A popular treatise on photography

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A POPULAR TREATISE

PH OTOGRAPHY

A DESCRIPTION OF, AND REMARKS ON, THE

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D. VAN MONCKHOYEN.

TRANSLATED BY W. H. THORNTHWAITE, PH.D., F.G.S.

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LONDON:
YIETUE BROTHERS & CO., 1, AMEN CORNER,

PATERNOSTER ROW.
1863.

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PREFACE.

THE high repute of D. Yan Monckhoven on the
Continent as a practical photographer, and the very
favourable reviews which his works have from
time to time received from the leading photographic
journals in this country, have led to the following
free translation of his " Traite Populaire de Photo-
graphy sur Collodion." The alterations and emen-
dations which have been made in the original text,
it is hoped, will render the whole more immediately
available to the English reader, and acceptable as a
handbook of photographic art.

W. H. THORNTHWAITE.
April, 1863.

CONTENTS.

Chapter Page

Introductory 1

I. The plan followed in this work 6

II. On the preparation of substances required in the manu-
facture of photographic collodion . . . .11

III. Preparation of photographic collodion .... 20

IV. Cleaning glass plates, &c 25

V. On the dark room, and photographic laboratory . .28

VI. Coating with collodion and sensitising the plate . . 30
VII. Photographic cameras, lenses, &c. .... 36
VIII. On the glass room in which the sitter is placed, and the

rules to be observed in taking portraits and landscapes 48
IX. Development of the latent image obtained in the camera-

obscnra 55

X. Fixing and strengthening the negative image . . 64
XI. Varnishing the picture . . . . . .67

XII. The dry collodion, collodio-albumen, and tannin processes 7 1

XIII. Positive collodion process 84

XIV. The stereoscope 89

XV. Printing positive proofs 98

NOTES.

Appearance of negatives 121

Distillation of ether 121

Preparation of pyroxyiine 122

Employment of the iodides and bromides . . .122

Nitrate of silver stains 123

Preparation of the nitrate of silver bath . . . 124

Preparation of pyrogallic acid 124

Photographic optics 125

Spots on the collodion film . . . . . .130

Crystallisable acetic acid 131

A GLANCE

AT THE

PEINCIPAL PHOTOGRAPHIC PEOCESSES

NOW IN USE.

INTRODUCTORY.

AMONGST the various methods which have been from time
to time proposed for the production of pictures by the
chemical agency of light, and comprehended under the
general term Photography, there are only four — the
DAGUERREOTYPE, CALOTYPE, ALBUMEN, and COLLODION
processes — which have been to any extent practically
successful.

The photographic piature is obtained in the —

Daguerreotype process, on polished metal plates ;
Calotype, on paper ;

Albumen, on a film of albumen on glass ;
Collodion, on a film of collodion on glass.

And it is an interesting fact that, although at first sight
these processes do not appear to have any connection with
each other, there nevertheless does exist one general
principle of action, which will be obvious, even to the
superficial observer.

THE DAGUERREOTYPE. — This process was. discovered by
Niepce and Daguerre. A silver, or silvered copper, plate,
highly polished, is placed in the dark on a china dish, con-
taining iodine. The vapour of this substance combines
with the silver of the metallic plate in such a manner as
to produce iodide of silver, a substance sensitive to light.
In fact, it is sufficient to expose it behind a perforated card
in the daylight for some considerable time to produce an
impression ; but should the time of exposure be much
shortened there will not be any picture visible on the

& PHOTOGRAPHIC PROCESSES.

layer of iodide of silver, although such really exists, and
can be developed, or made to appear. This can be effected
by placing the plate over mercury heated to about 148°
Fahr., so that it receives the vapours which arise there-
from, when an exact image of the perforated card will be
apparent in a very few seconds. There always remains a
certain quantity of iodide of silver which has not been
altered by light, because it has been protected from the
action of this agent by the opaque body which covered
. the plate in certain places. If this iodide of silver were
not removed, it is easy to understand that it would become
changed as soon as exposed to the light ; and therefore
it is necessary to dissolve it by a body which has received
the name of a fixing agent. Many substances dissolve
iodide of silver, such as the various iodide*, cyanides, and
alkaline hyposulphites ; but amongst these the most useful
is the hyposulphite of soda.

The Daguerreotype process just described will be per-
ceived to essentially consist of a layer of iodide of silver,
the use of a developer to bring out the latent picture, and
a fixing agent for removing that portion of the iodide of
silver not acted upon by the light.

THE CALOTTPE process was the invention of Mr. Fox
Talbot, and, in consequence, is sometimes termed Talbo-
type. It consists in spreading, on a sheet of paper, first a
solution of iodide of potassium, and then a solution of nitrate
of silver. These two bodies, by their mutual reaction,
produce a yellowish-white, insoluble powder ; then, by
washing the paper in water contained in a porcelain basin,
all the excess of nitrate of silver is carried away, and
finally there results a paper the pores of which are com-
pletely impregnated with iodide of silver. If this iodised
paper be exposed to the light, behind a perforated card,
the iodide of silver will become black at the places where
the light strikes upon it ; or if a very short exposure
be given to the paper, on examination by yellow light no
image will be perceived. The picture can, however, be
developed by immersing the paper in an aqueous solu-
tion of gallic acid, mixed with a very small quantity of
another aqueous solution of nitrate of silver and acetic
acid. This mixture constitutes Mr. Talbot's developer.

INTRODUCTORY. O

At the end of some minutes the image shows itself, increases
in vigour, and becomes very distinct ; the paper is then
removed from the basin of gallo nitrate of silver, washed
in water, and the iodide of silver not affected by the light
is dissolved out with a solution of hyposulphite of soda.

The two processes of Daguerreotype and calotype,
although employing such different substances as metal
and paper, nevertheless have many points of resemblance,
as in both the pictures are obtained on iodide of silver,
requiring development and subsequent fixing ; but when
the respective pictures are examined, a very important
difference will be perceived in their general aspect. A
proof taken by the Daguerreotype will exhibit a counterpart
of the original, with all the lights and shades correct. If
it be a view taken with the aid of a camera, the sky will
appear white, the trees a little darker, and the shadows
black as in nature ; and, in the case of a portrait of a person
standing before a white wall, the picture of the wall will
be white, the hair and features differently tinted, and the
dress black ; consequently, it is usual to call this image
direct, or positive.

It is quite different with the calotype picture ; in fact,
the view will have a black sky, the trees lighter, and the
shadows white ; and, if it were the portrait, the wall black
and the dress white ; or, in other words, the picture will
in every respect, as to depth of tint, be the reverse of the
original, and for this reason is called indirect or negative.

Figs. 1 and 2 give an idea of these negative and

Fig. 1. <• Fig. 2

positive images. Thus Fig. 1 represents a black cross on
a white ground. If it be reproduced by the Daguerreo-
type an exact copy is obtained; whilst if the calotype
process be used, the result will be an inverted image, or
the cross will be white on a black ground; in fact a
B 2

PHOTOGRAPHIC PROCESSES.

negative image, as shown at Fig. 2. Figs. 3 and 4 show
another example of these negative and positive proofs.*

There are many drawbacks against the employment of
the Daguerreotype process ; for instance, the plate pos-
sesses a dazzling brightness, which forces the observer to
incline himself in some favourable angle to be able to
examine the details of the picture ; besides, it must be
protected by glass, because the image which it bears on its
surface is destroyed by the least friction ; lastly, and this

Fig. 3.

is above all its principal disadvantage, it only gives a single
image, whilst the other methods furnish an indefinite
number. When a negative image is once obtained, it can
be employed to produce a series of other images, which
will also be reversed in relation to the negative, and con-
sequently positives. Take for example Figs. 3 and 4.
Suppose Fig. 3 the model to be reproduced, Fig. 4 will be
the negative image on the paper. But if the latter be laid on
another sensitive sheet of paper, and exposed thus arranged

* Sec Note 1.

INTRODUCTORY. 5

to the sun, its rays will pass through the white part&; and
impress the sensitive paper which is underneath, but will
be stopped by the black parts ; and thus will the facsimile
of Fig. 3 be produced. It will be understood that the
same negative Fig. 4 can be used as often as required, and
an unlimited number of positives analogous to Fig. 3 thus
obtained.

From the necessity and manner of employing a paper
negative to produce the required positive impressions, a
very correct idea will be formed of the motives which have

Fig. 4.

led photographers to replace paper by a more homogeneous
substance ; however fine a surface paper may appear to
possess, if it be examined by transmitted light it is always
very uneven in texture, which circumstance greatly
injures the delicate tints and sharpness of detail in the
positive proofs.

THE ALBUMEN PROCESS. — The white of an egg, other-
wise called albumen, is a transparent liquid, which, spread

O PHOTOGRAPHIC PROCESSES.

on a plate of glass, leaves by evaporation a coating as
clear as the glass itself, so that when employed as a
photographic vehicle the most minute details are preserved
with perfect fidelity.

The manner of operating with albumen is exactly the
same as for the negative paper. In the albumen, properly
prepared, is dissolved a small quantity of iodide of potas-
sium ; this is spread on a well cleaned plate of glass ; the
dried glass is immersed in nitrate of silver, exposed to the
light in a camera, developed as a proof on paper, and fixed
by hyposulphite of soda.

The advantage that albumen offers over paper, is the
production of finer details in the picture. It is not, how-
ever, at all an easy or sensitive process, and therefore
unsuitable for taking portraits, as at least ten minntes
exposure is required, even in a very good light, to pro-
duce an impression.

THE COLLODION PROCESS, which employs a film of
collodion spread on glass, possesses all the good qualities
of albumen, with the very great advantage of being, at
least, sixty times more sensitive, and withal easier of
execution. It is this process, and the subjects imme-
diately connected therewith, that will be treated upon in
the following chapters.

CHAPTER I.

THE PLAN FOLLOWED IN THIS WORK.

IN this chapter it is intended to give a brief summary of
the subjects to be subsequently described in detail under
their several heads.

If a little pyroxyline or gun-cotton be immersed in
a mixture of about one part in volume of alcohol, and two
parts of ether, it will almost entirely dissolve. In order
to obtain a sufficiently transparent solution, it must stand
for twenty -four hours in a bottle well corked, and then
be poured out into another bottle, taking care not to dis-

THE PLAN FOLLOWED IN THIS WORK. t

turb the thick part which remains at the bottom. This
clear liquid is collodion.

If a small quantity of collodion be poured on a glass well
cleaned, the ether and alcohol will evaporate, and leave on
the glass a transparent film. This film is very firm, and
adheres strongly to the glass ; it is that which serves as a
vehicle for the photographic materials; or, in clearer terms,
it is that which is destined to form the surface which will
retain the photographic image. It may easily be con-
ceived that for the purpose of rendering this film sen-
sitive to light, iodide of silver must be formed in its
texture ; this is done by dissolving iodide of potassium,
or some other iodide, in the collodion.

It is important to choose a proper iodide, but for the
present purpose the use of a collodion containing iodide
of potassium will suffice to trace what results and changes
take place. On a well-cleaned glass plate pour a certain
quantity of collodion in such a manner as to cause it to
flow over its surface ; then incline the plate, that the
excess of liquid may flow off. After the ether and alcohol
are evaporated, — or, in other terms, after the plate has
become dry, — a coating of pyroxyline will be obtained ;
but this time it will have an iodide intimately mingled
with it.

In proportion as more or less gun -cotton is dissolved
in the mixture of ether and alcohol, a liquid of greater
or less density is obtained, and consequently the thickness
of coating of pyroxyline will also vary on the glass. The
proportion of iodide added to the collodion also regulates
the quantity which remains on the glass ; from which it
follows that it is not a matter of indifference what formula
is employed in its preparation : on the contrary, it is
necessary to study with the greatest care the relative quan-
tities of the. chemical substances which constitute photo-
graphic collodion. These quantities will depend upon the
temperature, and yet more upon the results desired to
be obtained.

The glass plate having the collodion spread over it, is
now sensitised by being dipped into a solution of nitrate
of silver, which converts the iodide of potassium into
iodide of silver, sensitive to light.

It need hardly be mentioned that the iodide of silver

8 PHOTOGRAPHIC PROCESSES.

being affected by light, the preceding operation of sensitis-
ing ought to be done in the dark. This word ought not
always to be taken literally ; in photography, we under-
stand by darkness a light too feeble to affect the sensitive
coating. A wax candle is generally used, or ordinary
daylight neutralised by a yellow glass; for a glass of
this colour prevents any action on photographic sub-
stances.

The sensitised plate now requires to be placed in a
camera, an apparatus composed of a box of wood and an
arrangement of lenses, which possess the property of
forming with perfect accuracy an image of any required
object on the sensitised plate. As a general rule, the col-
lodion plate is left in this apparatus from ten to twenty
seconds, according to the brightness of the object ; it is
then removed, and taken back into the dark room.

If at this moment the collodion film be examined with
attention, no trace of an image will be perceived, but it
can be made to appear in the same manner as has before
been mentioned, by developing with gallic acid. There
are also many other developers for bringing out the latent
image, such as pyro -gallic acid, proto -sulphate of iron,
proto -sulphate of uranium, &c. Whatever the developer
may be that is used, it is dissolved in water, and poured
over the coated surface of the glass. In a few seconds
the image appears as a negative, and the reduction is
allowed to proceed ; or, in other terms, the proof left to
darken, until it is judged to be sufficiently distinct. The
glass is then plunged into water, which removes all soluble
substances, then into a fixing solution, such as cyanide of
potassium, or hyposulphite of soda, which dissolves the
semi-opaque coating of iodide of silver ; finally, the glass
is washed in a current of cold water, and dried in the air.

If the proof be examined by transmitted light, it will
be found to be a true negative ; that is to say, supposing
a view has been taken, the sky, the white houses, and
in general all objects strongly illuminated, are shown of
a black colour; while dark objects, on the contrary, ap-
pear transparent (Figs. 3 and 4).

The use of such a negative as before' mentioned,
is to give a number of other proofs either upon glass
or upon paper ; and if the tints be in good harmony

THE PLAN FOLLOWED IN THIS WORK.

with the original model, a satisfactory picture will be
obtained.

To understand the above requires a proper compre-
hension of the principle, that in spite of the opposition
of lights and shades shown in a negative, with respect to
a given model, there must nevertheless be preserved a
perfect harmony between the tints. This phrase may
appear obscure, but a well selected example will make it
clear. Suppose a series of ten bands be fixed on a wall,
of which the first is absolutely black, the last perfectly
white, and the others of intermediate tints. The first will
then be black, the second of a greyish black, the third a
little less dark, the fourth still less, and thus lighter and
lighter, to the perfectly white.

If a corresponding figure be reproduced on collodion,
it will be found, if the nega-
tive be a good one, that these
ten tints are completely in-
verted. In the place of the
first black tint of the model,
will be one perfectly trans-
parent on the negative, whilst
the last will be of an opaque
black, the intermediate ones
having a regular gradation ; for
if it were otherwise, a proof
taken from such a negative
would not represent the true shades of the original model.
The Figs. 5 and 6 are intended to show this effect on
three bands ; but the result would be analogous for any
larger series.

The conditions necessary to obtain this exactitude are,
that the coating of collodion, be of proper thickness, and
sufficiently furnished with iodide of silver to yield a de-
composition of such intensity as to produce a thick coating
of reduced material ; for if the light has not been able to
decompose enough iodide in the coating of collodion, a
perfect black can never be produced. It follows, then, to
obtain an intense negative, there must be employed a thick
collodion strongly iodised, and a concentrated bath of
nitrate of silver.

The foregoing are the general details for producing
B 3

Figs. 5 and 6.

10 PHOTOGRAPHIC PROCESSES.

negatives upon collodion. This process, however, like
that of the Daguerreotype, can be made to "give direct or
positive proofs at one operation ; but in that case the
picture requires to be viewed by reflected, instead of by
transmitted, light.

All the operations necessary to obtain a negative upon
collodion require to be performed in rapid succession. But
if it be wished to delay the exposure and development
of the picture for some time after sensitising the plate, it
is re -coated with gelatine, or other suitable substance.
The advantage of this method of operating, besides
allowing some time to elapse between the exposure and
development, is that it does not require the whole of the
materials to be taken to the place where it is wished to
operate ; and consequently, although much less sensitive
than wet collodion, is very applicable for views, &c. This
method is known by the name of the Dry Collodion Process.

Some remarks on the stereoscope, an instrument par-
ticularly adapted for viewing photographic pictures, and
full details for printing positive proofs from collodion
negatives, and a few notes on optical photography and
other photographic subjects, will complete the work.

The following is a list of the subjects treated on in the
respective chapters : —

CHAPTER

II. The Preparation of the Substances required in the manufacture
of Photographic Collodion.

III. The Preparation of Photographic Collodion.

IV. Cleaning the Glasses.

Y. The Dark Room, or Photographic Laboratory.
VI. Coating with Collodion and Sensitising the Plate.
VII. Photographic Cameras, Lenses, &c.
VIII. The Glass or Operating Room, and the Rules for taking Views

and Portraits.

IX. Development of the Image obtained in the Camera.
X. Fixing and Strengthening the Negative Image.
XI. Varnishing the Collodion Coating.

XII. Dry Collodion, including the Collodio-Albumen and Tannin
Processes.

XIII. Positive Collodion Process.

XIV. The Stereoscope.

XV. Printing Positive Proofs.

Notes on Optical Photography and other Photographic Subjects.

PKEPARATION OP SUBSTANCES FOR COLLODION. 11

CHAPTER II.

ON THE PREPARATION OF SUBSTANCES REQUIRED IN THE
MANUFACTURE OF PHOTOGRAPHIC COLLODION.

A MIXTURE of alcohol, sulphuric ether, and gun-cotton
forms a liquid called plain collodion, to which is added,
to render it suitable for photographic purposes, an iodide
or bromide ; it is then termed iodised or sensitised col-
lodion.

1. Alcohol.

Spirits of wine, or alcohol, is a liquid well known, and can
generally be procured sufficiently pure for photographic
purposes ; it boils at about 172° Fahr., and burns with
a bluish flame without leaving a residue. One hundred
ounces by weight of alcohol measure about 125 fluid ounces,
and 100 fluid ounces weigh about 80 ounces. It should
be perfectly clear, transparent, and absolutely free from
any floating impurities ; should it be otherwise, it must be
carefully filtered. The operation of filtering, applicable
to other liquids as well as alcohol, is thus performed. A
circular sheet of filtering paper is first folded. in two, as

Figs. 7, 8, 9, 10. Method of folding Filtering
Papers.

Fig. 11. Apparatus for
Filtering.

represented by Figs. 7 and 8 ; then a new fold is made in
the middle, Fig. 9 ; the filter is then opened out, as shown

12

PHOTOGRAPHIC PROCESSES.

at Fig. 10, and placed in a funnel, 6, furnished with its
support, Fig. 11. The alcohol or other fluid
to be filtered, is poured carefully into the fil-
tering paper, through which it will pass per-
fectly clear. Should the first portion that
runs through not be quite bright, it must be
returned to the filter. When a very rapid
Fig. 12. Plaited filtration is desired, the filter paper may be
folded into a number of plaits, as shown at
Fig. 12, which affords a larger surface of paper for the
liquid to pass through.

The strength of alcohol is conveniently ascertained by
a specific gravity hydrometer. This instrument is formed
of glass, Fig. 14. It consists of a glass bulb with a glass
stem attached at the top, and a smaller bulb filled with
mercury, to serve as a counterpoise at the bottom. In
the stem is placed a graduated scale of specific gravities,
and the whole is so arranged that when
placed in pure distilled water, the instru-
ment floats, and the surface of the water is
coincident with 0 or I'OOO on the scale. When
placed in alcohol or any fluid lighter than
water, the hydrometer sinks according to its
strength or specific gravity. A test-glass or
cylinder, Fig. 13, is used to hold a sample of
the alcohol or other liquid to be tested, and
care must be taken when the hydrometer is
placed in it that it floats perfectly free in the
fluid, and that no air bubbles attach them-
selves to its surface. The specific gravity is
then immediately indicated by noting the
degree cut by the surface of the fluid. Alcohol, suitable
for photographic purposes, should not have a greater
specific gravity than *819. Its best strength is about
•803 to -810.

2. Ether.

It is comparatively easy to procure alcohol of sufficient
purity for photographic use, to what it is to obtain pure
sulphuric ether. Wlien manufactured on a large scale for
ordinary pharmaceutical purposes, there is generally so

Figs. 13, 14.
Hydrometer
and Glass.

PREPARATION OF SUBSTANCES FOR COLLODION. 13

little care taken, that the ether becomes contaminated with
eulphovinic acid, aldehyde, or, worse than all, a peculiar
principle resembling ozone, which is capable of decom-
posing iodides and liberating free iodine, therefore highly
detrimental to its photographic action. The formation
of this substance is much accelerated by the joint action
of air and light ; the knowledge of this circumstance is,
therefore, of some importance to photographers, as it
indicates a very necessary precaution to be taken to keep
ether, and liquids containing it, particularly collodion, in
well filled and closed bottles.

Sulphuric ether is a colourless liquid, and very volatile ;
when poured into water it floats about like oil, and a very
small quantity is dissolved. It is much lighter than water,
100 ounces by weight of ether being equal in volume
to 135 ounces by weight of water. Ether is tested as to
its strength by the specific gravity hydrometer, in the
same manner as described for alcohol on the opposite page.
It should have a specific gravity of "750 to *720 to be of
any use in photography.

In consequence of the highly volatile nature of ether,
and its vapour being very explosive when mixed with
atmospheric air, it is necessary, to prevent accidents, to
avoid pouring ether from one vessel to another in a
close room, or in proximity to a fire, or flame. As
the vapour of ether is much heavier than the air, it
naturally tends to fall, and therefore it is a proper
precaution to take, when employing ether or fluids con-
taining it — as collodion, for example — by artificial light,
to have the source of light situated at some distance
above the vessel from which the ether or collodion is
poured.

Ether, if not sufficiently pure for photographic purposes,
can generally be made available by the following method
of rectification : —

Into a tall bottle, Fig. 15, is to be poured the ether to
be purified, together with one-fourth of its volume of
water, and the opening closed with a cork ; the whole is
then strongly agitated, and left to settle for some few
minutes. Two layers of liquid will be perceived, the
under layer being water slightly etherised, and the upper
ether. The cork is now removed, and the shorter end

14:

PHOTOGRAPHIC PROCESSES.

Fig. 16. Fig. 15.

of an ordinary glass syphon, having a small bore, and
previously filled with water, is introduced through the
neck of the bottle, and quite to the bottom of the liquid.
The smallness of the bore, and
keeping the finger over the
longer end of the tube, will
enable the above to be done
with facility, without the water
from the syphon running out.
The finger being removed, the
syphon begins to act, and the
etherised water from the bottom
of the bottle is quickly drawn
off. When the under layer has
nearly disappeared, the orifice
of the tube is again stopped with the finger, and the
syphon removed.

A fresh quantity of water is now poured into the
bottle containing the ether, which is again agitated and
drawn off by the syphon as before explained.

This operation is called " washing," and the ether after
this process is called " washed ether."

If bent glass tubes can be conveniently made or
obtained, the following arrangement may be found more
convenient than the ordinary syphon, it is shown at
Fig. 17 : A, the bottle where the ether
and water is shaken together ; it is fur-
nished with a good cork pierced with two
holes, in one of which is fitted a narrow
tube (a) about §ths of an inch internal
diameter, and in the other, a curved
syphon tube (6), of which the shorter
end inside the bottle reaches to the
bottom. If the cork be properly fitted,
it is only necessary to blow slightly
through the tube (a) to cause the
liquid to rise in the tube (6) and flow
over. When nearly the whole of the
underlay er of liquid has passed over, the
syphon is stopped with the finger, the
cork removed, and the fresh quantity of water added,
and the operation gone through a second time.

Fig. 11. Bottle with
Syphon.

PREPARATION OF SUBSTANCES FOR COLLODION. 15

The ether having been well washed, now requires to
be dried and distilled ; this is done by pouring the ether
remaining in the washing bottle into a distilling vessel
containing some few pieces of quicklime.

A convenient arrangement of apparatus for the distil-
lation of small quantities of ether, is shown at Fig. 18 ;
where larger quantities are operated on, the glass retort
should be replaced by a vessel of zinc or tin plate. A is
a small furnace for' charcoal, B a vessel of copper or iron
of some convenient form, to hold a small quantity of water,
C a glass retort or other vessel, the opening of which
is attached, by means of a cork, to a small leaden tube
about the thickness of the little finger, and 1 J yards long ;

Fig. 18. Apparatus lor distilling Ether.

a portion of this tube is surrounded by another about
2 inches in diameter, and f ths of a yard long ; the top and
bottom of this tube is closed perfectly water-tight round
the smaller tube, it has also an overflow tube (a) at the
top part, -and a funnel and tube (6) at the bottom,
through which a stream of cold water can be passed
from any convenient vessel, as F, and discharged into the
receptacle H. The end of the small leaden tube is bent
so as to dip into a perfectly clean bottle (G) ; in every
other respect the figure will convey a correct idea of the
construction of the apparatus.

When about to be used, each separate part of the
apparatus should be perfectly cleaned and washed out

16 PHOTOGRAPHIC PROCESSES.

with water, and arranged as described and shown in the
cut. The glass retort (0) or other vessel, is filled for
about one -fourth its volume, with small pieces of quick-
lime, and the washed ether poured on to it until two-
thirds of the bulk of the retort is filled ; the end of the
leaden tube is then attached to the neck of the retort, and
the refrigerator E D arranged in an inclined position,
and firmly fixed by its support (d) so that the bent end
of the tube dips into the mouth of the bottle, G, which
is to receive the distilled ether. The whole being thus
arranged, a small quantity of water is poured into the
vessel B, so that the lower portion of the retort 0 is
immersed in it, forming what is called a water bath;
some lighted charcoal is now placed in the furnace A,
and the water in the vessel B becoming heated, com-
municates its heat to the ether in the retort, which begins
to evaporate, and in a short time drops of ether appear
at the bottom of the leaden tube, and the distillation
begins.* The water in the vessel B gets more and more
heated as the bulk of ether in the retort diminishes, until
no more drops are perceived to fall from the end of the
tube ; the fire is now removed, the apparatus separated,
and the retort (0) or other vessel at once cleaned out,
for should this be delayed, it becomes very difficult of
performance.

The heat of the fire must be kept as much as possible
from the bottle (G) containing the distilled ether, and a
current of very cold water passed through the refrigerator
E D, otherwise the ether vapour is not condensed. Sul-
phuric ether, rectified in the manner described, although
not absolutely and chemically pure, is nevertheless well
adapted for photographic purposes.

3. Gun-cotton.

Gun-cotton, also termed " pyroxyline," is nothing more
than ordinary cotton combined with peroxide of nitrogen.
It can be prepared by plunging cotton wool for a few
minutes into concentrated nitric acid, then washed in
water and dried; but in order to obtain a good pyroxy-
line for photographic purposes, a particular process must

* See Note 2.

PREPARATION OF SUBSTANCES FOR COLLODION. 17

be followed, and a rigorous attention paid to each
separate detail. Gun-cotton in appearance much re-
sembles ordinary cotton, but it is heavier, and its fibres
break more easily ; it possesses also a slightly yellow tint,
which resembles that of raw cotton as imported into
Europe from the colonies. It is insoluble in water,
alcohol, pure ether, sulphuret of carbon, or chloroform,
but it dissolves in acetate of ethyle and methyle, methylic
alcohol, acetone, and also in alcoholised ether.

Pyroxyline burns with violence when brought in con-
tact with any flame ; so much so as in many instances to
answer the purpose of common gunpowder.

The solution of gun-cotton in alcoholised ether is called
collodion, and is employed in surgery and photography ;
but for this latter purpose it requires to be specially
manufactured.

The following is the method of preparing gun-cotton for
photography, although we strongly recommend its being
purchased ready made, as photography being now so ex-
tensively employed, gun-cotton is prepared on a large
scale, and at a low price.

In a porcelain mortar is placed 2 ozs. of saltpetre in
fine powder, and over it is poured 3 ozs. by weight of
sulphuric acid of commerce. With the pestle, or a large
glass tube, the materials are well mixed, so as to obtain
a homogeneous paste. In this is immersed, in successive
portions, £ oz. of carded cotton, free from any mechanical
impurities. The cotton is pressed down with the pestle
until thoroughly wetted and imbedded in the liquid paste.
The mortar is then covered with a plate, to prevent the
nitrous vapours which are given off from vitiating the air
of the laboratory. It is also advisable to perform this
operation, if possible, in the open air.

The cotton is left in this mixture for ten minutes;
the mortar is then placed in an inclined position, and
water poured into it, at the same time pressing the cotton
with the pestle so as rapidly to remove the excess of acid.
After washing for a half minute in this manner, it is taken
up with the hands and thrown into a wooden tub filled
with water, and well kneaded ; or else held under a water-
cock, and constantly worked about, and from time to time
pressed strongly between the hands. This washing should

18 PHOTOGRAPHIC PPtOCESSES.

be thoroughly done, until a portion of the cotton, when put
in contact with blue litmus paper,* does not produce a red
stain. It is then strongly pressed, and left to dry in the
air or in the sun, having previously spread it out thinly,
so as to present a large surface to the air. When the
cotton is dry it is preserved in glass bottles, well stopped.
Gun-cotton, thus prepared, very often gives traces of sul-
phate of potass ; but as this substance is absolutely inso-
luble in ether and alcohol, it is of no importance.

Large quantities of gun-cotton should not be bought
or prepared at one time, as it appears to be liable to
decompose by keeping.

Gun-cotton, or pyroxyline, can be prepared according
to the formula given above from paper, linen, or hemp ;
but these preparations have not been sufficiently studied
for us to recommend their employment in photography.

At the end of this volume (JSfote 3) some details are
given relative to the manufacture of gun-cotton on a large
scale by a mixture of nitric and sulphuric acids. In
general, the gun-cotton so prepared is less soluble than
that which has just been described ; it, however, yields
an excellent collodion, especially adapted for coating large
plates, from its being very adherent.

Gun-cotton was discovered by M. Schonbein, a Ger-
man chemist, in 1846. The photographic process which
employs collodion as its basis was first described by
Mr. Archer, in England, in 1851. M. Schonbein prepared
gun-cotton by steeping cotton in monohydrated nitric
acid. Afterwards M. Meynier discovered the advantage
of using a mixture of concentrated nitric and sulphuric
acids, and the method of preparation with saltpetre and

* Blue litmus paper is turned red by acids ; red litmus paper is turned
blue by alkalies. These two papers can be bought ready prepared, or
they can be made in the following way : — Half a pound of litmus, in
small cakes, is boiled in an iron vessel- with one quart of water for some
minutes, and then poured through a fine piece of linen, to separate the
undissolved portion. This solution is spread over paper by means of a
camel's hair brush, and the blue paper thus obtained hung over a cord to
dry. To make the red paper, a small quantity of vinegar is added to the
foregoing blue liquid until it becomes of a reddish colour. It is best to
cover the paper on both sides, and to cut it into small bands, which
should be kept in closed bottles, so as to prevent the action of acid or
alkaline vapours.

PREPARATION OP SUBSTANCES FOR COLLODION. 19

sulphuric acid is due to M. Marc Antoine Gaudin, calcu-
lator in the Bureau des Longitudes of France.

In connection with the method of preparing collodion,
presently to be described, will be indicated some other
important points as further guides to the selection or
manufacture of a good gun-cotton.

4. The Iodides and Bromides employed in the Prepara-
tion of Photographic Collodion.

A great number of iodides, bromides, and their com-
pounds have been at various times proposed for sensitising
collodion, but the formula most to be recommended is a
mixture of iodide and bromide of cadmium. In Note 4
will be found some remarks on the employment of the
iodides and bromides of potassium and ammonium.

Cadmium is now easily procured, almost in a pure state,
and at a comparatively cheap price. This metal is generally
found in commerce in small cylindrical ingots, about four
inches in length, and one -fourth in diameter. Its purity
can be known by its making a ringing crackling noise
when bent, like tin. If it bends with difficulty, and pro-
duces no sound when bent, it contains some other metals,
usually copper and zinc.

Iodine is a crystalline substance, having the aspect of
black-lead, or plumbago, volatile at a slight increase of
temperature, giving off purple vapours, highly corrosive,
and irritating to the eyes ; it should always be preserved
in glass-stoppered bottles. It is obtained from the ashes
of burnt sea-weeds.

Bromine. — This substance is obtained from sea-water,
after all the common salt has been removed by boiling.
It is a very dense, dark red liquid ; its vapour is highly
injurious and corrosive, and, from its great volatility, is
always kept under a stratum of water or sulphuric acid,
and in glass-stoppered bottles. Both iodine and bromine
are easily procured from any chemist.

Iodide of cadmium is thus prepared : — In a glass flask,
containing a quart of water, at first put in 8 ozs. of iodine,
and immediately after 4 ozs. of cadmium in small pieces.
The flask is placed on a stove, moderately heated, in such
a manner that the water in the flask shall be kept only

20 PHOTOGRAPHIC PROCESSES.

warm, not boiling. At the end of a few hours, especially
if shaken from time to time, the liquid, from red, which it
was at first, will become entirely colourless. Leave it
to cool, and then filter. The cadmium that remains may
be used for another operation.

The solution of iodide of cadmium thus obtained, is
evaporated in a porcelain capsule. After a certain time
crystals will appear in the liquid. It is then placed on a
very hot store, where all the water is driven off, and a dry
mass obtained. The resulting substance is detached from
the capsule with a knife, then reduced to a fine powder
in a mortar, and finally preserved in a stoppered bottle.

The iodide of cadmium thus prepared is of a yellow tint,
very soluble in water and alcohol, but less soluble in ether.

Bromide of cadmium is made by pouring 6 ozs. of
bromine into 1 quart of water, contained in a stoppered
flask ; 4 ozs. of cadmium, in small pieces, are now added,
and the flask closed. This mixture is left for some days,
and very carefully shaken from time to time ; the liquid
gradually becomes discoloured, from the absorption of the
bromine ; when this takes, place it is filtered and evapo-
rated to dryness, as described for iodide of cadmium.

Bromide of cadmium is of a white colour, and less
soluble in water and alcohol than the iodide. These sub-
stances, when prepared for sale on a large scale, are
obtained beautifully crystallised, which may be taken as
an evidence of their purity.

CHAPTER III.

PREPARATION OF PHOTOGRAPHIC COLLODION.

As the preparation of photographic collodion requires a
considerable degree of nicety in the operations of mea-
suring and weighing, it will not be out of place here to
make a few remarks relative thereto that may be of some
utility to the practical photographer.

Liquids are measured in glass vessels graduated into

PREPARATION OF PHOTOGRAPHIC COLLODION.

21

ounces, drachms, and minims, the indicating signs and
relative quantities of which are shown
in the following table : —

1 pint contains 20 ounces, ^ xx.

5 j, or 1 ounce, contains 8 drachms, 5 viij.

5 j, or 1 drachm, contains 60 minims.

Three of these graduated glasses
will be found necessary — one of the
shape Fig. 19, to hold 1 pint, and Fig.2o. Fig. iy.
divided into ounces; another of the Divided Measuring Glasses,
same shape, to contain 2 ozs. and divided into drachms,
and a small measure, of the form of Fig. 20, holding
2 drachms and graduated into minims. When used for
measuring liquids, they should be held horizontally, on a
level with the eye, and the fluid poured in until its surface
reaches the line corresponding with the required figure
on the glass. As these graduated glasses have lines cor-
responding with each other both at the front and back, the
proper position of the measure as regards its level is easily
shown.

\Fig. 21. Table Balance.

The table balance, Fig. 21, will be found the most con-
venient form for weighing quantities up
to 2 Ibs. It should have a set of weights
from \ oz. to 2 Ibs.

For weighing smaller quantities, the
hand scales, Fig. 22, is required. The pans
should be made of glass, and there should
be a suitable set of weights, from \ grain
to 2 drachms. Glass is the best material
for the scale-pans; but if formed of metal,
it will be requisite, before proceeding to
weigh any chemical, to place a piece of Fifft 22. Hand
paper of equal dimensions in each pan, by Scales,
which arrangement the whole of the substance is con-

22 PHOTOGRAPHIC PROCESSES.

veniently removed after weighing, and any injurious action
avoided. When fluids are required to be weighed, a
glass or other vessel to hold the liquid, is first accurately
balanced or counterpoised, and then the weighing done
in the ordinary manner.

The preparation of Iodised Collodion requires the
following substances : —

Ether, sp. gr. -720 3 ounces.

Alcohol, sp. gr. -805 li ,,

Gun-cotton 16 grains.

Iodide of Cadmium in powder 18 ,,

Bromide of Cadmium ,, 6 ,,

The gun-cotton is first put into a suitable glass bottle,
afterwards the iodide and bromide of cadmium and the
alcohol. The mixture is then strongly agitated to dis-
solve the salts of cadmium, and to open the fibres of
the cotton, and facilitate its subsequent solution. The
ether is now added, and the whole again well shaken
until the cotton is dissolved, when the bottle is closed
with a good cork, and left to settle for twenty -four hours,
after which the clear and limpid portion is decanted into
small glass bottles for use.

From the circumstance that collodion containing the
iodiser as above is liable to decompose, it will generally
be found preferable to prepare the collodion and iodising
solution separately in the following manner.

Plain thick Collodion, without iodides or bromides, is
first prepared as follows : —

Into a bottle of about one quart capacity is placed —

No. 1.

Gun-cotton 450 grains.

Alcohol 7 ounces,

Ether 25 „

These materials are very strongly agitated together,
and left to settle for some days.

A solution of iodide and bromide is also prepared
thus : —

No. 2.

Alcohol - 3f ounces.

Iodide of Cadmium 154 grains.

Bromide of Cadmium 54 grains.

PREPARATION OF PHOTOGRAPHIC COLLODION. 23

The iodide and bromide of cadmium should be ground
very fine in a porcelain or glass mortar with a small
quantity of the alcohol, then the remainder added, and
when the salts are dissolved, the whole carefully filtered.
The clear solution must be preserved in a well-stopped
bottle.

To prepare Sensitised Collodion, pour into a four-
ounce bottle — •

Thick Collodion (No. 1.) 1 ounce.

Solution of Iodide and Bromide (No. 2.) ... 3 drachms.

Alcohol 6 drachms.

Ether If ounce.

Immediately after the bottle has been well shaken, so
as properly to mix the ingredients, the sensitised or
iodised collodion is ready for use, but is improved by being
kept a few hours after sensitising before being applied.

Both the plain collodion and the alcoholic solution of
iodide and bromide of cadmium can be preserved for any
length of time without deterioration, provided they are
kept separate and in well-closed bottles ; and the sensi-
tised collodion can, therefore, be prepared when required
with great facility.

The formula for sensitised collodion just given will be
found to work best at a mean temperature of 60° Fahr.
When the weather is very hot a little more alcohol must
be added, and the quantity of ether slightly diminished ;
and, on the contrary, when the atmosphere is very cold
the alcohol may be diminished, and the ether increased.

When a glass plate is coated with collodion, a larger
quantity is poured over its surface than is really required,
the surplus being received in a bottle ; it will therefore
be easily understood that after a considerable number of
plates have, been coated, the proper relative proportions
of the constituents of the collodion will have been dis-
turbed by evaporation, and that both ether and alcohol
must be added to bring it to its normal condition. It
must be borne in mind in making the required addition of
ether and alcohol, that ether being much more volatile
than alcohol, a larger relative proportion will have evapo-
rated, and consequently a larger quantity of ether mast
be used than of alcohol.

24: PHOTOGRAPHIC PROCESSES.

If the layer of collodion on the glass appears too thin,
a little of the thick collodion, No. 1, must be added ; if,
on the contrary, it be too thick, and in consequence does
not spread evenly over the glass, it can be diluted with
a small quantity of a mixture of two parts of ether and
one of alcohol.

If the collodion film detaches itself from the glass plate
after being sensitised in the silver bath, it indicates that a
larger proportion of ether is required, or that the gun-
cotton employed is not suitable, in which case recourse
may be had to a gun-cotton prepared according to the
formula given in Note 3, which produces a very adhesive
collodion, especially applicable when glasses of large
dimensions are employed.

If too much alcohol be added to the collodion, the film
is liable to become detached, and the coating itself has a
wavy uneven appearance. If there be too much ether
the layer is very adhesive, but it is difficult to get the
collodion to spread itself evenly over the plate, especially
if it be of any large size.

Collodion ought to be preserved in well-stopped bottles,
but it is indifferent whether bottles with glass stoppers
or furnished with good corks be employed ; they ought,
however, as much as possible, to be kept quite full, and
in the dark.

Iodised collodion is never good the first day of its pre-
paration ; it must be kept for at least two days to acquire
all its properties ; neither must it be kept too long, for
impressions are then taken with it less rapidly.

Collodion is very unstable; sometimes without any
apparent reason it becomes slow in producing im-
pressions ; at other times it changes to a red colour at
the end' of a few days. In this latter case recourse ought
to be had to a new preparation, and care taken to ascer-
tain if the materials previously employed were sufficiently
pure. The colour of good collodion is commonly of a
very light lemon colour, although sometimes completely
colourless.

A very clear and perfectly settled collodion must
always be made use of. The following is an excellent
little apparatus for pouring out collodion free from
sediment.

CLEANING GLASS PLATES, ETC. 25

A very tall and narrow bottle must be procured of the
form indicated by Fig. 23. The cork a is pierced with
two holes made with a round file ;
two small glass tubes are fitted to it,
of which A goes a little way through
the cork, and the other is bent down
in the form of H> only one branch is
shorter than the other. The longer
branch is dipped into the collodion at
a short distance from the bottom.
After a certain quantity of collodion
has been used for several hours, what
remains should be poured into the
bottle by lifting the cork a, which
must be again replaced. The next
morning the collodion will be per-
fectly settled, and by blowing into
the tube A, the clear liquid passes by the tube D a B,
from the extremity of which it is received into a proper
bottle.

Care must be taken that the surface of the collodion be
lower than the extremity of the tube B ; should it be
otherwise the tube must be raised by causing it to pass
through the cork, or else the collodion would continue
to flow after the required quantity had been decanted.

CHAPTER IV.

CLEANING GLASS PLATES, ETC.

GLASS plates for photographic purposes are employed
with ground edges — that is to say, the glasses, after
being cut with a diamond, are ground on their edges by
means of a fine file, aided by oil of turpentine. The
object of this operation is to prevent the operator from
cutting himself upon the sharp edges of the glass.

In place of crystal sheet, ordinary patent plate, or
even flatted crown glasses may be used, especially for

Zb PHOTOGRAPHIC PROCESSES.

the smaller-sized (under half- plate). Patent plate being
more perfectly polished than flatted crown, is also more
easily cleaned, and therefore preferable.

Whatever be the kind of glass employed, the following
is the method which should be pursued in cleaning the
plates whether they have been used before or not : —

A mixture of equal quantities of nitric acid and water
is made, and the glasses covered therewith on both sides
by the aid of some cotton-wool fastened to the end of a
stick ; and as each plate is successively treated in this
manner, they are placed against the wall to drain.

Instead of nitric acid a solution of carbonate of potash,
of the strength of one pound to one quart of water, may
be advantageously employed. The liquid acts energe-
tically upon plates that have been previously used, and
is free from the objection to which nitric acid is open,
namely, that of staining the hands yellow.

It is always a good plan to clean a number of plates at
the same time — as many as twenty, for instance — because it
is necessary to allow the alkaline or acid solution to act for
at least an hour. The plates are then submitted to the
action of a strong current of water, and rubbed at the same
time on both sides with a sponge, in order to remove all
impurities. It is almost unnecessary to add that they are
finished by allowing the water to flow in all directions,
copiously, on the inclined plate, to carry off every trace of
dust. The glasses are then placed in a grooved frame, similar

Fig. 24. Support for Cleaned Plates.

to Fig. 24, which precludes the necessity of description,
where they are allowed to drain and dry. The photo-

CLEANING GLASS PLATES, ETC.

27:

grapber should furnisli himself with several of these
JraiDing frames of different sizes, for they will be found
very convenient.

The glass having been cleaned, is not yet sufficiently
pure to receive the collodion : it is further necessary to
resort to a more complete polishing. For this purpose an
oak plate -holder, of the form A B, Fig. 25, and of
suitable size should be used. At the end B is placed a
piece of wood about the thickness of a crown -piece. A

Fig. 27. Fig. 26. Fig. 25.

Tripoli Bottle and Plate-holder.

groove, c d, admits of a second piece, e, fixed underneath
by a clamp-screw, Fig. 27, to fix the plate a b, of any
size within the dimensions of the plate-holder.

In addition to this, there should be near at hand a box
containing powdered tripoli, and a bottle furnished with
a tube of small bore, Fig. 27, containing alcohol. The
glass being fixed on the plate -holder, Fig. 27, is well
dusted with tripoli, a few drops of alcohol are poured
upon it, and then, by means of a little cotton -wool, or
papier Joseph, the mixture is rubbed all over, carefully
avoiding contact between the fingers and the glass.
The rubbing is repeated, but without pressing too hard,
until the alcohol has entirely evaporated, and the plate is
dry. The excess of adherent tripoli being removed by a
c 2

28 PHOTOGRAPHIC PROCESSES.

dry linen cloth set apart for this especial purpose, the
final polish is given with an exceedingly dry buckskin or
chamois leather, which should also be used exclusively for
this operation.

The plate is then removed from the plate -holder, its
edges and back wiped, and placed in a grooved plate -
box. Care should be taken that that side of the glass
which has been polished for the reception of the collodion
film, should in each case face the same way, in order to
avoid errors in pouring on the collodion.

The plates should never be cleaned more than twelve
hours before using, especially if the box in which they
are contained is likely to be carried about, as in that case
they would again become covered with minute particles
of dust

CHAPTER V.

ON THE DARK ROOM, AND PHOTOGRAPHIC LABORATORY.

IN the practice of photography, three different rooms are
necessary : one well lighted, in which the sitter is placed ;
another of commodious dimensions, which serves the
purpose of a laboratory ; and a third made quite dark, in
which are performed all those operations which may not
see the light of day.

The laboratory should be of such dimensions as are
adapted to meet the wants of the photographer. Amateurs
generally take plenty of room, because in most cases it
costs them nothing ; but professional photographers are
oftener obliged to content themselves with a small apart-
ment, which frequently serves the double purpose of dark
room and laboratory.

However this may be, it is best to have a large room,
where preparations can be made, positive proofs printed,
&c., on the ground floor, well furnished with drawers
and tables.

The dark chamber ought to be, on the contrary, very

DARK ROOM, AND PHOTOGRAPHIC LABORATORY. 29

simple. Two or three tables are sufficient, and the light
ohould either be entirely excluded by pasting black paper
over the windows, and the operations conducted by the
light of a candle or a gas jet, surrounded by a square
lantern of yellow glass, or else, as often preferred, the dark
room is so arranged that the light comes exclusively
through a frame of yellow glass about 10 inches by 8 inches,
and this covered with a sheet of very thin white paper, in
order to impede the passage of the direct solar rays. A
hinged frame is fitted in front of this square of yellow
glass in such a way as to admit of its being totally or
partially covered, in order to diminish or increase the
amount of illumination at pleasure.

Fig. 28. Dark Chamber.

It is necessary to select glass of a deep yellow colour,
and avoid the paler kinds.

The drawing (Fig. 28) represents the dark chamber
which has been used for many years by M. Monkhoven.

The entrance is at the bottom of the room, and the
door, for greater security, covered with a black drapery.
A cistern of water, furnished with a tap, supplies the
necessary means for washing, and underneath this is

30 PHOTOGRAPHIC PROCESSES.

placed the sink, with a pipe to convey the waste water
outside. On one side should be placed the dishes used
for nitrate of silver bath, and for sensitising albumenised
paper, and on the other those which appertain to fixing,
and other operations incompatible with the nitrate of
silver solution. Shelves should also be fitted up to
support funnels while filtering, bottles, &c.

A second reference to Fig. 28 will show the arrange-
ment by which the amount of light is regulated; it will
be seen, in fact, that by lowering the yellow frame, which
is shown in that position in the drawing, the room
becomes inundated with light. This frame need be
closed only when the plate is immersed in the nitrate
of silver bath, and during the development of the image.
When the required intensity has been attained in the
last operation, the plate is washed and the frame lowered
in order to see more clearly. If the sun shines on this
window, it is absolutely necessary to paste over it some
thin paper to stop the too direct rays.

CHAPTER VI.

COATING WITH COLLODION AND SENSITISING THE PLATE.

THE nitrate of silver bath is prepared by dissolving —
Pure Nitrate of Silver 2 ounces.

IN

Distilled or Bain Water 24 ounces.

This liquid is filtered and poured into a gutta-percha
tray. The collodion, spread upon the glass, is plunged into
the nitrate of silver bath ; the film whitens by the trans-
formation of the iodide of cadmium into iodide of silver,
which is sensitive to light, and it is in this state that it
should be exposed in the camera.

Such is a general statement of the process to be now
described somewhat in detail.

COATING AND SENSITISING THE PLATE.

31

The collodion ought to be contained in a bottle with
a wide month (Fig. 29), which month should always
be carefully cleaned before pouring the col-
lodion on the glass.

The box containing the cleaned glasses
being placed in the dark chamber, a plate is
withdrawn, and the dust removed from the
polished side by means of a large badger-hair
brush ; then holding the plate by one corner
(Fig. 30), in the right hand, the collodion is
poured upon it from the left hand, com-
mencing at the corner B. It is then allowed
to flow by inclining the plate from left to right,
and finally draining back into a separate
bottle from the corner D, Fig. 31. If, at this moment,
the plate be examined in a particular light, it will be seen
that it is covered with an infinity of small ridges in the

Fig. 29

Fig. 30. Coating tiie Plate.

direction B D (Fig. 30) ; but on inclining the plate
rapidly from left to right, these ridges will disappear.
As soon as this happens, the plate is ready to be immersed
in the nitrate of silver bath ; but it is always advisable
to wait a few seconds (and how many, experience alone
can indicate precisely), so that the film may be suffi-
ciently " set." There are certain characteristics by which
it may be determined if the right moment has arrived for
sensitising the plate ; these are : —

1. If the plate is immersed in the bath before the

32

PHOTOGRAPHIC PROCESSES.

collodion has been allowed time to " set," the film will
become detached in fragments ; and, in this case, it will
be necessary to filter the bath.

2. If the immersion take
place at the right time, the film
whitens gradually.

3. If, on the other hand, the
film be allowed to become too
dry before immersion, it
whitens instantly, and a good
proof is never obtainable under
these circumstances.

Up to a certain point it is
not difficult to determine when
the plate should be immersed
in the nitrate of silver bath. It
will be found if the plate is
looked at in a certain light, that
it has assumed a dull, un-
polished appearance. This,
which is the right moment
for immersion, will be arrived
at in summer probably in about
twenty seconds, while in winter it will probably take
sixty seconds.

Nitrate of silver bath is very easy to
prepare. It is quite as well for those
whose operations are conducted on a
somewhat extensive scale to have a
considerable quantity of bath solution,
and keep it in a large bottle to which is
adapted a funnel and filter, Fig. 32.
The same filter will last a long time ;
and, on leaving work, the nitrate of
silver bath whicli has been used during
the day is poured into the filter, and in
this way a solution in proper condition
is always maintained at hand.

. 32. Apparatus for For the nitrate of silver bath, dishes
fi%1i™rNBlrth.e °' in gutta-percha, porcelain, or wood with
glass bottoms, are used, Figs. 33, 34, 37.
Gutta-percha dishes are, perhaps, most frequently em-

Fig. 31. Receiving the Collodion
into a separate Bottle.

COATING AND SENSITISING THE PLATE.

33

Figs. 33 and 34. Dishes in

Porcelain and Wood with Glass

Bottom.

ployed,* but as vertical baths in glass and gutta-percha
are also used, we shall say a few
words in reference to them.

The reason why we recom-
mend a gutta-percha dish in
preference to one in porcelain
is, that the film itself can be
better seen, as also the impuri-
ties which float in the solution.

There are several methods of
immersing the plates in the
nitrate of silver bath ; and as
this is one of the most impor-
tant points in the present chapter, we will pause to con-
sider it somewhat in detail.

The dish containing the nitrate of silver bath being
much larger than the plate,
is raised at one end, Fig. 38,
in order that the solution
shall accumulate at the op-
posite end ; the plate, pre-
viously coated with collo-
dion, is placed against the other edge, and held there by
means of the finger or a silver wire hook; lowering then
the plate by a continuous motion, and allowing the dish at
the same time to assume the
horizontal position, the liquid
flows at once, and without
stopping, over the whole of the
plate : after this the dish
should be raised and lowered
during a minute or so. Then
introducing underneath the
plate a hook made of flat-
tened silver wire, Fig. 35, and
by its means withdrawing the
plate from the bath, it will be
seen to be covered by a num-
ber of veins which show that the nitrate of silver bath

Fig. 37. Gutta-percha Di.h.

Figs. 35, 36, 39,

* This remark is correct only as far as regards the practice of conti-
nental photographers, — in England glass and porcelain baths are always
employed.

c 3

PHOTOGRAPHIC PROCESSES.

has not thoroughly penetrated the film, and that, there-
fore, the plate should be raised and lowered alternately
until the silver solution flows evenly and smoothly over
the whole surface of the film.

It is at this point that the plate should be withdrawn,
the fingers being covered with India-rubber finger-stalls,

in the absence of which
box -wood forceps, or an
American clip, should
be used, as the nitrate
of silver blackens the
hands very strongly
(Note 5). The plate
is allowed to drain from
the excess of adherent
nitrate of silver solution,
and is then placed in
the camera frame.

This method of ope-
rating requires only a
small quantity of nitrate
of silver bath solution,
which is accordingly
exhausted in a propor-
The plan we are about to describe

Figs. 40, 41. Vertical Glass Bath.

tionately shorter time.

requires, on the contrary, a large bulk of solution, which

COATING AND SENSITISING THE PLATE.

has the advantage of becoming very slowly exhausted.
Moreover, a vessel may be used which is only just large
enough to allow the plate to be immersed and withdrawn
with freedom.

The solution is contained in a vertical bath, either of
glass or gutta-percha, Fig. 40 ; and by means of a hook
or dipper of gutta-percha, which is introduced on the
lower side of the vessel, the plate is immersed by one
continuous motion into the fluid, raising and lowering
it alternately as before. The plate is finally withdrawn
ready for exposure, when the ridges or lines thereon have
disappeared. In Note 6 are given details for the prepa-
ration of nitrate of silver bath.

Another plan we can much recommend is as fol-
lows : — Two silver hooks are first procured, made oi
flat sheet silver, and bifurcate, of the shape shown in
Fig. 37. The nitrate of silver bath being contained in a
dish (Fig. 42) of gutta-percha, the plate is held between
the two hooks, the film
being uppermost, and
plunged at one stroke
beneath the liquid, tak-
ing care at the same
time that one end is
immersed before the
other, for unless this be
done the liquid will spirt
out of the dish. The
plate being once fairly
covered by the solution,
one of the hooks is re-
moved ; and with the
other the plate is raised
and lowered, in order to
get rid of- the veins or greasiness of which we have spoken
above.

Instead of two hooks, it may be found more advan-
tageous to use the two combined in one, as shown in
Fig. 42. We may observe, in passing, that the silver
hooks may be replaced by others made of whalebone.
In order to make these, it is necessary to hold them in
the flame of a spirit-lamp until they bend, and to allow

36 PHOTOGRAPHIC PROCESSES.

them to cool, maintaining pressure in the proper curve
by means of the fingers until quite cold.

Whichever method is followed in immersing the plate
in the nitrate of silver bath, it is indispensably necessary
that it be the result of one steady and continuous motion;
for if this be not the case, lines will be formed upon the
film, which will become apparent very soon in irreparable
stains.

To preserve the hands from the action of nitrate of
silver, some amateurs use India-rubber finger-stalls, or
gloves of the same material ; but such apparatus will be
found very inconvenient, and those who intend to be suc-
cessful in photography should make up their minds before
going into it, to sacrifice the delicacy of their hands and
the whiteness of their shirt-cuffs.

We presume it is hardly necessary to observe that, at
the time of sensitising the plate, the room should be made
quite dark — an operation easily accomplished by moving
the shutter in front of the yellow glass until the light is
almost entirely excluded. With a little practice this will
be found comparatively easy.

As soon as the plate is placed in the camera-back, the
window and door may be opened, and the bath covered
with a plate of glass, in order to preserve it from dust.

CHAPTER VII.

PHOTOGRAPHIC CAMERAS, LENSES, ETC.

THE common camera-obscura is supposed to have been
discovered by Baptiste Porta, about the year 1590. It
may be simply described as a box, at one end of which
is fixed a piece of ground glass, and at the other a convex
or magnifying -glass, mounted in a sliding tube to regulate
the focus.

All convex or concave glasses are called lenses; the
focus of a convex glass or lens is the distance between

PHOTOGRAPHIC CAMERAS, LENSES, ETC. 37

the glass when exposed to the sun, and the point or spot
of light where the rays unite (Fig. 43). (See Note 6.)

If the distance between the A

magnifying lens and the ground
glass of an ordinary camera, be
regulated to the focus as de-
scribed, and the lens directed
towards some distant objects, it
will be seen, on so shading the
ground glass with a black cloth Ftg' 43>

placed over the head as to prevent any lateral rays of
light falling on it, that the image of those distant objects
are clearly represented reversed on the ground glass. If
the camera be now directed to some near objects they
will not appear distinct, and the lens will require to be
drawn out further from the ground glass before they are
shown with perfect sharpness. This adjustment of the
lens is called focussing the image.

It will be found impossible, however, to focus the
whole of the objects perfectly ; there will always be cer-
tain parts of the picture which want distinctness. But if
a piece of cardboard, having a small hole in it, be placed
& short distance in front of the lens, the image on the
shaded ground glass will become much more distinct
and sharp, or, in other words, the picture can be better
focussecl. Any similar arrangement to that described is
called a stop or diaphragm.

The foregoing remarks will explain the principles and
construction of the photographic camera, which essentially

Fig. 44. Ordinary form of Photographic Camera.

consists of two parts — the lens or objective, and the box
or camera. However, it will be easily understood that

38

PHOTOGRAPHIC PROCESSES.

these two apparatuses, to be rendered suitable for the
various purposes of photography, must of necessity re-
quire more special and compli-
cated construction than has been
described.

The ordinary form of a photo-
graphic camera, Fig. 44, consists
of a box, B, in which slides
another box, A, holding the frame
C with the ground glass. For
• the purpose of fixing the sliding
part A, a board, D, is fastened to
the box B in which is a groove,
as shown in the drawing. On
the lower side of the box A is
fixed a plate with a thumb-screw
passing into the groove. Thus,
within certain limits, the two
boxes A and B can be adjusted to
various lengths, and fixed at the
required focus by the aid of the
thumb-screw. The lens is placed
in front of B.

This form of camera has gene-
rally a single sliding-box, A ; but
sometimes, however, for the sake
of portability, they are constructed
with several slides. The mate-
rial of which these cameras are
made is usually mahogany or
walnut wood.

The tripod, or camera stand,
for supporting the camera, is
usually of two kinds — one for
travelling, the other for use in
the operating room for portraits,
&c.

The travelling stand, Fig. 45.

consists of a strong wooden or
I*. 45. Tripod Stand. ^j ^^ ^ ^.^ ^

made to slip three feet, which for greater strength and
firmness are made double. These feet for convenience in

PHOTOGRAPHIC CAMERAS, LENSES, ETC.

travelling, can easily be doubled up, and removed from
the triangle by unscrewing the joints.

There are many different models of tripod stands for
travelling, but they are all more or less on the principle
of the one just described, and are made lighter or stronger
as may be required for the size of camera. A black

Fig. 46. Stand for Operating Room, and Camera for " Cartes de Visite."

cloth, so constructed as to cover over the extended tripod
stand, forms a convenient dark chamber for changing
sensitised glasses from or to the camera back when dry
collodion plates are employed.

The stand used in the operating room or studio, not

PHOTOGRAPHIC PROCESSES.

requiring to be moved any distance from place to place,
may be of a much stouter and heavier construction than
the ordinary tripod stand. The form of camera stand repre-
sented Fig. 4(5, combines solidity with facility of adjust-
ment. The upper board supports the camera, and in order
to allow of a tilting motion is connected with two half
circles of wood, which can be fixed in position by a thumb-
screw to an upright sliding frame, moving in a socket of the
firm tripod stand. This sliding frame serves to adjust the
height of the camera. Sometimes this form of stand has
a winch, with rack or chain, to facilitate the raising and
lowering of the camera. This addition is very convenient,
especially when a heavy camera is employed.

A convenient form of camera for travelling, and suit-
able for plates 12 inches by 10 inches, and larger sizes, is
represented at Fig. 47. B is a fixed box, pierced in front
with a round hole, to which is attached the lens. Under-
neath, and on the side (c) are two pieces of brass, in each
of which can be fixed a thumb-screw, as seen at a. The
sliding body A has also two similar pieces, one at d, the
other underneath, each having a thumb-screw. The top
of the tripod (which is seen in the figure) has a hollow,
in which a long piece of wood b can be fixed ; this has a
groove in the middle, to admit the two thumb -screws.

Fig. 47. Camera without a Tail-piece.

By this arrangement, on turning the screw a, a very
great degree of firmness is given to the part B of the
camera ; also to the tail-board 6, and the top of the
tripod. The sliding body A can be drawn out or in,
and fixed as the operator wishes. The instrument can
also be used on its side (the two pieces of brass which

PHOTOGRAPHIC CAMERAS, LENSES, ETC.

41

are seen at c and d serve for this purpose), enabling up-
right views to be taken with the same facility as long ones.

This form of camera is more convenient than the ordi-
nary form, Fig. 44, especially for taking large views ;
besides which, the immoveable tail-board of the model,
Fig. 44, prevents its being conveniently used on the side
for upright pictures.

Another form of camera, suitable both for the operating
room and for travelling, is represented, Fig. 48. It will

A.

Fig. 48. Bellows-body Camera.

be found extremely light and portable. The construc-
tion of this form of camera will be easily understood from
the cut. M is a square bellows body, connected with the
wooden frames A, a. The frame A, holding the lens, is
firmly fixed to a board n, n, which can be lengthened or
shortened at will. The frame a holds the ground-glass
frame and dark slides.

Whatever may be the form of camera employed, the
general principles to be observed in its use are the
same. For the purpose of illustration, suppose a camera
mounted , on its stand, as shown in Fig. 55, p. 49, and
directed towards a person who stands for a model. On
drawing out the sliding body more or less, a point is
reached where the proper focus is obtained. As before
mentioned, the head of the operator and the top of the
camera must be covered with a black cloth, so that the
sharpness of the image on the ground glass can be properly
examined. Fig. 55 represents an operator focussing a person
who is placed before him. If the ground glass be replaced

42

PHOTOGRAPHIC PROCESSES.

Fig. 9. Camera, or Dark Frame.

by a glass plate, covered with sensitised collodion, an image
will be obtained representing the model. The proper
placing of the sensitised plate is accomplished by means
of a frame represented in Fig. 49, and which is always

sold with and forms part of
the camera. This frame, or
camera back, is represented
open, in order to make the
figure better understood. The
glass plate, coated with collo-
dion, after having been taken
out of the silver bath and well
drained, is placed in the ca-
mera frame, with the layer of
collodion towards the shutter
a (which has been previously
closed) ; then the door b is
shut and fastened with hooks,
so that the sensitised layer
is thus preserved from the
light. The ground-glass frame is then removed from
the camera, and the frame (Fig. 49) put in its place.
If the thin sliding board or shutter a be now raised, the
sensitised surface of the glass plate, being exactly in the
same position as occupied by the ground glass, receives the
same image. When it is thought that the light has acted
long enough, the shutter a is closed, the frame removed,
and taken into the dark room, where, on opening the door 6,
the glass plate is removed, and submitted to an operation
to be described under the title of developing the image.

The inner portion of the frame that
holds the sensitised plate has project-
ing corners of silver wire, so arranged
that the plate only touches at these
parts. Thus the woodwork of the
frame is in a great measure protected
from the corrosive action of the nitrate
of silver; and if the precaution be
taken of placing a piece of blotting -

Fig. 50. Glass Frame. PaPer °n the lower Comers and back of

the plate, previously to closing the door
6, the risk of drops of nitrate of silver injuring the frame,

PHOTOGRAPHIC CAMERAS, LENSES, ETC.

and falling during its transport from the dark chamber
to the operating room, will be avoided.

With a camera of a certain size it is very often required
to take smaller pictures, as well as the full size the lens
will produce. This is accomplished by having some extra
frames of wood (Fig. 50) fitting into the larger frame, and
carefully adjusted, that when the
plate is placed in one of these extra
frames its surface shall be exactly
coincident with the position of the
ground glass upon which the focus
was obtained ; if otherwise, it would
be impossible to produce a sharp
and distinct picture.

The glasses employed in photo-
graphy are usually of patent plate,
although good ordinary glass may
be employed for very small sizes.
The glass plates are kept in grooved
wooden boxes (Fig. 51).

There are two kinds of photographic lenses — those
called single lenses, for views ; and double, or combination
lenses, for portraits.

The following are the diameters and focal lengths of
portrait and view lenses suitable for the various sized
glasses usually employed : —

51- Plat9 Box-

FOR PORTRAITS.

Size of Pictures.
Inches.

Ninth size . . .
Quarter plate . .
Ditto for rapid action
Third size ditto
Half plate ,. . .
Whole plate . .

3b,

5
8$

y2

0 1

T

44

Diameter of Lenses.

Focal Length.

Inches.

Inches.

. it

3J

: | :

5^

7

'. si

7
9J

FOR PORTRAITS AND GROUPS.

Size of Pictures.

Inches.

9 by 7

10 „ 8

12 „ 10

15 „ 12

Diameter of Lenses.
Inches.

a

Focal Length.
Inches.

13
15
19

44: PHOTOGRAPHIC PROCESSES.

FOR VIEWS.

Size of Pictures. Diameter of Lenses. Focal Length.

Inches. Inches. Inches.

6 by 5 ... If ... 8

7 ,, 6 ... 2 ... 10
9 „ 7 ... 2| ... 14

12 „ 10 ... 3 ... 16

16 „ 12 ... 4 ... 24

The single, or view lens, is composed of an achromatic
lens, mounted in a tube of brass (Fig. 52), as shown in
the figure. D, the brass cover
of the lens. F, a small brass
tube, holding diaphragms of
various sizes. 0, the brass tube,
having the lens at A screwed
within it, and also furnished with
an outside screw, which allows
the whole mounted lens to be

52. Single, or View Lens. fixed t() the Hng Qf m^ ^

which is attached to the front of the camera.

The view lens is used in the following manner : — It
is fixed to the camera by being screwed into the brass
ring ; the cover D is removed, when the image may be
focussed. All the diaphragms should be removed, except
the one to be employed. The smaller the opening of the
diaphragm, the sharper the image ; but then a longer
time will be required to produce an impression. Thus,
a diaphragm of J inch requires four times as long exposure
as one of -J- inch ; but then the picture produced is much
sharper. It is thus that the operator can, when required,
sacrifice sharpness of detail for rapidity of action.

The lens requires from time to time to be cleansed with
a soft wash-leather ; but in remounting the same in its
cell, it is of the greatest importance that the convex side
of the lens should be towards the sensitive plate.*

The compound, or portrait lens, is composed of a
greater number of lenses. It has a compound lens in
front, which is very thick, being formed of two cemented
together, like the view lens, and two other lenses at the

* View lenses are sometimes mounted, with the diaphragms or stops
fixed in the large tube holding the lens, which either slides in another
tube or is actuated by rackwork, to facilitate the obtaining a correct focus.

PHOTOGRAPHIC CAMERAS, LENSES. ETC. 45

back. Whenever the lenses are removed to be cleaned,
or for any other purpose, it is important that they be
replaced in exactly the same order as when purchased,
otherwise the picture produced can never be good and
sharp. Fig. 53 shows the form of the double, or com-

Fig. 53. Double, or Compound Lens.

pound lens. D is the cover, or cap ; B G, a double tube,
sliding one over the other, capable of being adjusted by
turning the milled head F connected with the rackwork.
Its use is, after the focus has been roughly obtained, by
drawing out the sliding body of the camera, to finally
adjust the same with the greatest ease and nicety. C is
a portion of a larger tube, adapted to screw upon the
tube B, and serves to protect the lens from lateral rays
of light : B, A, the ends where the lenses are fixed.
G, the tube, having a screw at the end for the purpose of
attachment to the ring E. This ring of metal is fixed by
screws upon the front of the camera. H, a diaphragm,
or stop, fitting the interior of the tube 0.

The above are the chief points of difference between
the two varieties of lenses known as the single and
double. The brass mountings of both forms are blacked
inside, to prevent internal reflection, and should this dull
black coating be at any time ren-
dered im'perfect, it can be repaired
by the application of a mixture of
lamp-black and gum -water.*

* In the most recently improved form
of compound lens, the sliding body is pierced
so as to allow a series of diaphragms, or
stops, to be introduced between the two
lenses, as shown in the illustration, Fief. 54.

mi • • • •

1 his arrangement is more correct in prin-
ciple, and produces better results, than the simple external stop.

4:6 FHOTOGKAPH1C PKOCESSES.

With respect to the optical differences of these two
forms, and their special uses, it is to be noted that
the single lens, although of the same size as the double
combination, does not give so brilliant an image upon
the ground glass, because the diaphragms intercept an
enormous quantity of light. The double lens, on the
contrary, has two. lenses, combined in such a way that a
diaphragm is not necessary ; consequently, the images pro-
duced are well illuminated. By stopping off a single lens,
the sharpness of the image is rendered perfect, whereas
with the double combination such a degree of sharpness
cannot be obtained ; therefore the first is employed for
views and buildings, and the latter for portraits.

Another consideration also influences the selection.
It is easy to be understood that a sensitive coating is
impressed more easily in proportion to the brilliancy of
the light striking upon it. Thus, a lens of 3 inches in
diameter, with J inch stop, will require one hundred times
longer exposure than a double combination of lenses of
the same diameter to produce the same picture. Now, is
it not easy to expose for as long a time as may be required
for a view, landscape, flowers, or inanimate objects, so as
to obtain, what ought to be the chief aim, extremely
fine detail in the picture ? In most cases, therefore,
although rapidity can be gained by enlarging the stop,
results will show it had better be avoided. With the
single lens just mentioned, a view, illuminated with the
sun, can be easily obtained in twenty to thirty seconds,
and if there be any persons in the view, they will without
doubt be copied. If, with the same single lens, an endea-
vour be made to take a portrait of a person placed in
the shade, it will require from three to five minutes. Is
it possible to remain so long without moving ? Certainly
not. Now the double lens will allow such a portrait to
be taken in ten seconds ; and although it gives a picture
not quite so sharp as the single lens, it nevertheless is
greatly preferable, and would in reality produce a sharper
picture, for with the single lens no one could remain per-
i'ectly immoveable during a sufficient time.

In certain cases it is also necessary to use a stop with
the double combination lens; but instead of a stop of
^ to J inch for a lens of 3 inches diameter, one of from
I to 1J inch is all that is required. Fig. 54 shows such

PHOTOGRAPHIC CAMERAS, LENSES, ETC. 4:7

a stop at H ; it is placed in the hood 0 of the lens, and
is chiefly employed when a group of portraits is required
to be taken. For the purpose of more clearly compre-
hending the reason for the use of a diaphragm when taking
groups, &c., with a double or compound lens, it may be
remarked that, the more extended the space occupied by an
object, the more light will there be on the ground glass ;
but at the same time, with the double lens there loillbe less
sharpness. An intermediate course is therefore adopted ;
that is to say, a diaphragm is employed, whereby a loss
is incurred in the matter of exposure for the sake of
gaining sharpness and definition.

Generally speaking, a single lens gives so perfect a defini-
tion to the whole of the object, that the operation of obtain-
ing a good focus is extremely easy. It is not so, however,
with the double combination lens; therefore, as a rule, the
head of the sitter should be carefully focussed, and a little
of the details sacrificed, if necessary, to obtain this point.

Compound lenses are manufactured and sold for taking
pictures of a certain size ; this must be understood to
mean the utmost of their capabilities, and those photo-
graphers who may be desirous of obtaining first-class por-
traits should always employ a larger lens than is absolutely
required. The following is a list of compound lenses par-
ticularly adapted to produce the finest portraits of the
given dimensions : —

Size of Picture. Diameter of Lens. Length of Focus.

Inches. Inches. Inches.

4J by 3J ... 2| ... 7

6i „ 4f ... 3J ... 9!

8J „ 6J ... 4± ... 11

10 „ 8 ... 4J ... 15

A new form of lens has lately been constructed for
views, consisting of two lenses, which allows a great
degree of sharpness to be obtained with more flatness of
field than the ordinary single lens. They are termed
orthoscopic or caloscopic. In a special note (Note 8), will
be given a description of some of the principles of optics,
a proper understanding of which will render more clear
many of the foregoing details.

For taking " carte de visite pictures " the best size of
compound lens that can be employed is 2f inches in dia-
meter and 5-inch focus.

4:3 PHOTOGRAPHIC PROCESSES.

CHAPTEE VIII.

ON THE GLASS ROOM IN WHICH THE SITTER IS PLACED,
AND THE RULES TO BE OBSERVED IN TAKING PORTRAITS
AND LANDSCAPES.

To take an artistic portrait, or to choose the most favour-
able point of view for a landscape, requires an artistic
taste not to be acquired by reading, but allied in its cha-
racter to a natural instinct, of which instruction only
develops the germ, while practice simply modifies and
perfects the details. The remarks on the subject-matter
of this chapter will therefore be of an essentially practical
nature.

The general detail and arrangement of an operating
room suitable for photographic purposes, is represented
in the cut on succeeding page. It should be in some
elevated position, either on the roof of the house or on a
platform specially erected for the purpose. The side next
the south should be entirely closed, whilst the other,
towards the north, is glazed. The sheets of glass em-
ployed should be of moderate thickness, as a protection
from storms of hail, &c., and as white as possible — rather of
a bluish tint than approaching at all to a green or yellow
colour. It is of importance to attend to the colour of
the glass used for the operating room, for, should it be of
a green or yellow tint, a considerable amount of actinic
rays* are cut off, and the exposure necessary for a good
portrait is greatly augmented.

The glass rooms should be furnished with curtains
having cords attached to them, by means of which the
too energetic action of the light may be moderated, and
proper direction given to it. In the figure it will be
seen that three sets of squares are shown — the upper one
(of ground glass), which is parallel with the floor or
ceiling ; the lower one, which replaces the wall ; and the
middle one, which is on the slope.

* Those rays of light which produce chemical action, and are found
at the blue and violet end of the spectrum.

THE OPERATING ROOM.

49

If now, with the object of producing an artistic effect,
it be desired to inundate the front of the model or sitter
with light, the lower and middle set of curtains should be
more or less closed. If a lateral lighting be desired, the
curtains of the upper window should, on the contrary, be

closed. The good taste of the operator must, however,
guide him as to the best disposition of the light.

On the right of the engraving, Fig. 55, is represented
the shaft of a column, against which the model may lean ;
also a balustrade, with a landscape painted in distemper ;

50 PHOTOGRAPHIC PROCESSES.

and near the middle a white marble chimney-piece of the
style of Louis XV. ; all of which accessories, or others of
a similar character, will be found to aid in imparting a
general appearance of elegance to the resulting picture.

The colour of the walls exercises a marked influence on
the result. They should not be painted either red, yellow,
or green, for these colours have a very weak photographic
action, and throwing around them, as they do, tints of
their own colour, tend to prolong very materially the time
of exposure. Violet and blue colours are preferable, but
as they produce whites in the print, and as a wall painted
either deep blue or violet produces a result exactly similar to
a white wall, they should not be used for the background,
or that portion behind the sitter. Bluish grey is a mixed
tint which, on the whole, yields the best results, and is
a colour with which the whole of the glass room may be
painted, except that, according to taste, some parts may
be more or less deep than others.

It will be found very convenient to have several move-
able backgrounds, each painted with a different depth
of colour, so as to be used according to the colour of the
dress, &c., of the sitter, and thus produce the most effec-
tive contrast.

Oil colour is very disagreeable on account of its reflec-
tion. It will be found best to employ a mixture of slaked
lime, litmus, and lamp-black with which the whole of the
room may be painted, simply varying the proportion of
black. The same colour will serve to paint the floor of
the room; but if a carpet be employed instead of paint,
it is equally important that it should be of a greyish
tint.

In reference to the best colour for dresses to be worn
by sitters, the same remarks apply as have been made re-
specting that of the glass room ; that is to say — neutral
tints, analogous to grey, violet, and blue, come out well,
while red, yellow, and green, yield results of an oppo-
site character. By increasing the exposure, however, in
some cases, and diminishing it in others, the undue
predominance of any particular tint can be materially
diminished.

When one or more persons are to be taken, they should
be allowed, in the first place, to assume an easy, natural

THE HEAD-REST.

51

position, and then, by placing behind each a head-rest,
in such a way as to retain them in the position chosen,
the required steadiness of the upper portion of the body
is secured.

It is not necessary that the sitter should press the head
too strongly against the head-rest, but on the contrary, it
should only lightly touch ; because too great a pressure
restrains the respiration, thus imparting to the sitter an
appearance of constraint and uneasiness.

There are two kinds of head-rests. One in iron, or of
iron and wood, is represented in Fig. 55. The lower
part consists of a tripod and tube of
brass weighing about 40 Ibs., which serves
to prevent vibration in the upper por-
tion, which is applied to the head. This
consists of an iron tube having one piece
forked, and capable of being adjusted and
fixed by a screw in any desired position.

These head-rests are made to stand on
the ground; but Fig. 56 shows one con-
structed so as to be attached to a chair.

This form of head -rest is generally made
of hard wood : — e is a flat piece of wood,
to be adapted to the back of a chair ; two
clamping screws, //, are attached to it ;
i i a grooved board which comes behind
the chair. It may be easily raised and
depressed, and is fixed in any desired
position by turning the screws f f. b b,
a double -jointed piece for adapting to the
position of the head, and capable of being
fixed by means of the screws shown in
the figure. The whole of this piece may
be raised an<J lowered, and fixed at d. a
is a moveable forked piece, against which J
the sitter leans. It will be easily per- f
ceived that the back of the chair must
come between the pieces e and i i. _

Figure 55 shows also the manner of Fiy 56 Head-rest.
obtaining a focus, in connection with
which may be observed that too great an inclination
should never be given to the camera ; as a rule it is
D 2

52 PHOTOGRAPHIC PROCESSES.

best to have the lens about the height of the chest. A
very slight inclination of the camera will then be suffi-
cient to get a correct image of the sitter from head
to foot.

In taking a portrait from a sitting position, it is best
to lower the camera-stand a little, and thus avoid too great
distortion.

The nearer the camera is brought to the sitter the
longer the exposure ; and inversely, the further the camera
is removed, the shorter the exposure. And it is in this
way that the time of exposure may be varied from one
second to three hundred. But as a general rule, in taking
a full-length figure in summer, the plate should be exposed
twenty seconds, while a sitting position will require thirty
seconds. In winter these times of exposure should be
increased one-half.

The following is a general summary of the operations
involved in taking a portrait. The direction and amount
of light are the first things which claim attention, then
the attitude of the sitter. Focussing is the next opera-
tion, during which the sitter should be requested to keep
still, though not maintaining perfect immobility. The
plate should now be prepared in the dark room, on re-
turning from which any alteration which may have taken
place in the pose of the sitter during the absence of the
operator is corrected, and efforts made, by cheerful con-
versation, to induce an agreeable expression. Then,
when everything seems in order and ready, a final and
rapid adjustment of the focus is made; the focussing-
glass is withdrawn and replaced by the camera-back,
containing the sensitive plate. The lens is now un-
covered and the plate exposed, the necessity of complete
stillness having been previously enjoined on the sitter,
explaining, however, at the same time, that he may
breathe in the ordinary way, and if necessary wink, but
not move his eyes from the spot where first directed.
The time of exposure having expired, the lens is covered
and the slide of the camera-back closed, and the develop-
ment proceeded with in the dark room.

With reference to the means to be employed to estimate
the time of exposure in seconds, it will be found best to
read the time from a good watch with a second-hand,

RULES FOR TAKING VIEWS AND PORTRAITS. 53

though the same object may be attained by suspending
a leaden or wooden ball by means of a cord 39^- inches
long. If the pendulum so constructed be made to oscil-
late, it will be found to mark seconds of time with
sufficient accuracy.

It has been already mentioned in chapter seven, that
lenses of a different construction are necessary for land-
scapes from those which are used for portraits. For
views and architectural 'subjects a single achromatic lens
is sufficient, but for portraits a double combination is
necessary. It has also been stated that the form of
camera-stand, Fig. 46, and cameras, Figs. 47 -and 48,
are those most applicable for landscape photography.

The rules which can be given for taking views are
much more simple than those for portraits. In point of
fact, success depends mainly on the taste of the operator
in selecting the landscape which he desires to reproduce,
and the particular point of view from which it is seen.
The focussing is accomplished in the ordinary manner.

It is only necessary to add, that views are taken by
the wet as well as the dry collodion process. With the
latter all that is required is a grooved plate -box, con-
taining some prepared plates, a camera-stand, and a large
black cloth with which to cover the legs of the camera-
stand, when it becomes necessary to replace an exposed
plate by one which has not received the luminous impres-
sion. With the wet collodion process, a photographic
tent, or a light tent carriage, is indispensable ; and the
operator must also take with him all the paraphernalia
of dishes, baths, bottles, &c., which form the necessary
furniture of a dark room.

Notwithstanding these difficulties, the wet collodion
process is to be preferred for the reproduction of archi-
tectural subjects and landscapes near great cities. But
for a long voyage, the dry collodion process is certainly
the best.

In the wet collodion process, the nature of the result
(good or bad) is known at once on the ground ; while
with dry plates the character of the picture is not ascer-
tained until the development is effected, which almost
invariably takes pjace at a great distance from the locality
in which the view was taken.

54: PHOTOGRAPHIC PROCESSES.

Iii large cities and flat countries it is very easy to have
a tent or light carriage of waterproof cloth, carried, or
drawn if need be, by a porter or guide — an arrangement
which offers the advantage of allowing the operator to
stop wherever he pleases, and conduct the work with
great facility.

Generally, before taking views, a preliminary visit is
made, with the object of ascertaining the best points of
view, and on such occasions the iconometer, or view

meter, Fig. 57, is found
very convenient. It re-
quires to be expressly
constructed for each
focus of lens and size
of camera, and resem-
bles very much in ap-
pearance an opera-glass.

Fig. 57. Iconometer. V . *

It consists of a small

lens, a camera, of the shape of an opera-glass, and a square
focussing glass. By turning the lens towards the view it
is represented reversed on the ground glass ; and in this
way the operator can judge whether his large camera
will take in the whole or what portion of the required
view.

Instead of the iconometer with lens and ground glass,
a more simple one may be employed, which in many
respects, however, is similar to that indicated in Fig. 57.
The observation is made through the front opening, and
on the large circle behind (to the left in the figure) a
rectangle is described equal to that which is yielded by
the lens attached to the camera. It is then only neces-
sary to observe what objects are included in the field of
vision, in order to ascertain what will be reproduced on
the ground glass. The iconometer with lenses is, how-
ever, the most convenient for general use, as it affords an
opportunity of knowing whether in the case of taking an
architectural subject, for example, the operator is or is
not too close, for then the vertical lines incline towards
a point, like the furrows in a horizontal field.

DEVELOPMENT OF THE IMAGE. 55

CHAPTER IX.

DEVELOPMENT OF THE LATENT IMAGE OBTAINED IN THE
CAMERA-OBSCURA.

As soon as the proper time has elapsed for exposure, the
sensitised plate must be withdrawn from the light by
closing the shatter of the camera-back, which is then
taken into the dark room. After carefully closing the
shutter in front of the yellow -glass window, the plate is
removed from the frame. If it be now examined, there
will very rarely be any traces of a picture ; it can, how-
ever, be made apparent by covering the surface which
has been exposed to the light with a solution of some
substance capable of reducing the salts of silver to the
metallic state.

Among the reducing agents which can be employed in
photography, may be mentioned protonitrate of iron,
sulphate of iron, pyrogallic acid, protosulphate of uranium,
protosalts of osmium and titanium, (fee. ; but of all these,
pyrogallic acid will be found the best for developing the
negatives, and protosulphate of iron for obtaining direct
positives on glass.

Pyrogallic acid is a white crystalline solid, without
smell.* It is soluble in water, alcohol, and ether, and
its solution in either of these menstrua becomes rapidly
decomposed on exposure to the air and light, especially
if the solution be alkaline. This substance alters very
soon even when it is dry. If a small amount of moisture
be present, however, the decomposition proceeds with
increased rapidity, being expedited by the foreign matter
which it contains. Thus it is better — -first, to keep
the pyrogallic acid bought in shops in small stoppered
bottles ; secondly, to keep it in the dark ; thirdly, never
to prepare with it more developing solution than is likely
to suffice for a day's consumption..

It is usual to add to the pyrogallic some other acid, as

* For its method of preparation see Note 7«

OO PHOTOGRAPHIC PROCESSES.

much to preserve the solution as to develop the picture
uniformly ; distilled water also must be employed, or at
least rain-water, well filtered : that which is obtained
during a storm contains ammonia or nitric acid, and is
therefore unfit for use.

Solution of pyrogallic acid for developing, is thus pre-
pared : — A flask of about 1 pint capacity is obtained, and
made perfectly clean ; to this is adapted a funnel, fur-
nished with a filter, as shown in Fig. 11. Upon this filter
throw 15 grs. of pyrogallic acid ; then 15 ozs. of distilled
water being measured off, and 1 oz. of crystallisable acetic
acid* being added thereto, the whole is well stirred with
a glass rod, and poured on to the filter containing the
pyrogallic acid, which latter dissolves as the liquid is
passing through. The filtration being complete the funnel
is removed, and the flask stopped lightly with a cork, and
set aside for use in the dark.

MM. Davanne and Girard have proposed the substi-
tution of citric for the acetic acid, in which case the
following formula may be employed : —

Distilled Water 12 fluid ounces.

Pyrogallic Acid 15 grains.

Citric Acid 15 „

"Whichever formula is adopted, the method to be followed
to develop the picture is precisely the same ; and it is
important to note that the development should take place
as soon as possible after the plate is sensitised, and on no
account should a longer time than five minutes be allowed
to elapse between these operations.

The plate, on removal from the frame, is held by one
corner (the same by which it was held when
the collodion was poured over it) ; then
a sufficient quantity of the developing solu-
tion to cover the plate being placed in a
glass (Fig. 58), is poured by a continuous
operation over the collodion surface, and the
plate inclined alternately in every direc-
Ftg' 58' tion,-in order that the whole film may be
covered without delay. Then suddenly turn the plate up-

* See Note 11.

DEVELOPMENT OF THE IMAGE. Of

right, holding it by the opposite corner to that from
whence the liquid flows into the glass.

Fig. 59. Developing a Negative Proof.

The same solution is again poured on the plate, inclin-
ing it constantly from right to left, in order that the liquid
may be kept in continual motion. The
image gradually appears ; and when it is
considered sufficiently developed, the plate
is washed by dipping it, at first very care-
fully, into a shallow porcelain tray, filled
with water ; it is then placed under a small
stream of water, after which it is fixed.
It is desirable, for washing the plate, to
use a little apparatus represented in
Fig. 60. It is simply a flask, filled with
distilled water. The cork is perforated,
so as to admit of the passage of two tubes. Fi[
The highest — that which is to be blown through — passes
D 3

58

PHOTOGRAPHIC PROCESSES.

through the cork, and terminates directly under it ; the
other, on the contrary, rests in the water at the bottom of
the bottle. The draughtsman has reversed this arrange-
ment in the figure by mistake.

In using this wash-bottle, it is held by the neck while the

operator blows through
the higher tube, by which
means the water is pro-
jected through the exit
tube, and may be directed
over the surface of the
film, beginning at the
centre, and passing gradu-
ally to the edges, thus
avoiding disruption. Fig.
61 shows the operation
better than any verbal
description.

In order to avoid taking
the plate in the hand, an
India-rubber plate-holder
is sometimes employed
with advantage. Fig. 62
shows a glass plate at-
tached to such a plate -

i. washing the Film. holder. To do this the

plate is placed on a level table, arid the holder grasped
by the globe part in such a way as to force out the air ;
the edges are then moistened, in order to make them
adhere more perfectly, and the pressure is withdrawn at

the moment of bringing
the plate-holder in con-
tact with the glass by
pressing the edges of it.
Although the air has
been forced out of the
bottle, its elastic sides
re -assume their shape,
and the vacuum left in-
side causes the plate to
Fig. 62. Pneumatic Plate-holder. adhere very firmly to

the plate -holder. To detach it, it is only necessary to

DEVELOPMENT OF THE IMAGE. 59

compress the bottle as before. The picture having been
developed and washed, is now fixed, an operation to be
described in the next chapter.

The process of developing the picture, although appa-
rently simple, is, nevertheless, a very delicate one, and
one on which depends, in great measure, the success of
the positive proof; it will not, therefore, be out of place to
enter a little more into detail. The latent image produced
by the action of light upon the iodide of silver, is brought
out by the action of pyrogallic acid, aided by the nitrate
of silver, with which the collodion film is impregnated.
If too much pyrogallic developing solution is poured from
the developing glass on to the plate, the details of the
picture appear but slowly, and if too little there will not
be enough to cover the plate completely ; thus the medium
lies between the two extremes.

Sufficient developing solution should be poured into
the glasb to cover the plate freely and completely, and no
more ; and this should be poured on and off, and allowed
to flow in various directions, in order to facilitate the
mixture of the developer with the adherent nitrate of
silver. By this method of manipulating it will be found
that the development proceeds uniformly, and may be
observed from time to time by examining the plate by
transmitted light, as indicated in Fig. 59.

The development is continued according to the pre-
ceding directions until the required amount of intensity is
obtained, and the plate is then rinsed with water to remove
the developing fluid, so as to prevent its continued action.

At an ordinary temperature the picture is generally
sufficiently developed in two minutes ; but if it is necessary
to force the development, it will seldom prove a successful
picture. At a higher temperature it sometimes becomes
necessary to stop the development in half a minute, to pre-
vent the high lights from becoming too dense. Experience
alone can give the knowledge necessary to determine
exactly the when and how in this delicate operation.

As soon as the solution of pyrogallic acid covers the
plate, the sky and the high lights of the picture begin to
appear on the primrose-tinted film of iodide of silver ; a
few seconds after, the minor details make their appearance,
becoming more and more vigorous, and, as often occurs

60 PHOTOGRAPHIC PROCESSES.

in a landscape, the sky darkens so much, that it is even
difficult to see the sun through it. This will give an idea
of the amount of intensity which the image acquires ; and,
without experience, it is very difficult to indicate the
exact moment when the pyrogallic acid should be removed
by treatment with cold water.

The quantity of acetic acid added to the pyrogallic
also exercises an important influence on the results, and
in proportion as it is increased the more slowly the image
appears, and the more vigorous it is in character. When,
for example, a negative has to be developed taken from

Fig. 63. Positive Proof. From a Stereoscopic View by Ai. j

a group of persons among whom there are some having
on white dresses, a large proportion of acetic acid is
necessary; while, on the contrary, a dull, grey, sombre
monument develops best with a small proportion of acetic
acid. The time and character of the development of a
picture also enables a conclusion to be arrived at, as to
whether the exposure in the camera has been too long or
too short.

DEVELOPMENT OF NEGATIVES. 61

In this latter case it is with difficulty that the sky and
the other high lights of the picture are developed, and
detail in the shadows is never obtained ; even after long
waiting the image will not appear, in which case it is
necessary to take a fresh negative.

Fig. 64. Negative Proof, examined on the Side of the Glass not covered
with Collodion.

If, on the contrary, the exposure has been too long, the
negative is red and uniform ; after fixing, there is an
absence of vigour in the blacks, and there is a general
fogging spread over every part of the image ; the develop-
ment also ,has taken place very rapidly. In each case
another negative must be taken.

The most frequent error is over-exposure, arising from
an inability to realise the possibility of taking a picture
in so short a time.

For the purpose of illustration, suppose the monument
represented at Fig. 63, representing a portion of the
Acropolis at Athens, is to be reproduced.

The sun illuminates these statues with all its meridian

62 PHOTOGRAPHIC PROCESSES.

splendour; strong shadows are therefore a necessary con-
sequence, which, in order to be correct, ought to be in
the negative.

Beginning with a negative which shall not have been
exposed in the camera more than five seconds, and suc-
cessively increasing the time of exposure, five seconds in
a series of five negatives, the following will be the
result : —

The first negative will be very slow in developing ;
after several minutes the sky will with difficulty be traced,
and some faint indication may be obtained of the parts
most strongly lighted.

In the second these portions will have acquired much
more vigour, and the shadows even will begin to yield
some indication of detail. The third negative will be a
good one ; but the fourth will be, in every respect, all
that could be desired, possessing a due amount of vigour,
and presenting the aspect of Fig. 64.

The fifth negative, although exposed a longer time,
will have acquired a greyish colour. A good negative is
blue ; but too long an exposure gives it a dull grey ap-
pearance. The shadows, instead of being transparent,
like glass itself, have upon them a sensible deposit, owing
to the too rapid development.

In proportion as the exposure is increased in any sub-
sequent negative, the grey colour tends to become red ;
there is a difficulty almost in distinguishing the shadows
and the sky ; and, in one word, the negative loses all its
vigour.

The above are the principles upon which the photo-
grapher should proceed in the correction of his negatives.

It would be useless to pretend that an accurate judg-
ment can be formed except by long experience. It is not
until after several months of assiduous research, and after
continual disappointment, that the beginner will acquire
that accuracy of judgment at a glance which will guide
him in the fugitive indications of the amount of exposure
necessary for a given subject ; but, when once this know-
ledge is acquired, he will be amply rewarded by the
small number of defective negatives, as well as by the
amount of photographic knowledge acquired during the
apprenticeship.

SPOTS AND MARKINGS.

63

It frequently happens that negatives are spotted, or

covered with curious markings, either in parts or entirely.

The four accompanying figures are some examples of

Fig. 68.

these spots, taken from M. de la Blanchere's work ; the
description of them, together with practical directions for
their avoidance, will be found in Note 9 at the end of
the volume.

64: PHOTOGRAPHIC PROCESSES.

CHAPTER X.

FIXING AND STRENGTHENING THE NEGATIVE IMAGE.

IT has been before stated that when the image is suffi-
ciently developed, the plate should be washed with
water, so that the pyrogallic acid may be well removed.
Should the film show any tendency to detach itself, this
operation must be performed with considerable care. The
email shutters may now be opened, so as to uncover the
whole of the yellow windows. The light in the dark
room is thus increased, although it still retains its yellow
tint.

The result thus obtained is a negative image, but still
partly obscured with iodide of silver, which is now to be
removed. For this purpose it must be plunged into a bath
composed as follows : —

Water 40 ounces.

Hyposulphite of Soda 8 ounces.

In about half a minute, if the bath is fresh, and some few
minutes if the bath has been much used, all the yellow
coating of iodide of silver is dissolved, and there remains
on the collodion film only the pure silver compound con-
stituting the photographic image.

Hyposulphite of soda is a crystallised substance, very
soluble in water4, and can be purchased at a very cheap
price.

The. solution of hyposulphite of soda may be contained
in a vessel of zinc or gutta-percha. It does not stain the
hands ; on the contrary, it will remove recent stains of
nitrate of silver.

Great care should be taken that the vessel containing
the bath of hyposulphite be kept separate, and that the
fingers be well washed before proceeding to take another
picture, because contact with this salt spoils both the
collodion and nitrate of silver bath.

In fixing the proof, it should not be allowed to remain

FIXING AND STRENGTHENING THE NEGATIVE. 65

too long in the bath of hyposulphite, otherwise the fine
details will be injured. The entire solution of the iodide
of silver is easily perceivexl by examining the back of the
glass. The iodide of silver being of a pale yellow colour
is easily seen, and it is, however, necessary that the last
traces of this colour be allowed to disappear. When this
result is obtained, the glass plate should be taken out and
plunged into a bath of cold water.

The solution of hyposulphite will serve a considerable
time before it is exhausted, and then it is of so little cost
that a fresh solution is easily made.

When the negative proof is immersed in the hyposul-
phite, the vessel containing it may be taken to the day-
light, which will enable the operator better to see when
the yellow coating of iodide of silver is quite removed.
Ordinary daylight from this time has no action on the
picture.

After the fixing is complete, it is of the greatest
importance thoroughly to wash the collodion surface,
especially if a great number of proofs are to be printed
from it; this becomes more difficult when the coating has
a great tendency to detach itself from the edges of the
glass. Nevertheless, even under these circumstances,
with a little attention it may be perfectly washed. When
the collodion is good, and especially if the gun-cotton
has been prepared according to the formula indicated
in Note 3, there will not be the least fear of such an
accident. •

When the film appears liable to detach itself, the small
apparatus, Fig. 60, which has already been described, is
made use of. The current of water is carefully directed
from the middle of the plate towards the edges, constantly
varying the inclination in such a way that the water
always flows from the centre towards the sides. By these
means the coating is prevented, as far as practicable, from
being totally removed. Care must also be taken when
the glass is left to drain, as the coating wrinkles and
bends by its own weight. This effect shows itself while
the coating is yet quite wet. When the excess of water
lias disappeared, a little care will enable the coating to be
drawn to its proper position by the aid of the finger.

To properly wash the coating the glass should be

66 PHOTOGRAPHIC PROCESSES.

placed, during five minutes at the least, in a large vessel
of zinc filled with water. If the coating separates in any
part the glass must be very gently removed, and the
detached parts arranged and brought together by a
very fine and light jet of water applied to the required
places. We have often in this way replaced a film upon
the glass after it has been entirely removed and torn at
the edges, and in spite of all obtained good results.

If the glass be not sufficiently washed after removal
from the hyposulphite, the film becomes sticky, and after
awhile disappears altogether, or, at least, becomes strongly
stained.

It is after removal from the hyposulphite of soda that
the proof can be best examined as to its quality. It ought
to be of a bluish colour ; the sky and high lights a strong
black, and the deep shades nearly transparent.

If at this moment a good photographer judges that his
negative is wanting in vigour, he commences another;
but if this is impracticable, recourse must be had to inten-
sify ing. This operation must be done after the proof is
fixed and washed, and before it is dried.

Generally speaking, an intensified negative is worth
but little ; and, to repeat, a good operator will rather re-
commence another negative than intensify. However, if
required, the best method is as follows : —

The glass plate, after the rinsing which follows the
fixing, is plunged into a porcelain vessel containing a
solution of bichloride of mercury in water.

Water 10 ounces.

Bichloride of Mercury to saturation.

(To saturate the water with bichloride of mercury, this
Bait, after being powdered, is introduced into a bottle
filled with water, and well agitated.)

In a few minutes the coating assumes a milky-white
appearance. The plate is now removed and washed with
the greatest care, and then plunged into a solution of

Water 10 ounces,

Liq. Ammonia 1 ounce;

when it immediately becomes darkened. On being taken
from this bath the plate is washed with water, and then
placed against the wall to drain and dry.

VARNISHING THE PICTURE.

67

The best method of drying glass plates consists in
placing them (Fig. 69) resting
by their upper edge against the
wall, and their lower edge upon
a sheet of bibulous paper, which
very quickly absorbs the excess
of water.

If the plate is required to be
quickly dried, the coated sur-
face ought to be from the wall ;
and, on the contrary, if it is re-
quired to be slowly dried, the
coated surface is placed towards
the wall. In this latter case,
the particles of dust do not so
readily attach themselves to the
surface of the picture.

The intensifying which we have described is very
powerful ; but it is capable of being regulated, by leaving
the plate, for a few seconds only, in the bath of bichloride
of mercury. The less time the plate is in the solution,
the smaller the quantity of ammonia required to darken
it. After a few years, a proof intensified by this method
loses its vigour, and becomes even more feeble than it
was before. Several other methods for intensifying have
been proposed in various photographic works ; none of
them, however, can be recommended in preference to
that described. At the same time, if a good proof be not
obtained at the first attempt, by far the better plan will
be to try again, as it is by this means alone that real
perfection can be attained in the photographic art.

Fig. 69.

CHAPTER XI.

VARNISHING THE PICTURE.

WHEN the proof is fixed, washed, and dried, its surface
exhibits by reflected light a fine metallic appearance ; if
the development has been carried too far, the coating

bS PHOTOGRAPHIC PROCESSES.

appears covered with a metallic dust, which, however,
can be partially removed with the aid of a very soft
brnsli. By transmitted light the picture has an entirely
different appearance, perfectly opposite to that exhibited
by reflection.

As a collodion negative is required to furnish a consi-
derable number of positive proofs upon paper, and for
which purpose the collodion surface requires to be placed
in contact with the sensitive paper, it becomes necessary
to protect this coating by a sufficiently hard varnish, so
that the plate can be easily handled without risk ; other-
wise the soft coating would be very liable to injury.

There are two excellent varnishes suitable for the pur-
pose— amber varnish, and the white gum, or Soelinee
varnish.

The amber varnish is thus prepared. A quantity of
yellow amber, broken into small pieces, is placed in a
bottle so as to occupy about three -fourths of its capacity.
A mixture of equal parts of chloroform and ether is now
poured into the bottle, in such a quantity that the amber
is hardly covered. After some few days the liquid con-
tents of the bottle are poured upon a filter, and the pale
yellow liquid which passes through is amber varnish.

The solid fragments of amber are allowed to remain
in the bottle, to which can be again added the mixture of
chloroform and ether, and a fresh quantity of varnish
obtained. The same amber will serve for a dozen or
more times, if care be taken to keep the bottle well closed.

To prepare the gum -lac, or Soehnee varnish, place in a
bottle —

Gum-lac White * 21 ounces.

Alcohol 35 ounces.

The bottle* is now well stopped and left several days,
being well agitated at frequent intervals ; the liquid is
then left to settle as much as possible, the clear portion
poured off, and the remainder filtered. The whole of
the liquid can be filtered ; but it is not recommended, as
it passes very slowly through the paper. The colour of
this varnish is of a pale yellow, less deep than the
chloroform.

Instead of making this preparation in a bottle at the
ordinary temperature, it will be found a more expeditious

VARNISHING THE PICTURE. 69

plan to employ a flask (containing the materials), placed
in hot water. If the flask, thus kept heated, he agitated
from time to time, the gnm-lac can be dissolved in about
half an hour. There is always a whitish deposit, which
does not dissolve either in cold or hot alcohol ; this must
be allowed to perfectly settle before the varnish is poured
off for use.

The amber varnish is very easily applied ; the collodion
surface of the plate, on which the picture is formed, is
covered with it in the same way as the collodion was
applied, the excess of liquid being received in the bottle.
In a few seconds this varnish is dry. It is well, however,
to expose the plate for an, hour to the sun before being
used for printing from.

It is more difficult to make use of the white gum-lac
varnish, because the plate then requires to be warmed.
For this purpose it is carefully exposed to the flame of a
spirit lamp, or before a clear fire, taking care that the
heat is equally applied by moving about the glass plate
at some distance from the fire, or above the flame, if this
be employed.

The temperature of the glass should be such that,
when applied to the back of the hand, it can i>e borne
without inconvenience. If too hot, the varnish flows
with difficulty over the surface; and if too cold, it does
not dry sufficiently quick, and becomes chilled or partially
opaque. This varnish is applied like collodion, the
excess being received in the bottle, and when the surface
appears dry, the heat is continued a short time longer, so
as to cause a proper transparency and adhesion of the
coating.

It is especially difficult to use the gum-lac varnish for
plates of large size, for which, all things considered, it
is generally best to employ the amber varnish. The
negatives are less firmly varnished, and, in consequence,
not able to yield so large a number of proofs ; but, on the
other hand, it is much more easily applied.

It constantly happens that a number of transparent
round spots appear on the negative, which require stop-
ping out before the positive proofs are obtained from it,
otherwise these white spots would form corresponding
black ones on the prints, which cannot be removed. If,

70 PHOTOGRAPHIC PROCESSES.

on the contrary, the spots on the negative be black or
opaque, white spots are formed on the positive proof,
which are comparatively easy to be touched out by a
little water colour.

Touching out a negative requires very careful manipu-
lation, and a properly arranged apparatus for the purpose
will be found very convenient, Fig. 70. The wooden top

Fig. 70. Apparatus for touching out Glass Proofs.

of a small table is removed, and a thick sheet of glass,
supported by an iron framing, is substituted. Below is
arranged a large sheet of white paper, stretched upon a
frame, or else a looking-glass, of which the inclination
can be varied by some such contrivance as shown in the
figure.

The light reflected from the looking-glass or paper,
enables the proof, which is laid on the glass -plate form-
ing the top of the table, to be conveniently examined by
transmitted light.

The transparent spots are then touched out with a very
fine camel's hair pencil, and some dark colour mixed with

THE DRY COLLODION PROCESS. 71

honey or oil.* Some persons touch out the spots with
Indian ink, mixed with a small quantity of Prussian blue,
before the plate is varnished. This plan, however, cannot
be recommended, as the subsequent varnishing is apt to
destroy the colour applied.

Light spots on paper proofs are easier to touch
out with water colour of the same tint as the print,
than glass negatives are : therefore, whenever circum-
stances allow a choice to be made, preference should be
given to the former. For example, if there should be a
white spot on the negative, with which nothing can be
done, it will be better to make it a black one, which, by
printing white on the paper proof, can be then easily
tinted of the proper colour.

CHAPTER XII.

THE DRY COLLODION, COLLODIO-ALBUMEN, AND TANNIN
PROCESSES.

1. The Dry Collodion Process.

ONE of the most unfortunate circumstances connected
with the practice of photography on wet collodion, is the
necessity, in travelling, for the photographer to employ
a tent, which adds greatly to his luggage. This incon-
venience is due to the fact that the operations of sensi-
tising and developing must quickly follow each other, for,
if too long a time elapses between them, the nitrate of
silver crystallises on the surface of the glass, and causes
an infinite number of small spots to be formed over the
entire surface of the picture.

If the glass plate, covered with its sensitised coating

* M. de la Blanchere gives the following formula : —

Peroxide of Iron, or Rouge ; Chromate of Lead,

or Ivory Black 10 parts.

Gum Arabic, Saturated Solution 2 „

White Honey 2 „

Sugar Candy 1 part

72 PHOTOGRAPHIC PROCESSES.

of collodion, be washed with distilled water when re-
moved from the silver-bath, and left to dry, it loses
nearly all its sensibility, and will give but very imperfect
pictures.

M. Desprats and M. Dubosq have partially remedied
this fault : the former, by adding half per cent, of
resin; the latter, some few drops of amber varnish to the
collodion ; in whichever of the two methods it is pre-
pared, it must be used exactly as ordinary collodion,
with the exception that when the glass is removed from
the silver-bath, it is to be well washed and dried in the
dark. Plates thus prepared will preserve their sensibility
for many days. The time of exposure in the camera
ought to be tripled, and the development made with solu-
tion of gallic acid.

M. Dupuis recommends the adoption of the following
process. Ordinary iodised collodion is employed, and the
glass plate after being sensitised, is well washed in distilled
water. A solution of dextrine, in ten times its weight of
water, is left to settle, and then decanted, so as to be free
from impurities. A requisite quantity of this solution is
poured over the sensitised glass plate, recently washed,
and while still moist, in such a manner, that it spreads
evenly over its surface ; it is then drained and dried.

The plates thus prepared will keep good for several
days ; but the time of exposure in the camera must be
tripled, that is to say, if with wet collodion, 30 seconds of
exposure is required, it will be requisite to give 90 with
a plate prepared with dextrine.

Before developing the plate, it is washed with pure
water. An apparatus, consisting of a flat-bottomed
flask, &c., similar to that described page 57, is useful
for this purpose. The picture is developed with pyro-
gallic acid.

A great number of other dry processes have been pro-
posed ; but two, above all others, have obtained the prefer-
ence of the photographic public, as well in England as in
France and Germany, these are the collodio albumen
process of M. Taupenot, and the tannin process of
Major Russel. These two processes will, therefore, be
described in all their details.

THE COLLODIO-ALBUMEN PROCESS. 73

2 The C ollodio-albumen Process.

As by this process a considerable number of plates can
be prepared in a few hours, which is very convenient,
especially for obtaining stereoscopic positive proofs upon
glass, which will presently be described. The following
will be found an excellent method, and one which will
enable a hundred of these plates to be properly pre-
pared, in two operations of four hours' continuous work,
it being understood that the glasses do not exceed the
dimensions of 9 inches by 7 inches, and that they are all
cleaned beforehand.

In the dark room are arranged two vessels of gutta-
percha, one beside the other, both containing a silver-bath
composed of —

Water 35 ounces.

Fused Nitrate of Silver 1050 grs.

One bath only may be employed, but with two the opera-
tion, as will be perceived, is much quicker.

Ordinary negative collodion may be used, but it will
be found an improvement if the collodion is a little less
iodised, such as is obtained by adding to the ordinary
collodion — of which the formulae has been given at page 22
— one third of its volume of a mixture of about two parts
of ether and one of alcohol.

Collodion, ordinary, (page 22) 3 ounces.

Ether, 5 fluid drs. \ , __

Alcohol, 3 do / ' -1 ounce.

For the purpose of facilitating the description, the
glass plates will be designated by the letters A, B, C, and
the nitrate of silver baths by numbers 1 and 2.

A glass, A, is coated with collodion and plunged into
the first silver-bath (No. 1). A second glass is now
coated with collodion, and plunged into the second bath
(No. 2).

By the side of the silver-baths should be placed a
vessel of gutta-percha of considerable depth, and filled
with filtered rain-water, or better, with distilled water.
This bath ought to be as capacious as possible.

When the first glass, A, has been a sufficient time in
the silver-bath, No. 1, which is ascertained by the dis-

E

74: PHOTOGRAPHIC PROCESSES.

appearance of the greasy veins which have been spoken
of at page 35, it is taken out and placed in the bath of
water contained in the vessel of gutta-percha.

A third glass, 0, is then coated with collodion and
plunged into the silver-bath, No. 1, from which the first
glass was taken, and then the glass in the bath of water
is removed, and placed in a large wooden tub (Fig. 71)
tilled with rain-water, and sufficiently large to hold from
eight to ten glasses, placed side by side.

Fig. 71. Tub for Washing Plates.

The second glass, B, is now taken from the silver-bath
and plunged into the bath of water in the gutta-percha
vessel. It is left here while another glass is coated with
collodion and sensitised, and when that is finished the
second glass, B, is taken from the water, to be placed in
that contained in the large vessel Fig. 71. The plate, C,
is removed to the bath of water, a fresh plate inserted,
and the same series of operations repeated for the number
of prepared plates required.

It will be understood that this method of preparation
being a continuous one, is necessarily very rapid. When
the large vessel of water is filled with plates, they are to
be taken out and placed inclined against the wall, resting
at the bottom on some bibulous paper, and with their
prepared or collodionised surfaces towards the wall, as
described at page 67.

If the operation be conducted on a small scale, with
one glass at a time, then, when the first plate is taken
from the silver-bath and plunged into the water-bath,
another plate is coated with collodion and placed in the
nitrate -bath, and during the time it has to remain in it,

THE COLLODIO-ALBUMEN PROCESS.

75

the first plate is removed to a fresh quantity of water
contained in a trough of wood or gutta-percha.

Whichever method be employed, the result will be the
same, provided that care be taken to remove the whole
of the nitrate of silver, which covers the plates, with
abundance of water ; if the trough be small, the water
must be often changed; but if it be of large size, this
may be dispensed with.

When the whole of the plates are prepared, some
solution of common salt is added to the water contained
in the gutta-percha trough.

A white precipitate is formed of chloride of silver,
which can be retained until of sufficient quantity,
with other residuums, to be reduced into metallic
silver by fusion in an earthen crucible with carbonate of
soda.

Each glass plate should remain in the water at least
ten minutes, and ought to be kept upright, the better
to remove all the soluble salt of silver from the texture
of the collodion coating.

The glasses, coated with collodion and washed as just
described, must be covered while still
moist, with iodised albumen, which is
thus prepared: —

Fresh fowls' eggs are broken
across the middle, the whites care-
fully separated, and then poured into
a glazed earthen vessel, to which is
added a quantity of iodide of potas-
sium, equal to 7 J grains to the white
of each egg employed. Before adding
the iodide of potassium to the white
of egg, it should be dissolved in an
equal weighjb of water ; for example,
if ten, twenty, or fifty eggs be used,
75, 150, or 375 grains of iodide of
potassium are required, dissolved in
75, 150, or 375 grains of water.

The whole is then beaten completely into froth by

means of a bundle of twigs, represented at Fig. 72, or of

tinned iron wire, mounted in a handle, Fig. 73. This

froth is left to itself in a glazed earthen vessel, Fig. 74:,

E 2

Fig. 72. Fig. 73.

76 PHOTOGRAPHIC PROCESSES.

for twelve hours, when the greater portion is resolved
into clear albumen, which can be poured off into a wide-
mouthed bottle. This iodised albumen is used to pour
over the collodionised glasses after they have been taken
from the trough, Fig. 71, and drained for one or two
minutes on a wooden shelf, Fig. 69.

Fig. 74. Albumen beaten into Froth.

M. Taupenot employed fermented albumen ; but it is
now not generally used or to be recommended.

Iodised albumen can be preserved for a considerable
time during winter, but in summer it is apt to decompose
very rapidly. It should be kept in well-closed bottles
in a cool place.

During the time that some of the glasses require to
remain in the silver-bath, those which have been drain-
ing against the wall are to have a small quantity of the
albumen poured on each, and allowed to run over every
portion of the moist collodion surface ; the glass is then
held vertically, so as to allow the excess of liquid to flow
into a separate bottle, which, for the sake of distinction,
will be called B.

A fresh quantity of the iodised albumen is now
poured on the glass, and made to flow over every portion
of its surface, the excess being received back into the
bottle.

The glasses thus albumenised are left to dry, the
upper part of each leaning against the wall, and the
lower resting on some blotting-paper, as shown at Fig. 69.^

THE COLLODIO-ALBUMEN PROCESS. 77

The albumenised surface should be towards the wall, to
avoid dust.

The reason for giving the plates two coatings of
albumen is that the tirst application serves to remove the
water which impregnates the collodion surface and allows
the second quantity to give a perfectly uniform coating.
The albumen contained in the bottle, B, can be used a
considerable number of times for giving the first coating
or until it becomes too diluted with the water derived
from the plates, when a fresh quantity must be used ;
whereas, that employed for the second coating, on the
contrary, can be used as often as required.

The glasses, when removed from the bath of water,
should not be allowed to dry before being albumenised,
otherwise the albumen is spread with difficulty on the
surface, and stains are subsequently produced.

The albumen should not be applied sparingly to the
glass, but at the same time it should not be allowed to
flow over to the back of the plate ; if this should happen,
it is best removed, when perfectly dry, with some bibulous
paper moistened with water.

Walking about the room when the albumenised glasses
are being left to dry should be avoided as much as
possible, so as to prevent any particles of dust, <fec.,
settling on them. In about twelve hours they will be
sufficiently dry, when they can be preserved for an in-
definite time, if placed in a grooved box to protect them
from damp and the direct light of day.

All the foregoing operations are to be done in the
dark room, and when finished, the water in the large
bath may be thrown away, but that in the smaller bath
of gutta-percha should be retained, for the purpose of
precipitating the silver it contains, as before described.

The following is a resume of the first series of opera-
tions, in their proper order, that each glass undergoes : —

1. Cleaning.

2. Coating with collodion.

3. Sensitising.

4. Washing for a few moments in the first bath of

water contained in the gutta-percha vessel.

5. Washing a second time in a bath, where it is left

for several minutes.

78 PHOTOGRAPHIC PROCESSES.

6. Leaving to drain.

7. Coating with iodised albumen, which, has been

before used for removing the excess of water.

8. The immediate application of another coating of

fresh iodised albumen.

9. Lastly, leaving it to drain and dry.

On the evening, or at most the day before requiring to
use the plates for taking views, they must be submitted
to a second series of operations, so as to render the
iodised albumen surface sensitive to light.

A great number of albumenised glasses may by pre-
pared at a time, because they can be kept for an indefinite
period ; whereas, no greater number of them should be
sensitised than will be used in a very short time, as they
then rapidly deteriorate by keeping.

For sensitising the glasses a bath of aceto-nitrate of
silver is required, composed of —

Distilled Water 16 ounces

Glacial Acetic Acid 1 „

Fused Nitrate of Silver , H „

This bath requires to be filtered before being used, and
a gutta-percha dish should be employed for it. After
being used for a few weeks it becomes of a yellowish
tint, that can, however, be removed by being shaken up
with some kaolin. As a matter of precaution the kaolin
may always remain at the bottom of the bottle, and the
liquid decanted from it when used.

At the side of the bath of aceto-nitrate of silver should
be placed another of much larger size, filled with filtered
rain-water.

An albumenised glass is immersed with one quick
movement into the aceto-nitrate of silver, and left there
for fifteen seconds or more, it is then placed in the bath
of rain-water, which is shaken a short time so as to
remove the excess of nitrate of silver. This being done,
it is taken out of the water and left to dry against the
wall in the manner previously described. It is almost
needless to say that the operation of sensitising must be
done in the dark room with a yellow light. The glasses
thus sensitised, when dry, are ready to receive the im-
pression in the camera, after which they can be kept for

THE COLLODIO-ALBUMEN PROCESS. 79

a fortnight before being developed, although, as a rule,
the shorter time that elapses between the sensitising and
development the better will be the result. To obtain
good proofs, not more than three days should intervene
between the two operations. In summer especially, the
time should be as short as possible ; in winter it may be
longer without so much risk of injury.

The sensitised glasses ought to be preserved in grooved
boxes free from chinks or cracks through which the
daylight might pass, and kept as dry as possible.

When required for use they are placed in the ordinary
collodion frame for views. There are, however, some
frames particularly devised for dry plates, which hold
two glasses and have two slides, first one of the glasses
is exposed to the light, and then the other, by simply
turning round the frame.

The time of exposure for a collodio-albumenised plate
is fully double or treble that required for ordinary collo-
dion. Experience alone will guide the operator in this
particular.

As the pictures are generally developed after returning
from an excursion, it is an excellent plan, to ensure a
good proof of any particular view, building, &c., to take
two impressions, but with different times of exposure.

The collodio -albumen process is also particularly well
adapted for obtaining transparent positives on glass.
For this purpose the sensitised surface of the prepared
plate is put in contact with the varnished surface of the
negative, and placed in a close frame similar to that used
for exposing the plate in the camera. By opening the
sliding shutter the diffused light of day is allowed to act
for three or four seconds, taking care that in arranging
the glasses in the frame, the light passes through the
negative before striking the sensitised plate. The plate
is then taken into the dark room, and developed in the
ordinary manner.

When this process is followed the positive picture
obtained has a very good effect if placed before a win-
dow ; it should be mounted with a plate of ground glass,
the albumenised surface of one in contact with the
ground surface of the other, and the two plates united
by a border of black paper pasted round the edges.

80 PHOTOGRAPHIC PROCESSES.

The following is the method of developing the col-
lodio -albumen plateo : —

Place in a porcelain capsule 15 grains of gallic acid,
and pour over it 3£ ounces of hot distilled water, and
mix them well with a glass rod ; when the gallic acid is
dissolved, or nearly so, add 13 ounces of cold water, and
filter the whole into a bottle for use.

This liquid is poured into a porcelain dish to about
the depth of an inch, and to each quantity of three ounces
employed is to be added one -fourth of a drachm of the
following solution : —

Distilled Water 35 ounces.

Fused Nitrate of Silver 230 grains.

Glacial Acetic Acid 9 minims.

And care should be taken that the whole be thoroughly
mingled together, otherwise stains will be formed on the
surface of the negative.

The exposed albumenised plate is to be quickly
plunged into this liquid, the coated surface upwards,
and raised up and down for several times by means of a
hook so that the fluid flows well over its surface. It is
necessary that the porcelain dish should be adapted for
the purpose, and with a flat bottom so that the glass
may be perfectly immersed in the solution.

At the end of the first hour or two the sky and other
parts highly illuminated will hardly have made their
appearance, but in the succeeding two hours the proof
usually comes out with extreme vigour. It is always
well to watch this operation so as to stop it so soon as
the development is complete, which, however, sometimes
takes as long as twelve hours. The colder the weather
the longer the time required. In winter it is preferable,
and sometimes necessary, to develop in a warmed
apartment.

Very often in about three or four hours the develop-
ment of the image can be accelerated by renewing the
gallic acid and doubling the dose of nitrate of silver,
that is to say, to each 3 ounces of solution of gallic acid
add a half instead of a quarter drachm of the aceto-
nitrate of silver; but if this is done the dish must be kept
agitated, otherwise the particles of reduced silver which

THE COLLODIO-ALBUMEN PROCESS. 81

are formed would attach themselves to the picture and
entirely spoil it.

To succeed well, two conditions are indispensable — a
warm room, about 68° Fahr., and a slow development.
It is also very important that the gallic acid should not
be allowed to become coloured and muddy ; if this should
happen, the glass must be washed, so as to remove the
thick and decomposed gallic acid from its surface, and
placed in another dish with some fresh solution of gallic
acid, to which has been added a less quantity of aceto-
nitrate of silver than was employed at first.

This last observation is most important, and the opera-
tion is one that cannot be too often repeated ; with a
proper attention to the time of exposure and consequent
regulation of the doses of gallic acid, the picture should
be well and perfectly developed in about four hours.

To finish off the proof, it is washed with water when
taken from the gallic acid bath, and fixed with hypo-
sulphite of soda in the manner described for the ordinary
wet process — a final washing completes the picture. It
is useless to varnish the plate, as the albumen itself
forms an excellent preservative coating.

As the beauty of a collodio-albumen proof greatly
depends upon the proper time of exposure in the camera,
it may be useful to give some of the indications of a too
short or too lengthened action of light.

If the exposure has been too short, the picture does
not come out well even after twelve hours of develop-
ment and repeated changing of the gallic acid solution,
the sky alone is distinctly marked, all the other parts of
the proof have *a general grey tint, without the least
vigour. Nothing can remedy this fault. If, on the con-
trary, the exposure has been too long, the sky shows
itself very quickly, as well* as the other light parts of the
picture. In* about an hour the proof exhibits a con-
siderable amount of intensity in all its details. If the
development be now stopped, a passable picture may be
obtained ; but if it be continued, the whole of the image
becomes grey, and the sky, although apparently very
dark, because viewed by reflection from a white ground,
is, nevertheless, also grey. Over exposure is likewise indi-
cated by a red tint, which the proof takes after being fixed.
F 3

82 PHOTOGRAPHIC PROCESSES.

"When the time of exposure has been correct, the sky
begins to show itself in about an hour, and very gradually
increases in intensity, and becomes of an absolute black,
even when viewed as a transparency after fixing. The
whole of the details are shown with great vigour, while
the shadows are perfectly transparent.

If the sky should not be sufficiently dark, and it is not
possible to take another proof, recourse may be had to
stopping out with a little Indian ink mixed with honey
and water, and a soft camel's hair pencil. It is,however,
next to impossible to do this operation in such a manner
that some of the details on the horizon are not injured.

3. The Tannin Process.

This dry process derives its name from the use of
tannin — a bitter principle obtained from gall-nuts —
as a preservative agent. To Major Russell is due the
credit of having introduced it.

The glass to be prepared should be cleaned with great
eare, particularly from any greasy substances. This is
conveniently done with a mixture of Tripoli powder,
spirits of wine, and solution of ammonia. A tuft of
cotton is dipped into this mixture and rubbed over its
surface for a minute or so ; then well rinsed in water and
rubbed dry with a clean cloth.

The glass, just before being used, should be wiped
with a perfectly dry and warm cloth, and then coated
with the following solution : —

Nelson's Patent Gelatine ; 20 grains.

Distilled Water 10 ounces,

Alcohol \ ounce.

Dissolve and filter; this solution will keep good for a
considerable time.

This gelatine solution is applied to the glass in the same
way as ordinary collodion, taking care that the whole of
the surface is covered, and that the back of the plate be
not soiled. The superfluous liquid is received back into
the bottle, and the plate set to dry, as shown at Fig. 69 ;
when well drained, remove the accumulation of fluid very
carefully from the lower edge of the plate by a piece of

THE TANNIN PROCESS. 83

blotting-paper drawn along it. When the surface is dry,
warm gently by the fire, and retain for use in a grooved
box. As plates thus coated will keep good any length of
time, any required number may be prepared, taking care
that the backs of them are quite free from stains of gelatine.

The gelatinised glass is now coated with old iodised
collodion in the usual manner, taking particular care that
the whole surface of the plate be covered; it is then im-
mersed in the silver-bath employed for the wet collodion
process (page 34), and allowed to remain in it from
three to five minutes.

Remove the sensitive plate from the bath, and wash it
freely under a water-tap for about a minute, it will then
be ready to receive the preservative solution, composed
as follows : —

Tannin 60 grains.

Distilled Water 4 ounces.

Filter through paper, and measure out two separate por-
tions according to the size of the plate to be prepared,
allowing about two drachms in each quantity for a stereo-
scopic plate. The first portion of tannin solution is
poured over the washed coating of the sensitised plate
two or three times, so as to remove the water adherent to
it, then the other quantity is poured on and off, and the
plate placed on end on a piece of blotting-paper, and
allowed to dry in a perfectly dark and warm place.

After exposure in the camera, which averages from
one to three minutes on a favourable day, and from four
to eight minutes in dull weather, the picture is to be
developed, for which purpose the following solutions are
required : —

No. 1. ( pyro&allic Acid 72 grains.

I Alcohol 1 ounce.

Dissolve and keep in a stoppered bottle.

C Nitrate of Silver 20 grains.

No. 2. -j Citric Acid 20 „

C Distilled Water 1 ounce.

Dissolve and filter should any white or other precipi-
tate be formed. To three ounces of distilled water add
half a drachm of No. 1, and if the plate to be developed

84: PHOTOGRAPHIC PROCESSES.

be a stereoscopic size, take three drachms of this solution
and add to it from ten to twenty minims of No. 2 ; this
forms the developing fluid.

The exposed plate is first moistened with distilled
water, which must he done quickly and evenly, other-
wise stains are produced, and then the developing fluid
poured over its surface and kept slightly in motion.
The development must be carefully watched, and if in a
short time the sky comes out strongly, but. is not followed
by the other details of the object, the plate was not long
enough exposed, and the developing fluid must be poured
back into the measure, and say ten minims of No. 1
added, so as to increase the quantity of pyrogallic acid.
If the whole of the picture, however, appears to come out
at once, a few drops of No. 2 is to be added, so as to in-
crease the density of the sky.

When the picture is properly developed, it is fixed
with a solution of hyposulphite of soda, washed and
varnished as described lor the wet collodion process.

CHAPTER XIII.

POSITIVE COLLODION PROCESS.

THE positive collodion process is very similar in its gene-
ral details to the negative, and will generally be found
much easier of manipulation, from its not requiring the
like amount of accuracy.

Preparation of the Collodion.

Iodide of Cadmium, or Ammonium 15 grains.

Pyroxyline 15 „

Ether 3* ounces.

Alcohol 1£ ,,

The pyroxyline and the iodide of cadmium are first in-
troduced into a dry flask or bottle, and the alcohol poured
upon them, and the mixture shaken violently for about
a minute ; the ether is then added and the contents fur-
ther agitated, and finally set aside all night. The clear
supernatant portion may now be carefully poured on from

POSITIVE COLLODION PROCESS. 85

the white deposit at the bottom of the bottle, or instead
of decanting, it may be preferable to use a small syphon
bottle as shown at Fig. 23, the action of which has
already been explained.

The positive collodion thus prepared should, like the
negative, be preserved in the dark in well corked or stop-
pered bottles.

Should the collodion produce a fogged image, or in
other words, if the plate becomes covered with a film of
reduced silver, underneath which there is obviously a
very good picture, this defect may be remedied by adding
to it a few drops of the following solution : —

Alcohol 85 ounces.

Iodine 150 grains.

A small quantity of this liquid is added to the collodion,
so as to impart a pale amber colour thereto.

Patent glass plates are not required for direct collodion
positives, and the reason is very simple. When negatives
are taken they are afterwards applied to sheets of sensi-
tised paper with some degree of pressure, in order to
obtain the positive impression, on which account it is
necessary that the plate should be perfectly flat and
free from striae, otherwise the striae would be reproduced
upon the paper, and the glass very liable to fracture
from the pressure. Such is not the case, however, with
direct positives ; here the purity and flatness of the
glass is by no means so important, and ordinary flatted
crown may therefore be used. Some photographers em-
ploy glass of a deep red or purple colour, in which case
it is unnecessary to varnish the plate.

Whatever kind of glass plate be adopted, it should be
chosen as flat as possible, otiierwise there will be difficulty
in getting them into the camera back; but the colour in
no way affects the beauty of the image, any more than
bubbles or other mechanical surface detects.

It has been previously explained, when describing the
negative collodion process, how the plate is cleaned, and
in what manner the collodion is poured on the glass ; no
further remarks are therefore needed on the subject be-
yond reminding the reader that the collodion should be
poured upon the plate in the dark room, in order to be

86 PHOTOGRAPHIC PROCESSES.

ready as soon as the film is set to plunge it into the bath,
which is composed as follows —

Distilled "Water 35 ounces,

Fused Nitrate of Silver 2i „

Filter. Prepare also the following solution —

Water 3i ounces.

Acetate of Ammonia 30 grains.

And, after filtration, pour it into the bottle which contains
the above solution of nitrate of silver. A crystalline pre-
cipitate is produced which requires several days to deposit
before the bath will be ready for use. It may, however,
be used a few hours after mixing by resorting to filtration;
but it is always better after a few days' keeping.

The bottle containing the bath should have a funnel
and filter adapted to it, through which the solution ought
to be always filtered after use, so as to be ready for each
day's work, the same filter serving almost indefinitely.

The mixture of acetate of silver with the nitrate not
only produces increased rapidity, but tends to maintain it.
It has, moreover, the advantage of preventing fogging ;
but to this end it is necessary to be always kept in the
dark.

The details of manipulation, as before mentioned, are
the same as have been described for the negative process,
except that the exposure is reduced about three -fourths
and the development effected by protosulphate of iron
instead of pyrogallic acid.

A saturated solution of protosulphate of iron is pre-
pared by pouring half a gallon of boiling water on two
pounds of green vitriol, or ordinary protosulphate of iron,
stirring well together ; allow it to cool and then filter.

This saturated solution is, of course, much too concen-
trated for use ; the developing solution is therefore pre-
pared from it in the following manner —

Water 18 ounces.

Saturated Solution of Sulphate of Iron 8 ,,

Ordinary Acetic Acid of Commerce If ,,

Ordinary Alcohol 1 „

Sulphuric Acid 1 ,,

This solution should be contained in a vertical bath with
a dipper, and the plate immersed therein for fifteen seconds

POSITIVE COLLODION PROCESS. 87

after exposure, which will be found amply sufficient to
develop the picture in all cases.

On withdrawal from the bath the image ought to possess
very little intensity, if otherwise it might be regarded as
an indication that the proof would not be a satisfactory
one. However this may be, the plate is now well washed
with water, fixed with cyanide of potassium, and dried as
has been described under the negative process.

It is only after fixing that a correct idea can be formed
as to whether the exposure has been correct or not, and
practice alone will enable the operator to determine the
point. If any trace of fogging should become apparent,
a few drops of the alcoholic solution of iodine may be
added to the collodion, the formula for which has been
already given.

It may not be out of place here to give a few explana-
tory remarks in order that the reader may fully com-
prehend the essential difference between a positive and
negative collodion picture.

A negative proof being intended to possess varying
degrees of opacity to transmitted light, it is necessary
that the film should have in it a sufficient quantity of
material to suffer various amounts of decomposition in the
process of development ; to this end, not only is a thick
collodion employed, but also one fully charged with iodide.

With a positive the case is entirely different, the film
is extremely thin, for unless it were so the whole would
be patchy, owing to the light having penetrated the film
and effaced the delicate details by reflection. It is,
therefore, of the highest importance to use the thinnest
possible collodion, which yields, on leaving the bath, a
film only faintly opalescent.

For fixing, cyanide of potassium is a more appropriate
agent than hyposulphite of soda, as it yields a more
agreeable t'one. It requires, however, to be used with
great care on account of its highly poisonous character.
The removal of the unaltered iodide by its means may
be effected either by immersion or by pouring the solution
over the plate. The fixing solution is prepared by mixing
together —

Water 35 ounces.

Cyanide of Potassium li to 3 ounces.

88 PHOTOGRAPHIC PROCESSES.

Longer contact of the cyanide than is absolutely neces-
sary should be avoided, as the delicate detail is apt to
suffer, and when the iodide is removed, which may be
ascertained by the transparency which the plate acquires,
it should be freely washed with water, dried, and var-
nished.

The varnish, if the picture be taken on a colourless
glass, must be black on the plain side, and colourless or
" crystal varnish " on the film side ; when purple glass,
however, is used, the black varnish may be dispensed
with.

A solution of gum arabic is sometimes poured over the
film side of the plate, instead of varnish. Some operators
omit all kind of protection; this is, however, a mistake,
as pictures which are not covered either with gum arabic
or crystal varnish, very quickly assume a tarnished and
disagreeable aspect.

To communicate an extra amount of whiteness to direct
positives they are sometimes treated with bichloride of
mercury after the final washing ; the general tone, how-
ever, is usually sufficiently cold, and therefore its employ-
ment cannot be recommended in an artistic point of view.

The method of operating is as follows : — Cold distilled
water is allowed to take up as much bichloride of mer-
cury as it will, and, the solution being filtered, the positive
is immersed therein until it assumes an appearance as white
as snow, which will be in about one minute, after which it
is washed and varnished in the usual way. These proofs
should be preserved from the direct action of the sun's
rays, otherwise they become very much weakened in a
few months.

The different methods of mounting in passe-partouts,
(fee., involve operations of so strictly mechanical a nature
that they need not be entered into in this place, as the
means of carrying them out are soon acquired by practice.

Glass positives are very easy to take, although some
practice is necessary to attain to any great degree of
excellence. The pictures should have a mirror-like
aspect, and the blacks extremely pure. Sometimes a
certain amount of fogging takes place, marring the bril-
liancy of the picture; this may be removed by washing
the picture while still wet, immediately after fixing, with

THE STEREOSCOPE. 89

an alcoholic solution of iodine of 15 grains to the ounce.
The length of time must be determined by the extent
of the fogging, and can only be ascertained by practice.
When it is considered that the action of the iodine has
been sufficiently prolonged, it is washed off, and the plate
again immersed in the cyanide fixing bath, and finally
washed and dried.

CHAPTER XIV.

THE STEREOSCOPE.

THIS instrument shows in relief, as one picture, two dis-
similar views of the same object, mounted together either
on plate or paper. The following is an explanation of
this singular phenomenon. If, for example, a square-
based pyramid be examined with the left eye, the eye
being placed in the axis of this pyramid, it is very
evident that it will present the appearance of a square
intersected by its two diagonals, and a drawing of it
would, in fact, be represented by such a figure. But if
the left eye be now closed, and the right eye opened, it is
equally clear that one side of the pyramid will be more
visible than the other, and that in proportion to its
height.

Now, if this same pyramid be viewed with both eyes
at the same time, the two different images combine upon
the retina in such a way as to produce the appearance of
a single solid pyramid, in perfect relief, or, in other words,
the effect is stereoscopic.

If the pyramid, instead of being in relief, were hollow,
and the left eye, as before, placed on a line with its axis,
a square figure intersected by its two diagonals will be
seen; but immediately upon opening the right eye, the
effect will be exactly the reverse of what occurred in the
case of the figure in relief. In the former case, it was
the side of the pyramid to the right which impinged
mostly on the right eye, but in the case of the hollow

90

PHOTOGRAPHIC PROCESSES.

figure, it would be, on the contrary, the left eye which
receives the larger impression, and in consequence thereof,
the effect upon the two eyes would be different, and
instead of producing the sensation of solidity or relief,
the combined images produce the appearance of tollow-
ness, or in other words, are pseudoscopic.

It is upon this principle that the stereoscope is founded,
the two views employed together are each taken by a
camera, as near as possible under the same conditions as
naturally presented to each eye. The prismatic glasses
of the instrument superpose the two views in such away
that but one image is percieved by the two eyes, and
that in relief.

To Professor Wheatstone is due the credit for the
elaboration of this theory and the application of photo-
graphy thereto ; also the invention of one modification of
the instrument. Mirrors were employed in its construc-
tion, and it is known as the reflecting stereoscope. Sir
David Brewster replaced the mirrors by prisms, and it is
this improvement which has rendered it so popular and
portable.

The relief of near objects is easily explained, by the

large angle formed by the
visual rays brought to
each eye ; but as this angle
becomes more and more
diminished in proportion
to the distance of the ob-
jects, it becomes at last
very difficult to appreciate
relief, and inconsequence,
the situation of large
masses can only be judged .
of by comparison with
those which are near.

The original stereo-
scope was composed of
small half lenses, which
Fig. 75. Prismatic stereoscope. turned in brass tubes in
such a way as completely to superpose the two views ; but
now the small lenses are replaced by large square prisms,
let into the upper portion of the stereoscope, and this not

THE STEREOSCOPE. 91

only affords a larger field of view, but also makes the
instrument more easy to manage.

Fig. 75 represents a prismatic stereoscope. The slides to
be viewed are introduced through a groove at the bottom ;
it is furnished with a centre partition, which assists in the
superposition of the two images. The upper portion is
shown detached, or open, the better to exhibit its general
construction.

For the best instruments the two prisms are achromatic,
or else replaced by two achromatic lenses, by which their
definition is rendered as perfect as possible. A very con-
venient form of stereoscope for showing a number of
slides is now constructed, whereby as many as fifty pic-
tures can be viewed consecutively, by merely turning a
small button. This arrangement consists of a stereoscope
fixed at the top of a deep box containing the views,
which are attached to a kind of endless chain, on moving
which the pictures are presented as required.

There are many other forms of stereoscope, the whole
of which, however, with the exception, perhaps, of the
reflecting stereoscope for viewing large pictures, being
constructed on the general principle and arrangements of
the foregoing, any further description would be un-
necessary.

Stereoscopic views are always of small size, except

Fig. 76. Twin-lens Camera with Double Back. Fig. 77.

those before mentioned for the reflecting stereoscope, and
are taken on glass and paper ; those on glass are viewed
as transparencies, but the paper slides are examined by
reflected light, for which purpose there is usually attached

92 PHOTOGRAPHIC PROCESSES.

to the stereoscope some such contrivance as is represented
at Fig. 75, like a small door in front.

The most simple method of obtaining stereoscopic
pictures certainly consists in taking the two proofs at the
same time, with the apparatus as represented in Fig. 76.
It is composed, 1st, of two double achromatic combinations
of exactly the same focal length ; 2nd, of an ordinary
expanding camera, furnished, however, with a back, having
two shutters (Fig. 77).

The following is the method of operating : —

Whenever the two lenses are not exactly to the same
focus, it is necessary to begin by focussing a near object,
such, for instance, as a plaster bust. When a perfectly
sharp image is obtained upon the ground glass with each
of the lenses, the rack and pinion adjustment must not
be again touched, but the focussing of any subsequent
figure must be accomplished by drawing in or out the
expanding or inner body of the camera.

This, however, will not suffice, if the distance of the
bust from the camera has not been so regulated as to be
that which will be most suitable for a portrait. For this
apparatus will serve only for portraits, and that, too, for
portraits taken at a very short distance ; otherwise, the
proofs will be wanting in relief.

As would be inferred from the shape of the back, a
glass is chosen much longer than it is wide, upon which
the two negatives are taken at the same time. The
prints obtained from these negatives are reversed, that is
to say, when each positive is cut for the purpose of being
mounted upon card, it will be necessary to paste the left-
hand picture on the right side of the card, and the right-
hand print on the left of the card.

When, with this apparatus, it is desired to take views,
a diaphragm or stop must be inserted between the two
lenses, but the two proofs can, however, no longer be
taken at the same time, for the distance between the two
lenses is not sufficient to give the proper amount of
stereoscopic relief for distant objects.

A board with moveable guides is therefore placed upon
the camera-stand, as represented at Fig. 81, and two
cross lines are drawn upon the ground glass of the
camera. One marks the centre on one side ; the second,

THE STEREOSCOPE. 93

that on the other. The camera is then pointed in such a
way that the same object in the landscape comes on
the centre of the cross lines, for without this the proof
would not be properly centred.

The two negatives then are taken separately, and
require transposing when they are mounted on the card.
But this reversing or transposition may be, however,
accomplished in the instrument itself, so effectively, that
when the negative is placed in the stereoscope, the
objects appear in relief.

For this purpose, suppose the apparatus, Fig. 76, is in
the position as represented in Fig. 81. Instead of taking
with the right-hand lens the right-hand negative, and
with the left-hand lens the left-hand negative, let the ope-
rations be reversed. Take the left picture with the right
lens, and vice versd — the right picture with the left lens.

When it is desired to take landscapes only, the camera
represented in Fig. 78 is generally used. It is an ordinary
quarter-plate camera, which is converted into a stereo-
scopic camera by the addition of three pieces of apparatus,
two of which are represented in Figs. 79 and 80.

In Fig. 79 will be seen a grooved piece of wood, with
two rebates and a catch in the middle of the upper one,
and a ground glass sliding between them ; this is stopped
in the middle by the catch before mentioned. This
piece of wood is screwed to an ordinary camera-back,
the door of which is reversed.

Two diagonal lines are drawn upon the ground glass.
When it is desired to take a stereoscopic view, the board
with two moveable rebates,
as represented in Fig. 81, is
brought into use.

The following is the method
of proceeding. The camera,
Fig. 78, is first placed in one
of its positions, and directed
towards the view — then in
the second position, and
directed towards the same
point. These two views will **' 78' ^Tfew" &tereuscopic
appear upon the ground glass exactly the same, but
they are not so in reality.

94: PHOTOGRAPHIC PROCESSES.

The ground glass being withdrawn, the camera is placed
on the right hand of the operator, who looks at the view
which is- before him. Replacing the focussing glass by
the camera-back, which is introduced on the right side
of the piece of wood (Fig. 79), it is obvious that it is

Fig. 79. Frame with Ground Glass. Fig. 80. Frame for Sensitive Plate.

that part of the glass which is on the left in the back
which will be first uncovered, as is shown in Fig. 80. The
slide being drawn, and the time of exposure having
expired, the door is closed. Fig. 78 shows the position
of the camera for the first picture, that is to say, the right-
hand one.

In the second position, that of the left, the camera-
back is made to slide between the two rebates until it is
checked by the brass catch; the second picture is then
taken.

These directions seem complicated, but in practice they
prove very simple. The principle being once understood,
it is easy to follow the description.

There remains a third method of operating, which
is still more difficult. When it is desired to take views
of animated objects or groups, the necessary interval
which elapses between the two positions of the camera,
just described, renders it inapplicable for the purpose,
as in all probability the objects must have moved, and
the two views would not be alike. Under these cir-
cumstances two quarter-plate cameras are used, furnished
with lenses whose focal lengths are exactly equal, and
the operation is conducted as is shown in Fig. 81. Great
care must be taken to open and close the two shutters at
the same time, or at least very quickly one after the
other, as it is obvious that if one plate be longer exposed

THE STEREOSCOPE. 95

than the other, the development must take place un-
equally, and the two proofs will be unequal also.

Fig. 81. Position of the two Cameras for Instantaneous Views.

In order that the two negatives should be exactly
alike, the two plates should be collodionised at the
same time, and immersed one after the other in the same
nitrate -bath, from which they should be simultaneously
withdrawn.

In reference to the development, a dish is used with
a glass bottom and wooden sides, or of solid glass,
and the two plates are placed therein, one by the side of
the other, in order that both may be developed with
the same pyrogallic acid. This is the only way to
obtain proofs of nearly equal intensity, for it is, indeed,
quite a chance that they should be exactly alike ; a
little difference will not, however, materially affect the
result in printing.

Positive proofs should be reversed: the one which was
taken on the right should be on the left in the card, and
in order that this may always be done correctly, it is
advisable to mark each of the negatives when taken
separately.

The apparatus for cartes de visite, at page 39, is, in
fact, nothing more than the apparatus, Fig. 76, with
a back like Fig. 80. It consists of a camera to which
four lenses of equal focal length have been adapted,
furnished with a sliding back. From this arrangement
it follows that when the lenses are arranged as shown in
Fig. 76, there will be eight negatives taken on each plate,
and that each pair will be stereoscopic. The cost of the
apparatus may, however, be materially lessened by using
a whole-plate camera fitted with a pair of twin-lenses,

96 PHOTOGRAPHIC PROCESSES.

as in Fig. 76, and arranged so as to slide together on its
rising front ; in this way four carte de visite pictures may
be obtained on one plate. A number of negatives are
taken on one plate, because the printing of an equal
number of proofs separately would be much more costly
and troublesome.

It remains to consider the proper angular distance
which should separate the two cameras represented in
Fig. 81, so as to produce the desired result.

If several square-based pyramids, of various heights,
be placed successively on the same spot, and examined
with one eye from a fixed point over and slightly to the
side of the pyramids, it will be perceived that each time
a pyramid is changed, that the relative position of the
apex alters, and that this displacement is greater the
taller the pyramid viewed, or in other words, the relief
is more visible. If these pyramids be now viewed again
with one eye, but this time not on one side, but directly
on a line with their axes, they will, although all differ-
ing in height, nevertheless present the same appearance
of a square cut with its diagonals.

Thus, each time that the height of the pyramid varies,
the visual angle becomes greater, and the relief is con-
sequently more striking.

But suppose for a moment that it is desired to repro-
duce the pyramid, what angle should be employed?
should it be the angle of vision, or a larger one ?

In view of what has been said above, it is evident
that if a larger angle be used, the pyramid will appear
in the stereoscope higher than it really is, and as the
photographic apparatus does not furnish any standard
of comparison by means of an object of known height
placed side by side, a false idea will be conveyed of
the true size of the pyramid.

When the angle is too great, the object is distorted.
This defect is, so to speak, very general in all repro-
ductions of statues, portraits, &c. The relief in these
cases is, with very few exceptions, greatly exaggerated.
And thus it happens that when a statue is reproduced in
this way, the- head often seems so much in advance, that
it becomes really monstrous.

It should always be borne in mind when objects are to

THE STEREOSCOPE. 97

be reproduced which are of known size and proportions,
such as statues, portraits, animals, &c., that if a large
angle be employed the image will be distorted.

For views and landscapes an excessive relief may be
obtained without detriment to the picture, on the con-
trary, with a decided improvement in effect, at the same
time attention must be had to the character of the view.
If, for example, the foreground of the picture be very
near the operator, a small angle (about 2°) must be used,
otherwise the two pictures will not become superposed in
the stereoscope. If, on the contrary, the view offers but
little difference between the various planes, advantage may
be taken of this, and a larger angle, -±° for example, may
be employed.

The stereoscopic angle is reckoned from the nearest
point of the view to be taken; this point forming the
apex of the triangle, and the distance between the two
cameras being the base, or rather the arc, of the angle.

When the operator has chosen his point of sight, the
eye should estimate the difference between the cameras
and the nearest point in the view to be taken, which will
determine whether an angle of 2° or 4° be preferable.
The following table will, to a certain extent, serve as a
guide for beginners to judge the value of an angle, that
of 2° being selected as an example : —

Distance of the Object from the Cameras. Distance between the Cameras.

Yards. Inches.

1 1-26

2 2-52

3 3'78

4 5-04

5 6-30

6 7'56

7 8-82

8 10-08

9* 31-34

10 12-60

15 18-90

20 25-20

25 31-68

30 37'80

35 44-28

40 ... 50-40

98 PHOTOGRAPHIC PROCESSES.

CHAPTER XV.

PRINTING POSITIVE PROOFS.

THEORETICALLY, the printing process is one of the greatest
simplicity : — One side of a sheet of paper is first imhued
with a solution of common salt, and dried ; it is then
treated with a solution of nitrate of silver. A white
substance, called chloride of silver, is formed in the texture
of the paper, which has the singular property of becoming
rapidly darkened on exposure to the sun ; it is on this
account that when it is prepared the operation should be
performed in the absence of daylight, and the sensitive
paper preserved in a dark box.

It is evident that if paper so prepared be placed behind
a negative, and exposed to daylight, a positive image will
be produced on the paper. And, in order to its preserva-
tion, it will be necessary to remove the whole of the chloride
of silver unacted on by light, without affecting those por-
tions which constitute the image ; this is readily accom-
plished by soaking the proof for a quarter of an hour in a
solution of hyposulphite of soda, and then washing most
copiously in water to remove every trace of this fixing
agent from the texture of the paper.

The proof thus completed is the final result of all the
operations which have been previously described.

The foregoing description gives the general principles
of the printing process ; a successful result, however, can
only be attained by the exercise of the greatest care and
attention to many important details, which will be treated
of under the following heads : —

1. Salting the paper, that is, treating the paper with a

solution of common salt, or chloride of ammonium.

2. Sensitising the paper, by floating on a. solution of

nitrate of silver.

3. Exposing the prepared paper to light, and the

apparatus used for this purpose.

4. Fixing the image formed bv lioht, and imparting

an agreeable tone.

5. Mounting the proofs, that is to say, giving the final

touches before delivering them to the public.

SALTING THE PAPER. 99

1. Salting the Paper.

Suitable paper for positive proofs is now manufactured
expressly for the purpose, and can readily be obtained
both in England and on the continent. It is not, how-
ever, every sheet in the ream as obtained from the manu-
facturers that ought to be employed. Those that are
uneven in texture, and blemished with black and other
spots, must be rejected.

While selecting paper it is important to touch only the
edges of the sheets, because, however dry the fingers may
be, they always leave a slight imprint which, sooner or
later, will produce a stain.

It is also necessary to ascertain the right side of the
paper to which the chemicals should be applied; this
may be done by examining the paper by reflected light,
and is that side most uniform in its character and freest
from lines. Each sheet, as selected, should have the
wrong side distinguished by a pencil mark.

Positive paper should be moderately thick. A ream
should weigh about 22 Ibs., the size being 22 inches by
17 inches; but, generally speaking, for albumenised paper,
the ream should not weigh less than 24 Ibs., especially if
it be required highly glazed ; while for ordinary salted
paper a weight of 18 Ibs. to the ream will be found suf-
ficient. The paper may be salted with various chlorides,
such as the chlorides of barium, strontium, potassium,
ammonium, &c. ; and although it was once thought that
each salt imparted a characteristic tint to the proof, a
contrary opinion is now entertained ; however, chloride of
sodium, or common salt, which is always to be obtained
in a fair state of purity, is now generally used.

The salt is dissolved in distilled, or rain-water, in the
proportion of 12 grains to the ounce, and the solution fil-
tered into a dish large enough to hold a whole sheet of
paper, and measuring, therefore, about 24: inches by
19 inches. The preparation of whole sheets of paper at
one time will generally be found most advantageous, and
they are afterwards easily cut to any smaller sizes that
may be required.

The paper is spread out or floated on this solution in
the following manner : — The opposite ends of the sheet
F 2

100

PHOTOGRAPHIC PROCESSES.

are held, and the paper bent as represented in Fig. 82,
and the middle of the paper being brought into contact
with the liquid, the two ends are regularly lowered until
the whole of one side just floats on the surface. The side
of the paper previously marked with a pencil should be
uppermost.

The paper ought to remain on this bath five minutes in
winter and three minutes in summer, at the end of which

Fig. 82. Salting the Paper.

time it is withdrawn by means of a pair of horn or box-
wood forceps and held for a little while over the dish, to
drain ; it is then attached to two clips, or other means
of suspension, and hung on a line to dry (Fig. 84).

If the operator, or rather amateur, should not be often
performing this operation it may be found more conve-
nient to use smaller sheets, and to suspend them in the
manner indicated in Fig. 83; whichever method of sus-
pension, however, is adopted, a small piece of white
bibulous paper should be attached to the lower corner or
corners, in order to aid the draining. of the salt solution.

Paper thus salted is preserved in a portfolio, and, as it
does not undergo any alteration by keeping, it may be
prepared in large quantities at a time.

Albumenised paper yields positive proofs of great

SALTING THE TAPER.

101

delicacy and fine colour. It is, however, a little more
difficult to prepare.

White of egg is heaten into a snow-white froth, add-
ing, for each 10 eggs, 150 grains of salt, reduced to fine

Harginj the Paper to Dry.

Fig. 84.

powder ; then, when the albumen has accumulated by
being allowed to remain at rest (see Fig. 74, and pages 75,
76), it is poured into a large flat porcelain tray, and used
, in the same manner as the ordinary salting-bath, except
that the viscous nature of the albumen requires greater
care in floating.

It is very difficult to albumenise large sheets of paper.
The first operation should be the removal of bubbles by
means of a card, and this must be done very effectually,
because wherever there is a bubble the liquid does not
touch the paper, and the consequence is a white spot in
the print.

It is advisable to keep the paper which it is intended
to albumenise in a clamp place for a few days before
using, otherwise it gets into folds on the liquid, and
bubbles are sure to form. When, however, the paper is
damp it spreads with the greatest facility on the albumen-

102

PHOTOGRAPHIC PROCESSES.

bath, and no fear need be entertained as to the formation
of the fatal bubbles. These precautions are specially
applicable to large sheets, the small ones being compara-
tively easy of manipulation.

The large sheets are very difficult to suspend. An
excellent plan is to attach the sheets, on being withdrawn

Fig. 85. Drying of Large Sheet?.

from the bath, to frames of cardboard by the aid of pins,
as shown in Fig. 85. In this way the tearing of the
sheet, and its frequent falling to the ground, is avoided.

There is not much purely albumenised paper used ;
that which has been prepared with a mixture of albumen
and water being preferred, on account of the more
moderate brilliancy given to the sheets. From 10 to 40
per cent, of water may be added to the pure albumen;
but the more water, the less brilliant the paper.

For portraiture a paper prepared with pure albumen

SENSITISING THE PAPER. 103

should not be used, on account of its excessive brilliancy ;
but rather plain salted paper, or paper prepared by float-
ing on a mixture of equal volumes of albumen and
water containing 4 per cent, of salt. Albumenised paper
should be preserved in tin or zinc boxes, closed from con-
tact with a damp atmosphere, for if it absorbs moisture
it becomes rapidly changed, especially in summer time.
Whether the amateur prepares his own paper, or whether
he buys it, there are always some bad sheets. Sometimes
there are great lines arising from the draining of the
albumen towards one point, sometimes the gloss is greater
at one place than another, without the reason being very
obvious.

2. Sensitising the Paper.

This operation should be performed in the dark, or at
all events in a moderate light. Daylight does not act by
any means so energetically on positive paper as on collo-
dion; nevertheless, it is advisable to have a room specially
arranged for the purpose.

To this end the windows should be furnished with
yellow blinds or frames, which will admit a large body
of light, having no action on the prepared paper.

Paper is sensitised by floating it for three or four
minutes on a silver-bath of 20 per cent.

. Water 20 ounces.

Kecrystallised Nitrate of Silver 4 ,,

This solution is poured into a perfectly clean dish, and
the paper floated thereon, in the manner shown at Fig. 82.

If the proportion of nitrate of silver be much reduced
the proofs will be wanting in vigour ; from which circum-
stance, as often as 100 sheets of paper, 9 inches by 7,
have been sensitised, half an ounce of nitrate of silver
should be added to the bath.

In order to avoid soiling the fingers, and also the stains
which would be produced by the contact of the clips, it
is best to turn up a corner of the sheet (Fig. 86), which
prevents its absorbing any of the nitrate of silver, and
may, therefore, be taken hold of for hanging up the sheet.
Instead of hanging the sheets of paper by hooks (Fig.
87), they can be more conveniently suspended by some

104: PHOTOGRAPHIC PROCESSES.

little articles, supplied with india-rubber springs, known as
American Clips (Fig. 88).

It is only necessary to press on the ends of these clips in
order to open them, and to withdraw the pressure after

Fig. 87.

inserting the paper, which is then held with the greatest
tenacity. Figs. 83 and 84: show how these improved clips
are used.

Small pieces of white blotting-paper should be attached
to the corners of the sheet from which the
solution is draining, and the drops of nitrate of
silver may be collected in test-glasses (Figs.
83 and 84), although the drops so collected
serve only for transformation into chloride of
silver.

The dry sensitised sheets shoul d be used
within a day or two after preparation, unless pre-
served in a box with chloride of calcium, to be
presently described.

The silver-bath may, of course, be used until it is
exhausted, remembering always to add the half ounce of
nitrate of silver for every 100 sheets 9 inches by 7, as
before mentioned. It must, however, be filtered every
time it is desired to sensitise a fresh batch of paper.

A special bath should be used for albumenised paper,
to which should be added one -fortieth of its weight of
kaolin, which should always be kept at the bottom of the
bottle, shaking it up from time to time, and regularly
allowing it to settle. This kaolin maintains the bath in a
colourless condition, for without it the solution would
acquire a deep yellow colour which would be communi-
cated to the proofs.

When a number of sheets have been sensitised, they

SENSITISING THE PAPER.

105

are placed in portfolios, one on the other, handling them
only by the edges, in order to avoid contact of the fingers,
which produces stains. They should be used within three
days.

Fig. 89. Apparatus for preserving Sensitised Paper?.

If it be desired to preserve sensitised paper for some
months, an apparatus must be employed consisting of a
box with an air-tight cover, and containing some dried
chloride of calcium. Figs. 89 and 90 represent two forms
of the apparatus. Fig. 89 consists of a square zinc or tin
box, about six inches deep, furnished with
a false bottom, on the top of which is
placed the sensitised paper, and under-
neath a metal or porcelain basin filled with
pieces of dried chloride of calcium) the
whole is closed by a well-fitting lid, which
can be rendered air-tight by pasting a
strip of paper around the joining.

The other form, Fig. 90, is a very con-
venient, one for travelling. The outer
cylinder B and cover A are made of zinc
or tin plate ; the inner core E D is formed
of canvas or metal gauze, and is filled with
pieces of dried chloride of calcium. A
sheet of blotting-paper is first rolled round
this core, and afterwards the sheets of f
sensitised paper; it is then put into the l
cylinder, the lid adjusted, and a band of Fiff- 9°»
vulcanised india-rubber placed over the joining, as shown
at 0, which renders the whole air-tight.

Whenever anv of the sheets of paper are required to
F 3

PHOTOGRAPHIC PROCESSES.

be taken from either form of apparatus, it should be closed
again as quickly as possible, because the chloride of calcium
very rapidly attracts moisture from the air; from which
circumstance its peculiar action of keeping perfectly dry
the air in the interior of the boxes depends.

When the chloride of calcium has been some time in
use, it becomes covered with moisture, and eventually
converted into a liquid, and its action destroyed. So soon
as any moisture is perceived, it ought to be placed in a
moderately hot oven, in a porcelain or iron vessel, until
perfectly dry, when its properties will be entirely restored.
Thus the same quantity of chloride of calcium can be used
over and over again for any length of time required.

3. Exposure of the Prepared Paper to Light.

A printing frame is procured, furnished with screws

for large plates, and with
springs for small nega-
tives. The instrument
(Fig. 91) consists of a
simple wooden frame,
at the bottom of which
is a strong piece of
plate glass, which should
be always well cleaned
- on both sides before
I using. The negative is
placed on this glass with
the plain side down-
wards, while the sensitised side of the paper is brought
into contact with the collodion film, which is, of course,
uppermost.

In order to maintain perfect contact between the sen-
sitised paper and the negative, the printing-frame is fur-
nished with a hinged board lined with cloth or felt, and
kept in its place by transverse bars with springs or screws.
If it be desired to examine the progress of the printing,,
one of the transverse bars is removed, the hinged board
is opened, and one half of the paper bent back, as shown
in Fig. 92. This operation should, of course, not be per-
formed in the direct sun -light, but in the shade.

Fig. 91. Printing Frame.

EXPOSURE OF THE PREPARED PAPER.

107

A consideration of the following list of successive
changes, through which the paper passes, will guide the
operator in judging when a print has been sufficiently
exposed.

'Fig. 92. How t.i examine the Acli^n of Ligh , on the Paper.

The paper turns —

1. Very pale blue.

2. Pale blue.

3. Clear bluish purple.

4. Deep purple.

5. Black.

6. Metallic greyish black.

7. Olive, or greenish bronze.

It is not sufficient that the picture when examined, as
shown in Fig. 92, should seem to be printed deep enough,
because the fixing agent removes a great deal of the depth
of the colour; on this account, and in order that the
finished print should possess the proper depth of tone, it

108 PHOTOGRAPHIC PROCESSES.

is necessary that the tint imparted by exposure in the
printing frame should be much deeper than is required
for the finished picture.

The time, then, for withdrawing the paper from the
action of the sun or light, depends solely on the method
of fixing, and is best learned by experience.

Pressure -frames should be made with the greatest care,
for if, for example, the back for pressing the paper against
the glass should not be quite flat, the paper will in some
places be away from the negative, while in other parts
the contact will be complete, and the resulting positive-
image will bear evidence of unequal sharpness, thus
marring the beauty of the picture.

Professional photographers, who generally have a great
many negatives to print from, arrange the pressure -frames
on a framework, so constructed as to admit of the angle
of inclination being altered in such a way as to receive
the solar rays perpendicularly.

The more vigorous and fully developed the negative,
the more brilliant and satisfactory is the resulting positive
proof. But if the negative be a weak one, it is possible,
notwithstanding, to produce a passable print from it by
prolonging the action of the
solar rays. To this end the
frame is exposed not to the
direct rays of the sun, but to
diffused daylight. Or better
still, the printing frame may
be covered, as shown in Fig.
94:, by a light frame, upon

which is stretched a piece of

fig. 03. v^nette G:asscs for Gia~ thick white paper. When it
is desired to produce portraits

with a white background, glasses with yellow borders
and white centres are employed, called vignette glasses,
as shown in Fig. 93.

It will be understood that the yellow portion of these
glasses prevents the passage of the chemical rays, and as
the action of light on the chloride of silver takes place
only through the colourless portion of the glass, that is to
say, in the centre, it follows that from an ordinary negative
a picture may be obtained with a white background.

EXPOSURE OF THE PREPARED PAPER.

109

When the background of a negative is not sufficiently
developed, or is defective through any other cause, it be-
comes very difficult to remedy. Some persons paint in the
background, others cut out the figure from a positive print
and paste the matrix, or background portion, on the

iij. 94. Movcable Framework for Printing Positives.

negative ; but in either case the outline of the picture is
always hard and disagreeable. A better plan is to cover
the pressure frame with the vignette glass, Fig. 93,
taking care, of course, to place the oval in such a posi-
tion that only the bust shall be printed, while the defective
background is as much as possible masked.

The following is the method adopted when'it is desired
to produce the effect of clouds in a proof ; firstly, a negative
is taken with the ordinary exposure, in wrhich the sky
will be perfectly black; secondly, another negative is taken

110 PHOTOGRAPHIC PROCESSES.

with such a short exposure that nothing appears when the
developing solution is poured on but the sky. With this
short exposure the effect of clouds is very successfully
obtained.

A positive being printed from the first negative will have,
of course, a white sky ; this being placed under the second,
or cloud negative, the foreground of which is covered with
cotton wool in such a way that light can pass only through
that portion of the glass bearing the image of the clouds.
The outline of the objects in the landscape is covered
with cotton wool, the fibres of which have been well
pulled out, in order that the hardness which would be
otherwise produced may be moderated and toned down.
An exposure of a few minutes will be found sufficient to
produce the desired effect.

To produce a similar effect artificially is even still more
easy. In taking the negative it is arranged in the expo-
sure that the sky shall not be too deep, and the desired
cloud effects are painted, not on the film, but on the
other side of the glass. It should be remembered, how-
ever, that the effect produced in the positive proof will
be the reverse of what is painted on the glass.

A recently varnished negative should not be imme-
diately printed from under the direct rays of the sun, for
however good the varnish employed may be, it invariably
sticks a little when freshly applied. Instead of exposing
to direct sunlight, use diffused daylight, or better still,
cover the pressure -frame with a case or covering of white
paper.

Paper should be made perfectly dry after sensitising,
and before being placed in contact with the negative,
otherwise the moisture in the fibres of the paper will be
volatilised by the sun's heat, and condense on the negative,
which will soon become blackened by the nitrate of silver
of the paper. When this is discovered in time, the spots
so produced may be removed by cyanide of potassium ;
the operation, however, requires great dexterity and
judgment.

Negatives should never be allowed to remain all night
in contact with paper at all damp, as the depression of
temperature induces a condensation of moisture on the
surface of the glass, and brings about the same untoward

TONING AND FIXING THE PRINT. Ill

result as occurs under the circumstances detailed in the
preceding paragraph.

Unusual precautions are necessary in the use of albu-
menised paper, which easily sticks to the negative, and
shows stains wherever it is touched. It should be handled
only by the extreme edges.

It is very important that the woodwork of pressure -
frames should be well put together, so that no warping
shall occur through changes of temperature or differences
in the hygrometric condition of the atmosphere ; other-
wise the prints will not be equally sharp over the entire
surface, owing to the unequal contact between the paper
and glass induced by the warping. Moreover, the nega-
tives are very likely to become cracked from the same
cause.

A great many sheets of positive paper may be prepared
at a time, on the sole condition of keeping them in a box
with chloride of calcium, as described at page 105. This
box, however, ought not to be opened oftener than is abso-
lutely necessary, but enough paper should be withdrawn
at one time to serve for two days' consumption.

Before placing the negative in the pressure-frame, the
plate -glass should be carefully wiped, in order to avoid
the accumulation of dust on the proof.

When the paper is placed in the frame the screws must
be tightly adjusted, so as to secure it against the slightest
movement when the hinged back is opened to examine
the progress of the printing.

The frame itself should be a little larger than the
hinged back, in order that the latter may open without
difficulty. If it be so tight as to require on effort to
open it, there will almost invariably occur a displacement
of the negative, and a consequent doubling of the outline
in the proof.

4. Toning and Fixing the Print.

The process of toning is employed to impart a pleasing
tint to the proof, and the object of fixing is to remove
the unaltered chloride of silver by immersion in a solu-
tion of hyposulphite of soda.

In order to avoid constantly touching the proof during

112 PHOTOGRAPHIC PROCESSES.

these operations, horn or boxwood forceps are employed,
or glass rods bent as shown in Figs. 95 and 96.

Fig. 95.

Many formulae have been given for toning and fixing
the prints, in some of which
the two operations are con-
ducted simultaneously ; in
others the fixing is done be-
fore the toning, and in a third
the toning is effected before
the fixing.

The latter process, how-
Fig' 96* ever, is the one by which the

best results and the greatest permanency are obtained.
It consists of four operations : 1. Washing the print, to
remove the free nitrate of silver adhering to the surface,
and which has remained unchanged by light. 2. Toning
in a weak solution of chloride of gold, to which a small
quantity of carbonate of soda has been added. 3.
Washing again to get rid of the chloride of gold. 4.
Fixing in a solution of hyposulphite of soda.

The chloride of calcium box (Fig. 89) serves as well
for the preservation of proofs which have been exposed
to light as for sensitised paper. As it is desirable to fix
a large number of proofs at one time, it is recommended
that the operator should at the outset provide himself
with three, at least, of the chloride of calcium boxes ;
one for preserving the white chloride, another for the
paper ready for immediate use, and the third for paper
which has been exposed under a negative.

The room set apart for the production of positive
proofs should be on the ground-floor, and the panes of
glass darkened with yellow paper ; it should be furnished
with several large wooden troughs for washing, and an
assortment of porcelain or brown stoneware trays for

TONING AND FIXING THE PRINT. 113

hyposulphite solutions, &c. There should also be an
abundant supply of water. 9

The proofs being taken either from the pressure -frame
or the chloride of calcium box, are plunged one after the
other into a porcelain pan containing rain-water, which
is changed for every hundred prints. This bath should
be at least one foot deep.

By far the greater quantity of the nitrate of silver
withdrawn from the sensitising bath still remains on the
surface of the paper after exposure to light. The bath
of rain-water dissolves the nitrate of silver, and when
the water is thoroughly charged therewith, it may be
treated as described at page 75, by throwing in an excess
of common salt, which produces a precipitate of cholride
of silver.

There should not be more than ten prints washed at a
time in this bath, and special care should be taken to
prevent any hyposulphite of soda from falling therein,
on which account the bath may be advantageously covered
with a plate of glass, and the prints touched only with
boxwood forceps.

When the prints have been for about ten minutes in
the water, they are taken out one at a time and immersed
in the toning-bath. To prepare the toning-bath, make
the two following standard solutions : —

.- - f Bicarbonate Soda 2 drachms.

' (Water 32 ounces.

_- 2 f Chloride Gold 30 grains.

(Distilled Water 32 ounces.

Take one quart of water and dissolve in it two drachms
of common salt; then add one ounce of solution No. 1
and one ounce of No. 2. This toning-bath should be
kept about ten minutes before being used.

The first prints which are immersed in the bath after
the addition of the chloride of gold tone rapidly ; but in
proportion as the gold is taken up, the toning proceeds
more slowly, when more of solution No. 2 will have to be
added. To accelerate the toning in winter, the solution
may be slightly warmed by setting the dish on a sheet
of plate iron heated with a spirit lamp.

The chloride of sodium or common salt is added to the

114 PHOTOGRAPHIC PROCESSES.

bath to transform into chloride the nitrate of silver which
has not been washed out, and which would otherwise
decompose the Chloride of gold.

The prints being put into the toning -bath will first
become red, and will then pass successively through all
the intermediate tints between red and black. The toning
can be stopped at any stage by immersing the print in a
tray of clean water, which should be kept at hand for the
purpose.

The real colour is only seen after immersion in the
hyposulphite fixing solution, and it is at this stage only
that the operator can judge to what tint he should tone
his pictures, in order that they should finally possess the
desired colour. As a general rule the bluish black
changes to a pure black in the hyposulphite ; less toning
than is required to give the bluish black produces prints
more or less brown ; if the toning is pushed further than
the bluish black, the prints will be ashy coloured and flat
when dry.

Prints which have to be toned black must be printed
deeper than those which have to be toned purple or
brown, for the toning-bath has also a bleaching action,

Prints on albumenised paper require for toning a larger
quantity of gold than prints on ordinary salted paper.

The toning-bath may be used over and over again, by
adding from time to time more gold and bicarbonate of
soda; but, as hyposulphite of soda is liable to be acci-
dentally introduced into it, it is advisable, where a large
number of prints are produced, to make a new one every
day.

In order to judge of the colour of the proof it should
be withdrawn from the gold-bath by means of a boxwood
forceps, as, on account of the yellow colour of the bath,
it is difficult to form an accurate estimate while the print
remains therein. The same remark may be applied to
the colour of the panes of glass in the printing room. It
has been said that they should be covered with yellow
paper, but this applies, of course, only to those panes
which illuminate that part of the room in which the
prints are either withdrawn from the pressure -frame or
placed therein, or where the first washing with plain
water takes place. All the other operations may be

TONING AND FIXING THE PRINT. 115

safely conducted by daylight, although it will be found
quite as well to preserve the whole of the workshop from
the direct action of the solar rays by means of blinds.

The prints, as soon as they are taken out of the toning-
bath, are immersed in water ; they are then washed
several times, and put into the fixing-bath, which is
composed as follows : —

Hyposulphite of Soda 8 ounces.

Water 1 pint.

The fixing will generally require from ten to fifteen
minutes ; but it is easy to understand that the longer the
bath has been in use, the more will its capacity for dis-
solving chloride of silver become exhausted, and the
longer will the print require immersion, so that, one
pound of hyposulphite of soda will not fix more than one
hundred prints, 8J in. X 6 Jin.; but as this salt is very
cheap, to use it liberally will make but a fractional in-
crease in the cost of the prints.

The hyposulphite bath should, then, be often changed,
and when out of use it may be kept for the purpose of
extracting the silver.

The proof which comes from the last bath is now
rinsed in a wooden trough filled with water, to remove
the excess of adherent hyposulphite ; then allowed to
soak for two hours in a second trough, and for three
hours in a third. There should be an extra trough or
dish for every twenty-five prints of 8J in. X 6| in.
When the prints are allowed to remain longer in the
water than is specified above, they lose their beautiful
colour and become yellow.

It is sometimes desired to finish the washing of a print
somewhat hurriedly, and yet to ensure the complete
removal of every trace of hyposulphite of soda; when
this is the case, the proof is placed on a glass plate of
suitable size, and moved about under a stream of water
from a tap falling from a height of about six feet. The
motion imparted to the glass should be so regulated as
to allow the water to fall on every part of the proof in
succession, without tearing it or causing its separation
from the glass. Five minutes of this energetic washing
removes the hyposulphite more effectually than five hours

116 PHOTOGRAPHIC PROCESSES.

soaking in the troughs of water, although it is obvious
that the consumption of water is much greater. A badly
fixed or imperfectly washed print undergoes spontaneous
alteration after a few weeks.

The following may be received as practical rules to
avoid the fading of prints.

As silver forms, with hyposulphite of soda, a double
salt, slightly soluble in a feeble excess of hyposulphite
of soda, but on the contrary very soluble in a con-
centrated solution, — and as this double hyposulphite
of silver and soda decomposes with great facility, — it
is very important that concentrated solutions should be
used, in order that the double salt shall be dissolved as
soon as formed.

A bath such as that of which the formula has been
given, must not be used too long, and for the same reason
too many proofs must not be immersed therein at one
time, especially if there be not sufficient space between
each proof to allow the bath to exert its full solvent
action.

All the formula3 which prescribe the addition of an
alkali or an acid to the bath should be unhesitatingly re-
jected. The chloride of gold of commerce is sometimes
very acid, in which case it may be replaced, if desired, by
a white salt known by the name of Sel d'Or de Fordos
et Gelis ; this must be very much diluted before mixing
with the hyposulphite of soda.

If the proof, through insufficient washing, contains
hyposulphite of soda, it will have, when dry, a sweet
taste, and will fade in a very short time.

Finally, all fermented or fermentable substances for
mounting photographs, should be rejected. Nothing but
recently prepared starch-paste should be used, and the
proof should be allowed to dry very rapidly when mounted,
in order that no acid principles may be developed by
fermentation.

In rainy climates in winter — in England, for ex-ample
— it is sometimes necessary to expose the paper for a
whole day to the light before a positive can be obtained.
Albumenised paper being much more rapid than simple
salted paper, will therefore be preferred, although even
this will sometimes fail to produce a positive in a reason-

TONING AND FIXING THE PRINT. 117

able time, in which case recourse may be had to the follow-
ing expedient.

Plain paper being cut to the proper dimensions, and the
reverse side marked with a pencil, is allowed to float
for about one minute on a bath composed of 300 grains
of iodide of potassium dissolved in 35 ounces of water.
This bath serves until it is exhausted, and the paper when
dry and placed in a portfolio will keep a long time. The
paper so prepared is rendered sensitive to light by floating
(in the dark, of course) on a bath of nitrate of silver for
one minute. The bath is composed of —

Water 3i ounces.

Fused Nitrate Silver 30: grains,

Glacial Acetic Acid 300 „

The paper is withdrawn from the bath, well drained, and
rapidly dried between folds of blotting-paper, in order to
remove the excess of -solution, and prevent its touching
the back of the paper. This operation is repeated with
a second and even a third sheet of blotting-paper. It is
necessary that the sensitised sheet should be damp, but
not to such a degree as to stain the negative, upon which
it should be pressed very lightly.

The exposure to diffused daylight varies between five
and fifteen seconds ; a long exposure yields a flat picture,
deficient in brilliancy — in a short one the sky only
appears.

The paper is carefully removed from the negative, and
placed on a sheet of glass with the sensitised side upper-
most. A solution is then made of 15 grains of gallic
acid in 35 ounces of warm water, to which is added 3|
drachms of glacial acetic acid. This is filtered and
spread very quickly by means of a brush or glass rod over
the sensitised side of the sheet. The image appears very
rapidly, and as soon as the desired effect is arrived at,
the paper is plunged into water to arrest the action of
the developer.

After washing, it is toned with chloride of gold, as
described at page 113, and it is then washed for two hours
in a large trough of water.

118 PHOTOGRAPHIC PROCESSES.

5. Mounting the Proofs.

Whatever process may have been adopted in the pro-
duction of the positive print, it has finally to be pasted
on Bristol board, and rolled.

Nothing is more simple than the mounting of a proof.
It is cut into any suitable or desired form, and the back
covered with starch-paste. It is then spread on the
Bristol board, a piece of blotting-paper laid over it, and
the whole rubbed with the hand in every direction, in
order to ensure complete contact between the print and
the board. This being done, it is allowed to dry in the
air, and subsequently rolled in a lithographic or other
press, by which it acquires a finishing gloss, which is
entirely absent in unrolled prints.

Poirier's press, represented in Fig. 97, is very applic-
able for this purpose. It is composed of a steel roller, E,
the axle blocks of which are moveable in a vertical direc-
tion ; double levers are employed to make the necessary
adjustment, and the power is applied at & b. It is suffi-
cient to move one only of these heads in order to move
the other, there being an arrangement of cog-wheels
for this purpose. However, for delicate adjustments,
the power is best applied to each screw-head separately,
which, in turning, depresses two screws attached to the
axle -blocks, these latter sliding between two edges of
cast-iron.

The other part of the apparatus consists of a plate of
planed polished steel, a a, or of a very flat lithographic
stone, which receives its backward and forward motion
from a toothed wheel, moved by a still smaller one, which
in its turn is moved by a long lever or handle.

Upon this steel plate two very smooth and specially
prepared cards are placed, between which the proof to be
rolled is laid. The screws being adjusted, and the motion
imparted, the steel plate moves on, turning the cylinder
at the same time. An enormolis pressure is thus brought
to bear uniformly over the whole surface of the card, and
after two or three movements to and fro, the screws 6 b
are slightly tightened, and the rolling repeated.

The proof thus becomes pressed into the cardboard,

TONING AND FIXING THE PRINT.

119

and acquires a splendid gloss. To mount stereoscopic
views and cartes de visite, they should be cut by means of
a steel or glass mould and a good knife.

It is a good plan to paste a great many proofs on one
card, in order to effect the glazing by one operation.

A beautiful gloss can be imparted to stereoscopic and
carte de visite proofs by varnishing them. This varnish is
made as follows : — One ounce of white lac is dissolved

Fig. 97. Rolling Press.

in ten ounces of warm alcohol, and after allowing the
bottle to stand for several weeks, the clear portion is
decanted for use.

This varnish is then applied in a similar manner to
that adopted by French polishers in polishing cabinet

120 PHOTOGRAPHIC PROCESSES.

work ; it has been introduced into commerce under the
name of Crystal Enamel.

The picture having been mounted, is sized with a warm
solution made by dissolving 10 grains of Swinborne's
gelatine in 1 ounce of water, and either hot-pressed or
burnished with an agate burnisher. It is then coated
with the crystal enamel, applied in the following manner :
— A tampion of cotton -wool saturated with the liquid is
wrapped in a piece of clean white calico rag, the outer
surface of which is touched with a drop or two of linseed
oil : this is gently and evenly applied with a circular
motion over the whole surface to be enamelled, until the
picture becomes brilliant. It is, lastly, finished off by
applying, in the same manner, alcohol and linseed oil.

NOTES.

NOTE 1 (page 4).
APPEARANCE OF NEGATIVES.

The difference of the reverse appearance of an ordinary negative on
glass or paper, and the direct one exhibited by a metal plate, is simply
apparent and not real, and arises solely from the mirror-like appearance
in those parts of the silver plate not acted on by light. And this explains
the reason why it is necessary to give to these '(daguerreotype) pictures a
particular position in relation to the angle at which the light strikes
them. At other angles, when, for example, the light is directly reflected
from the surface of the metal, the image appears as a negative.

NOTE 2 (page 16).
DISTILLATION OF ETHER.

The object aimed at in the distillation of a liquid is the separation of
any solid substance which it holds in solution, or any liquid of a dif-
ferent constitution with which it may be mixed. In the instance under
consideration, it is necessary to separate the ether, not only from the
chloride of calcium upon which it has been dried, but also from the
alcohol and water which it contains.

The boiling point of ether being about 96° Fahr., and of alcohol ] 74°
Fahr., and water 212° Fahr., it follows, that if a mixture of the three be
submitted to the action of heat, the ether will be almost completely
volatilised before any sensible evaporation of the alcohol or water has
taken place. A tube thermometer, having its stem passed through the
cork, and its bulb so arranged as not to come into contact with the
liquid, will indicate a temperature of about 96°, rising higher in propor-
tion as more alcohol and water become evaporated. To secure pure
ether, the temperature should not rise higher than 104°.

G

122 PHOTOGRAPHIC PROCESSES.

The first portions which come over should not be used, as they gene-
rally serve only to cleau the condensing tube, and, consequently, contain
impurities. From two pints of ether, therefore, the first ounce and a
half which comes over should be rejected.

NOTE 3 (page 18).
PREPARATION OF PYROXYLINE.

The cotton should be chosen free from defects and any contaminating
organic matter. A mixture is then made of

Sulphuric Acid (Sp. Gr. 1*8) 38 fluid ounces.
Nitric Acid (Sp. Gr. T4) 19 do, do.

This is stirred with a glass rod, and if examined by a thermometer will
be found to indicate a temperature of 176° Fahr. ; the operator should
therefore wait until it cools down to 140° Fahr. before plunging in the
cotton.

The quantity of cotton to use is about 1,050 grains, which is added to
the acids, about one-fourth or one-fifth part at a time, squeezing it with
the glass rods in order to force out the air imprisoned between the fibres.
When all the cotton is immersed, the containing vessel is covered with
a plate to keep in the nitrous vapours, and at the end of ten minutes the
cotton is withdrawn, and copiously drenched with water, as before
described. The pyroxyline thus obtained is less soluble in ether and
alcohol than that obtained by the ordinary method ; but it is especially
useful when great tenacity of film is required.

NOTE 4 (page 19).
EMPLOYMENT OF THE IODIDES AND BROMIDES.

Besides iodide and bromide of cadmium, a great number of other
iodides have been used, among which may be mentioned those of potas-
sium, sodium, ammonium, zinc, &c.

Many photographers confine themselves to the use of the iodides
of potassium and ammonium, but lately iodide of cadmium has come
generally into use.

More recently has been proposed, especially for copying pictures, a
collodion, containing iodide, bromide, and chloride of ethylamine. The
following is the formula which has given the best results : —

NOTES. 123

Alcohol 1'i ounce.

Ether 2'f „

Pyroxyline 15 grains.

Iodide of Ethylamine 1'2 ,,

Bromide ditto 04 ,,

Chloride ditto 0'2 „

Although iodide of ethylamine is not found in commerce, it is very
easy to prepare. It is an organic iodide, containing nitrogen, and the
elements of alcohol, but is nevertheless more stable than iodine of ammo-
nium, and yields pictures of remarkable delicacy.

NOTE 5 (page 34).
NITRATE OF SILVER STAINS.

Nitrate of silver is reduced by contact with all organic substances, and
as finely-divided metallic silver is black, it follows that this substance
blackens everything it touches, as every photographer knows. Many
methods have been proposed for the removal of these spots. The follow-
ing is the best.

The hands become inevitably stained while conducting the manipula-
tions involved in the sensitising and development of the plates, but it is
not until some hours have elapsed that the stains, at first scarcely visible,
deepen to any great extent; and it is only when a great number of
proofs have been taken that the method about to be proposed is required
or advisable.

It consists simply in well washing the hands in a saturated solution
of hyposulphite of soda, kept expressly for that purpose. Two or three
minutes' contact are found sufficient to remove every trace of the stain.
Instead of hyposulphite of soda, iodide of potassium may be used in the
same way. After the hyposulphite, it is advisable to wash the hands
with soap, and with powdered and sifted pumice stone.

If the stains are very old, it is better to allow them to wear away by
time ; however, as they sometimes are obliged to be removed, in that
case, a mixture of cyanide of potassium and iodine applied to the fingers
by a brush, or otherwise, will, if aided by the use of a lump of pumice
stone, rapidly restore the hands to their normal condition, after which
they should be well rinsed with plenty of water.

In the use of this latter re-agent for the purpose indicated, it is
important to remember that cyanide of potassium is an energetic poison,
which acts not only internally, but externally, by absorption ; so that it
should never be used when there is the slightest wound or scratch upon
the hands.

If this advice be neglected, serious results may follow. It is also
advisable that this mixture should only be prepared at the time of using
it, and that every vessel which has contained it should be carefully
cleaned.

G 2

124 PHOTOGRAPHIC PROCESSES.

NOTE 6 (page 35).
PREPARATION OF THE NITRATE OF SILVER BATH.

Into a graduated glass is placed 1,200 grains of nitrate of silver, upon
which ia poured 7 ounces of distilled water. When the nitrate is all dis-
solved, which can be hastened by well stirring with a glass rod, there is
to be added 3 drams of an alcoholic solution of iodide of cadmium, con-
taining 10 grains to the ounce ; a yellow precipitate is immediately pro-
duced. The whole is well agitated together, and left to itself for about
one quarter of an hour; more distilled water is then added to make up
the quantity of 35 ounces ; it is then filtered, and is ready for use.

NOTE 7 (page 55).
PREPARATION OF PYROGALLIC ACID.

This substance was discovered by Scheele, who supposed it to be sub-
limed gallic acid. It contains the elements of gallic acid, minus those
of carbonic acid.

Dry and pure pyrogallic acid has the form of lamellar needles, or
elongated plates, which are soluble in 2J parts of water at ordinary
temperature, and a little less soluble in ether and alcohol. It has a very
bitter taste, and when quite pure, does not redden tincture of litmus. A
solution of the pure acid will keep, so to speak, indefinitely, especially if,
as is the case when it is prepared for photographic use, an acid be added.

It is of the highest importance to keep pyrogallic acid in stoppered
bottles, in the dark ; since, unless this be done, it gradually turns brown,
through combination with the oxygen of the air, and its properties
injured.

Pyrogallic acid is prepared by boiling bruised nut-galls, with seven or
eight times their weight of water, for three or four hours, replacing the
water as fast as it evaporates. The whole is then thrown on a strainer,
and the dirty cake of nut-galls being submitted to powerful pressure, in
order to remove all the liquid.

The mixed liquors are then evaporated, first, by rapid ebullition, and
afterwards more gently, until they acquire the consistence of an extract,
which extract is rendered perfectly dessicated by careful drying in a
stove.

This product is then heated for ten or twelve hours in a flat iron
vessel, over the top of which is stretched a piece of perforated paper, the
whole being covered by a conical paper cap. The vessel is placed on a
sand-bath, and the temperature, which should not rise higher than 420°
Fahr., is indicated by one, or, still better, two thermometers. And this
is the most delicate part of the operation. If the heat be insufficient, no
result is obtained, and if it be too much heated, another product is
obtained which contains no pyrogallic acid.

Operating in this way, 100 parts of dry extract yield 5 parts of pure
pyrogallic acid, and at a more advanced stage of the sublimation, 5 parts
of impure acid, which may be purified by resublimation.

NOTES. 125

NOTE 8 (page 47).
PHOTOGRAPHIC OPTICS.

The reader will readily understand that it is by no means easy in BO
limited a work as the present to give a clear idea of photographic optics ;
the observations to be made will therefore be confined to demonstrations
of the fundamental principles only of the most advanced of the sciences.

The ultimate constitution or essence of light is entirely unknown.
Newton entertained the idea that luminous bodies threw out in all direc-
tions exceedingly minute corpuscles, which, on coming into contact with
the optic nerve, produced a certain effect, which has been distinguished
by the term " luminous effect." It has, however, been since proved that
the hypothesis of Newton does not accord with facts, and the view most
generally entertained is to the effect, that there exists in space, per-
meating our atmosphere and all existing bodies, a luminous ether of
extreme tenuity, to which luminous bodies have the property of com-
municating a vibration similar to that which takes place when a spring
is suddenly struck ; and it is this vibration, communicated with an almost
inconceivable rapidity to the optic nerve, which produces the effect
which is called light.

It is not certainly known whether this last hypothesis is a correct one,
but it is certain that it adapts itself most completely to all the known
facts of optics, and thafcit has materially aided in the discovery of some
of them.

It is well known that light travels in straight lines at a rate of 240,000
miles in a second of time.

Reflection of light is that effect which takes place when light falls on
a plane mirror.

The light which falls on a mirror from a luminous point is called the
incident ray, and that which reaches the eye from the mirror is called
the reflected ray; and if a perpendicular be elevated from the point
where these two rays meet, it will be found to make two equal angles,
or, in other words, the angle of incidence and the angle of reflection are
equal.

Reflection takes place with equal regularity from the surface of curved
mirrors, but the image is modified according to the character of the
curve, which sometimes enlarges, sometimes diminishes, sometimes re-
verses the image, and sometimes gives an erect image.

Refraction is that phenomenon which is shown when a stick is plunged
into water, by its appearing as though it was broken. It is also a well-
known fact, that the bottoms of rivers appear to be a great deal nearer
than they really are, and that in consequence great mistakes are some-
times made in judging of their depth ; this phenomenon also belongs to
refraction. In one word, refraction of light takes place whenever a ray
of light deviates from its original course by passing through a transpa-
rent body of greater or less density.

In the first place will be considered the most simple case (Fig. 98),
in which a ray of light R is incident on a plate of glass A, whose two
sides are parallel. At the point where the ray R comes into contact
with the glass, imagine a perpendicular line to be drawn, and then

126

PHOTOGRAPHIC PROCESSES.

observe what happens to the luminous ray. (The perpendicular here
mentioned is distinguished by the term normal?) Experience has shown
that the angle R N, formed by the luminous ray and the normal ray,
is greater than the angle formed by the same ray in the interior of
the glass with the same normal ray prolonged ; but this angle is constant
for the same quality or character of glass. On leaving the glass the ray
assumes a direction parallel to the direction of the primitive ray.

It follows, then, from what has been stated, that a ray of light falling
on the surface of a piece of glass is refracted both on entering and
leaving the glass.

Figs. 99 and 100 illustrate the same fact, and also show the reflec-
tion of a ray from the large face of a triangular prism.

Fig. 99.

Fig. 100.

' Fig. 98.

The study of refraction becomes more difficult when the two surfaces
of glass, instead of being parallel, are placed at an angle in relation to
each other (Fig. 101). Suppose two of these faces AC, AB, and a
luminous ray R0 falling on cue of the surfaces. If it were not a prism,

Fig. 101.

the ray would follow the direction R M ; but as the ray R0 is bent, as in
the preceding case, it approaches towards the normal in the direction o oft
the angle outside the prism being greater than the angle inside. But
the reverse happens on the second face A B, at the point o\ and the ray
leaves in the direction o{ R' in such a manner that the ray, first impelled
in the direction R M, is finally sent in the direction of R', from which it
follows, that a ray of light is altered in its direction by its passage
through a piece of glass, the two sides of which are not parallel.

NOTES.

127

Glass lenses are convex discs, ground and polished, having an exterior
figure of a spheroidal character. Their principal effect is, that when
they are exposed to the suu, the parallel rays of that luminary r r (Fig.
102), unite at a certain point, called the focus, all the rays converging
towards this point. Inversely, a luminous point being placed in the
focus/ of a lens A, emits rays which, on leaving the lens, are parallel

Fig. 104.

r r r r. It therefore follows, that a convex lens is in effect an assem-
blage of prisms, the inclination of the two faces of the glass from the
centre to the circumference being such that the parallel rays undergo an
analogous deviation, which causes them to meet at the focus. Fig. 104
is intended to illustrate this proposition.

In concave lenses the effect is entirely different. If solar rays r r
impinge on a concave lens A (Fig.
105), these rays, instead of uniting,
disperse themselves in the direction
r( r(. It is, however, usual to regard
the point f as the focus, resulting
from the ideal prolonging of the rays
r* r* and focal length the distance
A/

105> If refraction consisted only in a

simple deviation of the rays of light,
it would be a comparatively simple matter, but, unfortunately, it is no
so ; the ray is not only bent, but decomposed into its primary colours.
This statement may be easily verified by examining a white object on

128

PHOTOGRAPHIC PROCESSES.

a dark ground through one of the ordinary prisms used for ornamenting
chandeliers. The white object will appear fringed with all the colours of
the rainbow.

The same phenomenon occurs when a ray of light R (Fig. 101) is
allowed to fall on the surface of a prism. The refracted ray o' R* con-
sists not of one white ray, but of seven different colours. Convex lenses
produce the same effect. Thus, the solar rays a a falling on a convex
lens (Fig. 106) do not reunite in one single point, but produce at R a
white image, bordered above by red, and below by violet.

Fig. 106.

107.

It is possible, however, to unite two prisms (Fig. 109) in such a way
that the rays &' b falling thereon, shall leave it at a* a void of colour ;
such a combination of glasses is called an achromatic prism. These
prisms are composed of two kinds of glass — crystal, or flint, and crown, or
ordinary glass.

There are not only achromatic prisms, but lenses, which yield images
free from colour. The curve which a particular kind of glass is to
receive in order that the compound lens shall be most effectually achro-
matised, forms the subject of a mathematical calculation. The curve is
then imparted by grinding the glass by hand in a suitable tool.

Fig. 108.

Fig. 109.

Fig. 110.

Fig. 111.

There are many different kinds of lenses. Fig. 108 shows three forms
of non-achromatic convex lenses, and Fig. 110 these same lenses achro-
matised. Figs. 109 and 111 concave lenses non-achromatic and
achromatised.

In order to explain the application of lenses in photography, it

NOTES.

129

becomes necessary, in the first place, to describe a very curious pheno-
menon.

In looking at a well-lighted landscape, it is obvious that every point
of that landscape sends to us a ray of light, since, unless it were so, it
could not be seen at all.

Tf a hole be bored in the shutter of a perfectly dark room (Fig. 112),
and a sheet of white paper be placed a short distance from the aperture, it
will be seen that, as every point of the view emits luminous rays, a certain

Fig. 112.

number of these rays will pass through the opening into the dark chamber,
and being directed by the sheet of white paper, will produce thereon an
inverted image of the landscape.

If a convex lens be placed in the hole in the shutter, and the sheet of
white paper brought up to the focus of this lens, the image will be in-
creased so much in sharpness that it will seem quite easy to trace the
outline with a pencil, or, indeed, to make a finished drawing. Now, if
the sheet of white paper be replaced by another sheet of paper photo-
graphically prepared with some substances acted on by light — as the
compound of silver, for example — the image of external objects will, in
a longer or shorter time, be depicted thereon.

In Fig. 106 has been shown the remarkable fact, that the two
white rays a a become decomposed into rays of various colours ; but
what is still more curious is, that if the rays a a were red, they would
come to a focus at R ; if yellow, nearer the lens at J, and if violet, still
nearer at V. In one word, a lens acts equally only for light of one
colour, and unequally on diiferent colours. Lenses of the same form,
but of different glass, will also act differently on the same light ; and it
is precisely on this account that it becomes necessary to make a com-
bination of glasses of such forms that all the colours shall be equally
refracted and reunited in one point.

For this purpose lenses are made and placed very near to each other,
in some instances even united by Canada balsam, one lens, so to speak,
for each colour ; generally, however, the combination is confined to two
lenses, uniting only the two principal colours.

In the construction of photographic lenses, the relation between the
material, i. e. — the quality and kind of glass — and the form or curve
imparted to it is calculated in such a way as to unite into one focus the
yellow and the violet rays.

130

PHOTOGRAPHIC PROCESSES.

Sometimes double and sometimes single objectives are employed.
The double objective is composed of four lenses mounted in brass.
Fig. 53 represents such an one, and
Tig. 113 the arrangement of the lenses.
The poiut of the arrow is directed to-
wards the object to be taken. This
^ system of four lenses is arranged in
such a manner as to give a great deal
of light to the image, to the sacrifice, to
some extent, of sharpness. A single
Fig. 113. achromatic lens may, however, be em-

ployed which, while it gives less light,
wonderfully increases the delicacy of the details.

NOTE 9 (page 63).
SPOTS ON THE COLLODION FILM.

It is not intended to describe all the kinds of spots which are produced
on the collodion film, but only those which occur most frequently.

Spots are sometimes produced under the collodion film, and sometimes
upon the film. The first, always visible before exposure, arise generally
from imperfectly cleaning the plate. lu fact, the dust which remains
on the plate are centres of reduction for the iodide of silver constituting
the film, and thus form round spots.

Another source of spots arises from the presence of fatty particles in
the leather used for cleaning, and these produce stains such as shown at
page 63 (fig. 65).

In reference to spots produced on the film, they arise very often from
light solid bodies floating in the collodion. It is, therefore, of the highest
impoitance always to use a collodion which has stood some time.

It happens sometimes that the little crystals of iodo-nitrate which
float in the nitrate bath deposit themselves on the film, and on this
account some photographers pour their silver solution from a bottle, into
which it has been filtered, after sensitising a considerable number of
plates.

At other times the bottom of the plate is riddled with holes. These
are caused by the concentration of the nitrate on account of the plate
having been kept too long between the sensitising aud the development.

Sometimes, when the nitrate bath has not been filtered for a long
time, a pellicle of reduced silver is formed, which attaches itself very
firmly to the film. Veins also occur, which are aptly represented by
fig. 66, page 63.— (M. de la Blanchere.)

A similar class of stains sometimes occur, especially on positives, if
the bath contains an excess of alcohol, and they become visible on with-
drawing the plate from the sulphate of iron solution.

The stains shown in fig. 67, page 63, arise when too thick a collodion
is used.

NOTES. 131

Pyrogallic acid often produces spots. If the developer prepared there-
with contains too little acetic acid, foggy pictures are the result. If it
contains too much, the development proceeds very slowly. But spots
occur less frequently in the latter case than the former.

Should too small a quantity of pyrogallic be poured on the plate, stains
develop themselves at the corner, and sometimes spread on to the centre ;
and nothing will remove them.

If the pyrogallic acid developer does not spread itself immediately
across the plate, it produces lines which are as irreparable as those stains
described in the previous instance. It is also very important to main-
tain a constant backward and forward motion during development,
otherwise a series of little black points of reduced silver will attach them-
selves to the plate.

Hyposulphite of soda, imperfectly washed away, sometimes agglome-
rates after the lapse of a certain time, and then produces star-like spots
of the form indicated— fig 68, page 63. It is, therefore, of the highest
importance to remove the hyposulphite by repeated washing.

It remains to say a few words on fogging, the origin of which is two-
fold— the first, diffused light, and the second, alkalinity of the bath.

The evil from the first cause arises generally from the inferiority of the
yellow glass, which does not completely arrest the passage of the actinic
rays ; sometimes from the lamp or candle giving off too much white
light, from a hole in the camera back, or in the camera itself, &c.

The second of these causes, alkalinity of the bath, is much more rare ;
it occurs generally in summer time when the weather is very warm. A
few drops of acetic acid in the nitrate bath will obviate this defect.

NOTE 10 (page 56).
CRYSTALLISABLE ACETIC ACID.

Where crystallisable acetic acid cannot be obtained, its nse may, to a
certain extent, be dispensed with, by the following plan.

One thousand five hundred grains of caustic potash are dissolved in
35 ounces of distilled water, to which is added 750 grains of powdered
litmus, and the blue liquid is decanted into another bottle. This bottle
should be kept carefully stoppered. Having obtained some good ordi-
nary acetic acid, called purified pyroligneous acid, and a tube divided into
cubic centimetres, two cubic centimetres of the blue solution of potash
are poured therein. Now add, drop by drop, some standard crystal"
Usable acid, becoming solid when exposed to a temperature of about
40° Fahr. ; and after each addition, shake the tube. A point will be
reached at which the blue solution allot once becomes red ; it is at this
moment that the operation is completed.

A note is made of the amount of acid which was necessary to change
the blue colour of the potass solution ; and suppose, for example, this to
have been a quarter of a cubic centimetre. Now begin afresh, by mixing
the solution of litmus with twice its volume of water, an d also the crys-

132 PHOTOGRAPHIC PROCESSES.

tallisable acid with a similar proportion. This will allow the observa-
tion to be made more accurately as to the quantity of acid required to
redden a given quantity of solution of potash. Suppose that it is finally
ascertained that 10 cent, cubes of the blue solution require 1 to 1J cent,
cube of the crystallisable acid. Now perform a similar operation with
the pyroligneous acid ; this being much weaker, it will probably be found
that for 10 parts of the blue solution 3 J parts of this acid will be required.
The following equation is now made. If 1 J parts of pure acid correspond
to 3 J parts of ordinary acid, 10 of pure acid will correspond to x.

From this calculation is deduced the fact, that x is equal to 28 ; from
which it results, that every time 10 grains of crystallisable acid are
ordered in a formula, they may be replaced by 28 of ordinary acid : if 5,
14 only will be necessary ; if 30, 84 will be wanted, &c. &c.

The hydrometer cannot be used to determine the strength of acetic
acid, for its density bears no regular proportion to its saturating power,
or, in other words, to the relative quantities of acid and water.

The pure crystallisable acid solidifies between 50° to 60° Fahr.
Although the ordinary acid is only a mixture of pure acid and water, and
the first solidifies at, say 56° Fahr., and the second at 32", it does not
necessarily follow that the mixture shall solidify above 32°. The pure
acid, mixed with three times its volume of water, should, at first sight,
solidify at about 40° Fahr., but, in reality, it does not congeal until it is
cooled to 36° below the freezing point of water; from which it follows,
very weak acid cannot be purified by successive and fractional freezing ;
and it is only when more concentrated, that this method of purification
can be adopted.

INDEX.

Acetate of ammonia, use of, 86

Acetic acid crystallisable, 130

Aceto-nitrate bath for sensitising collodio-albumen glasses, 78

Achromatic lenses, 127

prisms, 127

Actinic rays, 48
Albumen, how prepared, 76
Albumen iodised, 75
Albumen process, 5
Albumenised paper, 101
Alcohol, properties of, 11
Amber varnish, 68
American clip, 104

Backgrounds, graduated, how produced, 108
Bath, nitrate of silver, for the wet collodion process, 30, 32, 123
• collodio-albumen process, 73

Balance, hand, 21

Balance, table, 21

Brewster's stereoscope, 90

Bromide of cadmium, preparation of, 20

Bromine, 19

Cadmium, 19

Caloscopic lenses, 47

Calotype, the, 2

" Cartes de Visite," camera, 39

lens for taking, 47

Camera obscura, discovery of, 36

principle of the, 36

photographic, 37

bellows-body, or portable, 41

" Carte de Visite," 39

for travelling, 40

stands, 38

Cameras, stereoscopic, 92

— positive collodion process, 86

— printing process, 103

134: INDEX.

Chloride of calcium, how employed, 1 05

gold, use of in toning, 1 13

sodium, use of in positive printing, 99

silver, how reduced, 75

Clouds, effect of, how produced, 110
Coating plates with collodion, 31
Collodio-albumen plates, development of, 80

albumen process, 73

Collodion, 6, 17

film spots on the, 131

for copying, 122

how decanted, 25

— iodised, preparation of, 22

how preserved, 24

positives, how whitened, 88

preparation of, 122

process, negative, 30

positive, 84

• dry, 71

Colours, separation of light into, 127

Combination lenses, for portraits and groups, 43

Crystal enamel, 119

Cyanide of potassium, use for the positive collodion process, 87

for removing stains, 123

Daguerreotype, 1

Dark frame for camera, 42

Dark room, 29

Developing solution for collodion negatives, 56

positives, 86 ^

: collodio-alburnen plates, 80

tannin process, 83

Dextrine, 72

Diaphragm, meaning of, 37

Direct image, 3

Dry collodion processes, 71

Drying box for sensitised paper, 105

Ether, apparatus for distillation of, 15
— properties of, 13

rectification of, 13

washed, 14

Exposure, to estimate time of, 52, 53

Fading of photographs, to avoid, 1 1 6
Fixing of positive paper proofs, 115

solution for negatives, 64

. positives, 87

tannin process, 84

Filtering, apparatus for, 11
Filters, how made, 11
Finger-stalls, 36,

INDEX. 135

Focus, how obtained, 41
Focussing, meaning of, 37
Fogged image, how rendered, 85
Fogging, how caused, 131, 132

Gallic acid, use of with calotype process, 2

collodio-albumen process, 81

— for rapid printing, 117
Gallo nitrate of silver, 3
Gelatine, Nelson's patent, 82

use of, 119

Glass clipping troughs, 34

plates, edges of, how ground, 25

how cleaned, 26

: dried, 67

preserved, 43

room, 48

colour of, 50

Gold, chloride of, use in toning, 113
Gun cotton, discovery of, 18

- preparation of, 16

Head rests, 51
Hyposulphite of soda, 64

Iconometer, 54

Incident ray, 124

Indirect image, 3

Intensifying collodion negatives, 66

Iodide of cadmium, preparation of, 19

ethylamine, 122

potassium, use of in rapid printing, 117

Iodine, 19

Iodised albumen, 75

Kaolin, how employed, 78 — 104

Laboratory, photographic, 29
Lenses, achromatic, 127

caloscopic, 47

concave, 126

• convex, 126

double or compound, 45

-focus of, 126

— orthoscopic, 47

portrait, 45

photographic, 43 '

various forms of, 127

— for views, how used, 44
Litmus paper, 1 8

Measures, glass, graduated, 21

136 INDEX.

Negative image, 3, 4

.Negative image, 3, 4
Nelson's patent gelatine, 82
Nitrate of silver bath, 30, 32, 123

preparation of, for negative process, 123

— stains, to remove, 123

use for collodio-albumen process, 73

use of in negative collodion process, 30

Dositive collodion process. 86

I llGgttilil. VG ^\Jll<JUllUll plU^^OO, U\J

• positive collodion process, 86

Orthoscopic lenses, 47

Paper, albumenised, 101

photographic, 99

salted, 99

Photographs, mounting of, 116 — 118
Photographic optics, 124
Pictures, formation of, by lenses, 128
Plate box, 43
Plate-holder, 27, 58
Pneumatic plate-holder, 58
Portrait lenses, 43
Portraits, rules for taking, 52
Positive collodion, preparation of, 84
- process, 84

• image, 3

— printing, rules for, 107

— prints, mounting of, 116 — 118

— proofs, fading of, to avoid, 116

fixing of, 115

toning of, 112'

varnish for, 118

Positives, collodio-albumen, 79

transparent glass, 79

Pressure frames for printing, 108
Printing frame, 106

process, 98

the rapid, 116

Prisms, achromatic, 127

refraction of, 125

Protosulphate of iron, use of, 86
Pyrogallic acid, preparation of, 129

use of, 55

Pyroxyline, preparation of, 6, 17, 122

Reducing agents, 55
Reflection of light, 124
Refraction of light, 1 24

through prisms, 125

Rolling press, for glazing proofs, 118
Russel's tannin process, 82

Salted paper, 99

INDEX. 137

Sel d'or, how used, 116

Sensitising collodionised plates, rules for, 36

solution, for paper, 103

for positive collodion, 86

Separation of collodion film, to avoid, 65

Soehnee varnish, 68

Spots on the collodion film, 131

collodion negatives, 63

Stains on collodion film, how caused, 131
negatives, 63

- of nitrate of silver, to remove, 123

Stereoscope, phenomena of the, 89

— Sir David Brewster's refracting, 90

Wheatstone's reflecting, 90

Stereoscopic angle, explanation of, 96

angles, table of, 97

cameras, 92

pictures, how mounted, 118

obtained, 93

Stop, meaning of, 37
Support for glass plates, 26

Tannin, from what obtained, 82

process, 82

Taupenot's process, 71
Toning process, the, 113

Varnish, amber, 68

for positive proofs, 118

soehnee, 68

Varnishing negatives, 67 — 69

~ positive collodion pictures, 88
View lenses, 43

meter, 54

Views, rules for taking, 53
Vignette glasses, 108

Washing bottle, 57

Washing collodion negatives, 65

Wheatstone's stereoscope, 90

Yellow light, action of, 48

James S. Virtue, Printer, City Road, London,

CATALOGUE

OF

gjprate anir

MANUFACTURED AND SOLD BY

HORNE AND THOBNTHWAITE,

121, 122, & 123, NEWGATE STREET,

LONDON, E.G.

LENSES.

£ s.

d.

£

s.

d.

£

s. d.

*

For

portraits, 4| by 3J

0

16

Oand

1

7

Oand 3

13 6

64 4}

2

0

0

„

2

17

6

„ 7

0 0

84 64

5

0

0

„

8

10

0

„ 15

15 0

For landscapes, 6 5

1

15

0

—

—

7 6

2

12

6

—

—

9 7

3

13

6

—

—

12 10

5

5

0

—

—

„ Stereoscopic

1

13

0

„

2

0

0

» 2

5 0

For Portraits, ditto

3

3

0

»

7

7

0

per pair.

CAMERAS.

£

s.

d.

£ 5.

d.

Walnut,

expanding .

from

0

11

6

to

1 10

0

Maho^aL

0

13

6

2 12

6

Ditto, best make

0

17

6

?>

5 0

0

Ditto,

folding, for views

3

0

0

J?

17 12

6

Ditto,

folding and expanding

ditto

4

10

0

fj

23 0

0

Ditto,

Stereoscopic

3

0

0

—

Ditto,

ditto, with lens

6

10

0

—

Ditto,

ditto, Binocular

4

14

6

)}

9 9

0

Ditto,

ditto, Powell's

7

7

0

t)

9 9

0

Ditto,

Schaw's Landscape

5

5

0

»

7 7

0

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£

t. d.

n

d.

Gutta Percha

from

0

2

8

to

1 2

6

Ditto, water-tight

.

0

7

6

„

1 16

0

Solid glass

0

6

0

„

1 15

0

Ditto, water-tight

.

1

1

0

„

2 17

6

Porcelain

0

3

6

})

0 14

0

Ditto Well Baths

.

0

3

0

n

0 8

6

GLASS PLATES FOR THE COLLODION PROCESS.

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