS PH4. 150 (1958).

Colourless transparent crystals or white powder. Corked bottle.

Solubility I part in 10-11 parts water.

Used as hardening agent (page 274), also in hypo-alum toning. (See
Jacobson; "Enlarging,".)

ALUM, CHROME. Chromium potassium sulphate. K2Cr2(S04)424H20. AS
PH4. 151 (1958).

Deep violet crystals.

Soluble I part in 5-7 parts water.

Used as hardening agent in hardening fixing baths (page 274).
AMIDOL. 2.4-Diamino-phenol hydrochloride. C,H3(OH)(NH4)2.HCI. AS
PH4. 127 (1965).

White to greyish needle crystals.

WS. 25 parts. SSS. 28 parts. SSC. 26 parts.

Strong developer without alkali (page 198).

401

AMMONIA. Liquid ammonia. NHiOH.

Colourless solution of ammonia gas in water, with penetrating smell.
.880 ammonia contains 35% NH3. .910 ammonia contains 25% NH,.
Corrosive and poisonous.

Used in reversal developers (page 243), and as blackening agent In
Intensifying (page 348).
AMMONIUM CARBONATE. Lump ammonia. (NH4)j.CO,.

White lumps or powder, ammoniacal smell. Keep in glass-stoppered
bottle.

Soluble I part in 4 parts water.

Used in special developers.
AMMONIUM CHLORIDE. Sal ammoniac. NH^CL AS PH4. 183 (1961).

White crystalline powder.

Soluble I part in 3 of water.

Used in preparing qulcl< fixing baths (page 266).
AMMONIUM BIFLUORIDE. Acid ammonium fluoride. NHiF.HF.

White powder. Attacl<s the skin, poisonous.

Easily soluble in water.

Used for removing gelatine emulsion film from glass plates (page 392).
AMMONIUM PERSULPHATE. (NHJaS^Oa.

Colourless crystals.

Soluble I part in 1.7 parts of water.

As reducer (page 344).
AMMONIUM THIOCYANATE. Ammonium Sulphocyanide. NH^CNS
BS 3750: 1964.

White deliquescent crystals.

Very soluble in water.

As a rapid fixing agent (page 276).
AMMONIUM THIOSULPHATE. Ammonium Hyposulphate. (NHj)^ SA-
BS 3310: I960; AS PH4.2S2 (I960).

White crystals.

Very soluble in water.

As a rapid fixing agent (page 276).
BENZOTRIAZOLE. CeH^Nj. BS 3309: I960; AS PH4.204 (1962).

White crystals.

Insoluble in water.

Antigofgant (page 92).
BORAX. Sodium biborate. Na,B,0,. l0H,O. BS 3311: 1961; AS PH4.230
(1961).

White powder or crystals.

Soluble I part in 17 water.

As mild alkali in fine-grain developers (page 204).
BORIC ACID. Boracic acid. H3BO3. AS PH4. 103 (1958).

White lamellar crystals, greasy feel.

Solubility I in 25 water.

As addition to fine-grain developers (page 206).
CALGON. Presumably sodium hexa-metaphosphate.

White powder or colourless crystals.

To prevent precipitation of calcium salts in hard water.
COPPER SULPHATE. Blue vitriol. CuSO^.SH^O. AS PH4.I80 (1958).

Blue crystals, poisonous.

Soluble I partin 3 water.

As bleach bath (page 345), and as intensifier (page 351).
CHLORQUINOL. Mono-chlor-hydroquinone, Adurol. CIC„H,(OH)2 AS.
PH4.I54(I964).

Greyish crystalline powder.

Very soluble in water.

Used as developer (page 195).

402

CITRIC ACID. C,HeO,.H,0. AS PH4.I02 (I9S8).

Colourless crystals.

Soluble I part In 0.75 water.

In physical developers (page 221).
FORMALIN. Solution of gaseous formaldehyde In water. H.CHO 37% w/v.
AS PH4. 1 52 (1958).

Water clear but faintly yellowish solution, poisonous with unpleasant
smell. Vapour dangerous to light-sensitive material.

Misclble in all proportions with water.

As hardening agent when diluted with water (page 396).
GLYCERINE. Glycerol. C3H5(OH)3.

Colourless thick fluid.

Misclble In all proportions with water.

As softening agent and in enlarging scratched negatives. (See Jacobson;
"Enlarging.")
GLYCIN. p-hydroxyphenyl glycine. CeHjOH.NH.CH^ COOH.

White crystals.

WS. 0.23. SSS. only traces. SSC. I2J parts.

Slow and very clean-working developer (page 196).
HYDROCHLORIC ACID. HCI. AS PH4. 104 (1958).

Colourless when pure, but often yellowish. Corrosive and poisonous.

Vapour dangerous to photographic materials.

In Chromium Intensifier (page 351), also for cleaning dirty vessels.
HYDROQUINONE. p-dihydroxybenzene. CeH,(OH)2. BS 3103:
1959; AS PH4.I26 (1962).

Colourless crystals.

WS. 5J-6. SSS. 4. SSC. 7i.

Widely used developer (page 172).
IRON ALUM. Ferric ammonium sulphate. Fe2(NHi),(S04)4.24H20.

Pale Violet crystals.

Soluble I part In 7 water.
IRON CHLORIDE. Ferric chloride. FeClj-eH^O.

Yellow masses.

Very soluble In water I In 0.6.

Used In Belltzki's reducer (page 343).
MERCURY CHLORIDE. Mercuric chloride. Corrosive sublimate. HgClj.

White crystals. Violent poison.

Soluble I In 16 water.

Used In mercury Intensifier (page 348).
MERITOL understood to be paraphenylenedlamlne pyrocatecholate

C,H,(NH,),CeH4(OH),.

Cream or greyish crystalline substance.

Used In fine-grain developers (page 211).
METOL. Methyl para-amlnophenol sulphate, CeH4(OH)(NH.CH3)iH2
SO4.

Colourless needles or prisms.

WS. 5. SSS. 2. SSC. 4i.

Developer of universal applicability (page 172).
ORTHOPHENYLENEDIAMINE o-phenylenediamine. 1.2-Diaminobenzene.

White crystals. More stable than paraphenylenedlamlne.

For fine-grain developers (page 210).
PARA-AMINOPHENOL HYDROCHLORIDE, p-aminophenol. C6H4.(NH,)
(OH). HCI. AS PH4.129 (1954).

Colourless crystals.

WS. 33. SSS. -. SSC. 3.

Rapid developer In caustic alkali solution (page 196). Basis of many
commercial concentrated developers.

403

PARA-PHENYLENEDIAMINE 1.4-Diaminobenzene. CeHj.(NH2)2. AS
PH4.I32 (1964).

White to brownish powder. Poisonous.

Used in fine-grain developers (p. 210).
PHENIDONE. 1-phenyl-3-pyrazolidone. CsHi„NaO. BS 3230: I960; AS
PH4.I36 (I960).

Colourless crystals.

Slightly soluble In water, readily in aqueous adds and alkalis.

Developing agent (page 198).
POTASSIUM BROMIDE. KBr. BS 3307: I960; AS PH4.300 (1962).

White cubic crystals or white powder.

Soluble I in 1.6 water.

Restrainer in developers (page 91), also in bleaching baths.
POTASSIUM CARBONATE. Potash. K2CO.3. BS 3751: 1964; AS PH4.229
(1962).

White powder, attracts moisture with avidity.

Soluble I In I water.

Alkali for developers (page 85), and as quick-drying medium.
POTASSIUM DICHROMATE. Bichromate of potash. K^Cr^O,. AS
PH4.300 (1958).

Orange red crystals, poisonous.

Soluble I part in 10 water.

For cleaning vessels (page 391).
POTASSIUM FERRICYANIDE. Red prussiate of potash. K3Fe(CN)e. BS
3752: 1964; AS PH4.302 (1958).

Dark red crystals, poisonous.

Soluble I in 2.5 water.

As reducer (page 342), and in bleach baths (page 373).
POTASSIUM HYDROXIDE. Caustic potash. KOH. BS 3753: 1964; AS
PH4.326 (1956).

Appears in sticks, flakes and pellets, strongly corrosive and attracts
moisture.

Extremely soluble in water, I in 0.5.

Strong alkali for developers (page 86).
POTASSIUM IODIDE. Kl. AS PH4.20I (1957).

White cubic crystals.

Soluble I in 0.7 water.

As addition to developer (page 378), and for intensifier (page 350).
POTASSIUM METABISULPHITE. K^SjOj. BS 3306: I960; AS PH4.277 (1957).

Colourless, hard crystals.

Soluble I in 3 water.

As preservative in developers (page 83), stop bath (page 271), as acidifier
in fixing baths (page 264), as clearing bath (page 247).
POTASSIUM PERMANGANATE. KMnO^. AS PH4.30I (1958).

Glistening violet black crystals.
Soluble I in 16 water.

As reducer (page 343), hypo test (page 291).
POTASSIUM THIOCYANATE. Potassium sulphocyanide. KCNS. BS 3822:
1965.

Colourless crystals, poisonous.

Soluble 1 in 0.5 water.

Addition to fme-grain developers (page 203), rapid fixing agent (page
276).
PYROCATECHIN. catechol. Orthodioxybenzene. CeH4(OH)j.

White crystals.

Developer (page 194).

WS. 33. SSS. -. SSC. 36.

404

PYROGALLOL. Pyro. Pyrogallic acid. Trioxybenzene. C.H,(OH)3. AS
PH4.I30 (1956).

Colourless crystals, poisonous.

WS. 52. SSS. 59. SSC. 42.

Developer (page 196).
SILVER NITRATE. AgNOj.

Colourless crystals, poisonous and strong caustic.

Soluble I in I water.

Physical development (page 219), intensification (page 351).
SODIUM BISULPHITE. NaHSOj.

Does not exist as a solid altliough listed in some catalogues. Sodium or
potassium metabisulpfiites are used, wliicli on dissolving in water give a
solution of the bisulphite.

Soluble I in 4 water.

Used for same purposes as potassium metabisulphite.
SODIUM BISULPHITE LYE. Average density 36° Baume = 1.33 sp. G.

Colourless or pale yellow fluid. Glass bottle with rubber stopper.

Used for same purpose as sodium bisulphite (see above).

SODIUM CARBONATE. Soda. Carbonate of soda. Na^CO^ and
Na^COj.lOHjO. BS 3305: I960; AS PH4.228 (1961) and PH.4227
(1961).

White crystals or powder. Crystal carbonate.

Soluble I in 1.6 water, anhydrous I part in 6 water.

Used as alkali in developers.
SODIUM CHLORIDE. Common salt. NaCI. AS PH4.203 (1956).

White powder.

Soluble I in 2.5 water.

Addition to mercury intensifier and copper bleach bath (page 345).
SODIUM HYDROXIDE. Caustic soda. NaOH. BS 3308: I960; AS PH4.225
(I960).

In sticks, flakes and pellets, strong caustic.

Soluble I In 1.7 water. (Generates heat on dissolving as does caustic
potash.)

Strong alkali for developers (page 86).
SODIUM PHOSPHATE, TRIBASIC. Na3POj.l2HjO.

White crystals.

Soluble I in 5 water.

As alkali in developers (page 378).
SODIUM SULPHATE. Glauber's salts. NajSOj.lOH^O.

Colourless crystals.

Soluble I in 2 water.

As addition to tropica! developer (page 228).

SODIUM SULPHIDE. Na2S.9H20.

Colourless crystals, somewhat corrosive.

Very soluble in water.

Used in intensifying and toning (see Jocofason ; "Enlarging.")
SODIUM SULPHITE. Na2S03.7HjO. BS 3303: I960.

White powder or crystals.

Anhydrous salt soluble I in 5 water.

Preservative in developers (page 81), as blackening agent (page 348).
SODIUM THIOSULPHATE. Hypo. Sodium hyposulphite. Na2Sj03. SH^O.
BS 3301 : 1960; AS PH4.25I (I960).

Colourless crystals or powder (anhydrous).

Soluble I in 0.7 water.

The universal fixing — agent (page 263).

405

SULPHURIC ACID. Oil of vitriol. H^SO.. AS PH4.I0I (1958)

Colourless oily liquid. Strong corrosive and poisonous.
Caution: When dilute acid is required, the acid must alv/ays be poured into
the v/ater, never the reverse, otherv^ise the reaction attains explosive
violence.

Used in bleach baths (page 345), cleaning solution (page 391).
URANIUM NITRATE. Uranyl nitrate. UOj(N08)a.6HsiO.

Yejlovifjsh crystals. Poisonous.

Soluble I in 0.5 v^ater.

Used in uranium intensifier (page 350).

406

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