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BY < N > 






Copyrighted 1899. 


Though much of a fragmentary nature has been written 
of the making of glass and its history, no attempt has here- 
tofore been made to bring under one cover information 
which will be of practical worth to those engaged in the 
manufacture of glass. The purpose of the present volume 
is to present the essentials of the art in a form of the greatest 
practical utility. The subject is much too large for the 
scope of any one book, but it has been the aim to include in 
this book the essential details, and to constitute a store of 
authorative information from which the expert and the be- 
ginner alike can draw with profit. The book is designed to 
be eminently practical. Its author is a practical glassmaker, 
and for years has been an active factory manager. He is a 
recognized writer on glass matters and has drawn from the 
practical experiences of a lifetime in the preparation of this 
book. In preparing the hundreds of recipes contained 
herein, the author has selected the best of the standard 
formulas from all quarters, whose worth has been proven by 
actual practice, and to these he has added his valuable 
private collection. 

That the work shall be an authority, all the chemical 
portion of the manuscript and recipes have been carefully 
revised by Dr. J. A. Koch, Dean of the College of 
Pharmacy, of the Western University of Pennsylvania, and 
the discoverer of several valuable formulas now in use in the 
glass trade. Dr. Koch in the past few years has several 
times been commissioned by the most prominent glass firms 
in this country to go abroad and investigate certain phases 


of the Continental glass industry. Therefor, his chemical 
knowledge of the glass making industry is unquestioned, and 
his revision of the present book gives it the stamp of the 
highest authority. 

To keep the book within convenient compass, all details 
as to estimates on factory construction, machinery, supplies, 
materials, etc., have had to be eliminated, but all such in- 
formation, not already in the possession of the reader, can be 
secured at length by addressing the Commoner and Glass- 
worker, of Pittsburg, Pa., the newspaper of the glass trade 
in all its branches. 

Glass and Pottery Publishing Co. 


The principal portion of the matter contained in the fol- 
lowing work represents the contents of a glassmaker's 
private note-book; and while the facts and figures therein 
were collected for personal edification, it hardly seems nec- 
essary to make any excuses for their publication, since not- 
withstanding the multiplicity of books on the same 'subject, 
there seems to be none exactly adapted to the wants of the 
average practical glassmaker. 

It has been the object to present the contents of this 
volume in a series of plain, practical essays, arranged in 
succession, as it appears to the writer, that to properly 
understand the aggregation, and proportionate association, 
of the elements of glass, it is necessary to first understand 
its principles and characteristics. It is for this reason that 
so much space has been devoted to the more important 
characteristics of glass, as the principles of definite propor- 
tion are dependent thereon. The various constituents of 
glass have also been given considerable space to afford a 
proper conception of their derivation, composition and 
effects, including simple tests and analyses for determining 
purity. An appendix has also been added, which contains 
miscellaneous information pertaining to the subject. 

All known works of authority have been consulted in 
the preparation of this manuscript. Especial indebtedness 
is due to Mr. James Reed, who so generously contributed a 
large portion of the recipes contained in the work. In con- 
clusion, the work is designed for the practical glassmaker; 
and the author presents Elements of Glass and Glass- 
making for his consideration, with the hope that, in some 
respect, it may contribute to the general fund of knowledge 
in glassmaking. 

Benjamin Franklin Biser. 

Cumberland, Md., Jan. 1, 1900. 


As a people, we are prone to overlook the interest centering 
in the commodities that alleviate the discomforts of life. By no 
means the least of these commodities is glass. Surrounded by 
articles representing it in almost every conceivable form, perhaps a 
mosaic, a stained window, a piece of filigree work, a richly cut 
bowl, a common tumbler, or a bottle, may excite our passing ad- 
miration ; yet, nine times out of ten, the inquiry — if inquiry at 
all — regarding its origin or production ceases with the simple def- 
inition : — "a product of sand," and the mind does not conceive 
the depth of romance underlying its origin and propagation. 
This fact does not only apply to those in the ordinary walks of 
life, but penetrates to the vital depths of the industry, reaching 
not only a large majority of those artisans who fashion it, but 
quite a few of thfcse who create it ; and while there always exists 
a superabundance of traditional data, inherited from generation 
to generation, father to son, so to speak, yet there is an almost 
absolute dearth of practical — to say naught of theoretical — in- 
formation in possession of the average glassworker regarding the 
substance he daily gives form and figure. 

Notwithstanding the universality of the present use of glass, 
its discovery was extremely ancient, and its history is so resplen- 
dent with achievements, queer facts, and characteristics, that it is 
truly romantic. For many centuries the properties of glass have 
caused it to be admired, and sought by all classes, and some writ- 
ers believe that it was in use to a greater extent among the an- 
cients — especially among the Romans during the imperial period 
— than in comparatively modern times. Dr. Johnson so ably il- 
lustrates a portion of its present uses in the following, that we 
quote : "Who, when he first saw the sand and ashes by casual 
intenseness of heat melted into a metalline form, rugged with 
excrescences and clouded with impurities, would have imagined 
that in this shapeless mass lay concealed so many conveniences 
of life as would in time constitute a great part of the happiness 
of the world ? Yet. by some such fortuitous liquefaction was 
mankind taught to procure a body at once in a high degree solid 
and transparent, which would admit the light of the sun, and ex- 
clude the violence of the wind ; which might extend the sight of 
the philosopher to new ranges of existence, and charm him at one 
time with the unbounded extent of the material creation, and at 

another with the endless subordination of animal life ; and what 
is yet of more importance might supply the decay of and succor 
old age with subsidiary sight. Thus was the first artificer of glass 
employed, though without his own knowledge or expectation. 
He was facilitating and prolonging the enjoyments of light, en- 
larging the avenues of science, and conferring the highest and 
most lasting pleasures, and was enabling the student to contem- 
plate nature and the beauty to behold herself." 

With all of its commendable qualities to adapt it to univer- 
sal use, glass is still a peculiar substance — unlike any other — and 
its definition is rendered difficult by the subtleness of its nature, 
and the variability of its constituents, each of which contributes 
largely to its peculiar quota of characteristics. Not by any means 
the least remarkable fact regarding it is its creation by the com- 
bination of materials plentiful in nature, of themselves crude and 
opaque, yet by fusion transformed into a lustrous, limpid, trans- 
parent substance which can be wrought by heat into forms and 
designs unrivalled in beauty. When in a melted state it can be 
poured like oil and molded to suit the will. As it cools it assumes 
that peculiar state of viscosity, in which its ductility is such that it 
can be drawn into hair-like strands which can be woven into cloth 
or tied in knots. Its elasticity is such that it can be blown to a 
gauze-like thinness, so as to float- upon the air. As it hardens, 
it becomes exceedingly brittle, and assumes a brilliant lustre and 
polish, yet retains its elasticity to such an extent that a globe of it 
filled with water and hermetically sealed, if dropped upon a pol- 
ished anvil will recoil two-thirds the distance of its fall and remain 
entire. It is a non-conductor of electricity, and a poor conductor 
of heat. If a ball of melted glass is dropped into cold water it 
produces no agitation in the water until its temperature is reduced 
to about one-half. Perhaps the most peculiar characteristic of 
glass is the change it undergoes by repeated or prolonged heat- 
ing, when it becomes devitrified or porcelain-like and crystalline 
in structure, (under ordinary circumstances glass is non-crystalline 
in structure). When exposed to the action of the elements any 
great length of time it assumes a variegated hue termed irides- 
cence ; this latter peculiarity is now given commercial import- 
ance, and is frequently produced artificially. Innumerable other 
peculiarities could be mentioned, and it is these queer facts which 
characterize it as a substance peculiar to itself. 

In a certain sense glassmaking is not only one of the oldest, 
but one of the newest occupations, and herein lies the romance 
of an art once dominant, virtually blotted out of existence for 
centuries, and restored. Its origin is unknown, but we have rea- 
sons to believe that it is as old as the earliest civilization, even as 
ancient as the art of brickmaking. Glass objects have been 
found under circumstances and in places indicating that they were 

in use before man learned to manufacture iron into useful forms ; 
and if glass was coeval with bronze, why may it not also have 
existed in the age of stone ? 

Ancient writers — especially Pliny — tell us a doubtful story, 
of its discovery by Phoenician merchants returning from Egypt 
to Syria with a cargo of natron (crude soda). Storm driven they 
landed on the sandy beach at the mouth of the river Belus, which 
flows from Mount Carmel and enters the sea near Tyre and Sidon ; 
and while cooking their food, rested their cooking utensils on 
blocks of the natron. The heat from the fire caused the natron 
to melt and form a flux that reduced the sand to glass. But this 
story is purely a fable, as the result would be impossible. As to 
the probable discovery of glass we are led to believe that there 
is little doubt that it was the result of an accident ; some one had 
the acuteness to notice its fortuitous production ; but who, ex- 
actly when, or where is absolutely unknown. 

A coarse colored glass is frequently produced in metallurgical 
operations as an accident ; and again, when vegetable substances 
which contain silica and an alkali (as straw) are burned, glass 
is very often found. The Egyptians were proficient in metal- 
lurgical operations, and for argument suppose it was discovered 
in the early days of metallurgy. The Egyptians ascribe the inven- 
tion of this art to Osiris. In Gen. IV:22, "Tubalcain, an instruc- 
tor of every artificer in brass and iron," takes the invention back 
when the first man was living. Metallurgy evidently had some 
influence on the early manufacture of glass, as the oldest specimens 
are always colored, which by analysis show the coloring agent to 
be of a metallic nature. Klaproth concluded that the variability 
of composition of the different ancient colored specimens showed 
evidences of being remelted metallurgical slags. Some writers 
think there was a possible chance for its discovery in connection 
with the art of glazing pottery. The Egyptians sometimes burn- 
ed large heaps of straw and vegetation, and to this some attribute 
the discovery of glass by that people. 

The earliest traces of its manufacture are found in Egypt. 
Archaeologists have discovered sculptured designs, representing 
glassblowers at work, which were made centuries ago, and on the 
rock tombs of Thebes you may see pictures of artisans blowing 
the shapes of glass through long pipes. There is an unmistakable 
evidence of glassblowing figured on the walls of the tomb of 
Mestaba of Tih, of the fifth dynasty, the earliest representation 
yet discovered — a time so remote that it fs impossible to give it 
a date in years — say, for instance, 4000 years B. C. Mummies in 
the tombs of Memphis wear necklaces of paste-glass beads. 
Memphis was built by Menes I, king of Egypt. Manetho figures 
his reign 5004 B. C, but Egyptian chronology is uncertain. On 
the tombs at Beni-Hassan are representations of glassblowers. 

These tombs are supposed to be of the period of Osirtasan I, 2500 
to 3000 B. C. But even given the date of the period in which 
these inscriptions were executed, the art certainly antedates by at 
least some centuries these periods, as development was slow at 
that day and centuries were certainly required to evolve the skill 
and perfection necessary to develop the art to the degree of which 
the ancient specimens are evidence. In general, it is believed 
that its discovery and use originated in Egypt, as its most ancient 
monuments are of that country. But it is not easy to trace the 
progress of glassmaking there. The objects found there rarely 
bear inscriptions, but the earliest specimen of glass bearing an 
inscription from which its date might be ascertained, was found 
at Thebes by Signor Drovetti many years ago, and is now in 
the British Museum. The hieroglyphics determined it to beof the 
eleventh dynasty, about 2423-2380 B, C. We conclude that 
glass was undoubtedly invented in, and radiated to all other coun- 
tries from Egypt, as the channels of communication can be traced. 
The Phoenicians also lay claims to its discovery, but they cannot be 

As an industry glassmaking spread from some common cen- 
ter. It grew and multiplied until it reached a point of develop- 
ment which in some respects has never been excelled, and perhaps 
never equalled. If the Syrian, Greek and Latin versions of the 
Old Testament are correct, glass was placed in the same cate- 
gory as gold. Vessels still exist of fine blue opaque glass edged 
with a comparatively thick plating of gold. Herodotus saw in the 
temple of Hercules at Tyre, a statue or column of emerald glass. 
Pliny speaks of a glass statue of Serapis, thirteen and one-half feet 
high, and an obelisk sixty feet high composed of four emeralds, 
which Apion and Theophrastus saw in Egypt. The invention and 
ingenuity of the ancients was most remarkable in producing vari- 
ety in glass, devising means of decoration, and methods of manip- 
ulation. Many processes now in vogue, which are supposed to 
be recent discoveries, have in reality been anticipated by the an- 
cients. To demonstrate this : Among the relics taken from the 
tombs of Thebes are specimens of glass coins with hieroglyphical 
characters, which prove that the Egyptians must have been ac- 
quainted with the art of pressing glass, while hot, into metallic 
molds. This has always been considered a modern invention. 
The Egyptians pressed glass into figures of deities, sacred em- 
blems ; adapted it for mosaic work ; colored it to imitate pre- 
cious stones ; worked it into beads and necklaces, and used clay 
and wire molds with which to form cups, vases, etc. The so-called 
Portland vase, and the vase at Naples, are beautiful examples of 
the later ancient art, and illustrate their skill and proficiency 
in manipulating and fashioning glass. Their ingenuity which de- 
vised so many modes of ornamentation, so many shades of color — 

primitive tools and impure materials considered — demands our 
unbounded admiration. Circumstances seem to demonstrate 
that the industry was carried on by many artificers, each working 
on a small scale. 

But a crash came to all of the splendor when the barbarians 
of the northern countries blotted out the power, and even serious- 
ly imperiled the civilization, of ancient Rome. (It may be re- 
marked that the Romans prior to this time had attained virtual 
supremacy in the art of glass.) In the mental and material pros- 
tration following the barbarian conquest, and during the dark 
ages, the art of glassmaking became but a flickering flame, pre- 
served from total extinction by the church in the one branch of the 
industry, that of mosaics and stained windows ; and ancient 
glassmaking for centuries was virtually a lost art. Eventually 
Venice was able, in secret, to recuperate her lost art, and at one 
time whole streets of Tyre were wholly occupied by glassworks. 
The Venetians did all they could to retain their secrets intact, 
even removing their factories to the island of Murano, in order 
to better guard the monopoly. So useful were the glassmakers 
at one time in Venice, their industry contributing such large reve- 
nues to the Republic, that to encourage those engaged in it to 
remain in Murano, the Senatg made them burgesses of Venice ; 
allowed them to wear a sword ; exempted them from the pay- 
ment of all duties and taxes, and allowed nobles and patricians to 
marry their daughters without loss of nobility, which also descend- 
ed to their issue. So stringent were their mandates that the 
Council of Ten forbade glassblowers from revealing the secrets of 
the art to strangers under extreme penalties. Arj extract from 
their laws in 1474 reads : "If any workman conveys his art to 
a strange country to the detriment of the Republic, he shall be 
sent an order to return to Venice. Failing to obey, his nearest 
relation shall be imprisoned. If he still persists in remaining 
abroad and plying his art, an emissary shall be charged to kill 

At one time the glass industry in Italy was governed by a 
council of glassworkers, composed of six glass-masters, who were 
elected during the Christmas festivities by a majority vote of 
their fellow-workmen, to serve one year. The orders of this coun- 
cil were imperative, and so recognized in the administration of the 
industry. It established the wages paid to the workers, allotted 
the nutnber of workmen to go to any foreign factory, and decided 
all questions pertaining to the welfare of the business. An oath 
was required from each man before starting to any foreign factory, 
obligating him to maintain secrecy ; zealously guard the interests 
of the craft ; uphold its traditions ; strictly obey all of its rules 
and laws, and return to Altare and report to the council no later 
than the feast of St. John (August 29th) each year, relative to the 


year's activity. So great was the desire to impart mystery to the 
art, that in times past it was the custom of the workmen when 
"pot-setting/' to attire themselves in the skins of wild animals 
and goggles, to protect themsevlis from the heat, and then pa- 
rade the neighborhood thus attired to the great alarm of the chil- 
dren and women. Even at the present day there still remains a 
fund of traditions and hereditary data, that in many cases is much 

But, while the Venetians especially, did all in their power to 
retain their secrets, and control the monopoly, the glassblowers 
chafed under restraint and gradually wandered from the folds 
of the councils and ignored their mandates, lured, no doubt, by 
inducements held out by foreigners, until Venice was compelled 
to compete with young but ambitious rivals, born with the grey 
dawn of a later day European civilization, who justly claimed a 
portion of what was regarded as the heritage of Europe. And 
thus Egypt, Rome, Venice, Germany and Bohemia, became cen- 
tury marks in the later history of glass, and glass became a criteri- 
on of civilization. 

Glassmaking of to-day is a new art, because but perhaps 
a century and a half have elapsed since it began to emerge from 
the almost total eclipse it experienced during the dark ages, and to 
the nineteenth century must be assigned nearly all the improve- 
ments which have placed it once again among the arts. Still, as 
we have ren^irked above, the ancients were familiar with many 
processes which we consider new ; and many of our improve- 
ments of to-day are simply lost processes rediscovered. As a 
whole, the constituents, their proportions, methods of aggrega- 
tion and association, and the manipulation of glass, are along the 
same general lines that guided the ancients ; and we have been 
but regaining that which has been buried beneath the dust of cen- 





The title "glass" is applied to such a perplexing variety of 
substances, both chemically and commercially, that it makes an 
exact definition, embracing all substances to which it is properly 
applied, extremely difficult. It would be comparatively easy to se- 
lect a single piece of any particular glass and define it, or two dis- 
similar kinds ; but not so when we conceive the innumerable va- 
riety of glasses, all of which contain conditions of similarity. 

A composite definition may be suggested as follows : A 
transparent solid formed by the fusion of silicious and alkaline 
matter, which assumes while passing through said state of fusion 
at a temperature sufficiently high, a fluid condition, and, as the 
temperature falls, passing from the fluid through a ductile, viscous 
state to a solid— devoid of crystalline structure, impervious and 
impenetrable to both gaseous and liquid fluids — a hard, brittle mass 
which exhibits, when broken, a lustrous fracture. 

Any product of fusion that is hard, brittle and vitreous, is 
chemically termed glass. Commercially the title designates (with 
a few exceptions), the silicates, or compounds of silica — a fusion 
of two or more simple silicates. A silicate is a salt of silicic acid ; 
a compound of silica with one or more alkaline or metallic oxides. 

The difficulty of an exact definition of glass lies in the fact 
that while glass is regarded as a chemical compound — a silicate — 
unlike most chemical compounds it has no fixed definite composi- 
tion in its several varieties, y£t the fundamental principles of all 
commercial glass are decidedly similar. 


Glass consists, generally speaking, of a mixture, (rather than 
a compound, as there is difficulty in determining the molecular 
composition of the constituent silicates), of two or more silicates 
united by fusion into a homogeneous, hard, brittle mass. The na- 
ture and molecular composition of these silicates^ determines the 
^\ variety or nature of the glass, according to the proportion of the 

base or bases associated with the silica. Silica (termed the di- 
oxide of silicon, ^(Si0 2 ) predominates as the essential element of 
virtually all manufactured glass. Combined with the silica are 
such bases as potash, soda, lime and lead. The bases may be 
termed alkali-metallic oxides, and with the silica comprise the fun- 
damental constituents of manufactured glass. Oxides and ma- 
terials other than these are used as auxiliaries for special purposes, 
as de-oxidizing and de-colorizing agents, and for imparting special 

colors, and properties of manipulation to the product of the com- 
bination of the resultant silicates of potash, soda, lime, etc. As 
an example : Flint glass is composed of silica, potash and lead ; 
or silica, lime and soda ; a double silicate in either case. Win- 
dow glass is a ter-silicate of potash, lime and soda. These silicates 
are not separately formed and then fused, but are simultaneously 
fused together by a double though continuous process without any 
break in its continuity, by being mixed and charged, and then 
fused to completion in the pot or furnace of the glassmaker. 

At least one alkaline base is always necessary in the creation 
of a silicate, and the quantities of the various constituents vary 
according to results desired. These proportionate quantities are 
determined by experience establishing formulae for the various 
glasses. These formulae constitute the basis upon which a glass- 
maker establishes his results. We have stated that glass is a sili- 
cate, single, double, etc. ; also that a silicate is a salt of silicic 
acid, (a compound of silicic acid with one or more alkaline or me- 
tallic bases), but it is well to further illustrate the subject. Analy- 
sis of a certain sample of glass will determine the quality or quan- 
tity of its constituents, but it does not set forth or determine the 
manner of their association. It is known that this association is 
affected by heat, but it requires a further investigation than analy- 
sis to determine the relationship that binds them together, and 
what chemical or physical changes heat develops, to convert these 
substances into an amorphous transparent body. If we take the 
different constituent substances of any particular kind of glass, 
and by mechanical means reduce their particles to the most infinit- 
esimal size, and create a most thorough admixture of them one with 
another, there is yet no affiliation of their molecules ; no adhesion 
or viscosity of substance; and no combination of atoms ensues, be- 
cause this is a physical or mechanical association. Hence, while it is 
of paramount importance in preparing the batch, as it facilitates 
the atomic combination when chemical action does ensue, yet of 
itself it effects no direct combination or molecular change of sub- 

Prior to any molecular change, the molecules of a given sub- 
stance must become disintegrated and decomposed, and their 
atoms be reassembled into molecules of new compounds ; hence, 
the first necessity is to break the cohesive bonds of the molecular 
structure and release the atoms. It is known that the cohesion 
between the atoms of a substance is least in a liquid or gaseous 
form, and for this reason it is necessary to reduce the mechanical 
mixture to a fluid condition. Heat is regarded as a mode of mo- 
tion — molecular motion — and supplies the agent now in question, 
and develops, when applied to this mixture, molecular energy 
sufficient to create fusion of the substance involved ; then suppos- 
ing that by fusion the substances are reduced to a fluid condition, 


and a general separation of atoms has ensued. Nature has sup- 
plied a certain form of general attraction called chemical affinity 
which, the moment the cohesive bonds are broken, asserts itself 
and re-assembles the atoms, and arranges them into molecules of 
new substances and compounds determined by the nature of their 
affinity, as the atoms of each substance have a certain affinity for 
the atoms of another substance, sometimes combining in several 
different proportions. Silica is a prominent example of the latter 
as it unites with the same metallic oxide in several different pro- 
portions, which is illustrated by the formulae of the silicates 
of sodium, (Na 2 0, SiOo : 2Na 2 0, Si02 : Na 2 0, 3Si 
2 : Na 2 0, 4Si0 2 ). When we mix sand (the commercial repre- 
sentative of silica) with lead (PbO.) (Litharge), and reduce this 
mixture by fusion to a state of fluidity, it will be found that the 
silica unites with the lead, forming silicate of lead ; likewise the 
energy excited in the silica by heat is sufficient to decom- 
pose the carbonates of potassium, sodium and calcium, creating 
corresponding silicates of these bases. Hence it is not too much 
to assume, that if the result of the fusion of sand and lead is sili- 
cate of lead ; of sand and potash the silicate of potassium ; of 
sand and soda the silicate of sodium ; of sand and lime the sili- 
cate^ of calcium ; that if these same substances be mixed and fused 
together simultaneously the result will be a mixture of the same 
silicates. The silica combining proportionately with affinity. 

While the special action of the various silicates will be given 
later, (see Raw Materials) it may be well to remark here a quality 
belonging to a mixture of silicates ; which is the fact that the fus- 
ing point of a mixture is considerably lower than the mean of the 
fusing points of the silicates constituting the mixture. Thus a 
glass containing three or more silicates is more fusible than a glass 
containing two silicates only, but less perfect in structure. Ex- 
perience teaches a glassmaker that as he increases his basic per- 
centage of alkali, or oxide, in his batch, he lowers its point of fu- 
sion ; but the product becomes softer, and while its density or 
specific gravity may have increased, yet its nature deteriorates. 
Silica is an essential element and the value of the product depends 
upon its proportion, and deteriorates as its percentage is de- 
creased, or the percentage of alkali or base is increased. It is well 
to bear in mind regarding the fusibility of the different alkaline 
bases, that they contribute to the fusibility of the silicates con- 
sistent with proportion. Of these the silicates of sodium and po- 
tassium are most fusible, potassium exceeding sodium. The sili- 
cates of lead are more fusible in proportion to base. The silicates 
of calcium are less fusible than those of potassium, sodium or 
lead, but assist in the fusion in a combination of silicates. 

While we are enabled to keep in mind the silica, alkalies, and 
oxides, comprising the principal constituents of glass, and even 

the approximate estimation of the quantity of each in the com- 
position of the different kinds of glass, yet, even in different speci- 
mens of the same variety, the proportions are so indefinite as to 
exclude all possibility of any definite classification. Chemically 
there is such a variation in the composition, and commercially the 
names that have attached themselves to the various glasses are 
so innumerable, that a definite classification is impossible either on 
a chemical or commercial basis. 

Glass is divided into two general classes : Natural and arti- 
ficial. By natural glass is meant that produced entirely by natural 
causes without any assistance from man. These natural glasses 
are found principally in the vicinity of volcanoes, and are known 
as mineral obsidian, Peles' hair, etc. Other natural glasses are 
known as water glasses, and are found in certain springs, and ab- 
sorbed in certain basaltic rocks. Artificial glass is that glass pro- 
duced in the arts, and manufactures, including the various glasses 
of chemistry. 

These two general classes (especially artificial) are sub-divid- 
ed, and the divisions titled according to circumstances. As the 
natural glasses have no special bearing on the subject, we will con- 
fine our classifications to the artificial glasses. As a chemical 
classification, that of Ure, which while not absolutely correct in 
some details, will fairly illustrate the subject. 

Soluble Glass. 

A simple silicate of potassium or sodium, or both. 

Crown Glass. 

A silicate of potassium and calcium. 

Bottle Glass. 

A silicate of calcium, sodium, aluminum and iron. 

Common Window Glass. 

A silicate of sodium and calcium, sometimes potassium. 

Plate Glass. 

A silicate of sodium or potassium, calcium and aluminum. 

Ordinary Crystal. 

A silicate of potassium and lead. 

Flint Glass. 

A silicate of potassium and lead. 


A silicate of potassium and lead, still richer in lead. 


Silica and stannate or antimoniate of potassium or sodium and 
lead (highly alkaline). 


Much of the so-called flint or crystal glass of present manu- 
facture, is generally a silicate of sodium and calcium, calcium su- 
perseding lead, and sodium superseding potash. The present op- 
portunities for procuring raw materials nearly pure, have altered 
the constituent silicates to a great extent, both economically and 

Commercial usage has apparently established four general 
and practical sub-divisions, viz. : 

I. Plate Glass. 

Which comprises ; rough plate, rolled plate, ribbed plate, 
and polished plate, having an approximate composition about as 
follows : 

Silica 74% 

Soda 12% 

Lime 5.5% 

II. Window Glass. 

Which comprises ; ordinary sheet ; colored, painted or with- 
out color. The different methods of applying colors occasion dif- 
ferent processes as : pot-metal, double or flashed, stained glass, 
or crown glass. Approximately the composition of window glass 
is : . 

Silica 73% 

Soda 13% 

Lime 13% 

HI. Flint Glass. 

This term has an extensive application, and includes prin- 
cipally all common or lime flint, or crystal glass. Its approxi- 
mate composition being about as follows : 

Silica 73% 

Soda 3 to 5% 

Lime 10 to 12% 

Lead flint is of greater specific gravity than lime flint, and is 
really the true flint glass. Its composition being about : 

Silica 52% 

Potash . . ; 14% 

Oxide of lead 33% 

Strass' is another flint glass very rich in lead, and used prin- 
cipally in the manufacture of artificial gems. Its composition be- 
ing about : 

Silica L .38% 

Lead T 53% 

Potash 8% 

Optical glass may also be classed as a flint glass, being both a 
lead and lime glass. 


IV. Bottle Glass. 

This is a glass coarse and inferior in quality, used extensively 
for the commonest grades of bottles and hollow-ware, and is usu- 
ally of a greenish, amber, or black color. Its composition is ap- 
proximately as follows : 

Silica 60% 

Lime 20% 

Potash 3% 

Iron 0.4% 

Alumina o. 1 '% 

The iron and alumina occur as impurities in the materials. 

Other Classifications. 

There are other varieties which might be mentioned. By 
special manipulation glass acquires such titles as, hardened or 
toughened glass, spun glass, ground, blown, pressed, cast, etched, 
engraved, figured, cut and embossed glass, etc. ; besides the en- 
amels, iridescent glasses, etc. To further illustrate, a classifica-. 
tion according to place of manufacture might be made as : Vene- 
tian glass, Egyptian glass, English glass, Bohemian glass, Ameri- 
can glass, etc. So taken as a whole, a definite classification is per- 




Viscosity — Disintegration — Devitrification — Decay — Specific 
Gravity — Ductility and Elasticity — Expansion — Con- 
traction — Tension — Tensile Strength — Metal- 
lic Combinations — Non-Conductiv- 
ity — Iridescence. 

The composition and the production of glass are curious, as 
it possesses peculiar chemical and physical characteristics which 
are entirely remote from any other material, and which isolate it 
as a capricious substance. 


Possibly the most important property of glass is its curious 
condition of viscosity. The crude materials when exposed to 
heat, decompose and generate gases, the evolution and expulsion 
of which carry off a major portion of all impurities, allowing the 
silicates to assume their various combinations and create glass, 
which assumes during its creation, by imperceptible stages, a liq- 
uid condition. In this condition it is too fluid to be adapted to the 
various processes of manufacture, but as the heat is diminished, 
or as it is chilled by exposure to air, it acquires a condition of vis- 
cosity ; a condition intermediate between liquidity and solidity. 
In its viscous state it is ductile and tenacious, and is best adapt- 
ed to the principal processes of manufacture. As the heat is allow- 
ed to diminish, or by a continued exposure to air, it rapidly as- 
sumes a solid condition ; hard and brittle. We have herein a 
substance susceptible of a triality — so to speak — of condition ; 
including a transformation from crude opaque to almost perfect 


When hot glass is cooled rapidly it becomes very brittle, es- 
pecially if the pieces are thick. The reason for this is that the ex- 
terior cools more rapidly than the interior, which prevents a uni- 
form contraction, and excites an undue tension that strains the 
molecular structure of the glass. By the exterior cooling while 
the interior is still hot, the molecules of the exterior become fixed, 
and as the interior cools it cannot contract ; this produces an 
undue molecular strain. Glass in this condition is easily affected 
by changes of temperature, the weather, slight vibrations, etc., 
which break the strained bonds of cohesion. This property is 



best illustrated by small pieces of glass known as "Ruperts* drops," 
or "devil's tears," which are prepared by dropping small pieces of 
very hot glass into water, and removing them as quickly as pos- 
sible thereafter. This gives a piece of glass with a hardened or 
chilled exterior, while the interior remains heated. Dumas ex- 
plains this phenomenon of glass by stating : "That as the outside 
is at once condensed or contracted by cooling, while the inside 
remains hot and consequently more distended, and when at last 
the central and more dilated parts of the drop become cool they 
must have retained points of adherence to the surface, and conse- 
quently occupy a larger volume than that which agrees with the 
temperature to which they are reduced. The central molecules 
therefore, must be much distended and exert a more powerful 
contracting influence on the surrounding parts. At the instant 
when a part of the envelope or outer portion is broken the mole- 
cules held by it briskly contract, draw in with them all the others 
and thus determine a multitude of points of rupture ; and as the 
effect is instantaneous the particles move very rapidly, and drive 
out the air before them producing a sudden dilation and contrac- 
tion of the latter." Again, if a similar drop made in the same way 
be taken and without fracture be buried in sand and reheated to 
the point of ductility and allowed to cool slowly with the sand, it 
will regain its normal condition, that is, the condition of glass 
whose molecular cohesion has not been strained ; and it may be 
broken with the same kind of fracture and facility as ordinary 
glass. (See Annealing.) 


Vitrification means a conversion into glass or a glassy sub- 
stance by heat and fusion. Hence, devitrification means the act, 
or process of depriving glass of its lustre and transparency. This 
is another curious feature of all glass, and by undergoing this re- 
markable change glass becomes dull, opaque and porcelain-like. 
Devitrification is nothing more or less than a crystallization of 
glass, as ordinary glass lacks crystalline structure. Glass manu- 
factured by ordinary processes is cooled suddenly, and the exces- 
sive internal tension thus caused is counteracted and reduced by 
annealing, but when the mass of metal is cooled slowly it acquires 
a crystalline structure. A mass of metal repeatedly reheated be- 
comes thoroughly devitrified in a short time, becoming tough, fi- 
brous, hard in nature, difficult to fuse, and with a multitude of sol- 
id grains dissenminated throughout ; full of "striae" and semi- 
opaque matter. A moment's thought will expose in this feature, 
one of the glassmaker's arch enemies ; a generator of cords and 
stones, and hard natured, lumpy glass, in a general way. The 
change of substance and structure is effected by repeated reheat- 

ing ; or takes place when glass is kept for any great length of 
time at a temperature near its melting point. If a workman in 
manipulating a piece of glass has occasion to reheat it an unusual 
amount, all phenomena of devitrification become manifest. The 
supposition is that the change of structure is effected by the partial 
separation of certain silicates (especially lime, as it is known that 
an excess of lime renders glass refractory and more liable to the ac- 
tion of devitrificaton) ; and by the more fusible alkaline silicates 
fusing at a temperature which is insufficient to melt the more re- 
fractory silicates. 

While most glass is subject to this change, that of a complex 
composition is more liable to be affected ; but those glasses with 
bases containing the earthy materials in excess, as lime, alumina 
and magnesia, devitrify easiest. Reaumer, Dumas, Pelouse, 
d'Arcet, and others labored to devitrify glass on an industrial scale, 
but with indifferent success. M. Garchey discovered a product 
not many years ago which he called Ceramo-crystal, and in this 
discovery he obtained that which other savants had sought in vain. 
They endeavored to devitrify the finished article of glass. M. Gar- 
chey devitrified the glass first, and then gave it form, and by so 
doing created a definite product, and at a nominal cost. The 
product by this process is a ceramic stone, unaffected by tempera- 
ture, water, or acids ; and it will withstand a general wear and tear 
that free-stone will not. 

Devitrified glass may be restored to a vitreous condition by 

Decay of Glass. 

Glass is subject to decay, both natural and artificial. We 
assume that glass is a remarkably hard substance, devoid of crystal- 
line structure, impervious to both liquid and gaseous fluids, and 
with ordinary use resists the action of water and alkalies, and, with 
a single exception the action of all acids ; preserving all its beau- 
ty, retaining its surface, and not losing the smallest portion of its 
substance by the most frequent use ; but under circumstances of 
ordinary use only, Sis all glass is affected by caustic alkalies, es- 
pecially in concentrated solutions which deprive it of its silicic 
acid. It yields readily to the corrosive action of hydrofluoric acid 
which decomposes the silicates of its composition, forming fluor- 
ides of its silica, and its metallic bases. Sulphuric, nitric, hydro- 
chloric and phosphoric acids under favorable circumstances will al- 
so decompose certain varieties. Even pure water by prolonged 
action exerts a decomposing influence, especially if boiling. Em- 
merling in his investigations found that the action of boiling solu- 
tions (including water) upon glass is, within certain limits, pro- 


portionate to the length of time exposed, and amount of surface in 
contact with the action of the liquids. 

Most acids in a dilute state, except sulphuric, attack glass 
less than water ; but the solvent action of solutions of salts whose 
acids form insoluble calcium salts, as sulphates, phosphates, car- 
bonates and oxalates, is greater than that of water, according 
to the concentration of the solution. Again, in solutions of salts 
whose acids form soluble calcium salts, such as chlorides, nitrates, 
etc., the action is less than water and decreases with the concentra- 
tion of the solution. It may be further said that with boiling liq- 
uids the action decreases in proportion to the decrease in tempera- 
ture of the liquid. The foregoing may serve as illustrations of 
some of the principal agents of artificial decay. The causes of nat- 
ural decay are : The atmosphere, the earth and their contents. 
The corrosive elements in all cases being moisture, assisted by car- 
bonic acid and ammonia. 

About the first sign of decay in glass is a colored tinge or 
iridescence, with a gradual increase to opacity, and finally de- 
composition. In a case of natural decay this process may require 
a lapse of years. But glass possesses internal enemies that are 
more formidable than its external, and an elimination of these 
internal influences would debar all exercises of natural decay, as 
the actual decay of the substance of glass is brought about by an 
excess of some of its constituents, generally its alkaline bases. It 
is known that the resistance to decay is increased or diminished 
as its composition varies to or from that required to form a defi- 
nite chemical compound ; and its constituents dissolve in about 
the same ratio as they are contained in the glass. Glass contain- 
ing a large amount of alkali when exposed to atmospheric mois- 
ture, for instance, is attacked by the simultaneous action of the 
moisture and carbonic acid. On account of its excessive alkaline 
base, a soluble silicate has been formed, which decomposes more 
rapidly under the decomposing influences than would a glass rich 
in silica, leaving a surface pitted for the collection of additional 
moisture and consequent forces to aid in its destruction. There- 
fore, a glass rich in silica is better adapted for durability. Some 
ancient glasses which were alkaline in structure owe their preser- 
vation to the presence of lime in their composition, although pres- 
ent as an accidental impurity. Some window glass, especially if of 
an inferior grade, presents illustrations of natural decay. A dull- 
ness of color after a lengthy exposure to the elements is a char- 
acteristic. This partial opacity is brought about by the combined 
action of the carbonic acid and atmospheric moisture, which de- 
velops an insoluble crystalline film of silica upon the surface of the 
glass, that is a result of the elementary action upon the silicates of 
its composition. 


Laying aside the fact that chemical action has been deter- 
mined as the principal agent in the decay of glass, other influences 
also physically exert disintegrating powers which seen? sufficient 
to account for at least a part of its decomposition, or rather dis- 
integration. Windows exposed to sunlight absorb a certain 
amount of heat, which warms and expands them each day, and 
vice versa, they cool and contract each night. To accomplish this 
an infinitesimal pulsation of the molecules evidently takes place 
with evjery change of temperature and minute as these tiny pul- 
sations are, they represent the expenditure of a large amount of 
energy. Joule calculated that a pound of glass in passing through 
ioo degrees C, had its molecules subjected to a force sufficient to 
raise 1 1.600 times its own weight to a height of one foot. Think 
then of the prodigious energy expended in a window panje which 
has been exposed to the heat of the noon-day sua for years, its 
molecules swaying with vibrations of temperature up and down. 
It is not the actual strength or force of the vibrations, but the 
number of times the tides of expansion and contraction fave "ebb- 
ed and flowed" through its substance. 

Surely this then is sufficient to break apart the bQjids of mu- 
tual attraction and create strata and laminations. Irregularities 
of expansive power ; conductivity ; or radiation, may even ac- 
count for irregularities in lamination. Hence, we can but assume 
that the dynamic influences of heat and cold accelerate the phe- 
nomenon of decomposition in glass. 

Specific Gravity. 

Refraction and Reflection. 

From a point, of view relative to the manufacture of the 
ordinary glass of commerce, but little attention is paid to its 
specifi'c gravity, but for the grades of glass intended for the refrac- 
tion of light, as, object glasses, lenses, artificial gems, etc., the spe- 
cific gravity is of importance, as the light refracting power of a 
glass increases with the increase of molecular weight, and is arti- 
ficially increased by the addition to its composition of materials 
which will add to its density, though density and power of refrac- 
tion are not strictly parallel. To a very great extent the specific 
gravity of glass, like its brilliancy, varies with its composition ; 
the heavier glasses being the most brilliant, as well as the softest. 
Hence, lime glass is lightest, bottle glass next, and lead glass is the 
heaviest. The temperature during vitrification also influences the 
density of glass, it being always least when the temperature has 
been greatest, occasioned possibly by a greater evolution of vola- 
tile matter. 


\ i 

A table of the approximate specific gravity of some of the 
different glasses follows : 

Lime Glass, Bohemian 2.396 (Dumas) 

Plate Glass 2.488 (St Gobain) 

Plate Glass 2.5257 (Fardday) 

Plate Glass 2.439 (Muspratt) 

Window Glass » 2.642 (Dumas) 

Bottle Glass 2.732 (Dumas) 

Bottle Glass 2,715 (Muspratt) 

Lead Glass (Crystal flint) .2.900 to 3.255 (Dumas) 
Lead Glass (Optical) .... 3.300 to 3.600 (Dumas) 

Ductility and Elasticity. 

Ductility of glass is analogous to viscosity, and while in a 
viscous condition it can be spun into filaments of great length 
and fineness, or blown to such thinness as to float upon the air, 
and can be molded into any form, retaining in cooling its trans- 
parency and lustre. When cold it cannot be wrought, as it be- 
comes at once hard and brittle. While glass may be termed the 
synonym of brittleness itself, yet its elasticity is such that when 
hot it may be spun into minute threads, which* when cold may be 
bent, twisted, woven into cloth, and. even tied in knots. Its 
elasticity is a remarkable phenomenon and exceeds that of almost 
any bther substance. This property is best exhibited when in the 
curious condition of glass-wool ; or if a ball of glass is let fall upon 
an anvil it will rebound two-thirds the distance of its fall ; or 
again if two glass balls be made to strike each other with a given 
force their recoil will be nearly equal to the original impetus, due 
to their elasticity. When a substance is elastic it permits a play 
of its particles, so that they return to their original position when 
the disturbing force is removed. 

Expansion and Contraction. 

One of the effects of heat is expansion, or increase in vol- 
ume. All substances expand when heated, and contract when 
cooled. Some of the effects of this phenomenon in glass have 
been mentioned. Heat is the result of molecular energy. The 
molectiles of any substance are in a constant vibratory motion, and 
the velocity of this motion determines the degree of heat. As 
the temperature increases, the mutual repulsion of the particles 
of heat overcomes the cohesive attraction of the molecular struc- 
ture of the substance into which it enters, making them less dense 
than before, thus enlarging their dimensions and causing what is 
termed expansion, (a) What is true of expansion is reversed for 
contraction, thus : Expansion increases with the increase of heat ; 
contraction increases with the decrease of heat. 

(a) See Order of.Expansion,;Appendix. 


In the manufacture of glass the various processes of anneal- 
ing are for the purpose of eliminating the deteriorating effects 
of contraction. The expansion of glass has also been duly provid- 
ed for in manufacture, as of recent years the efforts of manufac- 
turers to weld together glasses of different natures and thickness 
for commercial purposes have given rise to research upon the sub- 
ject of expansion. 

A report recently made by Dr. Schott, from which we quote, 
says : "That in the case of silicious glasses the co-efficient of ex- 
pansion increases with the percentage of alkali." When one kind 
of glass is to be welded upon another it is not necessary that the 
co-efficients of expansion should be approximately equal. In- 
deed it may be advantageous, he further says, to superpose a sec- 
ond glass of very different expansibility, as the articles made are 
never called upon to withstand a temperature so great as that at 
which they were originally formed. In 1885 Tscheuschner illus- 
trated by means of glass-wool, that a glass rod composed of two 
halves of different co-efficients of expansion, but approximate so- 
lidifying temperature, used together must, when spun, produce 
spontaneously a curly fibre, the diameter of which will be : 

(2+t) (a+a^ 

D=s — 

t (d-d') 

wherein a and a* are the co-efficients of linear expansion per 1 de- 
gree C, of the two glasses ; t the solidifying temperature, and s 
the thickness of the thread. Compound glasses are thus increased 
in tensile strength and resistance to change of temperature by 
combining at fusing temperature two separate glasses possessing 
different co-efficients of expansion. 

It may be best to speak of contractility rather than expansi- 
bility, since it is the phenomena of cooling after fabrication which 
chiefly need attention. If two plates of glass be welded together, 
and after cooling the double plate is curved, the more contractile 
glass will be on the inside. If two such plates are molded on a 
curved surface, the more contractile being on the outside, then 
after cooling the inside layer is kept stretched, the outside layer 
being on the contrary compressed. A vessel so constructed would 
be similar to a thick walled vessel which had been quickly cooled ; 
such a vessel breaks if the inner stretched layer is scratched. On 
the other hand vessels are greatly strengthened if both the inside 
and outside layers of glass are in a state of compression. This is 
the case with vessels composed of a single kind of glass which 
have been rapidly cooled by plunging them in oil, (see annealing), 
or with vessels made in three layers, of which the middle layer 
is the most contractile, so that the outer and inner layers are kept 


in a state of compression. Vessels so constructed have an import- 
ant advantage over those formed by cooling in oil, viz. : The prop- 
erties of the glass are not altered by subsequent heating. 

Tension of Olass. 

The tension and enforced equilibrium of a mass of glass rapid- 
ly cooled is exhibited by the application of an extremely hot sub- 
stance to a cold piece of glass ; or vice versa, which creates in the 
first instance an unequal expansion ; in the second instance, con- 
traction of the glass, which causes a fracture at or near the point 
of contact. A cold glass vessel immersed in very hot water will 
sometimes become badly fractured, dependent upon the uniform 
thickness of the walls of the vessel ; tension being excited be- 
tween the thick and thin parts. Sudden cooling at any one point 
of a heated piece of glass, as the impact of a moistened instrument, 
or the fall of a single drop of water, causes a fracture at that point. 
Glass workman take advantage of this fact in their vocation. 

isije and Crushing Strength, 

The tensile strength of a substance is its resistance to an en- 
forced separation of its parts (pulling apart). The tensile strength 
of glass is given at from 2,500 to 9,000 pounds per square inch, 
according to variety. The crushing strength has a higher esti- 
mate of from 6,000 to 10,000 pounds per square inch. The tensile 
strength of glass is considerably higher than that of granite. The 
crushing strength of glass and granite are about equal. Much 
depends upon the glass, how annealed, etc. The resistance is 
greater, of course, in glass well annealed, as there is less structural 
lamination and undue internal tension, than in glass improperly 

Manufacturers have experimented in a direction to determine 
a method to increase both the tensile and crushing strength of 
glass, but to a certain extent without any important or definite 
result from a commercial standpoint. Their experiments have 
been conducted with the assumption that the fragility of glass is 
due to the cohesive weakness of its molecules, and that if the 
molecules could be forced closer together, thus rendering their 
m^LSS more compact, the strength of the material would be in- 
creased. They have endeavored to bring about this result by cool- 
ing- the glass in various ways. (See annealing). 

Glass an<J Metallic Combinations 
Under Process of Heat. 


It may seem strange, yet it is sometimes necessary to solder 
glass and metals together. This has not only been successfully 
accomplished but the combinations may be carried to a greater 


extent. If glass be heated to the melting £oint of aluminffcrii, 
(700 C, — 1,292° F,) the aluminum may be spread on the Surface 
of the glass with an iron spatula, and the adhesion of tjie mttftf is 
vigorous. In like manner magnesium (M. P. 455° C, — 850 F,) 
also adheres, but much more readily when heated ; but, the facil- 
ity with which it is oxidized renders it less suitable for the pur- 
pose. The same may be said of cadmium, (M. P. 230° C, — 
446° F,). Zinc at a moderately high temperatttre possesses simi- 
lar properties, (M. P. 41 2° C, — 773° F.) Ordinary plurtibefrs' sol- 
der, alloyed with a small percentage of magnesium, can be spread 
on glass like wax. These alloys, however, are tepidly attacked by 
atmospheric moisture. Tin (M. P. 228° C, — 443° F,) alloyed with 
10 pet cent of aluminum spreads easily, and is more stable, but re- 
quires a higher temperature for its use. An alloy of titi with two 
to five per cent, of zinc has been found to work well. In experi- 
menting in this direction the glass must be perfectly clean, and fiO 
flux is required. It is advisable to moderate the temperature, as 
oxidation becomes energetic if it is raised too high. An ordinary 
soldering iron can be used. 

Non-Conductivity of Glass. 

As heat is generated by a motion of molectffes, so it is trans- 
ferred or conducted by the transfer of the motion 6f some parti- 
cles to other particles. Glass is a poor conductor of both heat 
and electricity, especially those glasses rich in silica. Thus those 
glasses rich in alkali make bad insulation. This non-conductivity 
of glass is a peculiar property ; if we stand by a window on which 
the sun is shining, we feel the warmth of the sun, but Jf we ibvtch 
the window-pane we find it cold ; yet if we take this same piece 
of glass and place it between us and an of dinary o£eri fire, it will 
shield us from the heat, but will become rapidly heated itself. In 
the first instance it transmitted most of the heat, and ki the latter 
instance it absorbed it. This is a remarkable peculiarity, and while 
plate glass may absorb but five per cent, of sun heat, it will absorb 
ninety-four per cent, of heat from a source of 400 degrees. Gen- 
erally speaking it may be stated that glass transmits the luminous 
heat rays, and absorbs the non-luminous. 

Richard Szigmondy,of Vienna, claims to have invented a new 
variety of non-conductive window glass which is opaque for heat 
rays. He claims for his invention, that a sheet of this glass one- 
quarter of an inch thick will absorb from eighty-seven to one hun- 
dred per cent, of the heat striking it. A comparison of the fea- 
tures of this new glass with ordinary glass — say plate glass with 
an absorbing power of five per cent. — makes it seem impossible in 
some claims at least. But if it is really opaque to luminous rays, 


it will keep a house cool in summer, and tend to keep it warm in 
winter, as glass non-conductive at one time, must be so at all 

Iridescent Effects in Glass. 

There is occasionally seen in examples of glass, (generally an- 
cient), which have been subjected to a process of decay, a wonder- 
ful beauty of tints of much brilliance and vividness of color. This 
is termed iridization, and the cause of this pleasing effect is the 
separation of the surface of the glass into extremely thin films, 
which refract and decompose the rays of light, giving them a 
prismatic effect. Sir David Brewster expresses very poetically the 
following sentiment : 'There is perhaps no material body that 
ceases to exist with so much grace and beauty, when it surrenders 
itself to time and not to disease." In damp localities, where acids 
and alkalies prevail in the soil, the glass rots as it were by a process 
which is difficult to study. It may be broken between the fingers 
of an infant. 

This iridescence may be frequently observed in window glass 
that has been exposed to the action of the elements for a great 
length of time. That it is caused by the action of decomposing 
effects separating the surface into thin films or scales, may be 
shown by immersing the glass in water, which saturates the films 
and unites them temporarily into one transparent mass with the 
more central undecomposed portion, when the colors disappear 
until the water evaporates. As the water evaporates the films 
again become separated by the intervening air and the colors 
again appear. 

It has been found that colored glass, especially blue, produces 
the most charming effects of iridescence. It may be said that 
the effects of iridescence are really due to the principle known 
in optics as ''interference," which is explained as follows : Color 
is caused by the vibrations of light waves of a certain definite 
length which, when they fall on the eye, give rise to the sensation 
of a certain definite color. The smallest rays impart the sen- 
sation of violet ; the next in size, blue ; the next, green ; the 
next, orange ; the next, yellow ; and the next, red. When the 
wave lengths exceed those of red they do not affect the vision at 
all ; and if the various wave lengths reach the eye at the same 
time the result is white light. Hence, interference may be inter- 
preted as a retardation of certain wave lengths by which some are 
absorbed or extinguished, and others are allowed to vibrate and 
impart their respective colors. We have assumed that this in- 
terference is effected by the filmy substance on the glass, but the 
nature of the film may not always be the same, in fact, is not always 


the same, and it is impossible to give one explanation of the causes 
which would apply to all cases. A thin film of any transparent 
substance applied to the surface of glass will produce interference ; 
or the glass may be blown to such a gauze-like thinness that its 
own substance forms sufficient interference, and will glow with 
color ; or again, glass may be so laminated that its upper strata 
will produce the necessary interference. 

As to when, and how the film on the glass arises is still a ques- 
tion. The film does not always appear to have been derived from 
the glass ; for instance, where it has been removed the glass has 
been found beneath quite smooth and polished. Peligot decided 
that the film was composed of silica and earthy silicates which may 
have been derived from the rain being impregnated with a certain 
quantity of silica, derived from the soil over which it ran. But 
while the exterior film may originate in this manner, the glass by 
continued exposure to the elements begins to undergo a change 
of structure, and the microscope will show that beneath this ex- 
terior film after removal, the surface of the glass is dotted all over 
with tiny holes and hollows ; and a sign of extreme antiquity of 
glass is its laminations, being split in layers and flakes. 

The nature of the glass modifies this structural weakening to 
a large extent, as it is greatest in glasses rich in alkaline bases. 
In the case of badly decayed glass the iridescence is not confined to 
the exterior films ; acids will cause these to flake off easily by dis- 
solving the silicates, when it will be found that the indented and 
irregular surface of the glass beneath will glow with rich, dark 

Iridescence has been artifically effected with fair imitations, 
by depositing very thin films of silicate of soda on the glass, 
but when attempts are made to change the glass itself to resemble 
and impart the glowing hues of antique specimens, nature demon- 
strates her supremacy, and her work is not easily duplicated. In 
Favrile galss, by a careful study of natural decay in glass, the 
effects of lustre and iridescence are obtained by arresting the pro- 
cess and reversing the action in a way to obtain the effects, and 
avoid the disintegration. The methods which have been successful- 
ly adopted apparently consist in so alternating the refractive power 
of the external layers of the glass that interference is brought 
about as if a film of some other substance were deposited. Such 
methods as the subjection of the glass to the vapor from volcanic 
ashes, and the combined action of heat, pressure and weak acids, 
have brought about very beautiful effects. The latter process 
has been patented in France and England by M. Clemendot. 



The preceding pages present as a synopsis, the definition, 
composition, classification, and some of the principal chemical and 
physical properties of glass. It is now the object to review the 
elements necessary in the practical composition of glass. As a 
preface to the following it is well to remember that it is almost 
impossible to lay down any rules for definite proportions of the 
different materials used in glass, as the composition of the different 
varieties is so variable as to preclude anything more than an ap- 
proximate estimate under this heading. 

Regularly organized companies are making the preparation of 
chide materials a specialty, and a glassmaker can offer no reason- 
able excuse on account of their impurity. Analysis and simple 
tests are available as an additional safeguard. A banishment of 
that "will-o'-wisp" — Luck — and a judicious exercise of common 
sense and careful judgment will almost invariably insure success ; 
always remembering that, none are infallible — wise men make 
mistakes, fools make blunders. If a mistake occurs some one is to 
blame, and a little search will locate the trouble, then "mark it" 
for future reference. One thing more ; don't "know it all :" ex- 
perience is a wise teacher and its students are numerous, and can 
very often offer a good suggestion. 

Raw Materials* 

If we take a sample of glass and analyze it, and determine its 
constituents, their natufe and relation, we discover that glass is 
composed of a silicate or •silicates. Chemistry teaches lis that 
a silicate is composed of an acid and a base, or bases ; and ex- 
periment demonstrates that the predominating acid in the silicate 
glass is silicaL ; the bases, lead, potash, soda and lime. It may be 
safely said that these comprise the fundamental elements of all 
commercial glass. To these, however, may be added the auxiliary 
elements, nitrate of soda, sulphate of soda, arsenic, antimony, man- 
ganese, etc., etc. 

From a chemical point of view potash, soda, oxide of lead, 
lime, etc., have a tendency toward the same general effect in glass, 
yet none of these can be substituted for the other or its analogues, 
as their distinct necessity results in the production of difference of 
fusibility, ductility, hardness, etc. 


Silica constitutes the true foundation of virtually all commer-, 
cial glass, and is the^only constituent that is universal, entering as 
it does, into the composition of all its varieties. It participates 


iri the constituency as an acid,. which combines with one or more 
bases, either alkaline or metallic, and creates the silicate glass. 

Silica is best defined from a chemical point of view, and its 
principal characteristics may be enumerated as follows : 

Silicon or silicium, (Si 28.3) is found in nature very abundant- 
ly as silicon di-oxide, or silica, (Si0 2 ) constituting flint, quartz, 
most sands and sandstones, (proportioned one equivalent of silicon 
and one to three parts of oxygen). 

When pure, it is a light white powder which feels rough when 
rubbed between the fingers, and is both inodorous and insipid. 

Chemically, it combines with bases forming salts, called sili- 

It resists the action of all acids except a mixture of nitric 
and fluoric acid, with which it readily enters into a solution. 

Silica is called an acid by most chemists because it is dissolved 
by the fixed alkalies. 

It is classed as a non-metal because of its non-conductivity 
of electricity and lack of so-called metallic lustre, and is classed 
with carbon and boron. It resembles carbon, inasmuch as it is 
known in the amorphous state forming two kinds of crystals, which 
resemble graphite and diamond. 

By nature it is quadrivalent, i. e. : Its molecules have four 
points of affinity or contact. 

Of itself, silica is incombustible in open air, or in oxygen 
gas ; even exposure to the flame of the blow-pipe effects no fusion 
or change of form. A reducing agent is necessary to effect its fu- 

While silica is present in all silicious glass, the relative propor- 
tion used differs greatly, not only in different varieties but in sam- 
ples of the same variety, owing in part to the inequality of its dis- 
tribution in crude materials. Almost the entire nature and quality 
of glass depends upon the amount of silica in its composition ; its 
relative hardness especially depends thereon, although it is some- 
times affected by the counteraction of the alkali or oxide used as 
a base. Lead, for example, tends to soften glass, making it more 
fusible and lustrous ; while on the other hand lime has a tendency 
to assist the hardening, making it more refractory and less sus- 
ceptible to the action of acids and alkalies. An excess of alkali 
as a base renders it soluble. Owing to the excessive alkaline bases 
some ancient glasses were of a soluble nature. And again, we 
owe the preservation of other ancient glasses to the presence of 
lime in their composition, although there as an accidental impurity. 

The resistance to melting and fusion increases with the per- 
centage of silica used. Experience teaches the glassmaker that, 
as he increases the basic percentage in his batch, he lowers its point 
of fusion, but the product is softer ; and while its density or spe- 
cific gravity may have increased, yet its nature deteriorates in cer- 


tain values. The resistance to corrosion and decay in glass also 
increases with the percentage of silica, provided the variation is 
not too great from or to that required to form a definite chemical 
compound. The conductivity of heat and electricity decreases 
with the increase of silica in glass ; hence, a glass poor in silica is 
not suitable for electric purposes. 

Silica is now used in glassmaking almost universally in the 
form of sand. This was also the practice among the ancients, sea 
and river sand being the earliest forms of silica used. In sand is 
presented the most available means for obtaining silica, not only 
from an economical point of view, but in many cases it is of great- 
er purity and value as a material, requiring but a nominal prepara- 
tion for use ; glass made from many natural sands being superior 
in every respect to that made from artificially prepared flint and 
quartz sands. Modern glass houses until some fifty years since, 
procured silica for the finer grades of glass by the expensive pro- 
cess of crushing and washing flint and quartz. The common title 
"flint glass" evidently originated therefrom. Even yet in certain 
European countries, where good sand is scarce, not only flint and 
quartz, but certain silicious rocks as basalt and trachyte, as well 
as certain alkaline rocks are used. Some of these rocks contain 
a large percentage of soda and potash. Some foreign basaltic 
rocks would require the addition only of a small percentage of lime 
to be productive of glass. (In so far as the necessary constituents 
are concerned.) One of these rocks, St. Gothard granite, shows 
by analysis : 

Silica 65.75% 

Alumina 18.28% 

Oxide of iron trace 

Lime trace 

Magnesia trace 

Soda 14.17% 

Potash 1-44% 

To which an addition of about ten per cent. 1 of lime would make 
a very fair glass. 

There are various grades of sand, which contain different 
percentages of silica ; but where freedom from color, perfect 
transparency and brilliance are essential, it is important to use the 
best grades of sand obtainable, as slight impurities, especially 
iron, even though present in but small quantities, will seriously 
impair all desirable properties in the glass. However, when qual- 
ity is a consideration secondary to cheapness of production, the 
quality of the sand is not so essential, as both iron and alumina 
are sometimes purposely added. The chief impurities in sand 
are iron and alumina, and the alumina is generally in the form of 
clay, loam, gravel and organic matter. Some of these impurities 
can be removed by burning and washing, but the iron and most 


of the organic matter can only be removed or neutralized Ly chem- 
icals. Iron is the most dreaded of all the impurities, as it not only 
destroys the color of the glass, giving it a greenish cast, but it is 
exceedingly difficult to neutralize its effect. Manganese is used 
to counteract this greenish color by neutralizing with its purplish 
tint the green into that limpid whiteness of color so desired in 
glass ; but glass so decolorized is liable under the action of sun- 
light to acquire a purplish tint. However, practically this does 
not affect the use of manganese. As to the allowance of iron in 
sand for any kind' of glass, there should not be more than one-half 
of one per cent., while for the finer grades of glass the least amount 
of iron possible. 

In examining sand as to its value for glassmaking purposes, 
microscopic examination is the best test, observing the following 
points : It should be perfectly white in color. It should not be 
very fine. The grains should be uniform, even and angular, rather 
than rounded. In very fine sand the grains are smooth and round- 
ed, and can only be used with difficulty, and very uncertain results, 
as such sand is liable to settle to the bottom of the "batch" and 
melting pot, preventing an even mixture of materials, producing 
consequently a glass uneven in nature and quality. Another test 
for sand is an acid test, in which the sand is heated in an acid. 
Sand so heated should not effervesce ; effervescence indicates the 
presence of lime. It should not lose color ; loss of color indi- 
cates the presence of clay, loam, or other foreign substances. Ox- 
ide of iron can be discovered by boiling the sand in hydrofluoric 
acid, and dropping into the solution thus formed a few drops of 
yellow prussiate of potash in solution ; the beautiful blue precipi- 
tate indicates the presence of iron in the most minute quantities. 
Use care in handling the acid and avoid inhaling the fumes that 
arise from it. Conduct the boiling in a small lead crucible, and 
heat it over a sand bath. Dilute the solution formed (when cool) 
with distilled water ; pour into a test tube and add a few drops of 
the re-agent, using a glass rod or any convenient dropper. 

These tests are simple qualitative tests and only indicate in a 
general way, the qualities of the impurities present. For an ac- 
curate knowledge of the quantity, a quantitative analysis is nec- 

The organic matter which carbonizes in the pot during the 
process of melting is removed as carbonic acid by the use of ar- 
senic, which is termed the great decarbonizer in glassmaking, as 
manganese is termed the great decolorizer. These decarbonizers 
are known as "brighteners," and purifiers. A great many glass- 
makers have adopted antimony, and have discontinued the use of 
arsenic ; economy suggesting the substitution. 

Analysis and color are not always indicative of the quality of 
the sand, as there have been instances when two kinds of sand, 


shown by test and analysis to be precisely similar, have produced 
different results as regards both color and quality of glass. Some 
yellow sands contain less iron, for instance, than other white sands. 
As a general rule, most sand used in glassmaking occurs as sand- 
stone, and is quarried in blocks, which must be crushed and pre- 
pared for use. In other cases while the sand occurs as rock and 
must be quarried, it rapidly disintegrates on exposure to air and 
moisture. At other quarries where the formation is saccha- 
roidal, or sugar-like, the sand rock has a very weak bond, and is 
rapidly detached from place with a pick, rapidly falling into a fine 
sand. All of these sands must undergo a process of preparation 
before they beccwne suitable for glassmaking purposes, by a pro- 
cess of crushing (when necessary), washing and drying. Burning 
is sometimes necessary (being an expensive necessity) when the 
sand contains an excess of organic matter ; as in some deposits 
of sand in which the available percentage of silica would be high, 
yet being so situated that the percolation of surface water for 
ages has carried so much decayed vegetable matter so far down 
through the deposit as to render actual burning necessary to re- 
store whiteness of color, and free it from the excessive organic 
matter. The heat of the furnace in melting, however, is generally 
sufficient, the carbonized matter being carried off as carbonic acid 
by the use of arsenic as explained above. 

While most of the sand used is quarried or mined, some glass 
is still made, as was the earliest glass,, from sea and river sand ; 
this generally being used, however, for the cheaper grades of glass. 
The quality of the sand is always an item of importance to the 
manufacturer of glass, and in many instances has determined the 
location of the plant for such manufacture. This was especially 
true in earlier times. England, France, Belgium, Austria, Swe- 
den and America, each have their quota of good sands. 

American sands, especially, show supremacy over all others, 
many of them being free from excessive organic matter and in 
an almost absolute state of purity, and the supply nearly inex- 
haustible. Throughout America are vast deposits and unmeas- 
ured veins, many of which show by analysis 99.90 per cent, pure 
silica. This is especially true of the deposits found in the New 
England states, New Jersey, Maryland, Pennsylvania, Illinois, 
Missouri, Minnesota, and various other states. 

England produces some very good glass, but her sands are 
not as good as others ; Alum Bay in the Isle of Wight, furnishes 
probably the best, of which the following is an analysis : 

Silica , 97% 

Alumina, magnesia, oxide of iron 0.02% 

Moisture o.oijo 


French sands are taken as a rule from the quarries in the for- 
ests of Fontainebleap. These quarries furnished sand for Eng- 
land, Belgium and Germany for some time. One analysis of this 
sand shows : 

Silica 98.08% 

Magnesia, oxide of iron 0.07% 

Moisture 0.05% 

Summing up the whole : Sand enters glass as its principal 
constituent, becoming the acid of its composition, giving it its 
hardness and strength in proportion, its so-called metallic nature, 
its limpid color (according to purity), its uniformity of manipula- 
tion and its brilliant transparency. 

A Method of Analyzing ft Compound to Determine 
Silica, Alumina and Iron. (Comstock.) 

Reduce the substance to an impalpable powder in an agate 
mortar, and mix with three times its weight of carbonate of pot- 
ash, or soda ; and decompose at a red heat in a platinum crucible. 
The mixture is then digested in dilute muriatic acid which effects 
solution. Evaporate solution to dryness, using care in regulating 
the heat near the close of the process to prevent the dissipation 
of the chloride of iron in vapor, as it is very volatile. By evap- 
oration the silica previously held in solution by the acid is deprived 
of its solubility, and by digesting the dry mass in water acidulated 
with mqriatic acid, the alumina and iron generally present are tak- 
en up and the silica is left in a state of purity, which is collected 
on a filter, carefully edulcorated, heated to redness and weighed. 

To determine the iron a considerable excess of a solution of 
pure potassa is added to the clear liquid containing the iron and 
alumina, which throws down these oxides and dissolves the alu- 
mina. The per-oxide of iron can then be collected on a filter, edul- 
corated until the washings cease to have an alkaline reaction, and 
well dried on a sand bath. Forty-nine parts of this hydrated per- 
oxide contain forty parts of the anhydrous per-oxide of iron. To 
determine the alumina the liquid in which it is dissolved is boiled 
with sal-ammoniac, when the alumina subsides. As soon as the 
solution becomes neutral, collect the alumina on a filter, dry by 
exposure to white heat, and weigh quickly after removal from the 

Base? and Other Materials, 

As has been stated previously, the bases are necessary as re- 
ducing and combining agents with the silica in the formation of 
the silicate glass, and the fusibility of the batch is increased with 
the proportion of the base or bases present. The bases are com- 
monly termed "fluxes," which technically, is a name given to any 
substajicje that assists in the fusion of another substance. In 


addition to aiding fusion, the relative hardness of any glass de- 
creases with the increase of the bases, (except lime). As to fusi- 
bility, the bases are about as follows : Lead, potash, soda, lime. 
As they are decomposed they generate the agitation in the pot or 
furnace which is so important, by allowing the escaping carbonic 
acid to carry off the ever present impurities. 

Their adaptability as a base may be determined by their eco- 
nomical power as a reducing agent. The principal bases do not 
enter the batch in the form in which they are found in the glass. 
Soda, as an example, is not used as soda, but as the carbonate 
of sodium, sulphate of sodium, chloride of sodium, or as nitrate of 
sodium. In the process of melting these compounds are decom- 
posed, the soda uniting with the silica forming glass ; the balance 
of the compound passing off as gas, or as impurities in the form of 
"glass gall," etc. The same process applies to the use of potash, 
lead, lime, etc. 

Sodium Salts. 

Sodium Carbonate (Soda — Soda Ash) Na 2 C0 3 . 

Sodium carbonate, commonly known as soda or soda ash, has 
materially displaced all other bases, and constitutes the principal 
base of most commercial glass at the present day. All glass, in 
fact, contains soda in some form, even the glass of the ancients 
was a soda glass, and the analyses of the most ancient glass known 
show in some cases an excess of soda. The chief source supplying 
the soda for the earliest glass houses was Egypt. It was called 
natron, and was obtained from the natron lakes of that country. 
It contained carbonate, sulphate and chloride of sodium, and was 
used in the proportion of about one part of sand, to three parts 
of soda. In more modern times, and until within the last few 
decades, the chief source of soda has been the ashes of certain 
plants, (chiefly those of the sea and seashore,) Spanish barilla, 
Scottish and Irish kelp, the Spanish soda of Alicant, and the roch- 
ette of Syria. They were all impure and produced a glass inferior 
in every way. The Spanish barilla, considered the best, only con- 
tained fourteen to thirty per cent. soda. 

The difficulties experienced with these impure materials, sup- 
plemented by a prize of 12,000 francs offered by the French gov- 
ernment, induced Nicholas Le Blanc, to devise a process (1790) 
of converting chloride of sodium (common salt, Na CI) into soda, 
which opened a new era in glassmaking. This process was in uni- 
versal use until about 1863, and may be briefly described as fol- 
lows : "Salt is decomposed with sulphuric acid, making salt- 
cake, which is sodium sulphate, containing more or less undecom- 
posed salt and some impurities. This salt-cake is mixed with 


coal and limestone and roasted in large revolving furnaces. The 
salt-cake is decomposed, and the soda is carbonated, making soda 
ash, but mixed with a considerable amount of undecomposed salt, 
salt-cake, caustic soda, and carbon, together with iron from the 
roasting furnaces." 

In 1863 Ernest Solvay devised the ammonia process which is 
simpler and more effective. "The Solvay ammonia soda is made 
from a purified solution of salt charged with ammonia, and treat- 
ed with purified carbonic acid. The precipitate after filtering and 
drying and heating is ready for the market, as an exceedingly pure 
carbonate." There is claimed for the ammonia process, the pres- 
ence of less iron and carbon than by the Le Blanc process ; and 
as it is the iron and carbon contained in impure sodas that is detri- 
mental to the ideal crystal white a glassmaker prizes, this feature 
alone makes the ammonia process preferable. 

Soda ash is used in glassmaking as 48 per cent., 
58 per cent, or as "dense 58 per cent." Densified ash is 
recommended in many cases, as it is less bulky in the pots 
and does not give off its carbonic acid too quickly before the glass 
is fully cleared. The general basic action of soda ash has been 
described in the introduction to the subject (bases). As a spe- 
cial action it may be said that it adds a brilliant lustre to glass, but 
unless it is unusually pure, it imparts a bluish-green tint which 
must be neutralized with manganese, or some oxidizing agent. 
One hundred pounds of soda ash loses during fusion 31.67 per 
cent, by evaporation and volatilization. 

It is customary for many persons to test the strength of alka- 
line solutions by the use of the hydrometer. The hydrometer 
may safely be used to compare different solutions of the same ma- 
terials, but not of different materials. 

The commercial valuation of soda ash is usually restricted to 
the determination of the percentage of "available alkali," contain- 
ed therein. Without entering into any exhaustive explanation, it 
is important to say regarding soda ash and its various tests, that 
public attention a few years ago was drawn to an error made by 
many analysts in attempting to apply the English commercial test 
for soda to samples of alkali, soda ash, etc. The result of which 
error is to make the test indicate, from one, to one and one-half 
per cent, more soda than it contains by the proper test. It seems 
almost unnecessary to state that no comparison can be fair if one 
soda is tested by the so-called "Newcastle test," for example, and 
another by the test for actual alkali. The mistake of these incor- 
rect tests originated in the fact that early chemists fixed the atom- 
ic weight of sodium at twenty-four, subsequent investigation^ 
have proved it to be twenty-three. Under this test the actual 
alkali (Na 2 O) is stated as 32/54, or 64/io8,of the total sodium car- 


bonate. The actual alkali in accordance with the true atomic 
weights of the elements in the compound, is 31/53 or 62/106, of 
the total sodium carbonate. The effect of this error is to increase 
the nominal percentage of alkali by 1.3 per cent (Newcastle test). 
Another still more incorrect test is the so-called "New York and 
Liverpool" method of testing alkali, which has been in use at least 
fifty years. Under this test the incorrect chemical equivalent for 
sodium carbonate (Na 2 C0 3 ), is employed, which calls for 32/53 
or 64/106 of the total sodium carbonate, which gives 3.226 per 
cent, more alkali than actually exists. To further illustrate the 
different systems of alkalimetry for soda ash, a sample containing 
48 per cent, actual alkali by the New York and Liverpool test ; 
by the English or Newcastle test would contain 47.11 per cent., 
or according to the English test for actual alkali it would contain 
46.5 per cent., and by the way it is sold on the continent of Eu- 
rope, by its strength in sodium carbonate (Na 2 CO a ), it would con- 
tain 79.51 per cent. Again, if the New York and Liverpool test 
equals 58.32 per cent., the Newcastle test would equal 57.34 per 
cent., the actual alkali test would equal 56.5 per cent., the Conti- 
nental test would equal (sodium carbonate) 96.60 per cent. But 
this method of testing has always been, and is still used by the 
soda trade, especially in England ; however, so long as buyers 
and sellers of soda understand the different test$, and know by 
which they are buying and selling no harm can be done ; but 
when the attempt is made to compare different makes of soda ash 
by different tests, confusion and trouble at once arise. It is not 
the purpose to burden the mind with any of the exhaustive chem- 
ical tests and methods of analysis, but we present an analysis which 
is simple and sufficiently accurate to meet most circumstances for 
glassmaking purposes. This analysis we take from the 'Taper- 
makers' Digest," viz. : 

Soda ash is always bought to contain so many per cent, of 
soda, actual soda, Na 2 O, generally 58 per cent. This soda ash 
is crystallized sodium carbonate, deprived of its water of crystalli- 
zation and is almost pure carbonate, Na 2 C0 3 , or two parts of sodi- 
um Na, and one of carbon C, and three of oxygen O. 

Na equals 23 Na 2 equals 23x2 equals 46. 

Put in the atomic weights we have : 

C equals 12 C equals 12x1 equals 12. 

O equals 16 O s equals 16x3 equals 48. 


Total. . . .106. 
Now take out Na 2 — Na 2 equals 23x2 equals 46. 

O equals 16x1 equals 16. 

1 • Total .... 62. 




or 62 parts in every 106 parts of carbonate are actual soda. Cal- 
culate to percentage 62/106x100 equal 58.3 per cent., for practical 
purposes 58 per cent. 

For this analysis the following is necessary : Normal sul- 
phuric, or hydrochloric acid ; this can be bought or can be pre- 
pared. A solution of methyl orange (one part methyl orange in 
1,000 parts of water). Use a plain burette, put on a rubber tube 
two inches long, a pinch clamp and a fine nozzle. Fill your bu- 
rette with acid, and having obtained your sample, weigh out on 
a watch glass, already weighed, 53 grams of your sample; dissolve 
in a 1000 cc. flask one-half full of water ; when all is dissolved 
make up to 1000 cc. with water. 

Take 10 cc. out, put in a beaker glass and add a couple 
drops methyl orange ; the color will turn straw. Now add cubic 
centimeter by cubic centimeter of your acid ; as soon as the color 
shows change read off from burette how many cc. have been 
used. Shake up gently and add another drop ; the color will 
change to dark straw, then red. The exact point to stop at is the 
moment of change to red, and note the number of cc. used. Re- 
peat with a fresh portion of 10 cc. and note again the number of 
cc. used ; and say we have from three different readings of bu- 
rette : 9.4, 9.5, and '9.6. 

9.4+9.5+9.6 equals 28.5-~3=9.5 average. Then we have : 
S3 grams to 1000 cc. diluted. 

0.53 gramme — 10 cc. — taken for test, takes 9.5 cc. and eve- 
ry cc. of normal acid, neutralizes .031 gramme of actual soda. So 
.031x9.5 equals total actual soda present .2945 grammes. This in 
percentage equals 2.945 divided by 5.300x100 equals 55.48 per 
cent., or is short by two and one-half per cent, full of 58 per cent. 
This shortage is most likely to be caused by absorption of water. 

Solubility of Sodium Carbonate (Drv) Na 2 CO.„ 

in 100 Parts of Water. 

Temperature degrees 100 parts water 1 part requires 

C. F. dissolve. water. 

io 50 .12.6 -7-94 

20 68 21.4 .4.67 

30 86 38.1 2.62 

35 95 59.0 1.69 

45 XI 3 46.2 2.16 

50 122 46.2 2.16 

55 I3 1 46.2 2.16 

60 140 46.2 2.16 

65 149 46.2 2.16 

70 158 46.2 2.16 

100 212 45.4 2.20 

NOTE— Centigrade degrees X nine-fifths+32— Fahrenheit degrees. 


^' ' Sodium Sulphate (Salt-Cake) Na 2 SQ 4 . 

Sodium sulphate is made by the action of sulphuric acid on 
sodium chloride. (See carbonate.) 

Glauber's salt, crystallized sodium sulphate (Na 2 S0 4 ioH 2 0) 
containing 10 molecules of water of crystallization, is soluble in 2.8 
parts water at 15° C, — 59 F ; in 0.25 part at 34 C, — 93 ° F ; 
and in 0.47 part of boiling water. On depriving Glauber's salt of 
its water of crystallization, 55.9 per cent, of its weight, salt-cake 
or dried sodium sulphate is obtained. One hundred pounds of 
dried sodium sulphate loses during melt about 56.31 per cent. 

Glass made with sodium sulphate is less liable to devitrify, or 
become ambitty, and will bear more lime than carbonate glass ; 
hence gives a harder glass with a better polish, and less liable to 
sweating. Sulphate glass is of a bluish color, while carbonate 
glass has a yellowish tint. 

Economy in cost encouraged the use of sodium sulphate, but 
it is being gradually replaced by the carbonate, A larger quan- 
tity of sulphate than carbonate, however, is required for the same 
amount of glass, as it requires from 130 to 150 pounds of sulphate 
to do the same work and produce the same quantity of glass as 100 
pounds of carbonate ; and its decomposition, and the clearing of 
the glass requires ten to twenty per cent, more fuel than 
carbonate glass requires. It also contains more iron than the 
carbonate, and its fumes are destructive to pots, breast-walls, etc. 
The adoption of sodium sulphate as a constituent of glass occurred 
about the middle of the present century, and was brought about 
by the researches of Gehlen. Glassmakers first proceeded very cau- 
tiously with sodium sulphate as a new ingredient, by mixing a 
small quantity of it with a large proportion of the carbonate ; 
gradually increasing the proportion to equal quantities of each ; 
and finally the carbonate was omitted entirely. This last gave 
them a cheaper material, but one that doubtless injured the col- 
or of their glass. The bluish-green tint imparted by sodium sul- 
phate was ascribed by M. Pelouse, to the presence of iron, the cor- 
rectness of which has since been proven. This defect he succeed- 
ed in eliminating to a certain extent, by the use of lime, which 
resulted in a sulphate, refined and productive of better results. 

The use of sodium sulphate involves the introduction of in- 
gredients which are not required when pure carbonate only is 
employed ; as the decomposition of the sulphate by silicic acid is 
accomplished slower and with much more difficulty, and it re- 
quires a higher temperature to effect fusion than with sodium car- 
bonate. Carbon is introduced generally in a proportion of one, 
or rather more than one equivalent, tp two equivalents of the sul- 
phate. The carbon abstracts from the sulphate one equivalent of 
oxygen ; the sulphurous acid which is thus formed is displaced 


by the silica, and silicate of sodium is the result. The disengaging 
sulphurous acid being decomposed much quicker than the sul- 
phate or salt-cake, hence it aids fusion. There seems to be no fix- 
ed proportion of carbon necessary for the decomposition of the 
sodium sulphate, and it has been demonstrated that decomposi- 
tion is materially assisted by the use of calcium carbonate. 

Another detriment to the glass without a thorough decompo- 
sition of the sulphate by carbon or other agent, arises in the fact 
of the dissemination of undecomposed sulphate in large quanti- 
ties throughout and on the surface of the glass. The fact of the 
difficulty of a uniform distribution of carbon in the "batch" so 
that each particle of sulphate may find immediately, for the pur- 
pose of its decomposition, the necessary quantity of carbon, has 
given rise to many inconveniences. Carbon has generally been 
used in the form of coal, charcoal, pitch, etc. These substances 
can be replaced — according to a foreign invention — by organic 
non-ferriferous substances with larjje contents of hydrogenous 
matter. This becomes liquid at a much lower temperature than 
sodium sulphate, while it developes at a higher degree of heat, 
gases and vapors which exercise a reducing action. Such sub- 
stances near at hand are mineral, vegetable and animal fats, and 
oils, as paraffine, ozokerite, tallow, resin, resinous oils, tar oils, 
liquid and solid olefiant bodies (carburet ted hydrogen) of the aro- 
matic order and their derivatives. By these substances liquefying 
at ordinary temperatures the distribution is more uniform, and 
contact with the sulphate much closer ; besides, the liquefaction 
occurring before the constituents of the batch have entered into 
fusion, insures a shorter melting period, and a quicker and better 
reduction of the sulphate. 

Sodium Nitrate (Chili Saltpetre, Nitre) NaNQ 3 . 

Sodium nitrate enters glass as an auxiliary base, in conjunc- 
tion with other alkaline bases, in a proportion of about one to five, 
as an oxidizing agent, and is therefore a decolorizer in action. Its 
soda unites with the silica similar to other sodium compounds. 

Its oxidizing properties facilitate fusion, and add purity to 
the glass and color by aiding in the expulsion of carbonaceous 
matter. One hundred pounds of pure saltpetre loses about 50 to 
S3 per cent, during melt. 

Sodium nitrate is found in nature as an incrustation upon and 
throughout the soil of certain localities in dry, hot countries, as 
for instance, in Peru, Chili and India. The formation of these ni- 
trates is to be explained by the absorption of ammonia by the soil, 
where it is gradually oxidized and converted into nitric acid. 


Sodium Borate (Borax) Na 2 B 4 Q 7 +ioH 2 Q. 

Slightly efflorescent ; soluble in 16 parts of cold, and in 0.5 
parts boiling water ; melts at red heat, and forms a colorless liq- 

This salt occurs in Clear Lake, Nevada, and in several lakes in 
Asia. It is also manufactured by adding sodium carbonate to the 
boric acid found in Tuscany, Italy. It forms colorless transparent 
crystals, but is sold mostly in the form of a white powder. 

Borax is a powerful flux, and is used in glass to facilitate fu- 
sion. It exerts a decided softening influence on glass by its great- 
er generation of agitation during fusion ; during which it assists 
largely in the process of purification. Many glassmakers, for 
reasons above, recommend borax as a preventive for "cords," 
"stones," etc., as by the increased agitation of pot contents many 
of the impurities causing "cords," etc., are dispersed and expelled. 
Borax glass assumes great fluidity, and is easily fused ; hence the 
salt is not used in large quantities. 

Sodium Chloride (Common Salt) NaCl. 

Inasmuch as sodium sulphate and sodium carbonate are both 
direct products of the chloride, it is but natural to suppose that 
chemists should turn their attention toward dispensing with the 
process of conversion, and utilize the chloride in the manufacture 
of glass by a direct union of sand and salt, without the intervening 
process. But such efforts have been without much success, as 
about the only glass made by such method is a black glass for bot- 
tles made in England. 

Mr. Chance thus defines a mixture of materials devised by a 
Mr. George Gore : "In which steam should be liberated through- 
out at a high temperature only, and therefore under the condi- 
tions most effective for decomposing the salt. In this mixture, 
sodium sulphate and carbon were dispensed with altogether, and 
they were replaced by a chemically equivalent mixture of sodium 
hydrate, and common salt ; these two ingredients being also in 
quantities chemically equivalent to each other, and representing 
together, as near as possible, the amount of alkali contained in the 
ordinary sulphate mixture. The mixture thus modified consisted 
of sand, cullet, chalk, common salt, sodium hydrate, arsenic, and 
manganese. In the reaction which took place the sodium hy- 
drate decomposed the salt at high temperatures and formed hy- 
drochloric acid, and anhydrous soda ; the former escaped as gas, 
and the latter united with the silica. Mr. Gore succeeded in ob- 
taining by this process a transparent glass, but the cost of the 
caustic soda rendered the mixture more expensive than the sul- 


Potassium Salts. 

Pottassium Carbonate (Potash, Pearl-Ash) K 2 C0 8 . 

The value of potash as a glassmaking material was known as 
early as the fifteenth century. Potash is more efficacious than 
soda in effecting fusion in the melting process, but more expensive. 
No coloring action is exerted by potash, but the brilliance of the * 
glass is diminished by it to a certain extent. One hundred pounds 
of 72 per cent, pure potash loses 22.80 per cent, during melt. 

Potash is not used now to any great extent. Some of the 
more expensive glasses, as "English flint/' are potash glasses. 
Some few ancient glasses show from one to two per cent., which 
was probably derived by chance from the soda used at that time. 
Potash in early manufacture was made from the lees of wine, fern 
ashes, wood ashes, beet-cake, grape-cake, etc. It was generally 
made by lixiviating wood ashes, which results in an impure car- 
bonate that must be calcined and refined, as for glassmaking 
purposes the quality of the glass depends upon the degree of puri- 
fication. Refined potash when calcined in a furnace until white, 
is known as "pearl-ash:" Potassium carbonate, the form in which 
potassium is principally used in glassmaking, is also prepared ar- 
tifically from the sulphate by Le Blanc's method. 

Potassium Nitrate (Saltpetre) KNQ 3 . 

Potassium nitrate is sometimes used as an oxidizing agent in 
the finer glasses. 

Potassium nitrate occurs in nature like sodium nitrate ; 
or it is manufactured by lixivating animal refuse matter mixed 
with earth and lime ; also made by the action of sodium nitrate 
on potassium chloride. 

Analytical Re-Actions of Potassium Compounds . 

I. Add to a concentrated solution of a neutral potassium 
salt, a freshly prepared solution of tartaric acid. A white pre- 
cipitate of potassium acid tartrate (KHC 4 H 4 O e ) is slowly form- 
ed. An addition of alcohol will facilitate precipitation. 

II. Potassium compounds color the flame of alcohol violet. 
The presence of sodium which colors the flame intensely yellow, 
interferes with this test, as it masks the violet caused by potassium, 
unless the flame is observed through a blue glass, or through a 
thin vessel filled with a solution of indigo. The yellow light is 
absorbed by the blue medium, while the violet passes through and 
can be recognized. 


III. All compounds of potassium are white, (unless the acid 
has a coloring effect,) soluble in water, and not volatile at a low 
red heat. 


Litharge, PbO. Red Lead, Pb 2 3 . 

The use of lead as a glassmaking material is an English in- 
vention and originated during the seventeenth century. It was 
brought about by the use of fuel which required covered pots to 
protect the glass from the impurities originating from the fuel 
which had been substituted for wood. By covering the pots the 
action of the heat on the materials contained in them was so re- 
tarded as to require a better flux. Lead is a powerful flux, and 
promotes fusion at a very low temperature. Its use as a constit- 
uent of glass for artificial gems, optical glasses, etc., for which pur- 
pose lead glass, on account of its surpassing brilliance and density, 
is specially adapted, antidated its use by the English in theirinven- 
tion of "lead flint," and possibly suggested its use to them. 

Lead is used in glass in the form of litharge, or as red lead. 
Litharge is obtained by exposing melted lead to a current of air, 
when the metal gradually becomes oxidized with the formation of 
a yellow powder known as "massicot/' At a high temperature 
this fuses, forming reddish-yellow crystalline scales known as lith- 
arge. By heating still further, in contact with air, a portion of the 
oxide is converted into di-oxide, (or per-oxide Pb0 2 ), and a 
bright red powder is formed. This is red lead, or minium, which 
probably is a mixture or combination of oxide and di-oxide of 
lead, Pb0 2 , PbO. Red lead is generally preferred in glass- 
making, on account of its finer state of sub-division, and it de- 
composes during the melting process into ordinary monoxide of 
lead and oxygen ; the latter facilitating the removal of impuri- 
ties. Ordinarily lead is used in glass in a proportion of about 33 
per cent. 

Lead glass is very dense and heavy, (specific gravity 2.900 to 
3.255 — Dumas) ; has a greater power of refraction — the refrac- 
tive power of glass is proportionate to its molecular weight or den- 
sity ; and is very brilliant. By nature it is "soft," is easily scratch- 
1 ed, and is less liable to breakage when exposed to sudden changes 
of temperature. Lead is used in conjunction with the alkali-metal- 
lic bases, potash, soda, etc., but potash is its principal co-base. 
An excess of lead not only makes glass "soft," but it imparts to it 
a yellowish tint, besides having an injurious effect upon the pots. 
The yellowish tint imparted, however, can be masked by the use 
of oxide of nickel. 


The silicates of lead are more fusible in proportion to the 
greater amount of base, (in fact any glass is less fusible in propor- 
tion to silicate, more fusible in proportion to base), and with equiv- 
alents it will melt at a red heat. On account of the difference be- 
tween the specific gravity of lead and that of the other materials, 
the use of lead is the cause of innumerable "cords" and "striae" 
disseminated throughout the glass. This trouble increases with 
the increase of density. The difference in specific gravity be- 
tween lead and its co-base, potash, is so great that it is like mixing 
oil and water. For this reason the materials for lead glass must 
be carefully mixed and melted, and worked out promptly. 

Lime and soda ash are gradually replacing lead and potash. 
While perhaps the so-called "lime flint" glass does not possess the 
surpassing brilliance of lead glass, yet its lustre suffers to the en- 
hancement of its qualities of hardness, resistance, and economy ; 
but lead is better adapted for use in glass to be colored than lime, 
as lead glass assumes a finer, fuller and more lustrous color than 
lime glass. For this reason lead is sometimes added to lime 
"batches" for colored glass, making them susceptible to a better 
color, and an improved quality. 

Analytical Re-Actions. 

Dissolve the lead oxide (litharge) in nitric acid, which makes 
lead nitrate, the only salt of lead which is easily soluble in water. 
To a solution of this salt add sulphuric acid. A white precipitate 
of lead sulphate is formed. 

Calcium Salts. 

Calcium Oxide, CaO. Lime. 
Calcium Carbonate CaCO a . 

Calcium carbonate, CaCO s , is one of the most abundantly oc- 
curring elements in nature, being found in the form of calc-spar, 
limestone, chalk, marble, shells of mollusca, etc., etc. 

Calcium oxide, CaO (burnt lime) is obtained on a large scale 
by the common process of lime burning, which is the heating of 
limestone, or any other calcium carbonate to about 8oo° C, — 
1472 F. The result is calcium oxide, or lime, a white, odorless, 
amorphous, infusible substance of alkaline taste and reaction. 

The use of lime as a constituent of glass is comparatively a 
modern discovery, although nearly all glass of all ages and coun- 
tries contained it in an indefinite proportion, (ancient glass three 
to eight per cent.). But it was generally present as an accidental 


impurity, yet to its presence we owe the preservation of the most 
ancient specimens of glass. Its definite use, and proper propor- 
tion, however, was arrived at slowly and by experiment. Lime 
was originally used in the form of chalk, which possesses a free- 
dom from iron (and iron is as detrimental to color when present in 
lime as in any other material). Lime is a very important element 
in glass, and it enters its constitution as an alkaline base — being 
classed as an alkaline earth — but its original use evidently desig- 
nated it as a cheap substitute for lead, and its alkaline co-bases, 
potash and soda, without any determination of its true merits, 
which have been developed by increased and continued use. 

An approximate proportion for the use of lime is about as 
follows : Plate glass, 5.5 per cent. ; window glass, 13 per cent. ; 
lime flint, 10 to 12 per cent. ; bottle glass, 20 per cent. It is chief- 
ly valuable in promoting fusion, supplying stability, and increas- 
ing insolubility of the glass if used in proper proportion ; but if 
used in excess it retards fusion, produces a milky appearance and 
makes it hard and liable to devitrify. Lime is introduced in the 
"batch" as carbonate (chalk, limestone, etc.,) ; as oxide, (burnt 
lime) ; or as hydrate, Ca(OH) 2 , (slacked lime). The use of cal- 
cium hydrate is nearly obsolete, as the oxide, and the carbonate 
are supplied in a condition that dispenses with the laborious and 
unsatisfactory process of slacking. 

In regard to the special action of lime, it may be stated that, . 
while it has been substituted for lead, its specific gravity is less ; 
and while it adds lustre to the glass, it does not impart the bril- 
liance that lead does. Lime increases the hardness of glass with- 
out coloring the product, and a fact worth mentioning is, that 
while chalk and limestone are both carbonates, glass made with 
limestone is harder, and cools and sets quicker than that made with 
chalk, which is possibly due to a general presence of jnagnesia 
in limestone. Lime can be used in a much larger proportion in 
conjunction with sodium sulphate than with sodium carbonate. 
This is advantageous, especially with window glass, as with an 
increased quantity of lime the glass becomes harder, assumes a 
better polish, and is less liable to surface exudation, technically 
termed "sweating." 

Lime is now obtained, commercially, in a finely ground con- 
dition and pure in quality, either as limestone or burnt lime. 
Most lime in burning absorbs a certain amount of those noxious 
elements, carbon and iron, and where burnt lime is used, that burnt 
with wood is recommended. The use of carbonate in the form of 
limestone is gradually being extended, and indeed can be recom- 
mended, inasmuch as it can be obtained finely ground and pulver- 
ized, and is just as available as the ground burnt lime, besides be- 
ing cheaper. The especial recommendation for ground limestone 


(carbonate) is on account of the greater agitation resulting in the 
"batch" from the use of limestone in its raw state. It is apparent 
to any intelligent glassmaker that to drive off the carbonic acid gas 
from the limestone before putting it in the furnace, must take from 
it a very valuable ingredient useful in producing glass. If the 
disengagement of the gas occurs in the furnace, the effect of its 
agitation is to help very materially in the process of clearing and 
cleaning the glass of impurities ; besides the decomposition of the 
ground limestone is slower than burnt lime, and this slow decom- 
position tends to continue the fining, or cleaning, process to the 
very end of the melt. 

One hundred pounds of calcium carbonate loses about 44 
per cent, during the melt, hence the use of about 50 per cent, more 
of ground limestone is recommended than burnt lime. One hun- 
dred pounds of hydrate (slacked lime), loses about 28 per cent, 
during melt. __ 

Method of Analyzing Calcium Carbonate. 

Take a known quantity of calcium carbonate and expose it 
for about one-half an hour to a full white heat. By this means the 
carbonic acid gas is expelled entirely, and by the loss in weight 
the quantity of each ingredient is determined, supposing the car- 
bonate to have been pure. 

In order to ascertain that the whole loss is owing to the es- 
cape of carbonic acid, the quantity of this gas may be determined 
by a comparative analysis. Into a small flask containing hydro- 
chloric acid diluted with two or three parts of water, a known 
quantity of limestone (or carbonate being tested) is gradually add- . 
ed, the flask being inclined to one side in order to prevent the 
fluid from being flung out of the vessel during effervescence. The 
diminution, in weight experienced by the flask and its contents, 
indicates the quantity of carbonic acid which has been expelled. 
Should the carbonate suffer a greater loss in the fire than when 
decomposed by an acid, it will most probably be found to con- 
tain water. This may be ascertained by heating a piece of it to red- 
ness in a glass tube, the sides of which will be bedewed with mois- 
ture if water is present. Its quantity may be determined by caus- 
ing the watery vapor to pass through a weighed tube filled with 
calcium chloride, by which the moisture is absorbed. 

Analytical Re-Actions. 

I. Dissolve calcium carbonate in hydrochloric acid until the 
acid is neutralized, and add either sodium potassium or ammonium 
carbonate, and a white precipitate of calcium carbonate CaC0 3 , 
is produced. 

II. Calcium compounds impart a reddish yellow color to 


Barium Carbonate, BaC0 3 . 

Barium occurs in nature chiefly as sulphate, or heavy spar, 
BaSo 4 , but also as carbonate or witherite, BaC0 3 , and its com- 
pounds closely resemble those of calcium (lime), being also like 
lime, an alkaline earth. 

Barium is used in glass as barium carbonate, BaC0 3 , but on 
account of its cost and impure state, it has not found its way into 
very general use. A witherite or carbonate comparatively pure, 
and especially free from iron and other impurities, was scarcely ob- 
tainable, and only at high prices. These objections, however, are 
being gradually overcome and carbonates are now being marketed 
as pure as 96/98 per cent., free from iron and lime ; which, in 
connection with its reduced cost, is gradually extending its use. 
The claim for the use of the barium carbonate in glass is as a 
substitute for lead, lime, or the alkalies, potash or soda, in that it 
imparts lustre, aids fusion, adds hardness, increases density, tends 
to reduce the liability of devitrification, and produces a glass that 
is very slightly affected by the atmosphere. Used as a substitute 
for lead, it is claimed that baryta-alkali glass melts as easily as lead- 
alkali glass, and that while baryta imparts density (like lead), it in- 
creases the hardness (like lime), without interfering with the den- 
sity. In its use as a substitute for lime and alkali, it hardens the 
product without retarding the fusion, and thus eliminates the li- 
ability of devitrification. But while it can be substituted in 
part, potash and soda cannot be entirely replaced by baryta. Ap- 

90 parts precipitated barium carbonate replace 100 parts lead. 

150 parts precipitated barium carbonate replace 100 parts potash. 

200 parts precipitated barium carbonate replace 100 parts soda. 

200 parts precipitated barium carbonate replace 100 parts lime. 

Analytical Re-Actions. 

Dissolve the carbonate in hydrochloric acid which forms ba- 
rium chloride (BaCl 2 +2H 2 0). It crystallizes in prismatic plates. 

I. Add sulphuric acid, a white precipitate of barium sulphate 
(BaS0 4 ) is produced immediately, even in dilute solutions. The 
precipitate is insoluble in all dilute acids. 

II. Add calcium sulphate (plaster of paris). A white pre- 
cipitate insoluble in all dilute acids is formed immediately. 

III. Barium compounds color flame yellowish-green. 

Auxiliary Elements. 

The accidental elements which usually discolor glass are iron 
and carbon, or carbonaceous matter. All glass exhibits a tenden- 
cy to change color or fade, brought about by the general impuri- 


ties present in. materials of all kinds ; as no material is absolute- 
ly pure. Iron and carbon are the most noxious elements, and 
are generally present in some proportion in nearly all materials. 

Thus the fading of glass is a natural defect, and to counteract 
this and other defects so detrimental to that limpid whiteness of 
color sought in glass, it is necessary to use certain substances 
whose counter-effects neutralize and subdue, by means of oxida- 
tion, the effects of the impurity or discolorizer present. Generally 
speaking the decolorizing agents are those which act by oxidizing 
the impurities. 

Manganese, arsenic, antimony, potassium nitrate, nickel ox- 
ide, cobalt oxide and zaffre, are all decolorizers. These ingredients 
are used in small quantities, as an excessive use brings about re- 
sults other than those desired, by their becoming colorizers in- 
stead of decolorizers. 


The use of manganese as a decolorizer has been known for 
several centuries, as Pliny wrote : 

"To the materials of glass they begin to add the magnetic 
stone." Which has been determined as meaning manganese. 

Manganese is found in nature either as di-oxide, Mn O 2 , or as 
sesqui-oxide, Mn 2 O s , and is darker in color than iron, considerably 
harder, and somewhat more easily oxidized. Four well defined 
compounds of manganese with oxygen are known in the separate 
state, viz. : 

Manganous oxide (monoxide or protoxide) MnO 

Manganous, manganic oxide MnO, Mn 2 03=Mn 3 04 

Manganic oxide (sesqui-oxide) Mn 2 O s 

Manganese di-oxide (bin — per — or black oxide) Mn0 2 

Manganese is a powerful oxidizing agent, on account of the 
facility with which it parts with a portion of its oxygen to any sub- 
stance which has an affinity for it, and in the manufacture of 
glass without color, manganese is of vast importance as a decolor- 
izer. It is one of the best and most effective agents in this capac- 
ity known. 

The especial use of manganese in glass is to mask or neutral- 
ize the greenish color imparted to the glass by the protoxide of 
iron. Manganese imparts to glass a pink or red tint, which be- 
ing complementary to green, neutralizes the color and permits the 
glass to transmit white light. Pellat refuted this theory, and 
claimed that the green tint of iron was not neutralized by the pink 
of manganese, by the pink being antagonistic to green, and thus 
subduing it ; but by the iron taking another charge of oxygen 
from the manganese and becoming per-oxide of iron, and produc- 
ing a reddish-yellow tint, while the protoxide produces a green 


tint. While it is asserted that decolorizing agents act by oxidiz- 
ing the carbon, or protoxide of iron, such may be the case with 
other decolorizing agents, yet it is not absolutely true in regard 
to manganese. The excess of oxygen in manganese assists very 
materially in washing the impurities from the constituents, and 
aids in purifying color in this way also ; but the greater richness 
of metallic manganese gives better results, especially if the ore 
is free from iron. An excessive use of manganese imparts an am- 
ethyst tint, and if the quantity is sufficient it will produce black. 
It s said that small quantities of nickel oxide and antimony act as 
efficacious decolorizers in place of manganese. 

Nearly all manganese ores are peroxide ores, and the perox- 
ide or di-oxide of manganese, (MnO £ ), composed of 63 parts of 
metallic manganese (Mn), and 37 parts of oxygen (O), is used ex- 
tensively. Manganese oxide (Mn 2 3 ), (sesqui-oxide), which is 
composed of 70 parts metallic manganese, and 30 parts of oxygen, 
is also used. Also manganese protoxide, (MnO), which is com- 
posed of 77.5 parts metallic manganese, and 22.5 parts oxygen. 
Ninety per cent, of an ore with a given test of Mn 2 O a (sesqui-) 
is as much as 100 per cent, of an ore with same percentage of 
(Mn0 2 ) (peroxide) ; which indicates a presence of 10 per cent, 
more metallic manganese in the sesqui-oxide, than in the peroxide 
or di-oxide. 

One hundred parts per oxide (MnO s ) evolve 18^ parts of 
oxygen. It appears that the use of manganese is being largely 
abandoned in European factories, especially in window glass. 
Mr. Thomas Gaffield, of Boston, Mass., by a series of very ingeni- 
ous experiments, demonstrated that under the action of air and 
sunlight, window glass containing manganese acquired, first a yel- 
lowish color, and under continued action gradually assumed a vio- 
let tint ; density of the color being proportionate with the amount 
of manganese present. While perhaps this demonstrates that 
manganese is not permanent as a decolorizer, yet the presence of 
iron in the glass may have considerable effect in this reaction, by 
the first reaction consisting of the higher oxidation of the iron 
producing a yellowish color, and the continued action of the ele- 
ments oxidizing the manganous oxide, producing a delicate vio- 
let color, which, blending with the yellow, results in red. How- 
ever, this applies principally to the use of manganese in window 
glass, and the purity of materials at the present day obviates the 
use of manganese in any large quantity. 

Analytical Re-Actions. 

I. Any compound of manganese heated on platinum foil 
with a mixture of carbonate of soda and nitrate, forms a bluish 


green mass ; giving a green solution in water, which turns red 
on the addition of an acid. 

II. Manganese compounds fused with borax on a platinum 
wire, give a violet color to the borax bead. 


Arsenic is obtained by roasting ores containing it. Such ores 
are heated in a current of air in furnaces having long chimneys, 
flues, or chambers, when the arsenic is converted into arsenous 
oxide, which is volatilized at that temperature, and as it passes off 
it is condensed and attaches itself to the walls of the chamber or 
flue. This is taken off and purified by a second sublimation when 
it forms the well-known poison called arsenous oxide (As 2 3 ), 
or white arsenic. 

Arsenic is used in glass as a decolorizer, or purifier, but where 
manganese acts on the effects of the iron present, and is termed 
"the great decolorizer of glass ;" arsenic acts principally on the 
carbonaceous impurities present and is termed "the great decar- 
bonizer of glass." In small quantities it promotes fusion, and 
decomposition of the other materials, and facilitates the dissipa- 
tion of carbonaceous impurities not otherwise disposed of, elimin- 
ating them as carbonic acid gas, as arsenic when exposed in small 
quantities to intense heat is decomposed, owing to the vaporiza- 
tion of the metal ; the oxygen is then available for cleansing pur- 
poses. An excess of arsenic, however, will produce a very objec- 
tionable "milkiness" of coler in the glass, which age increases. 

Arsenous acid, arsenic acid, and their salts exert their influ- 
ence at a temperature above the fusing point and are Volatilized. 

Analytical Re-Actions. 

I. Heat any arsenic compound after being mixed with some 
charcoal and dry potassium carbonate, in a very narrow test tube 
(or better, in a drawn out glass tube having a small bulb on the 
end), the arsenic is decomposed, and the metallic arsenic deposit- 
ed as a metallic ring in the upper part of the contraction. 

II. Heat arsenous acid upon a piece of charcoal by means of 
a blow-pipe. A characteristic odor of garlic is perceptible. 

NOTE — For years it has been a common custom in the glass 
trade to keep a large supply of arsenic in the manager's office or 
a place. much frequented. The poisonous fumes from the chem- 
ical permeate the atmosphere and have been directly accountable 
for the death, or ruined health, of many managers. Don't keep 
arsenic in a frequented place. 



Antimony is found in nature chiefly as the trisulphide(Sb 2 S 3 ), 
an ore which is known as black antimony, crude antimony, or stib- 
nite, and the oxides are obtained by roasting the sulphides. The 
metal is obtained by reducing the oxides by charcoal. Antimony 
is a brittle, bluish white metal, having a crystalline structure. 

The introduction of antimony as an ingredient of glass has 
occurred in recent years, and it may be termed a "brightener,"and 
is generally used as a substitute for arsenic, but not in conjunc- 
tion with arsenic. Used in small quantities antimony promotes 
fusion, and aids in the elimination of impurities, performing the 
functions of arsenic. Used in excess, however, its effects are del- 
eterious, as it destroys the nature of the glass. As a substitute 
for arsenic its proportionate use is about three-quarters to one. 

Antimony is commercially obtainable as : 

Ore, powdered 9<V"9 2 % 

Oxide 99% 

The so-called "needle" antimony, and metallic powdered. 

Analytical Re-Actions. 

Boil a piece of metallic copper in a solution of antimonous 
chloride — obtained by boiling the native sulphide with hydrochlo- 
ric acid. A black deposit of antimony is formed upon the cop- 
per. By heating the latter in a narrow test tube, the antimony is 
volatilized and deposited as a white incrustation of antimonous ox- 
ide upon the glass. 

Cobalt. Zaffre. Nickel. 

These oxides and their smalts are used in quantities of a few 
ounces each in lime and other flint "batches," as color neutralizing 

Smalt is an enamel, or glass colored with cobalt and powder- 
ed, and is generally used in connection with manganese, as a de- 

Oxide of nickel is a black powder, and in its native state is 
nearly always found in connection with cobalt. The nickelous 
oxide, which contains less oxygen than the oxide, is dull green in 
color. Both are effective as decolorizers, and impart to potash 
glass a bluish tint, and to soda glass a hyacinth tint ; used in 
excess they impart a violet tint. The tints imparted by nickel 
are constant. 

4 6 

Bone Ash. Calcium Phosphate. 

Bones contain about 30 per cent, of organic matter, and about 
70 per cent, of inorganic, most of which is tri-calcium phosphate. 
When bones are burned until all of the organic matter has been 
destroyed and volatilized, the resulting product is bone-ash. 
Bone-ash is used principally in the manufacture of opal glass, but 
the addition of a small quantity to a lime batch, assists in dispers- 
ing the impurities, and is recommended as a remedy for "cordy" 
glass. Avoid its excessive use in this capacity, as its tendency is 
to make the glass brittle and hard to fuse. 


So much has been said as to the effects of iron in glass, that 
but little more is necessary to be said at this particular place ; ex- 
cept that traces of it are present in many raw materials ; as sand, 
sodium sulphate, lime, baryta, etc., and as its effect is to impart a 
greenish tint to glass, where color is an object this tint must be 
neutralized or subdued by the action of decolorizing agents. 

Alumina. A1,0 3 . 

(Clay, Loam, etc.) 

In alumina the glassmaker has to deal with a material which 
is seldom purposely introduced into the "batch," but is always pres- 
ent as an accidental impurity, either in the materials, or brought 
by the action of the alkali on the walls of the pots, or furnace. It 
has the effect of rendering the glass less transparent (see opal), 
and in glass where brilliance and transparency are desired its pres- 
ence in excessive amount must be avoided. Excess of alumina 
renders glass liable to devitrification. % 


(Broken, or Waste Glass.) 

The use of cullet carries with it as much importance as any 
other material entering the composition of glass ; as where the 
homogeneousness of the product is desirable, the use of cullet 
should be guarded. In truth glass made from fresh "batch," with a 
very small quantity of cullet, is much stronger and better adapt- 
ed to the use of the finer grades of glass, especially that intended 
for beer, soda and other bottles which are subjected to high pres- 


Glass by being remelted loses strength, resistance and vital- 
ity, so to speak. Cullet is more fusible than raw materials, hence 
it aids fusion, and when properly disseminated throughout the 
"batch" in a uniform manner, it keeps the materials open, permit- 
ting the better escape of gases, and transmission of heat through 
the mass. Cullet should be carefully cleaned, especially if it is 
"chest" cullet — to which particles of iron adhere — as the effects of 
iron have been fully explained. It is best cleaned by keeping it 
immersed in a bath of dilute sulphuric acid at a temperature of 
about 180 F, for about twenty-four hours ; which removes the 
iron. It should be then thoroughly washed. 

Cullet should always be as near the nature of that of which 
it is to become a part, as possible ; otherwise the product will be 
stratified and lumpy. It should be pulverized, as large lumps are 
not properly disintegrated by the action of the fluxes, and a lack 
of homogeneousness is the result. When cullet is introduced in 
proportionate, well regulated and prepared quantities, it aids fu- 
sion ; prevents an undue volatilization of the alkalies, and pro- 
duces a uniform product. Used in excess, however, it makes glass 
lose strength, become very brittle, lose firmness, elasticity and re- 

Ordinary practice suggests a proportionate use of about one 
part of cullet to three parts of sand. 

NOTE — Such materials as manganese, antimony, bone-ash, 
cobalt, etc., which exert a coloring influence, will be found more 
fully exemplified elsewhere. (See colored glass.) 


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If we consult the preceding analyses of different glasses, we 
cannot fail to note how closely allied are the formulas used by 
people ancient and modern ; and of different countries far apart. 
Which demonstrates that in the production of glass, its constitu- 
tion must approach something near a definite chemical compound. 

Association of Materials. 

The association of the various ingredients for glass is perfect- 
ed by two separate and distinct processes, namely : That com- 
prising the mechanical association, in the preparation of the "batch" 
(as the associated raw materials are called), and mixing ; and 
that process comprising the chemical association, by process of 
fusion by heat, of the several mechanically associated materials 
into a distinct mass. 

Preparation of the Batch, and Mixing. 

(Mechanical or Preliminary Association.) 

As stated above, the first efforts towards the association of 
materials for glass are in the preparation of the batch. In doing 
this, the product desired should be well in mind, to determine the 
foundation of silica ; with sufficient base to give it the required 
support, a proper proportion of fluxing agents, and ample col- 
orizers, or decolorizers, and all accessories necessary to produce 
the glass required. 

Under their respective headings we have endeavored to illus- 
trate the general and special actions of the different materials en- 
tering into the composition of glass. It is impossible to lay down 
any definite proportion of materials for the different glasses, as 
glass is by no means a definite compound when made. The batches 
not only differ for the several kinds of glass, but different makers 
of the same kinds use the materials in widely varying proportions. 
Besides, irregularity of materials, and of furnace temperature, af- 
fect the composition. Careful calculation is always necessary to 
insure uniformity of result ; and a glassmaker must not run away 
with the idea that a formula once established is always infallible. 

It is important to remember that silica is the foundation of 
all commercial glass, and that the simplest compounded, hardest 
glasses, are cheaper than the softer glasses, and those rich in alka- 
li, but are more difficult of fusion. Also that glass loses strength, 
resistance, tenacity and lustre, as the base or flux is increased ; 
and that softness, hardness, tenacity, resistance to all deteriorat- 
ing influences (as acids, or action of the elements), brilliance, uni- 
formity, homogeneity, and color, are all features to be considered 
in the composition of the batch; and that the nature of the glass in- 


creases or diminishes as its composition varies from that required 
to form a definite chemical compound. All of which demon- 
strates the importance of a glassmaker possessing sufficient knowl- 
edge — technical and practical — to be able with well balanced judg- 
ment, to make a careful calculation as to what he wants, and how 
to get it. 

To begin with, too much care cannot be exercised in the 
mixing room ; even in the preparation of the simplest batches. 
All ingredients should be carefully weighed and sieved. All guess 
work should be strictly forbidden. The precepts of cleanliness 
should be rigidly enforced. Indifferent, careless workmen should 
not be tolerated. Two things especially important in the prepa- 
ration of the batch are : First : — That of having all materials re- 
duced to a pulverized condition. Second : — That of securing a 
thorough admixture of the batch. The importance of these fea- 
tures is obvious to the least intelligent mind. By reducing all par- 
ticles to their finest possible condition while in a raw state, a clos- 
er mechanical association is affected, and they expose more sur- 
face to all reducing influences ; effecting an earlier fusion of parti- 
cles, and a closer combination results. A thorough admixture of 
materials is necessary so that in the chemical association each par- 
ticle of sand may find its corresponding portion of alkali, oxide, 
etc., as may be required to insure homogeneity and uniformity. 
For the purpose of securing thorough and uniform mixing, the 
use of machinery is advised. A machine is tireless, and with prop- 
er attention, gives a definite result day by day. Tt is impossible 
to obtain workmen mixing by the time honored hand and shovel 
process, who do not at times become careless and indifferent. The 
results of such indifference are always conspicuous, and many of 
the faults and defects of glass can be traced directly to it. 

While most materials are now furnished in a finely pulverized 
condition, yet each material should be carefully sieved to remove 
all possibility of large lumps of soda, lime, etc., being incorporated 
in the batch, and from time to time should be tested for purity and 
regularity. Vigilance and watchfulness should never be relaxed 
in the mixing room. The use of the best materials obtainable is 
advised. While perhaps the first cost may be greater, yet they are 
economical in the end. Of course "the end may justify the 
means," but upon the whole, poor materials are expensive at any 
price. Good materials are readily available, and in dealing with 
such, calculations can be made to a close certainty, so far as ma- 
terials go. It should also be remembered that pots and furnaces 
cannot be adapted to suit the mixture ; the mixture must be 
adapted to suit them. \ 




Ttoe Melt. 

^ (Chemical Association.) 

After the materials have been thoroughly incorporated me- 
chanically, they are "filled in" (charged) the pots or tank for the 
purpose of completing the association. This constitutes the 
chemical association, and is comprised of two parts, viz. : Melting 
or fusion ; and "fining" (refining), and "standing off." 

During the period in which barilla, kelp and other crude 
forms of alkali were in use, the batch was subjected to a process 
preliminary to melting termed "fritting." This was a perheating 
iw tke purpose of effecting partial decomposition, removing mois- 
ture, and burning off any carbonaceous impurities ; and was ac- 
complished under the heat of a reverberatory furnace termed a 
"calcar arcfc," the residue being termed "frit." But the adoption 
of alkali prepared from salt has caused this process to be entirely 
abandoned. While perhaps in some instances it commends it- 
self ; yet generally speaking it is unnecessary. 

As the raw materials in melting lose bulk, sufficient batch 
cannot be charged at one time. The pots are first filled to their 
capacity with raw materials, which are allowed to partially melt, 
and in doing so they reduce their aggregate bulk, and sink in the 
pat, leaving room for additional filling, which is introduced at stat- 
ed intetvals. Generally one such re-filling, called "topping out," 
is sufficient and is introduced about ten to twelve hours after the 
first filling. It is important to allow the first filling time to reach 
q. state of fluidity before introducing any additional raw material. 
TWs avoids any interference with the first, or bottom filling ; and 
allows the free escape of all gases which would be partially pre- 
vented by the batch becoming fluid on the top first, and envelop- 
ing the material in the bottom with a fluid sheet ; (this is more 
especially the case with open pots), besides, when the bottom or 
first filling is reduced to fluidity first, it facilitates the fusion of any 
additional filling, and enhances the quality of the product. 

So much, indeed, depends upon the melt, that no pot or fur- 
nace should be filled with batch until the temperature to which 
it is exposed is sufficiently high to immediately reduce, and melt 
the materials to a condition of fluidity without any interference. 
This insures a perfect combination and association of all materials, 
by allowing the molecules of all substances to properly disinte- 
grate and combine into molecules of a new substance with a defi- 
nite chemical equivalent. The calculations relative to the constit- 
uents of the batch are based upon the above ; assuming that dis- 
integration will ensue, affinity assert itself, volatility cease, and 
regeneration be complete, at certain calculated periods. 

If after a pot has been "worked out," or after pot-setting, and 
the pot, or pots, are chilled, or the furnace is cold — and such is 


generally the case — it is inadvisable to "fill in" with cold batch 
until the temperature has been raised to a proper degree, ft 
is better by far to "set up" stoppers, and wait an hoar if acces- 
sary, as there is really no time lost in the melt by so doing. If 
the pot is hot the melt begins immediately, and goes forward Con- 
tinuously. If the pot is cold the batch does not begin to melt 
until the pot gets thoroughly heated, because batch is a very 
poor conductor of heat ; besides the introduction of coM ma- 
terials retards the absorption of heat by the pot, and encourages 
a "top melt." Again, the introduction of Cold material does not 
exert the injurious effects upon a thoroughly heated pot that it 
does upon one that is chilled. If the temperature is sufficiently 
high, the pots properly heated, and the action continuous, the fu- 
sion of the batch proceeds from the bottom up ; from the side* 
centerward ; and to a small extent from the top downward, which 
is demonstrated by the cone-like lump which floats in the semi- 
fluid mass, and is the last of the raw material to disappear, 

As the fusion continues, all moisture is evaporated, disin-- 
tegration ensues, gases and acids develop and exude, and in their 
evolutions carry off all impurities (a portion of which are depos- 
ited on the surface of the glass). These gases answer the purpose 
of stirring the semi-fluid mass, and generate an agitation of the 
particles as the least refractory materials are reduced, while the 
then fluid fluxes slowly envelop and reduce the more refractory 
materials, until a condition of fluidity of the entire batch is 
reached. As remarked above, if this is a continuous process the 
product will be homogeneous and even tempered ; but if the tem- 
perature falls below a point sufficient to properly continue the fu- 
sion and the proces is interrupted, the agitation ceases— leaving 
in suspension a part or all of the partially disengaged impurities, 
the removal of which requires a renewed agitation, which is much 
harder to generate by a simple increase of temperature, as a por- 
tion of the materials containing the necessary gases have been vol- 
atilized. A foreign substance must be introduced to generate new 
gases, and cause a forcible expulsion. Deep insertion of arsenous 
acid, a potato, an apple, or stirring with a stick of green wood, are 
remedies sometimes resorted to. (These remedies are very of- 
ten used for the removal of the pink tint, or "high color," impart- 
ed by excess of manganese.) By closing up the pot after intro- 
ducing the agent, the renewed agitation and consequent escape 
of gases, washes out a portion of the color or impurities. 

The worst feature of a slow melt at an insufficient tempera- 
ture is that the volatile ingredients of the batch escape at a lower 
temperature than that which is necessary to reduce the silica by a 
uniform attack of solvents, by which (the alkaline silicates melt- 
ing at a temperature insufficient to fuse the silica, and more re- 


fractory silicates) the glass produced assumes partially a crystal- 
line structure. Besides the melt proceeds principally from the 
top, and as explained above, envelops the lower portions with a 
fluid covering which retards the escape of the impurities, and de- 
velops nonuniformity, devitrification, foaming, stones, cords, bed 
color, and general indifference. "High color/' especially, is im- 
parted by the heat of the furnace being insufficient to reduce the 
manganese in proportion to the more fusible ingredients. 

There results from the process of melting a considerable dif- 
ference in weight between the raw materials and the product 
glass. This loss is occasioned by the disengagement of gases 
(other than oxygen, though this is expelled to a certain extent). 
In describing the different raw materials we have attempted to 
give an approximate estimate of the loss of some of them, but 
there is an estimated general loss of about one-sixth part of the 
total, including transfer of materials from the mixing room to 
the furnace, "filling in," and "working out," which also includes 
the loss by volatilization. This estimate is not definite, however, 
as glassmakers differ on the subject. 

The batch and general conditions must be regulated to suit 
the furnace and pots, as the time consumed in melting varies un- 
der the conditions of the furnace, pots and fuel, and it is impos- 
sible to give more than a general process idea. A small pot 
melts quicker than a large one ; likewise gas fuel will produce a 
better result than coal fuel; and coal is better than wood. 

The melting process proper ceases when the materials have 
reached a condition of fluidity. The metal — as it is called — is yet 
full of seeds, bubbles, and such impurities as do not fuse, and must 
be driven off. The process called fining consists of freeing the 
glass from these imperfections, and such as are infusible rise to 
the surface of the glass. Fining (termed by the Germans Heiss- 
schuren) is an abbreviation of re-fining, and means purification. 
At this particular period the temperature of the furnace must be 
as high as possible, in order that the glass may become very fluid ; 
which aids in freeing the infinitesimal seeds, bubbles and impuri- 
ties (estimated temperature 3,200° — 3,600° F.) The time oc- 
cupied by this process should not be too long, as a slow "plain- 
ing" generally results from insufficient heat, which means a lack 
of fluidity, and the bubbles, seeds, etc., cannot force their way out, 
which leaves a certain portion disseminated throughout the mass, 
while had the temperature been sufficiently high, and the glass 
very fluid, they would have risen to the surface ; the gases would 
have escaped, and the heavier impurities be available for removal. 
Owing to a certain amount of volatilization of potash and soda, 
at the higher temperature necessary, more of these ingredients 
are introduced in the batch than are contained in the glass. 


When the glass is entirely "plain" — and the fining process 
should not be interrupted until it is entirely so — and it is de- 
sired to "work" it ; it must be reduced from the state of fluidity 
to that of viscosity. This process is called "cold-stoking," or 
"standing off," (termed by the Germans, Kalt-schuren). It was 
the custom to bring about this result by lowering the temperature 
of the furnace. But the introduction of covered pots, and the 
cold air blast, obviate the necessity of reducing the furnace tem- 
perature, and make it possible to work from as many pots as 
is desired, while the temperature of the furnace is continued at its 
maximum, and the balance of the pots continue to' melt. This 
process of "standing off" has much bearing upon the general re- 
sult, and must be accomplished carefully, inasmuch as immediate- 
ly after a pot is opened the glass is in a spongy condition, with 
its surface generally full of impurities. By reducing the tempera- 
ture gradually, the glass settles and solidifies in a uniform measure, 
and allows the impurities to collect in a manner that permits of 
their removal by "skimming." 

But if the reduction of the temperature is forced, its surface 
becomes chilled immediately and the impurities remain in sus- 
pension, so to speak, and not available for removal. If a pot 
"comes around" slowly, give it time to refine, let it settle and so- 
lidify, then reduce the temperature gradually, and it will be pro- 
ductive of a far better result than if it is forced. Always keep 
in mind that glass made by a slow melt contains inherent proper- 
ties of devitrification which require but little to fully develop 
them. The use of water in cooling glass should be avoided as 
much as possible, and never be used in excess, as it destroys the 
nature of the glass by making it less tenacious and brittle, besides 
exerting an injurious effect upon the pots. 

Faults in the Glass. 

Faults in the glass are directly or indirectly traceable to some- 
body or something. Impure materials, improper proportions, in- 
different mixing, or insufficient heat to properly melt and "fine," 
will individually or severally produce faults in the glass, and will 
incriminate the buyer, metal-maker, mixer or teaser. Intelligent 
inquiry will generally fasten the fault to its proper source, when 
the best remedy for the disease is to remove the cause. 

In making glass it is always advisable to anticipate the re- 
sult, and exercise proper and timely precautions, by wise fore- 
thought and scrupulous attention to details, to prevent any de- 
velopment which may possibly arise to interfere with the result. 

One of the most prominent faults produced in making glass 
is the substance "glass gall" (salt water) (sandiver). This com- 
mon impurity is more or less produced with all glass, and it is a 


general error to suppose that it is entirely a by-product of salt- 
cake, or that it occurs entirely in sulphate of soda, or salt-cake 
glass, as fair grades of soda ash have been found to contain as 
much as eight to ten per cent, of sulphate of soda, which by im- 
proper mixing and fusion readily develops "glass gall/' Girardin 
by analysis defines the " constituents of "glass gall" in different 
glasses as follows : 

Window White Bottle 
glass hollow glass. 
Water absorbed from atmosphere. . . 1.65 0.10 1.00 

Sodium sulphate 83-30 ^S 1 55-9 2 

Catrium sulphate !0-35 6.00 25.00 

Sodium chloride 1.43 0.04 0.20 

Glass sand, alumina, phos. of calcium . 3.35 3.30 7.77 

Which demonstrates that it consists of non-fused particles of 
the batch, as chloride of potassium, sulphates of sodium and cal- 
cium, common salt, etc. As its specific gravity is less than that 
of glass, it usually rises to the surface of the metal, if the glass 
is properly melted and "fined." It may be well to repeat, that 
these impurities represent a certain portion of the denser matter 
which the temperature has not been high enough to decompose, 
and when they become congregated, they form a lumpy, tenacious 
substance which when the fining process is interrupted, remains 
disseminated in suspension throughout the melted metal, where it 
is held in partial solution and impairs the clearness and transpar- 
ency of the glass by its sub-division into white blotches and spots. 

As to remedies for this impurity, a specific one is to remove 
the cause, by the use of pure and proper materials, in just pro- 
portion carefully mixed. However, it is impossible to entirely 
eliminate it in certain glasses. The most available remedy is to 
maintain a temperature sufficiently high in the furnace to allow 
the glass to become very fluid, in which condition the chlorides, 
sulphates, eftc (which melt without mixing with the glass and 
must be expelled or decomposed) being lighter than the glass, es- 
cape or are readily driven to the surface, where they can be burned 
off by the use of moistened sawdust, pulverized coal, charcoal, etc. 
Or if allowed time, will accumulate in lumps and may be skimmed 
off. As sulphate of soda is the greatest generator of "glass gall," 
carbon in some form must be introduced in the batch with it. Car- 
bon facilitates the decomposition of the sulphate, and lessens the 
production of "glass gall." Anything which generates a violent 
agitation of the melted mass is efficacious in removing "glass gall" 
— as deep insertion of arsenic, potato, etc., and closing the pot for 
a period. 


Another fault attributed to the melt is that of "foaming." As 
a rule "foaming" is the result of insufficient heat to properly melt 
the materials. As has been already explained, the fusion of the 
batch in melting should proceed from the sides centerward, from 
the bottom upward, and never from the top downward. This 
insures uniformity of fusion, and allows all gases to escape in due 
proportion, and carry off their pro rata share of impurities. But 
if the fusion is effected by a cold melt, it is generally a "top melt," 
which means that the batch begins to melt at the top first and 
encases the balance of the raw materials in the fluid sheet that re- 
tards the escape of generating gases, which by being thus con- 
fined develop sufficient power to throw off the more fluid and vol- 
atile salts that have fused at a temperature lower than that requir- 
ed to reduce the more refractory materials. This semi-fluid mass 
rises sponge-like and foams over the pot. This action of the 
gases by driving the more fluid and volatile matter to the sur- 
face, deprives the silica of a large portion of its flux, solvents and 
purifiers, besides allowing the more refractory substances to set- 
tle downward; the melt is prolonged and the quality of the glass 
impaired. To avoid "foaming" it is advisable to never introduce 
the raw batch into either pot or furnace until they are thorough- 
ly heated, and the temperature high enough to effect a perfect 
and continuous fusion. In "topping out" always allow all prior 
fillings to reach a consistent condition of fluidity. 

Other common faults in glass are stones, waves, cords and 
striae. These faults all arise — to a great extent — from causes in 
common. The hard whitish-colored particles, and the knotty 
wavy veined tenacious substance are too familiar to the glassmak- 
er and worker to require any detailed description. Primarily 
these faults are the direct result of a lack of homogeneity in the 
melted glass — induced by one or all of the following conditions : 
improper materials, proportions, mixing, or fusion. 

Perfect fusion is perhaps the most important preventive, as it 
imparts to the glass an even density, and eliminates by volatiliza- 
tion such impurities as are the cause of the faults, and serves to 
partially overcome and equalize the bad effects of impure ma- 
terials, or imperfect proportions and mixing. Generally the 
cause and effects of devitrification will explain the presence of 
these faults. Perfect fusion eliminates devitrification. Large 
lumps of cullet glass inculcate waves and striae by not properly 
receiving the action of the fluxes, and while this cullet melts and 
becomes fluid, it does not disintegrate and incorporate itself uni- 
formly with the other ingredients. 

An excess of cullet is equally as productive of these faults, 
as glass, like other fusible substances, upon being remelted leaves 
a residue or "dross," and unless the temperature of the furnace is 


exceedingly high, and all agencies at work, this residue is not 
volatilized or expelled. Besides cullet being devoid of direct ox- 
idizing agents, it is difficult to derive sufficient gases from the 
other materials to remove this excessive cullet impurity, and it 
remains disseminated throughout the metal. For these reasons 
a thorough admixture of cullet with the raw materials is advised, 
in order to give it the greatest possible exposure to the direct 
action of the fluxes, etc. A cold furnace or pots, will produce 
cords, stones, etc., abundantly (see Chemical Association), by 
imperfect fusion. Lack of sufficient oxidizing agents is as pro- 
ductive of these faults as an insufficient temperature to effect per- 
fect fusion. Laxity in the mixture of materials of unequal den- 
sity, especially lead, produces cords and striae (the density of lead 
glass is a source of constant trouble). The denser portions of the 
silicates have a tendency to separate themselves, producing strati- 
fication; hence it is very important to secure a thorough admix- 
ture of materials. The density of lead is far in excess of that of 
potash and the other alkaline bases. 

The presence of alumina also inculcates cords, stones, etc. 
Alumina may be present in the batch purposely, or brought by 
accident from the walls of the pot. Alumina is very refractory 
and difficult to fuse. The incessant action of the fluxes (and other 
materials, especially cryolite), upon the walls of the pot or fur- 
nace, attacks them until they become corroded and full of in- 
dentations. The particles of clay and alumina thus torn down are 
deposited in the glass as stones, striae, etc. ; besides portions of the 
raw materials collect in these small holes or indentations, and are 
not exposed to the direct action of the fluxes, which leaves them 
crude and semi-fused. As the glass is worked below these places, 
the semi-fluid substance they contain is drawn out and distributes 
itself over the surface of the glass. For this reason it is difficult 
to produce glass free from cords in an old or worn pot. 

Glass remaining at the bottom of the pots any length of time, 
increases in specific gravity, and becomes infected with cords and 
stones, by the accumulation of the denser impurities being con- 
tinually deposited therein. Glass should never be allowed to re- 
main thus any length of time, but should be ladled into water, 
which in a measure ^disintegrates the mass into small particles, 
which present more surface to the action of the flux when next 
melted, and facilitates the removal of the faults. 

The above presents in a general way, the principal agencies 
whereby these faults originate. The most effective remedy, as 
with other faults, is to remove the cause. But inasmuch as the 
causes are numerous, and one or more always present, an entire 
elimination is very difficult. Pure materials, well manipulated, 
and such remedies as are productive of violent agitation, are ef- 


fective in. expelling and destroying them. The use of rings or 
"floaters" in pots and furnaces is recommended, as they displace 
but little glass, and while they do not prevent these faults, they 
serve to keep them out of the way while better glass is being re- 
moved. But when the action of the fluxes begins to corrode them 
they must be replaced with new ones, else they become fault mak- 
ers themselves. Bone ash, arsenic, antimony, or borax, incorpo- 
rated in small quantities with the batch have been recommended 
to facilitate the removal of cords, stones, striae, etc., by oxida- 



While perhaps the construction and maintenance of furnaces 
and like appliances, does not as a rule, fall under the direct prov- 
ince of the glassmaker, yet there are but few processes connect- 
ed with the manufacture of glass, which are not directly or indi- 
rectly dependent upon the influences of heat ; and the various 
characteristics of glass — to say nothing of its formation — are so 
effectively modified by its influences, that heat, its generation, and 
application, requires more than a glassmaker's transient atten- 
tion. In this connection the furnace performs an absolute and 
important part. 

The word "furnace" is elastic, and can be properly applied to 
a number of varied structures contingent to the industry. But 
the categorical definition of a furnace is applied more directly to 
the structure in which the raw materials are fused by heat into 
glass, and is so considered. For obvious reasons we must eschew 
more or less, all data pertaining to the furnaces of the ancients, 
and confine the following to those of more modern times. 

The modern glass-melting furnace is simply a modified form 
of the reverberatory furnace, which statement implies that the 
materials to be melted are exposed to the action of the flame, but 
not to the contact of the burning fuel. While various modifica- 
tions exist, yet modern furnaces <may be divided into two general 
classes, viz.: Pot furnaces and tank furnaces. Pot furnaces are 
constructed to assume different shapes, viz. : For window, plate, 
or bottle glass, they are built either square or oblong. For flint 
glass they are built round or oval. Tank furnaces are construct- 
ed to give either continuous or intermittent results without the 
use of pots, and may be of different shapes, but an oblong shape 
usually prevails. Both classes of furnaces are built to consume 
fuel by its direct introduction into the furnace, or by indirect 


combustion by effecting the generation of combustible gases in a 
separate apartment, and conducting them to the furnace proper 
for final and effective combustion. 

The ordinary direct-fired furnace may be said to Consist of 
two parts: The combustion chamber, and the draft passage or 
"cave." These two parts are separated by the grate, and "siege, v 
or -'bench." The grate may be round or square, dependent upon 
the shape of the furnace, and contains the fuel, which can be in- 
troduced from one or more openings termed "tease-holes." The 
grate generally occupies the center of the furnace, being sunk 
below the "bench" a few feet, and is connected with the combus- 
tion chamber by a walled cavity termed the "eye," into which the 
fuel is placed. The "siege" constitutes the raised bench-like por- 
tion of the combustion chamber upon which the pots are placed. 
The "cave" is an arched passage beneath the furnace for the ad- 
mission of air to the grate. Very frequently two caves are built, 
which cross at right angles beneath the grate, which facilitates the 
admission of air from all directions. 

The number of pots in a furnace vary from four to eighteen, 
and are reached for working or charging by a small arched open- 
ing, or "working hole," situated directly over each pot ; except in 
a flint furnace where covered pots are used, in which case the 
mouth of the pot is exposed on the outside of the furnace walls. 
The combustion chamber is surmounted bv a low flattened arch 
for the purpose of reverberating the flame and compressing it to 
intensity. For this reason the arch should be as low and flat as 
possible. The flame after reverberating is led to the exterior by 
means of flues, or small chimneys, constructed in or against the 
sides of the furnace. In the style of furnace used for window, plate 
or bottle glass, frequently no flues are used, the products of com- 
bustion making their exit through the working holes; the prime 
object of flues being to draw the flame completely over and 
around the pots, and thus aid reverberation. Besides, a flint glass 
furnace has no other exit for the products of combustion than the 
flues supplied to each pot. As it is essential that all flues should be 
kept clean, provision is made for the purpose. It was frequently 
the custom in earlier days to construct a furnace with two arches, 
one above the other ; the lower one constituted the reverberatory 
arch and the upper one the top of the furnace. The products of 
combustion congregated in the space between the arches and es- 
caped through a common flue in the top one. This space between 
the arches was also used sometimes for numerous purposes requit- 
ing heat. Again, instead of the top arch, the outside walls of the 
furnace are continued in the form of a truncated cone, or open 
chimney. In other cases the flues discharged their contents into 
the glass-house itself. 


In all cases a necessary draught is required to properly con- 
sume the fuel; hence different construction of furnace tops, or 
stacks, is necessary, according to fuel employed, draught being 
that action due to the difference in weight between the column of 
hot gases in the stack, and a column of air of equal height and 
area at the temperature of the atmosphere. Thus draught de- 
pends upon the difference in temperature of the gases within, and 
the air without, and the height of the stack. As we have re- 
marked, different fuels require different draughts, and after a 
height sufficient to produce the required draught is obtained all 
additional height of stack is a waste of money. This general de- 
scription is applicable more or less to all direct-fired furnaces. All 
efforts toward dimensions of furnaces are avoided here, as the va- 
riation is such as to exclude anything definite. 

Gas furnaces consist of two principal parts, viz. : combustion 
chamber and producer. Tank furnaces are constructed along 
similar lines, inasmuch as gas is the most effective fuel, and is 
generally used, although other fuels, as oil, are used to some ex- 
tent. The principle involved in a tank furnace is the entire aban- 
donment of pots. But it is not our purpose to enter into any 
general discussion of the various tank furnaces, but to simply out- 
line the more important principles involved. 

Owing to the time occupied in melting the materials for glass 
under the pot system, various experiments were made towards 
effecting a plan to melt and blow continuously, without adding to 
the cost, or affecting the quality of the glass. M. Chamblant de- 
vised a pot with a crooked pipe. Bontemps also mentions a pot 
with a partition. Siemens devised a pot with three apartments, 
and by demonstrating the feasibility of melting and blowing con- 
tinuously, these experiments led to the development of the con- 
tinuous tank furnace. The principle of the tank as specified by 
Dr. Siemens in 1872, was a long tank about four feet deep, with a 
semi-circular end, and divided by two transverse floating bridges, 
into three apartments, viz.: melting, refining and working. In 
some instances the floating bridges are dispensed with, as the ac- 
tion of the heat and glass disintegrates and destroys them, and a 
refining vessel ring haa been substituted opposite each working 
hole. This vessel gathers the melted glass at the lowest possible 
depth in the tank and raises it continuously to the surface, in a 
compartment prepared for the purpose, completely refined. 
These vessels vary in shape and style, and can be removed and re- 
placed when worn. To obviate the action of the materials used in 
the production of glass upon the brick and clay construction, Dr. 
Siemens devised a series of air passages, which kept the glass 
chilled along the walls and bottom and protected the parts ex- 


There are many advantages resulting from the use of a con- 
tinuous melting tank furnace; the principal reasons may be given 
as follows : Increased production, economy in working, dura- 
bility of furnace, regularity of working, and improvement in qual- 
ity of the glass. 

The success achieved by continuous melting tanks in making 
window glass led to successful efforts in the construction of small 
intermittent (commonly called "night melting" or "day") tanks. 
The greatest obstacle, however, has been the maintenance of 
color, caused by the glass melting principally from the top, leaving 
the bottom glass less fluid and more refractory. But the past dec- 
ade has rapidly developed the intermittent tank^ until at the pres- 
ent day a very fair grade of so-called flint glass is in many cases 
being produced. With these small tanks, gas fuel probably pro- 
duces the best results, but oil is being introduced as a fuel, with a 
marked degree of success. Coal is not often used as a fuel by di- 
rect firing for the better grades of glass, but can be used in* con- 
nection with super-heated air. One patent in this direction pro- 
vides for the air being heated in a cast iron chamber by radiated 
heat from the fire-box, or furnace, and is then conveyed in pipes 
to a point where the flame passes over the "bridge" wall, where it 
combines with the gases from the coal, and facilitates combustion 
in a very effective manner. The products of combustion, after 
travelling the length of the melting compartment, pass off through 
a stack at the end of the tank. 

In the construction of any furnace four general principles ap- 
ply, viz.: Intensity of the heat obtainable; regularity in mainte- 
nance of this heat; durability of parts exposed thereto; and econ- 
omy of fuel producing same. Upon the intensity of the heat de- 
pends the uniformity of the melt and homogeneity of the glass. 
The regularity of the heat actuates those influences which deter- 
mine the quality of the glass, as but slight variations of the ten> 
perature impair homogeneity and produce stratification. The 
durability of the furnace depends upon the stability of materials 
and construction. Where the furnace contains open pots, or is a 
tank, and the interior of the furnace is exposed to the higher de- 
grees of heat obtainable with gaseous fuel, clay brick, especially 
in the crown, are affected and the semi-fused matter drops into 
the glass, producing impurities. This defect is largely obviated 
by the use of brick and materials composed principally of silica, 
which are absolutely infusible if kept from contact with alkalies 
and other substances which would act as a flux. Economy of fuel 
is principally dependent upon the constrcution of the furnace and 
the methods of combustion. 

While tank furnaces are gradually gaining favor, they have by 
no means replaced the pot furnace in glassmaking. Yet the di- 
rect-fired furnace is slowly giving place to modifications which 


propagate economy in construction, fuel and heat. The applica- 
tion of artificial gas as a fuel is one of the most important im- 
provements in modern glassmaking. To say nothing of economy 
in fuel — and the possibility of the use of cheaper fuel — permitted 
by a gas furnace, the time of melting is reduced, production in- 
creased, and the product vastly improved. 

The so-called "deep eye" furnaces are modifications of the di- 
rect coal fired furnace, but are constructed with a view to facili- 
tate combustion by effectively combining air (generally super- 
heated) with the gases arising from the fuel, at or near the point 
of entrance into the furnace or combustion chamber. This com- 
bination is generally effected by a series of small flues around the 
"eye" near the top. 

The fact that combustion is facilitated by the introduction of 
super-heated air with the gaseous matter imparted by coal, at or 
near the point of ignition, was sucessfully demonstrated by Dr. 
Siemens when he introduced his producer and regenerative pro- 
cess and the Siemens gas furnace was the first successful one used. 
In this, as in other forms of gas furnaces (except natural gas), the 
solid fuel is first converted into a combustible gas in a "producer" 
outside of the furnace, and then burned in connection with heated 
air. Dr. Siemens was the first to apply the regenerative system to 
the pot furnace, the principle and construction of which was 
changed only so far as was necessary to apply the regenerative 
principle. The novelty of the Siemens process consisted in 
taking up the heat usually wasted and utilizing it to raise 
the elements of combustion formed by the producer to a 
high degree of temperature before ignition, by heating the 
gas and air employed in separate regenerative chambers heated 
by waste heat from the flame. These "regenerators" com- 
prised four chambers filled with fire brick, stacked loosely in 
checkerwork. The gas from the producer, passing through one 
chamber, and a current of air through another, meet and unite just 
before entering the furnace. These two chambers have been heat- 
ed to a high temperature prior by the escape of waste gases 
through them ; hence gases and air are brought to a high tem- 
perature during their passage through them, and readily ignite at 
their entrance to the furnace. The action is then reversed, and 
the gases and air pass through the second pair of chambers, while 
the waste gases reheat the first pair, and prepare them for again 
performing their functions when their turn comes. This alterna- 
tion occurs about every twenty or thirty minutes. 

The old style direct-fired furnace was a very simple affair. 
Ingram's furnace was intermediate between the direct-fired fur- 
nace and the gas furnace. Boetius' furnace was a forerunner of the 
Ingram furnace, and was perhaps the beginning of the resultant 
outcrop of "deep eye" furnaces. The so-called Gill furnace is 


an improvement upon the principle of the Boetius furnace, and 
has flues arranged to convey the air to the combustible gases 
evolved from the fuel. Direct-fired furnaces can be remodelled to 
this style, which claims economy in construction, fuel and pots, 
and insures an intense heat. The Nicholson furnace is an im- 
proved form of a French furnace, but differs from the Siemens fur- 
nace in not having the alternate regenerators. 

Innumerable improvements have been devised in furnace- 
building in late years, a recent instance being a furnace patented 
in Germany, which provides for the special heating and regulation 
of the temperature at will for each single pot, by the* burning gas 
entering the furnace at the center as in the old system. But for 
the uniform heating of the pots on all sides, or for the special heat- 
ing of any single pot, there are additional gas channels provided, 
which are met by air channels shortly before their entrance into 
the interior of the furnace. These additional gas channels are fed 
from a joint channel, which runs from the producers along each 
side of the furnace, gas and air supply being regulated by slide 

Furnace construction in Germany and Belgium is far in ad- 
vance of the art in our own country, andAmerican furnace builders 
so far seem content in copying the approved models of European 


The fuel used in the early glass-houses was wood, which was 
dried, or baked, until it was brown, to expel all moisture before 
using. Even in some countries at the present day wood, turf and 
peat are extensively used. The use of coal is by no means a re- 
cent invention, as it was in use during the time of Agricola. But 
the smoke and by-products of coal have always been a serious ob- 
jection, especially where the materials to be melted are exposed to 
the direct action of the flame by contact, as in tanks or open pots. 
Hence for a time wood was preferred. Oven-burned coke has 
been largely used in England to an advantage, and was especially 
recommended in the manufacture of the finer glasses on account 
of its freedom from soot, smoke and by-products. In this country 
, wood was used as late as 1865, but since that time coal has been 
used almost exclusively, until the discovery and application of nat- 
ural gas as a fuel ; but the gradual decline of this fuel has neces- 
sitated and developed other cheap fuels, as artificial or. producer 
gas, oils, etc. 

Fuels and their economic combustion constitute an import- 
ant issue industrially, more especially in the manufacture of glass. 
This, and the efficacious application of the resultant heat, should 
be a thoroughly familiar subject to the practical glassmaker. 


Heat is obtained by the combustion of fuel. Every fuel — wood, 
coal, oil or gas, contains a certain number of heat units which 
are given out by combustion, and no more heat can be obtained 
• from any given fuel than the number of heat units contained in 
it, which will be the same under all conditions, whether combus- 
tion is slow or rapid, or at a high or low temperature. A heat 
unit is reckoned by the amount of heat necessary to raise the tem- 
perature of a unit quantity of water one degree Centigrade. This 
is taken as unity, and the amount of heat necessary to raise the 
temperature of a unit quantity of other substances one degree, is 
expressed in terms of the amount necessary to raise the tempera- 
ture of water one degree. This relation is called the specific heat 
of a substance, thus — if the specific heat of water is I (one), alcohol 
only requires seven-tenths as much heat to raise its temperature 
one degree, hence it has a specific heat of 0.7. 

The heat units set free by the combustion of a fuel are ex- 
pended in two ways : First, by radiation, and being carried off 
by the hot gases passing up the stack. Second, absorbed by the 
surface to be heated. All things considered the loss by radiation 
is proportionate to the time occupied by combustion, hence it is 
economy to burn fuel quickly. 

As a general fuel, coal probably takes precedence over all 
others. In burning one pound of the average dried coal there 
is consumed about 2.45 pounds of oxygen, and 10.7 pounds, or 
140 cubic feet of air at 62 ° F, by which there is given off about 
14,700 heat units. Coal may be arranged in five classes, viz. : 

I. Anthracite, consisting almost entirely of free carbon. 

II. Dry bituminous coal, containing 70 to 80 per cent, car- 

III. Bituminous coking coal, containing 50 to 60 per cent, 

IV. Long flaming or cannel coal, containing 70 to 85 per 
cent, carbon. 

V. Lignite or brown coal, containing 56 to 76 per cent, car- 

There are two conditions on which the economy of combus- 
tion of any fuel depends: The method of firing and the supply 
of air. Bear in mind the fact that the object is to set free the 
entire amount of heat available, and in such a manner that the 
surfaces to be heated will most readily absorb it. As oxygen is 
the chief supporter of all ordinary phenomena of combustion, the 
combustion of a substance consists in the addition of sufficient 
oxygen to oxidize the substance. A combustible requires in the 
first place, to be heated to a certain degree before it will attract 
and combine with the oxygen from the atmosphere with sufficient 
force to emit heat. But as the temperature is elevated by the con- 


tinued absorption of oxygen, the combination of one portion of 
oxygen with the burning body causes the absorption of another. 
But different substances require different amounts of oxygen to 
oxidize them. Thus carbon requires two atoms of oxygen to one 
of carbon, and in burning any substance which is largely carbon, as 
coal, there must be an ample air supply from which sufficient oxy- 
gen can be extracted to completely consume the substance, 
Smoke is an evidence of incomplete combustion, but there may 
also be incomplete combustion when there is no smoke. 

Two forms of carbon are found in coal, one fixed, and an- 
other in a volatile or gaseous state. The volatile carbon is gen- 
erally combined with hydrogen, forming the so-called hydro-car- 
bons, which are readily given off upon the application of heat to 
the coal, and unless these gases are thoroughly mixed with air, 
and kept with it at a high temperature they are not consumed and 
escape up the stack as smoke. This is illustrated when a fresh 
supply of coal is added to the fire. There must always be suffi- 
cient air present to properly combine with these gases, or their 
combustion is not complete. Further than this, where there is a 
lack of oxygen the carbon, only partially oxidized, passes off as 
vapor, which when it comes in contact with a cold surface, or air, 
is condensed and partially reduced, forming black smoke. A 
thick bed of fuel furnishes another cause for incomplete com- 
bustion by allowing the oxygen in the air as it passes through 
.the heated fuel to combine with the carbon in unequal propor- 
tions. Ordinarily with sufficient air it is combined as one of car- 
bon to two of oxygen (C0 2 ). But if it is required to pass through 
too much hot fuel it absorbs more carbon and becomes CO, and 
if the air is not sufficient to allow it to take up another portion of 
oxygen and again become C0 2 , it will escape imperfectly 
consumed, as the carbon is only half oxidized. The quantity 
of air required varies with the fuel, furnace and method of 
firing, and becomes less in proportion as the temperature of the 
furnace and rate of combustion is increased. It may be well to 
mention that on account of the volatile matter which forms a part 
of some coals, provision should be made for the admission of air 
above the grates to aid in the consumption of the partially con- 
sumed gases given off by the coal. 

One ton of Pittsburg coal contains about 10,000 cubic feet 
of gas, 12 to 14 gallons of tar, and about 1,350 pounds of 
fixed carbon, and the heat units contained in it equal the heat 
units in about 200 gallons of Lima oil. 

The class of fuel always affects the design of the grate, as a 
clinkering coal, for instance," requires large air spaces ; a small, 
dry coal, small air spaces. There are different methods of firing 
coal; as that of spreading — when the coal is spread over the en- 


tire grate surface at one firing, which permits the escape of all 
volatile gases until the entire mass is ignited, and the flames rise 
above the coal. Another method is that of coking, by laying a 
bed of coal where it will be allowed to coke, when, after coking, 
it is pushed forward, upon the bed of incandescent coals and an- 
other bed of "green" coal is put in its place. This method keeps 
the bed of fire on the grate bright and incandescent, and allows 
the volatile gases which the heat causes the "green" coal to give 
off, to be led over the incandescent mass and be thoroughly con- 
sumed. Bituminous coals whose fractures show whitish films or 
rusty stains should be avoided, as they indicate the presence of 
sulphur and pyrites in the coal. 

We give herewith a table of some of the domestic coals : 












Nebraska . . . . 

New Mexico 








West Virginia 























































• ••••• ••••• ••• 








Pocohontas Field.. 


Natural gas needs no process to make it merchantable or 
valuable as an industrial fuel. The calorific value of natural gas 
as compared to artificial gases is generally quite high, and bulk 
for bulk it is one-third greater than enriched water gas. By a 
series of tests, Prof. F. C. Phillips, of the Western University, 
Allegheny, Pa., determined the heat units in 1,000 cubic feet of 
average quality natural gas to be 1,164,030 (British heat units). 
The specific gravity of natural gas varies from 0.55 to 0.60, as 
compared to dry air at 6o° F. The composition of nearly all 
natural gas closely resembles Marsh gas, CH 4 , and 85 to 98 per 
cent, of the whole is nearly equivalent to Methane, or Marsh gas 
(75 P er cent, of carbon and 25 per cent, of hydrogen). 


We give herewith two analyses of natural gas which will be 
sufficient to illustrate the general composition: 

Analysis of Natural Gas from Pennsylvania: 

Oxygen, (O) trace 

Nitrogen, (N) 9-54% 

Carbon di-oxide, (CQ 2 ) 0.41% 

Marsh gas, (CH 4 ) 90.05% 

Analysis of Natural Gas from Findlay, Ohio: 

Hydrogen, (H) 1.64% 

Marsh gas, (CH 4 ) 93-35% 

defiant gas, (C 2 H ) 0.35% 

Carbonic oxide, 0.41 % 

Carbonic acid, 0.25% 

Nitrogen, 3.41 % 

Oxygen, 0.39% 

Sulphureted Hydrogen, (H 2 S) 0.20% 

The amount of air required to consume 1,000 cubic feet of 
natural gas is slightly less than 11,000 cubic feet, or about one 
part of gas to 1 1 parts of air ; practically 1 to 10 gives good re- 
sults. Natural gas is undoubtedly an ideal fuel, but, in most 
districts it is fast diminishing, and is either 'gilt-edged" in price, or 
is so erratic and uncertain in its supply as to cause the manufac- 
turer much annoyance and loss. Hence those who adopted it as 
a fuel, as well as those who have felt its influences in competition, 
have sought an economic fuel to replace it. The nearest ap- 
proach to it as an industrial fuel is artificial gas, which for prac- 
tical, economical results and stability has all its advantages, and 
without doubt "producer gas" generated from bituminous coal in 
any standard gas producer is beyond question the best form of fuel 
yet instituted in the glass industry, as the economy of fuel is not 
only great, but the heat produced is intense and shows a direct 
saving in fuel of never less than 30 per cent., and often as high as 
75 per cent. 

The principle applied to a producer is as follows : The fuel 
is supplied at intervals through charging boxes, and descends 
gradually on an inclined plane set at an inclination to suit the 
fuel, until it reaches an open grate formed of flat horizontal steps, 
where the fuel is converted into a combustible gas which passes 
off through an "up-take" to the furnace. The production of 
combustible gases varies with the admission of air, and the process 
of gasifying the fuel occurs by the fuel becoming heated as it de- 
scends, when the hydro-carbon gases, water, carbonic acid and 
ammonia are evolved, which leaves about 60 to 70 per cent, of 
carbonaceous matter which is disposed of by the action of a cur- 



rent of air slowly entering through the grate, producing combus- 
tion in a regular manner upon the grate. Carbonic acid is a re- 
sult, which passes through the incandescent fuel where it absorbs 
another equivalent of carbon and becomes carbonic oxide, which 
is a combustible gas, and is incorporated with the other combusti- 
ble gases already evolved. Water is sometimes utilized by being 
brought to the foot of the grate, where it absorbs spare heat from 
the fire and ashes which converts it into steam, and as the steam 
passes through the incandescent fuel it is decomposed into its ele- 
ments, after performing its useful function by disintegrating the 

For many years producer gas has been utilized as a fuel under 
the regenerative system of Dr. Siemens, but for a long time it 
was a question apart from economy whether it was possible to 
use producer gas direct, and some of our most learned theorists 
decided that its direct use was impracticable. But it has been 
practically demonstrated that it can be, and is used direct with- 
out any connection with the regenerative process in furnaces, 
glory-holes, lehrs, and even under the boiler for generating steam. 
There are a variety of producers, which are all, however, modifica- 
tions of the same general principle, the prime object in all cases 
being to convert with the greatest economy, a given amount of 
fuel into combustible gases. Steam is sometimes used as an aux- 
iliary agent, but where steaim is used it is important to have the 
coking chamber of sufficient size to insure an economical con- 
version into gases, otherwise the application of steam becomes 
void as an improvement, as by some small producers not over 60 
per cent, of the coal is converted into combustible gases. Steam 
and air forced through a grate become converted into fixed gases 
when compelled to pass through a large body of incandescent coal 
in a coked condition, and as these gases (CO and H) come in 
contact with the fresh fuel on top of the coked portion, they drive 
off the volatile matter contained in the coal which mixes with the 
fixed gases generated by the coke. As has been said above, in 
some producers water is used as a seal around the base, which 
minimizes the loss of heat in the ashes by radiation, escape of 
heat and air up the sides, equalizes the draught, and utilizes the 
waste heat from the ashes in the generation of a steam vapor 
which rises through the fuel and softens the ash, disintegrates 
and prevents clinkers, and with its hydrogen and oxygen, after 
gasification, enriches the gas. 

During the past decade various schemes for utilizing cer- 
tain oils as fuel have been tried with indifferent success, from the 
fact that most of them were with crude petroleum, and re- 
quired a more or less complicated system of burners for gen- 
erating gases, or producing combustion in some other com- 
plicated manner. One of the most successful methods intro- 


duced is to use the cheap heavy oil of 34 to 40 specific grav- 
ity, which is more or less a refinery by-product. This oil 
generates immense heat energy, and can be successfully and 
economically burned in connection with an air pressure of 
from 2 to 7 ounces per square inch. This air meets the 
flow of the oil at the end of the burner and completely atom- 
izes it in a spray, furnishing just sufficient oxygen to perfect 
combustion. As a clean fuel, oil highly recommends itself, and 
petroleum residues have a high calorific value by being rich in 
carbon and of perfect safety. Their fire test is at least 200 F. and 
about 65 per cent, of their heat is effective as against 60 per cent, 
of coal. 

Benzine is another oil fuel used largely in certain branches 
of the glass industry. While perhaps the first cost makes ben- 
zine a trifle expensive, yet it is especially adapted as a fuel for 
"glory holes," particularly in the manufacture of bottles. It 
can be burned very successfully by means of a suitable simple 
burner, producing an effective, regular, uniform heat, and re- 
quires but little attentio n. 

Fire Clays. 

Their Preparation, Use for Pots, Etc. 

The clay adapted to use for pots should be as pure as pos- 
sible and very refractory, breaking with a clear, smooth, bright 
fracture, unctuous to the touch, free from lime and sulphide of 
calcium, the least iron possible being most desirable, Heretofore 
the German clays have been largely employed in this country, 
as the American clay when first used did not give the satisfac- 
tion that its analysis would indicate, but skill in its preparation 
has demonstrated its value and it is rapidly taking the place of 
the imported clays. There are large deposits of excellent pot 
clays in many localities in this country, the chief supply being 
derived, however, from Pennsylvania, Missouri and New Jersey. 
Missouri plastic clays are probably the most important of Ameri- 
can clays. They occur geologically in the coal measures under 
the seams of coal, and show a shrinkage of from two to nine per 
cent, in burning. Their fusibility ranges from 2500 to 2800 . 
Missouri clay is purer than the German clay, and is more refrac- 
tory, but not as dense, and it is found by experience that it will 
stand a more intense heat than any other clay, but German clay 
resists the action of the fluxes better. Hence the German and 
American clays are frequently mixed to overcome as much as pos- 
sible, the two difficulties. 

After clay is mined it is exposed to the disintegrating ac- 
tion of the weather for a considerable period. While the ac- 
tual effects of the weather are not definitely understood, yet the 
plasticity of fire clay is considerably augmented by the process of 


"weathering," as it is known, that organic matter is eliminated by 
oxidation, and the particles of clay disintegrated by moisture and 
frost. After being weathered sufficiently, it must be dried well 
and stored in a dry place. When it is perfectly dry the outside 
crust must be removed, and the lumps picked to pieces, and all 
substances, as pyrites, or bluish portions removed. The clay must 
then be ground, and carefully sieved, to eliminate all impurities, 
and the greatest care and cleanliness exercised in its manipula- 
tion, as even the fibre off a sack would spoil a pot. 

Regarding the selection and adaptability of a clay, Mr. H. 
J. Powell gives the theoretical composition of pure fire clay as : 
A1 2 3 , 2SiO a , 2H 2 0. In selecting clays for exposure to fire 
it must be understood that infusibility, stability and plasticity are 
important qualities. The infusibility increases with an increased 
proportion of silica, augmented by alumina, and diminishes with 
the increased proportion of the other constituents. Or in other 
words, as the fusible constituents rise above a certain proportion, 
the clay can be fused into glass. The color of unburned clay is 
hardly a criterion as to the quality, as it is often deceptive. Lime 
and magnesia oxides, especially in increased proportion, impart a 
whiteness in color, and again the color of the oxide of iron is of- 
ten concealed in unburned clay by the presence of organic matter, 
but is revealed by the action of heat. The investigation of a clay 
must include an examination of its physical properties, the per- 
centage of clay base, the determination of plasticity, amount of 
water required to make a plastic mass, the tensile strength, shrink- 
age in drying and burning, vitrification, viscosity, etc., etc. It 
is assumed that plasticity is due to the interlocking of the par- 
ticles, and that its tensile strength when dry, is an index of its plas- 
ticity when wet. That plasticity varies with the size of the grains, 
is demonstrated by the following series of tests : 

Tests of tensile strength of clays in different grades of fine- 

Per cent. 
Size of Per cent. Tensile strength 

mesh. water used. Maximum.Average. Plasticity ratio 

20 — 18.0 190 142 100 

20 — 40 19.3 196 182 103 

40 — 50 20.4 182 172 96 

70 — 100 17.5 183 176 96 

100 and smaller 78.6 143 135 71 


As a simple and practical test for fire clay, Mr. H. J. Powell, 
recommends the formation of the sample into a brick ; then 
break the brick into two pieces, and expose one piece to any re- 
quired heat to be burnt, while the other piece is retained for 
comparison. If the clay is of good quality the burnt piece will be 


white in color, and the fractured ends of the burnt and unburnt 
pieces will fit exactly. 

The simple use of a good quality of fire clay does not insure 
the quality of the pots made from it, as certain conditions are in- 
volved which must always be considered, viz. : The preparation 
of the clay, and the proportion of raw and burnt materials in the 
mixture; the judicious manipulation by the pot-maker; the 
method and manner of drying the pot; its annealing; the tempera- 
ture of the furnace; and the kind of glass to be melted. Possibly 
no two manufacturers prefer the same clay, or use the same pro- 
portion in their mixture, and when a manufacturer establishes a 
standard, there is rarely any deviation therefrom, for the obvious 
reason that experiments with pots are expensive. But where the 
value of a good clay is known, the result is, under proper condi- 
tions, as a rule good. 

There are several things necessary to be ascertained regard- 
ing the serviceability of clays, before any definite result can be an- 
ticipated, namely: The ratio of contraction by air and fire; the 
resistance to change in temperature ; the resistance to chemical in- 
fluences; and last, the proper proportion in mixture with other 
ingredients. These features can only be ascertained by test, analy- 
sis and synthesis; analysis to determine the elements of the 
original compound, and to ascertain those constituents requisite, 
that by synthesis, a compound definite in results may be formed. 
The analysis of a clay does not present any definite factors, but 
rather a maze of elements which must be separated into the anato- 
my of a structure ; for instance, the percentage of the plastic ele- 
ment — the true clay substance — must be determined, this rep- 
resents the muscle; the percentage of fusible material which 
melts when exposed to heat, and binds the particles together, 
this represents the binding tissue; and then the percentage of 
quartz, or flint, the skeleton. This resolves a clay into simple fac- 
tors, by which a pot-maker can determine whether the skeleton 
has strength, the binding tissue is sufficient, the plasticity — or 
muscle — excessive, or insufficient, and thus he can readily deter- 
mine the character of the mixture he will have to make. 

Regarding the mixture of clays, it is important that the raw 
clay be finely ground and sieved to insure plasticity, as pots made 
from plastic clay are quite as durable, and resist chemical action ; 
but the more plastic the clay, the more it is exposed to contrac- 
tion. Hence to obviate this, the plasticity or "fatness" of the 
clay is made less by the addition of coarser-grained burnt clay 
powder (chamotte), or ground pot scrap. These materials are 
called "leaners," and serve to bind the clay and heighten the resist- 
ance to sudden changes in temperature, by facilitating the escape 
of the water contained in the clay, during the drying process, as 


well as that of the chemically combined water, during the anneal- 
ing and burning of the pots. In making this mixture for pots, 
it is customary to use either eight parts, by volume, of finely 
ground burnt clay, and seven parts of pulverized raw clay, or four 
parts of finely ground burnt clay, three parts of finely ground 
pot-scrap, and six parts of pulverized raw clay. But the propor- 
tion in which clays are mixed is riot the same in all glass houses, 
as it is always to be considered whether a "fat," or meagre com- 
position is desired. Many pot-makers consider it inadvisable to 
mix in pot shell, or different clays, using the same grade of clay 
for raw, or burnt portions. When raw clay is used for the pro- 
duction of burnt clay powder, it is formed into cakes several inch- 
es thick, which are stacked loosely in an oven, allowing for the 
free circulation of heat, and uniformly roasted to remove all or- 
ganic matter, using great care in the regulation of the heat to 
prevent glazing on the clay. These cakes are then ground to a 
powder, as the size of the grain is very important, for plasticity 
and density increase with fineness, and contraction is propor- 
tionate and increases with density. Hence, while the finely 
powdered material improves the value of the pot in one direction, 
it is detrimental in another, as it increases the sensitiveness of the 
product to any change in temperature. This defect is partially 
avoided by using the "leaner," or chamotte, in a proportion of 
one-half coarse grained, and the other half powdered. This pow- 
der fills out the spaces between the larger grains, and acts as a 
binding agent, and supports resistance to change in temperature. 
While contraction is counteracted by the proportionate use of 
burnt clay, yet loss of plasticity and strength of materials vary 
accordingly, and, as a thin walled pot is efficient in melting glass, 
it is not wise to sacrifice plasticity to prevent contraction ; be- 
sides the pot is exposed to strong internal pressure, and disinte- 
grating agencies requiring resistance, hence strength is essential, 
and the injurious effects of contraction can be almost entirely 
eliminated by prudence and care in drying and burning the pots. 
In materials for furnace construction, where contraction is to be 
strictly avoided, "lean" mixtures are entirely necessary. 

After the clays which enter the composition have been care- 
fully sieved and prepared, they are measured into a lead or zinc- 
lined trough and are thoroughly mixed (dry), after which they are 
wetted with just sufficient pure, clean, lukewarm water to permit 
the thorough kneading of the mass, avoiding any excess of wa- 
ter, as an excess causes cracks and increases the shrinkage of the 
pots. This mass is called the "batch," and after being wetted 
it is allowed to stand a couple of days before kneading. The 
kneading may be acomplished by the artificial mastication of the 
mass in a "pug-mill," but the primitive method of "treading" con- 
stitutes the general process. This consists in tramping the mass 


little by littie with the bare feet, as it was commonly supposed 
that the warmth, elasticity and sensibility of the naked feet, de- 
velop the plasticity of the clay in a manner not equalled by me- 
chanical means. This operation is repeated several times at in- 
tervals of about thirty-six hours, by which means the materials of 
the batch are effectively bonded together, and all air bubbles, 
which would cause cracks in the drying process, are worked out. 
As another precaution, the material is formed into cakes which 
are thoroughly beaten, and a perfectly dense material is the re- 

The pot is modeled upon a board or stone, covered with gran- 
ulated pot shell or burnt clay, and after being finished, it must 
stand quietly in the place where it was made to avoid shaking 
until such time as it can be moved with safety. Care must 
be taken to continue the drying in such a uniform manner as will 
insure that the walls, top and bottom, dry in imison. This can be 
accomplished By covering the pot with linen, and maintaining 
a uniform temperature not exceeding 65 °, during the first stages 
of the drying process. In the pot room all draught must be ex- 
cluded, as the slightest draught causes fire cracks ; even the di- 
rect rays of the sun should be excluded. 

After the pot is sufficiently dry so that it can be moved with 
safety, it is advisable to place it upon a drying frame, and in a 
room where a temperature of about 90 can be maintained. 
The period of drying depends chiefly upon the size of the pot, 
and the time varies from four to twelve months. Too much can- 
not be said regarding the exercise of care and prudence in temper- 
ing the pots in the pot-arch, and their transfer to the furnace. 
The time occupied in tempering varies from four to seven days, 
and the result of this process adds or detracts much to or from 
the average life of a pot. Equal care must be exercised when the 
pots are tempered direct in the furnace, as is the custom with many 
manufacturers, especially at the beginning of a season. 

Pots are exposed to three dangers : Actual weight of melt- 
ed glass ; intense and prolonged heat ; and the corrosion of raw 
materials within the pot. As the strength and resistance of the 
pot depends upon the materials from which it is made, their ma- 
nipulation, and the care with w 7 hich it has been tempered and 
"placed," the first two Mangers are proportionate thereto. The 
internal corrosion is also augmented or resisted by like conditions, 
but can be at least retarded by "glazing," which consists in par- 
tially filling the pot with clean glass cullet, free from any flux, 
which, after it melts, is spread over the interior surface of the pot; 
this imparts to such surface a thin so-called "glaze," which pre- 
vents the deposit of clay from the sides of the pot by retarding 
corrosion. In "glazing" pots intended for the production of "col- 
ors," it is always advisable to use a more refractory glass than that 


which is to be melted in them — a glass highly silicious, and melt- 
ed at a high temperature. Pot-makers also avoid all sharp cor- 
ners, which would facilitate corrosion. Those common faults in 
most glass, "cords," and "stones," are frequently nothing more or 
less than an infusible aluminate formed by the combination of the 
alkaline or metallic ingredients of the glass, with the alumina of 
the pot, torri down by corrosion. Some materials, as lead, cryo- 
lite, etc., are much more severe in attacking the pots than others. 

The life of the pot cannot be predicted, and the breaking of a 
single pot often disturbs the furnace to such an extent, and others 
follow so frequently, that weeks will sometimes elapse before a 
complete reorganization can be effected. The very "wear and 
tear" and exposure of the others while setting one pot, is often 
sufficient to cause excessive breakage among the balance in the 
furnace. There are so many things seemingly unimportant which 
affect the average life of a pot, that it is difficult to define any real 
cause for breakage without involving other causes. Defective 
composition, injudicious handling, improper annealing, "starva- 
tion" by exposure to cold air while in the furnace, variation in fur- 
nace temperature, disintegrating action of corrosive materials, and 
many other causes can be ascribed. One especial precaution is to 
be recommended, that of reheating a pot after being "worked 
out," and before filling it with cold batch. In window glass fur- 
naces the pots as a rule, are all reheated, but in flint furnaces they 
are not. If the pots are closed up for an hour prior to the intro- 
duction of the filling, they become better able to resist the chill- 
ing influences of the cold batch ; besides, the melt begins almost 
immediately, whereas if the pot is chilled, the melt is retarded un- 
til the pot does become properly heated. 

In connction with fire clays we quote the following regard- 
ing some interesting experiments made by Mr. J. D. Pennock, 
to determine the heat, conductivity, expansion and fusibility of 
refractory clays in the form of fire brick ; in which he used those 
made of Grecian Magnesite, American Magnesite, Silica Brick 
and Belgium coke oven tiling. The following table shows their 
conductivity of heat respectively : Grecian, American, Silica 
Brick, and coke oven tiling ; also their respective analyses, spe- 
cific gravity, etc. As silica brick are now so extensively used in 
furnace construction, the following table gives interesting data : 








Per ia" 

S10 2 

Fe 2 8 + 
A1 2 8 




Grecian magnesite . . 

II n 















4 20 




American magnesite.. 
it u 







Coke Oven Tiling. . . . 

41 it 






• • • 



• • • • • • 


The Principles of Annealing as Applied 

to Glass. 

When we say that reliable strength and durability can, at 
present, only be imparted to glass by annealing, we have the entire 
context of the subject before us. 

The process of annealing is a distinct feature of the glass 
industry, yet notwithstanding its importance, there is possibly 
no other feature so little understood. Manufacturers seem gen- 
erally content with the primitive methods that have been hand- 
ed down from generation to generation, without making much 
perceptible effort towards definite improvement of the process, 
except perhaps in fuel. In this direction some advance has been 
made, as well as some improvements in general construction and 
appliances, although these improvements have been brought about 
with a view to facilitate the handling of the generally increased 
factory production, and not, we regret to say, with much regard 
to improvement in the application of the true hypothesis of an- 
nealing and its principles. The opportunities presented by the 
general improvement in fuel, and appliances for generating and 
manipulating heat; the advance in structural material; and the 
economy of modern methods of manufacture, as illustrated by 
other lines of industry, should surely be an incentive to the glass 
manufacturer to leave the foot-worn paths of imitation and en- 
deavor to improve his own methods to meet the demands of mod- 
ern trade. 

Annealing means to heat a substance, like glass, and then al- 
low it to cool gradually. There are at present but two success- 
ful methods of doing this : One by gradually withdrawing the 
glass — after being heated — from the heat ; the other by allowing 
the source of the heat to gradually become extinct. The first is 
applicable generally to "lehrs," and the latter to "ovens." 

From a scientific point of view, the hypothesis of the repulsive 
force between the molecules of a substance when excited by heat, 
is possibly the best explanation of the various phenomena con- 
nected with the cooling of heated glass. The force excited by heat 
has a tendency to cause all bodies to expand, and eventually 
change their condition of aggregation ; the body passing by 
gradual change from a solid to a liquid, and from a liquid to a 
gaseous condition — if continued far enough — as the physical 
pores, the existence of which this hypothesis assumes, increase 
in size by expansion. Therefore if the increase in size of its inter- 
molecular pores causes the liquidity of glass, it is not too much to 
assume that the gradual diminution or decrease in size of these 
same pores will result in the various stages of viscosity, ductility 
and solidity of the same substance. But if the glass is cooled 
rapidly, the outside walls. become intensely solidified, while the 

7 6 

molecules of the interior are withheld from uniting and reducing 
the internal porosity by adhesion to the solidified exterior. This 
difference in condition is aggravated by the poor conductivity of 
heat by glass. While in this condition, the glass is withheld from 
collapse by the intense solidity of its exterior walls. As soon as the 
solidity of these is weakened, disintegration naturally ensues. 
This is generally true of all glass cooled rapidly. On the other 
hand if the glass is allowed to cool gradually there is a gradual 
coalition of its molecules ; its pores become regularly and uni- 
formly closed and diminished in size throughout the entire sub- 
stance, and it acquires regular and reliable strength. 

Practically speaking, during the process of making and fin- 
ishing articles of glass, there is always an unequal chilling and 
contraction of parts, the thinnest parts cooling quickest, and 
the outside walls, on account of exposure to air, and contact with 
"block," "marver," molds or tools, chill and contract more 
than the interior. This creates layers, strata, and general lamina- 
tion of the structure. This structural defectiveness is caused 
by the irregular rushing of the molecules to adjust themselves dur- 
ing the process of cooling, being governed in their movements by 
the rapidity of the decreased temperature and exposure to chill- 
ing influences. The now apparent object in annealing is to obvi- 
ate this irregular molecular adjustment and its effects, by reheat- 
ing the manufactured articles to such a point, where, by expansion 
the molecules are enabled to coalesce and then cool gradually, and 
in so doing allow the "metal" to contract in a manner to avoid 
molecular strain, by allowing the molecules to re-set themselves 
in unison from the center outward, thus reversing the original 
cooling process. 

While annealing is of paramount importance, it is a distinct 
process of itself, and is inadequate to correct all the various im- 
perfections contingent to the manufacture of glass. If thfe glass 
is allowed to chill too much prior to its introduction to the in- 
fluences of the annealing process, its structure becomes so serious- 
ly laminated, that its faults are beyond correction by annealing ; 
from which it is readily assumed, that the quicker it is exposed to 
the influences of the annealing process, and the more heat retained 
by it when introduced to such process, the more beneficial the ef- 
fects of annealing become. While the different methods of an- 
nealing are conducive to the same common object, and are con- 
ducted along the same general lines, yet their various results are 
not strictly parallel, some being naturally better than others. 

The vital point in all annealing is uniformity and regularity, 
and is the keystone of the whole process. Heat, its source, gener- 
ation, uniform distribution and maintenance, constitutes the car- 
dinal feature of the process irrespective of method, and uniform- 
ity of result is commensurate with its consideration. So far as 


appliances for annealing are concerned, it would require an ar- 
ticle of much length to define the various constructions — primitive 
and modern, and inasmuch as they are all constructed along a 
common line, so to speak, parallel in method, we will forego any 
attempt at description. 

Of fuels for annealing purposes there are a variety, producing 
various results, which require more than passing mention, inas- 
much as they are conducive to the general result, be it good or 
bad. Wood, coke, gases (natural and artificial), and sundry oils, 
constitute the principal fuels. The latter mentioned — gases and 
oils — are productive of better results than coke or other fuel burnt 
by direct process of combustion over a grate. Oils on account of 
their cost and danger, until recently were not much used, 
although the results of their use have been efficient and satisfac- 
tory. However, recent appliances and methods have been devised 
that enhance the value of oil as a fuel, and insure its use with 
comparative safety, and it is steadily gaining favor as an economi- 
cal, effective fuel. Coke and gas are at present possibly the most 
extensively used fuels for annealing, but of these gas produces 
the best results, both from a point of efficiency and economy. 
Coke or wood fired appliances, as ovens and lehrs, are generally 
built in the old primitive way, with the fire-box or furnace on 
one side, separated from the oven or lehr proper by a bridge or 
fire-wall over which the flame and heat pass. In this method 
of construction there is a deficiency. This deficiency in a coke 
or wood fired appliance is that the bottles — by way of illustration 
— piled next to this fire-wall receive obviously more heat than 
those along the opposite wall. Besides with a coke fire the tem- 
perature is greatest when the entire bed of coke is ignited and 
aglow ; eventually this temperature decreases until it becomes 
necessary to replenish the bed of fire with fresh coke, which fur- 
ther reduces the temperature. As the freshly added coke becomes 
ignited the temperature is again increased in proportion to a 
point of thorough ignition, until it again becomes necessary to 
replenish the supply. This fluctuation of temperature creates a 
corresponding irregularity in the annealing process. Again, 
coke absorbs moisture from the. atmosphere and this moisture is 
expelled from the freshly added coke and becomes mingled 
with the heat. Variableness of draught through the grate ; 
variation of heat producing qualities of the different cokes ; ex- 
cess of carbon ; irregularities in firing, etc., all produce iregular- 
ities in temperature and hence irregular results. Some of these 
deficiencies have been eliminated by a modern improvement in 
lehr construction, by placing the fire box beneath, and leading a 
series of flues up, and opening into each side, which facilitates a 
better distribution of the heat, and combustion. 


With the use of oil or gas a majority of these discrepancies 
are entirely eliminated. Gas or oil jets and burners can be placed 
where they will be most efficient, and the article or articles under- 
going the process, can be virtually surrounded with a flame line, 
and a simple turn of a valve insures a regular supply of fuel, which 
properly placed effects a regular heat supply — the required essen- 
tial. We say "properly placed." The meaning of this is, that 
some manufacturers in making the change to oil or gas as fuel, 
simply pull out the grate bars and introduce the oil or gas pipes 
into the openings left, and continue to fire from one side of the ap- 
pliance. This is not proper placing for reasons above mentioned. 
The theory is void without practical execution, and without a 
regular, uniform heat supply and distribution, the essential fea- 
tures of the process are void. There is also an absolute necessity 
for uniform, constant and regular "heating up" and "cooling 
down" during the process, by permitting the product undergo- 
ing the process to approach the point of temperature necessary, 
regularly, and recede therefrom in like manner, not abruptly, 
as it is not the simple act of re-heating and then allowing to cool 
without regard to system and concordant principles, that effects 
the purposes of annealing. The process involves systematic lines 
of procedure by allowing the articles in question to approach the 
proper temperature with due method, consistent with regard to 
conditions of introduction, and after absorption of sufficient heat, 
methodical withdrawal therefrom. Nor is this all. Too much 
heat is possible, and the product may be spoiled in part or wholly. 
As to the actual temperature, circumstances govern this point, 
yet the temperature should be maintained at the highest possible 
point consistent with the safety of the product in process. Usual- 
ly the temperature ranges from 6oo° to i ,ooo° F, averaging about 
800 ° F. There is no excuse for lack of determination and main- 
tenance of a fair average temperature. The day of measuring the 
heat "by the eye" is past and gone ; pyrometric instruments de- 
signed for accurate heat measurement can be obtained at a very 
nominal figure, consistent with their commensurate value. 

Aside from the usual annealing process, various experiments 
have been conducted with a purpose to devise means to harden, 
temper or toughen glass, with a view to supercede the regular 
proces of annealing. In 1875 M. Alfred de la Bastie announced 
that he had discovered a method of tempering glass in such a man- 
ner that its strength would be greatly increased. He assumed 
that the cohesive weakness of its molecules caused the fragility 
of glass, and that if the molecules could be forced closer together 
the strength of the material would be increased. Failing to ac- 
complish this result by mechanical compression of the glass while 
hot and viscid, he endeavored to bring about the same result, after 


appliances for annealing are concerned, it would require an ar- 
ticle of much length to define the various constructions — primitive 
and modern, and inasmuch as they are all constructed along a 
common line, so to speak, parallel in method, we will forego any 
attempt at description. 

Of fuels for annealing purposes there are a variety, producing 
various results, which require more than passing mention, inas- 
much as they are conducive to the general result, be it good or 
bad. Wood, coke, gases (natural and artificial), and sundry oils, 
constitute the principal fuels. The latter mentioned — gases and 
oils — are productive of better results than coke or other fuel burnt 
by direct process of combustion over a grate. Oils on account of 
their cost and danger, until recently were not much used, 
although the results of their use have been efficient and satisfac- 
tory. However, recent appliances and methods have been devised 
that enhance the value of oil as a fuel, and insure its use with 
comparative safety, and it is steadily gaining favor as an economi- 
cal, effective fuel. Coke and gas are at present possibly the most 
extensively used fuels for annealing, but of these gas produces 
the best results, both from a point of efficiency and economy. 
Coke or wood fired appliances, as ovens and lehrs, are generally 
built in the old primitive way, with the fire-box or furnace on 
one side, separated from the oven or lehr proper by a bridge or 
fire-wall over which the flame and heat pass. In this method 
of construction there is a deficiency. This deficiency in a coke 
or wood fired appliance is that the bottles — by way of illustration 
— piled next to this fire-wall receive obviously more heat than 
those along the opposite wall. Besides with a coke fire the tem- 
perature is greatest when the entire bed of coke is ignited and 
aglow ; eventually this temperature decreases until it becomes 
necessary to replenish the bed of fire with fresh coke, which fur- 
ther reduces the temperature. As the freshly added coke becomes 
ignited the temperature is again increased in proportion to a 
point of thorough ignition, until it again becomes necessary to 
replenish the supply. This fluctuation of temperature creates a 
corresponding irregularity in the annealing process. Again, 
coke absorbs moisture from the atmosphere and this moisture is 
expelled from the freshly added coke and becomes mingled 
with the heat. Variableness of draught through the grate ; 
variation of heat producing qualities of the different cokes ; ex- 
cess of carbon ; irregularities in firing, etc., all produce iregular- 
ities in temperature and hence irregular results. Some of these 
deficiencies have been eliminated by a modern improvement in 
lehr construction, by placing the fire box beneath, and leading a 
series of flues up, and opening into each side, which facilitates a 
better distribution of the heat, and combustion. 


With the use of oil or gas a majority of these discrepancies 
are entirely eliminated. Gas or oil jets and burners can be placed 
where they will be most efficient, and the article or articles under- 
going the process, can be virtually surrounded with a flame line, 
and a simple turn of a valve insures a regular supply of fuel, which 
properly placed effects a regular heat supply — the required essen- 
tial. We say "properly placed." The meaning of this is, that 
some manufacturers in making the change to oil or gas as fuel, 
simply pull out the grate bars and introduce the oil or gas pipes 
into the openings left, and continue to fire from one side of the ap- 
pliance. This is not proper placing for reasons above mentioned. 
The theory is void without practical execution, and without a 
regular, uniform heat supply and- distribution, the essential fea- 
tures of the process are void. There is also an absolute necessity 
for uniform, constant and regular "heating up" and "cooling 
down" during the process, by permitting the product undergo- 
ing the process to approach the point of temperature necessary, 
regularly, and recede therefrom in like manner, not abruptly, 
as it is not the simple act of re-heating and then allowing to cool 
without regard to system and concordant principles, that effects 
the purposes of annealing. The process involves systematic lines 
of procedure by allowing the articles in question to approach the 
proper temperature with due method, consistent with regard to 
conditions of introduction, and after absorption of sufficient heat, 
methodical withdrawal therefrom. Nor is this all. Too much 
heat is possible, and the product may be spoiled in part or wholly. 
As to the actual temperature, circumstances govern this point, 
yet the temperature should be maintained at the highest possible 
point consistent with the safety of the product in process. Usual- 
ly the temperature ranges from 6oo° to i,ooo° F, averaging about 
800 ° F. There is no excuse for lack of determination and main- 
tenance of a fair average temperature. The day of measuring the 
heat "by the eye" is past and gone ; pyrometric instruments de- 
signed for accurate heat measurement can be obtained at a very 
nominal figure, consistent with their commensurate value. 

Aside from the usual annealing process, various experiments 
have been conducted with a purpose to devise means to harden, 
temper or toughen glass, with a view to supercede the regular 
proces of annealing. In 1875 M. Alfred de la Bastie announced 
that he had discovered a method of tempering glass in such a man- 
ner that its strength would be greatly increased. He assumed 
that the cohesive weakness of its molecules caused the fragility 
of glass, and that if the molecules could be forced closer together 
the strength of the material would be increased. Failing to ac- 
complish this result by mechanical compression of the glass while 
hot and viscid, he endeavored to bring about the same result, after 


appliances for annealing are concerned, it would require an ar- 
ticle of much length to define the various constructions — primitive 
and modern, and inasmuch as they are all constructed along a 
common line, so to speak, parallel in method, we will forego any 
attempt at description. 

Of fuels for annealing purposes there are a variety, producing 
various results, which require more than passing mention, inas- 
much as they are conducive to the general result, be it good or 
bad. Wood, coke, gases (natural and artificial), and sundry oils, 
constitute the principal fuels. The latter mentioned — gases and 
oils — are productive of better results than coke or other fuel burnt 
by direct process of combustion over a grate. Oils on account of 
their cost and danger, until recently were not much used, 
although the results of their use have been efficient and satisfac- 
tory. However, recent appliances and methods have been devised 
that enhance the value of oil as a fuel, and insure its use with 
comparative safety, and it is steadily gaining favor as an economi- 
cal, effective fuel. Coke and gas are at present possibly the most 
extensively used fuels for annealing, but of these gas produces 
the best results, both from a point of efficiency and economy. 
Coke or wood fired appliances, as ovens and lehrs, are generally 
built in the old primitive way, with the fire-box or furnace on 
one side, separated from the oven or lehr proper by a bridge or 
fire-wall over which the flame and heat pass. In this method 
of construction there is a deficiency. This deficiency in a coke 
or wood fired appliance is that the bottles — by way of illustration 
— piled next to this fire-wall receive obviously more heat than 
those along the opposite wall. Besides with a coke fire the tem- 
perature is greatest when the entire bed of coke is ignited and 
aglow ; eventually this temperature decreases until it becomes 
necessary to replenish the bed of fire with fresh coke, which fur- 
ther reduces the temperature. As the freshly added coke becomes 
ignited the temperature is again increased in proportion to a 
point of thorough ignition, until it again becomes necessary to 
replenish the supply. This fluctuation of temperature creates a 
corresponding irregularity in the annealing process. Again, 
coke absorbs moisture from the. atmosphere and this moisture is 
expelled from the freshly added coke and becomes mingled 
with the heat. Variableness of draught through the grate ; 
variation of heat producing qualities of the different cokes ; ex- 
cess of carbon ; irregularities in firing, etc., all produce {regular- 
ities in temperature and hence irregular results. Some of these 
deficiencies have been eliminated by a modern improvement in 
lehr construction, by placing the fire box beneath, and leading a 
series of flues up, and opening into each side, which facilitates a 
better distribution of the heat, and combustion. 


With the use of oil or gas a majority of these discrepancies 
are entirely eliminated. Gas or oil jets and burners can be placed 
where they will be most efficient, and the article or articles under- 
going the process, can be virtually surrounded with a flame line, 
and a simple turn of a valve insures a regular supply of fuel, which 
properly placed effects a regular heat supply — the required essen- 
tial. We say "properly placed." The meaning of this is, that 
some manufacturers in making the change to oil or gas as fuel, 
simply pull out the grate bars and introduce the oil or gas pipes 
into the openings left, and continue to fire from one side of the ap- 
pliance. This is not proper placing for reasons above mentioned. 
The theory is void without practical execution, and without a 
regular, uniform heat supply and- distribution, the essential fea- 
tures of the process are void. There is also an absolute necessity 
for uniform, constant and regular "heating up" and "cooling 
down" during the process, by permitting the product undergo- 
ing the process to approach the point of temperature necessary, 
regularly, and recede therefrom in like manner, not abruptly, 
as it is not the simple act of re-heating and then allowing to cool 
without regard to system and concordant principles, that effects 
the purposes of annealing. The process involves systematic lines 
of procedure by allowing the articles in question to approach the 
proper temperature with due method, consistent with regard to 
conditions of introduction, and after absorption of sufficient heat, 
methodical withdrawal therefrom. Nor is this all. Too much 
heat is possible, and the product may be spoiled in part or wholly. 
As to the actual temperature, circumstances govern this point, 
yet the temperature should be maintained at the highest possible 
point consistent with the safety of the product in process. Usual- 
ly the temperature ranges from 6oo° to i,ooo° F, averaging about 
8oo° F. There is no excuse for lack of determination and main- 
tenance of a fair average temperature. The day of measuring the 
heat "by the eye" is past and gone ; pyrometric instruments de- 
signed for accurate heat measurement can be obtained at a very 
nominal figure, consistent with their commensurate value. 

Aside from the usual annealing process, various experiments 
have been conducted with a purpose to devise means to harden, 
temper or toughen glass, with a view to supercede the regular 
proces of annealing. In 1875 M. Alfred de la Bastie announced 
that he had discovered a method of tempering glass in such a man- 
ner that its strength would be greatly increased. He assumed 
that the cohesive weakness of its molecules caused the fragility 
of glass, and that if the molecules could be forced closer together 
the strength of the material would be increased. Failing to ac- 
complish this result by mechanical compression of the glass while 
hot and viscid, he endeavored to bring about the same result, after 


appliances for annealing are concerned, it would require an ar- 
ticle of much length to define the various constructions — primitive 
and modern, and inasmuch as they are all constructed along a 
common line, so to speak, parallel in method, we will forego any 
attempt at description. 

Of fuels for annealing purposes there are a variety, producing 
various results, which require more than passing mention, inas- 
much as they are conducive to the general result, be it good or 
bad. Wood, coke, gases (natural and artificial), and sundry oils, 
constitute the principal fuels. The latter mentioned — gases and 
oils — are productive of better results than coke or other fuel burnt 
by direct process of combustion over a grate. Oils on account of 
their cost and danger, until recently were not much used, 
although the results of their use have been efficient and satisfac- 
tory. However, recent appliances and methods have been devised 
that enhance the value of oil as a fuel, and insure its use with 
comparative safety, and it is steadily gaining favor as an economi- 
cal, effective fuel. Coke and gas are at present possibly the most 
extensively used fuels for annealing, but of these gas produces 
the best results, both from a point of efficiency and economy. 
Coke or wood fired appliances, as ovens and lehrs, are generally 
built in the old primitive way, with the fire-box or furnace on 
one side, separated from the oven or lehr proper by a bridge or 
fire-wall over which the flame and heat pass. In this method 
of construction there is a deficiency. This deficiency in a coke 
or wood fired appliance is that the bottles — by way of illustration 
— piled next to this fire-wall receive obviously more heat than 
those along the opposite wall. Besides with a coke fire the tem- 
perature is greatest when the entire bed of coke is ignited and 
aglow ; eventually this temperature decreases until it becomes 
necessary to replenish the bed of fire with fresh coke, which fur- 
ther reduces the temperature. As the freshly added coke becomes 
ignited the temperature is again increased in proportion to a 
point of thorough ignition, until it again becomes necessary to 
replenish the supply. This fluctuation of temperature creates a 
corresponding irregularity in the annealing process. Again, 
coke absorbs moisture from the atmosphere and this moisture is 
expelled from the freshly added coke and becomes mingled 
with the heat. Variableness of draught through the grate ; 
variation of heat producing qualities of the different cokes ; ex- 
cess of carbon ; irregularities in firing, etc., all produce {regular- 
ities in temperature and hence irregular results. Some of these 
deficiencies have been eliminated by a modern improvement in 
lehr construction, by placing the fire box beneath, and leading a 
series of flues up, and opening into each side, which facilitates a 
better distribution of the heat, and combustion. 


With the use of oil or gas a majority of these discrepancies 
are entirely eliminated. Gas or oil jets and burners can be placed 
where they will be most efficient, and the article or articles under- 
going the process, can be virtually surrounded with a flame line, 
and a simple turn of a valve insures a regular supply of fuel, which 
properly placed effects a regular heat supply — the required essen- 
tial. We say "properly placed." The meaning of this is, that 
some manufacturers in making the change to oil or gas as fuel, 
simply pull out the grate bars and introduce the oil or gas pipes 
into the openings left, and continue to fire from one side of the ap- 
pliance. This is not proper placing for reasons above mentioned. 
The theory is void without practical execution, and without a 
regular, uniform heat supply and- distribution, the essential fea- 
tures of the process are void. There is also an absolute necessity 
for uniform, constant and regular "heating up" and "cooling 
down" during the process, by permitting the product undergo- 
ing the process to approach the point of temperature necessary, 
regularly, and recede therefrom in like manner, not abruptly, 
as it is not the simple act of re-heating and then allowing to cool 
without regard to system and concordant principles, that effects 
the purposes of annealing. The process involves systematic lines 
of procedure by allowing the articles in question to approach the 
proper temperature with due method, consistent with regard to 
conditions of introduction, and after absorption of sufficient heat, 
methodical withdrawal therefrom. Nor is this all. Too much 
heat is possible, and the product may be spoiled in part or wholly. 
As to the actual temperature, circumstances govern this point, 
yet the temperature should be maintained at the highest possible 
point consistent with the safety of the product in process. Usual- 
ly the temperature ranges from 6oo° to i ,ooo° F, averaging about 
8oo° F. There is no excuse for lack of determination and main- 
tenance of a fair average temperature. The day of measuring the 
heat "by the eye" is past and gone ; pyrometric instruments de- 
signed for accurate heat measurement can be obtained at a very 
nominal figure, consistent with their commensurate value. 

Aside from the usual annealing process, various experiments 
have been conducted with a purpose to devise means to harden, 
temper or toughen glass, with a view to supercede the regular 
proces of annealing. In 1875 M. Alfred de la Bastie announced 
that he had discovered a method of tempering glass in such a man- 
ner that its strength would be greatly increased. He assumed 
that the cohesive weakness of its molecules caused the fragility 
of glass, and that if the molecules could be forced closer together 
the strength of the material would be increased. Failing to ac- 
complish this result by mechanical compression of the glass while 
hot and viscid, he endeavored to bring about the same result, after 


appliances for annealing are concerned, it would require an ar- 
ticle of much length to define the various constructions — primitive 
and modern, and inasmuch as they are all constructed along a 
common line, so to speak, parallel in method, we will forego any 
attempt at description. 

Of fuels for annealing purposes there are a variety, producing 
various results, which require more than passing mention, inas- 
much as they are conducive to the general result, be it good or 
bad. Wood, coke, gases (natural and artificial), and sundry oils, 
constitute the principal fuels. The latter mentioned — gases and 
oils — are productive of better results than coke or other fuel burnt 
by direct process of combustion over a grate. Oils on account of 
their cost and danger, until recently were not much used, 
although the results of their use have been efficient and satisfac- 
tory. However, recent appliances and methods have been devised 
that enhance the value of oil as a fuel, and insure its use with 
comparative safety, and it is steadily gaining favor as an economi- 
cal, effective fuel. Coke and gas are at present possibly the most 
extensively used fuels for annealing, but of these gas produces 
the best results, both from a point of efficiency and economy. 
Coke or wood fired appliances, as ovens and lehrs, are generally 
built in the old primitive way, with the fire-box or furnace on 
one side, separated from the oven or lehr proper by a bridge or 
fire-wall over which the flame and heat pass. In this method 
of construction there is a deficiency. This deficiency in a coke 
or wood fired appliance is that the bottles — by way of illustration 
— piled next to this fire-wall receive obviously more heat than 
those along the opposite wall. Besides with a coke fire the tem- 
perature is greatest when the entire bed of coke is ignited and 
aglow ; eventually this temperature decreases until it becomes 
necessary to replenish the bed of fire with fresh coke, which fur- 
ther reduces the temperature. As the freshly added coke becomes 
ignited the temperature is again increased in proportion to a 
point of thorough ignition, until it again becomes necessary to 
replenish the supply. This fluctuation of temperature creates a 
corresponding irregularity in the annealing process. Again, 
coke absorbs moisture from the atmosphere and this moisture is 
expelled from the freshly added coke and becomes mingled 
with the heat. Variableness of draught through the grate ; 
variation of heat producing qualities of the different cokes ; ex- 
cess of carbon ; irregularities in firing, etc., all produce {regular- 
ities in temperature and hence irregular results. Some of these 
deficiencies have been eliminated by a modern improvement in 
lehr construction, by placing the fire box beneath, and leading a 
series of flues up, and opening into each side, which facilitates a 
better distribution of the heat, and combustion. 


With the use of oil or gas a majority of these discrepancies 
are entirely eliminated. Gas or oil jets and burners can be placed 
where they will be most efficient, and the article or articles under- 
going the process, can be virtually surrounded with a flame line, 
and a simple turn of a valve insures a regular supply of fuel, which 
properly placed effects a regular heat supply — the required essen- 
tial. We say "properly placed." The meaning of this is, that 
some manufacturers in making the change to oil or gas as fuel, 
simply pull out the grate bars and introduce the oil or gas pipes 
into the openings left, and continue to fire from one side of the ap- 
pliance. This is not proper placing for reasons above mentioned. 
The theory is void without practical execution, and without a 
regular, uniform heat supply and- distribution, the essential fea- 
tures of the process are void. There is also an absolute necessity 
for uniform, constant and regular "heating up" and "cooling 
down" during the process, by permitting the product undergo- 
ing the process to approach the point of temperature necessary, 
regularly, and recede therefrom in like manner, not abruptly, 
as it is not the simple act of re-heating and then allowing to cool 
without regard to system and concordant principles, that effects 
the purposes of annealing. The process involves systematic lines 
of procedure by allowing the articles in question to approach the 
proper temperature with due method, consistent with regard to 
conditions of introduction, and after absorption of sufficient heat, 
methodical withdrawal therefrom. Nor is this all. Too much 
heat is possible, and the product may be spoiled in part or wholly. 
As to the actual temperature, circumstances govern this point, 
yet the temperature should be maintained at the highest possible 
point consistent with the safety of the product in process. Usual- 
ly the temperature ranges from 6oo° to i ,ooo° F, averaging about 
8oo° F. There is no excuse for lack of determination and main- 
tenance of a fair average temperature. The day of measuring the 
heat "by the eye" is past and gone ; pyrometric instruments de- 
signed for accurate heat measurement can be obtained at a very 
nominal figure, consistent with their commensurate value. 

Aside from the usual annealing process, various experiments 
have been conducted with a purpose to devise means to harden, 
temper or toughen glass, with a view to supercede the regular 
proces of annealing. In 1875 M. Alfred de la Bastie announced 
that he had discovered a method of tempering glass in such a man- 
ner that its strength would be greatly increased. He assumed 
that the cohesive weakness of its molecules caused the fragility 
of glass, and that if the molecules could be forced closer together 
the strength of the material would be increased. Failing to ac- 
complish this result by mechanical compression of the glass while 
hot and viscid, he endeavored to bring about the same result, after 


numerous experiments, by immersion of the heated article in a 
bath of melted tallow or mutton fat at a temperature 68°-75° C, 
(i54°-i67° F,) ; ih this he was successful in certain lines. 

Mr. F. Siemens was another inventor who experimented in 
this direction with some success. He conceived the idea of tem- 
pering the articles by placing them in molds between cooled sur- 
faces, thus maintaining their shapes intact, and applying force if 
necessary, go as to press the molecules of the glass firmly together. 

Piper's process consists of heating the glass almost to the 
point of plasticity, and then subjecting it to the action of injected 
superheated steam, which produces a result about similar to De 
la Bastie's. 

These processes are attended with such difficulties as to mod^ 
ify to a certain extent their success. Besides they do not furnish 
as supposed, a substitute for annealing. They produce hardened 
glass, not annealed glass ; and while hardened glass will un- 
doubtedly stand rough usage better than ordinary glass, yet it is 
not unbreakable, and upon the slightest fracture it will become 
utterly disintegrated. The glass is hard, not tough, and it is the 
very opposite of annealed glass. Hardened glass is that in which 
the molecules have been tortured into their position ; while in 
annealed glass the molecules have been allowed to settle them- 
selves. Glass hardened by these processes is impaired for practical 
utility by its inability to be cut and fashioned, and its utter 
destruction by the slightest fractures. These are difficulties 
which have baffled the ingenuity of all producers of toughened 

In conclusion we say that reliable strength and durability 
can only be imparted to glass by uniform annealing. But in this 
the various fields presented by the factors, heat, and its uniform 
maintenance and distribution ; appliances for utility and econ- 
omy of process ; mechanism for successful manipulations, etc., 
present excellent and unlimited opportunities for progressive man- 
ufacturers to develop more modern and successful methods of an- 


The following tabular statement will illustrate the resistance 
and nature of fracture of glass under different methods of anneal- 
ing : 

Cooled in annealing oven . 
Cooled in open air 

<2 6.68 \ Clear aurfece breakage. 

(3 .... 4.69) 

1 12.66") A piece of 

2 9.52 (upper aur- 

3 9.90 [face thrown 

4 7 .22 J off. 

:e off 80 m. m."| 
• lir-J 150 m. m. I 1" 
rownl 80m.m. f^ * 
( 20 m. m. J 

(b) Medium red heat - 
(0} Bright red heat. 


(1 31.581 

J2 96.241 

13 23.65/ 

U 12.03/ 

31.97 > 

64.22 Andible detonation at splinter- 
Exceptional strong splintering. 

. 32.49 ) 

(A) Medium red heat {J 

(o) Bright red heat \ 2 29. 68 J- Faultless tubes. 

(3 36.03) 

Rapidly chilled to 140° from ,, „,„,,, „ . , . 

&> &.«.■«* {i::;:5:S} s S : rXt ri "' PTO 

(J) Medium red beat 1 41.60 

(e) Bright red heat 1 36.38 

Rapidly chilled to 180° from 

{a) Low red heat 1 38.86 

(b) Medium red beat 1.. ..16.66 

( o) Bright red beat 1 38.72 ^^ 


Analyses of Window Glass. 

French. English. Chance's. Russian. 

(Dumas.) (Cooper.)(Benrath.) 

69.00 71.40 71.27 

11. 10 15.00 20.10 

12.50 12.40 8.14 

7.40 0.60 


Silica 68.00 

Soda 10.10 

Lime 1 4-3° 

Alumina 7.60 

It is well to bear in mind that window glass is subjected to 
indefinite exposure to the weather, the action of which, under 
continued exposure generates chemical influences deleterious to 
the glass ; hence the glass should be so constituted as to afford 
the greatest resistance. In its constitution the silica should 

always be as high as possible. Manganese and oxide of nickel 
may be used as decolorizers, but are not recommended ; espec- 
ially manganese, as under the continued action of sunlight the 
color in glass containing manganese is not constant, and some- 
times assumes an undesirable violet tint. With the use of oxide of 
nickel the color is more constant, but arsenic is used as the prin- 
cipal decolorizer in most window glass. 


English Window Glass. 


Sand 60 Saltpetre 1 .... 15 

Pearl-ash 30 Borax 1 

Arsenic J4 

— 2 — 

§and ." . 60 Arsenic 2 

Pearl-ash 25 Salt 10 

Saltpetre 5 Magnesia w . 1^4 

— 3— 
Sand 60 Arsenic 2 

Pearl-ash 30 Salt 10 

Magnesia 2 

' — 4— 
Sand 560 Carbonate of sodium 119 

Sulphate of sodium 63 Chalk 154 

Arsenic 2 

— 5— 
Sand 448 Carbonate of sodium 168 

Sulphate of sodium 17 Chalk ( . . . 146 

Arsenic . . . . . 2 

♦• French Window Glass. 

Sand 100 Chalk 35 to 40 

Soda ash : .28 to 35 Arsenic 0.20 

Manganese 0.25 

Sand 100 Lime 6 

Sulphate of sodium 44 Powdered coal 4 

Sand ../..... 100 Lime 13 to 15 

Sulphate of sodium . . .58 to 75 Powdered coal 4.5 to 5.5 


Sand ioo Charcoal I J^ 

Salt cake 35 Manganese % 

Lime 25 Arsenic 1 

Cullet 100 

Sand 100 Charcoal 4 

Salt cake , . . 42 Arsenic 1 y 2 

Lime 34 Cullet 100 

ian Window Glass. 

— 11 — 

Sand 100 Carbonate of calcium (chalk) 40 

Salt cake 36 Charcoal 2 

Cullet 100 

— I2 — 
Sand 100 Carbonate of calcium 38 

Salt cake 42 Charcoal 4 . . . 4 

Cullet 100 

Bohemian Window Glass. 

Sand 100 Slacked lime 12 

Potash 40 Arsenic J4 

Saltpetre . . 2 Cullet 100 

Sand 100 Slacked lime 14 

Potash 40 Arsenic y 2 

Salt 5 Cullet ' 100 

German Window Glass. 

Sand 100 Nitrate of sodium 2 

Soda 28 Charcoal . : . 3 

Slacked lime 27 Arsenic :* 1 

— 16 — 

Sand 100 Nitrate of sodium 6 

Soda 40 Charcoal 6 

Slacked lime 35 Arsenic 2 

American Window Glass. (Salt Cake.) 


Sand 8000 Lime 2500 

Sulphate of sodium 2200 Powdered coal 40 

Arsenic 50 


— 18— 

Sand ioo Lime 24 

Salt cake 42 Charcoal 3 >4 

Arsenic 1J/2 

— 19— 

Sand 100 Lime 31 

Salt cake 35 Charcoal 7 

Arsenic 1 

— 20 — 

Sand 100 Lime 34 

Salt cake 38 Charcoal 5 

Arsenic J4 

American Window Qlass. (With Soda.) 

— 21 — 

Sand 100 Soda ash .7 

Salt cake 36 Arsenic 2 

Lime 34 Charcoal • 6 

— 22 — 

Sand 100 Soda ash 6 

Salt cake 32 Arsenic 2 

Lime 32 Charcoal 6 


Sand 100 Soda ash 8 

Salt cake 40 Arsenic 2 

Lime 40 Charcoal 6 

Crown Qlass. 



Sand 300 Lime 30 to 35 

Soda ash 200 Cullet 200 to 300 


Sand 100 Dry quicklime 17 to 20 

Sulphate of sodium 50 Charcoal 4 


Sand 400 Sulphate of sodium 560 

Quicklime 486 Chafcoal 25 


Sand .650 Cullet 250 

Quicklime .225 Pipe-clay 7 

Soda 200 Nitre 7 



Sand 300 Arsenic 4 

Sulphate of sodium 100 Charcoal 1 

Nitre 10 Manganese Vie 

— 29— 

Sand 400 Quicklime 64 

Salt cake 200 Charcoal 16 


Sand 600 Cullet 600 

Ground limestone 66 Manganese 1 

Soda ash 300 Cobalt Vie 




Plate Glass. 

Analyses of Plate Olass. 











British London 

Plate and 

Glass Co Thames. 





Mayer A Brazier. 





70.71 i 

[ 78.68 








[ 68 60 






Lime . r . t 








Manganese .. 


Sesqui- oxide 

• • • • 






• • • •  



In view of the fact that plate glass requires a certain degree 
of perfection, as great brilliance, clearness and purity ; a total ab- 
sence of striae, cords, blisters, seeds and stones ; permanence of 
color and durability, it can be readily seen that the purest mater- 
ials only should be used, and these manipulated with great care. 
Color is a very important consideration, and for reasons already 
mentioned manganese should never be used. De Fontenay in- 
troduced the use of oxide of nickel, which imparts a bluish tint 
to glass and is constant in color. Oxide of zinc has been used in 
plate glass to replace manganese, but results have not been entire- 
ly satisfactory, as Gerner claimed that oxide of zinc was liable to 
impart a yellowish tinge, which experience confirms, particularly 
if the glass is not rapidly worked out after fining. 

The older formulas encouraged the use of soda and potash, 
as in the earlier days of the industry a glass fluid and highly alka- 
line was required on account of the impurity of materials. But 
progressive economy, improved furnaces, etc., have gradually 
brought salt cake into very general use. 

Plate Glass Recipes. 

Old English. 

Sand ioo 

Soda 33 

Potash (refined) 6 

Cullet ioo 

Lime (hydrate) 12 

Manganese 0.5 

Saltpetre 2 


— 2 — 

Sand ioo Lime (hydrate) 20 

Soda (pure) 35 Saltpetre 2 

Manganese J4 


— 3— 
Quartz sand 100 Lime 20 

Sulphate of sodium 24 Cullet of soda glass 12 



Quartz sand 100 Lime 20 

Sulphate of sodium 50 Charcoal 2^4 


— 5— 
Sand 300 Carbonate of sodium 100 

Cullet 50 Slacked lime 43 


Sand 100 Arsenic 0.5 

Soda 33.33 Borax 0.5 

Lime 30 Carbonate of nickel 009 

Nitre 2 Red oxide of cobalt 0006 

Plate glass cullet 100 

American Practice with Salt Cake. 

— 7— 
Sand 720 Nitre ., 25 

Sulphate of sodium .450 Charcoal 5 

Quicklime 100 Plate glass cullet 425 

Sand 100 Charcoal 2.5 

Lime 35 Salt cake 38 

Arsenic 2 

Sand 100 Lime 37 

Salt cake 37 Charcoal 2.5 

Arsenic 1.5 

Sand 100 Lime 38 

Salt cake 40 Charcoal 4 

Arsenic 2 



— ii — 

Sand ioo Salt cake 35 

Carbonate of calcium 26 Charcoal 2.5 

Saltpetre 2 Manganese 0.25 

Knapp's Technology. 

— 12 — 

Sand 100 Soda 35 

Lime ' 5 Cullet 100 


St. Gobain; Old. (Analysis.) 


Silica 77.1 Alumina and oxide of iron . . .6 

Soda 16.0 

St. Qobain; Later. (Analysis.) 


Silica .72.1 Lime 15.7 

Soda 22.2 Alumina and iron trace 


— IS— 

Sand 100 Cullet 100 

Soda 60 Peroxide of manganese ... 1 

Carbonate of calcium 13 Smalt 05 

English Soda. 

Sand 400 Carbonate of sodium 250 

Chalk 30 


Sand 720 Carbonate of sodium 450 

Nitre 25 Lime 80 




Semi- White Sheet Glass Recipes. 

Sand 500 Ground limestone 160 

Baryta 140 Charcoal 10 

Salt cake 70 Cullet 500 

Sand 150 Carbonate of calcium 48 

Salt cake 52 Charcoal 4.5 

Cullet 125 

— 3— 

Sand iod Slacked lime 12 to 14 

Potash 45 to 50 Cullet 100 

Salt cake 10 to 12 Charcoal 1 

— 4— 

Sand 150 Cullet 100 

Salt cake 45 Common salt 18 

Charcoal 4 Ground limestone 45 

— 5— 

Sand 100 Charcoal . . ._, 3 

Salt cake 45 Ground limestone 18 

Sand 100 Charcoal 4 

Salt cake > 38 Ground limestone 26 

White Sheet Glass Recipes. 

Sand 100 Carbonate of calcium 26 

Potash 60 Cullet 100 

— 2 — 

Sand 100 Cullet 100 

Salt cake 38 Charcoal 3 

Carbonate of calcium 33 Arsenic 2 

— 3— 

Sand 100 Carbonate of calcium 38 

Potash 8 Cullet 100 

Salt cake 32 Charcoal 4 




Bottle Glass Analyses. 

Kind of Glass. 

French 1 

Sauvigny. . . J 
St. Etienne... 




Bohemian . . 1 
Champagne j 
Champagne . . 


German. ... 




Berthier . . . 

Berthier. . . . 



Manmeno . . 
Maumeno . . 


Benrath .... 
Benrath .... 























• • . • 





























of Iron. 









H ag- 


By bottle glass is generally meant the common grades of 
glass used principally in the manufacture of bottles ; as green, or 
amber colored varieties. 

The so-called "lime flint" bottle glass figures largely at the 
present day in the bottle industry ; in fact the past decade has 
wrought a revolution, in so far as to give flint glass bottles much 
prestige. For a long time flint glass bottles were regarded with 
disfavor, inasmuch as their cost alone excluded them from the beer 
and soda water trade, to say nothing of the current belief rife 
among the bottling fraternity that flint glass lacked the strength 
and resistance of green glass ; and that the liquid contents of a 
flint glass bottle were seriously impaired in strength and in color 
by the, action of light, which a green or amber bottle excluded, 
and thus protected its contents. But these objections have been 
nominally overcome, especially the first, as the price of raw mate- 
rials necessary for flint bottle glass is such that there is but little 
difference in the first cost, considering quality. Strength and re- 
sistance are acquired in glass by proportionate quantities of raw 
materials, proper melting and careful annealing, and the dete- 
riorating effects of light are not considered serious. Without 
doubt flint glass bottles command favor ; and even much of the 
green bottle glass of the present day assumes a similarity to flint 
which in many cases leaves a difference in color difficult to de- 
termine. Improved furnaces, decolorizers, purity of materials, 
etc., make such possible, and competition demands it. 

Regarding any glass intended for bottles, it is well to remem- 
ber that competition augments economy, and much discretion 
must be exercised to combine economy and stability. Regard- 
ing stability, it is well to keep in mind that resistance to corrosion 


and strength increases in proportion with the amount of sand 
melted — the product also cheapens accordingly — but difficulty of 
fusion is increased in proportion ; and what is true in regard to 
sand is just the reverse with regard to the alkaline bases as in pro- 
portion with increase in alkali, is resistance decreased, fusion fa- 
cilitated, and cost increased. Alumina increases resistance, but 
in excess renders glass liable to devitrification. Lime improves 
polish and brilliance, hardens the product, and aids resistance, 
but retards fusion when used in excess. Difficulty of fusion in- 
creases generally with decrease of solvents. Resistance also de- 
creases with increase of cullet. 

Regarding economy, cheap grades of sand can be used in the 
ordinary green and amber glasses ; the iron and alumina always 
present in impure sand are not objectionable, as both are frequent- 
ly added purposely. Salt cake furnishes a cheap solvent, but for 
reasons stated elsewhere, all traces of salt water must be removed 
before coloring oxides are added. Zaffre for blue, manganese for 
violet or black, and pulverized charcoal, cannel or anthracite coal 
for amber, furnish possibly the cheapest coloring agents. 

Bottle Glass Recipes. 
Belgian (Colne.) 

Sand ioo Pearl ash 20 

Sulphate of sodium 15 Limestone 5 

Green Bottle Glass with Salt Cake. 

— 2 — 

Sand , 100 Ground lime 34 

Salt cake 38 Charcoal 5 

Sand 100 Ground lime 38 

Salt cake 40 Charcoal 6 

Green Bottle Glass with Soda. 

— 4— 
Sand 100 Lime 32 

Soda 35 Cullet 100 

— 5— 
Sand 100 Lime 38 

Soda 40 Cullet 100 1 



Amber Glass Recipes. (For Bottles.) 

Sand ioo Salt cake 40 

Lime 38 Charcoal 8 

Cannel coal 14 

— 2 — 

Sand 100 Lime 35 

Soda 33 Cannel coal 11 

— 3— 

Sand . 100 Salt cake , . . 34 

Lime 32 Charcoal 4 

Cannel coal 8 

— 4— 

Sand 100 Lime .30 

Soda 35 Charcoal 9 





The idea of manufacturing glass from the waste cinder, or 
slag, of iron blast furnaces is by no means a new one. Iron slag 
contains many of the ingredients of common glass, and it is pos- 
sible that much of the early glass was metallurgical slag remelted. 
The sands prepared by pulverizing slag have been used in Eng- 
land, and on the continent of Europe for a long time as a constitu- 
ent of glass., 

An analysis of Welsh iron slag shows : 

Silica 40 

Lime 35 

Alumina 16 

Magnesia 6 

Alkali , 1 

Oxide of Iron 2 


A trace of sulphur is found associated with the lime in slag, 
but this readily passes away with heat. When the constituency 
of slag is once determined by analysis, and the proper proportion 
of additional materials has been determined, a very regular and 
uniform workable glass can be made, as actual experience has 
shown conclusively that the composition of slag is regular enough 
to warrant results sufficiently uniform for all practical purposes. 
Taking the above analysis as an example, it will be seen that the 
principal differences are in the silica, alkali and iron ; but by com- 
bining 100 parts of slag, 10 parts of soda and 60 parts of sand, the 
constituents are altered to a compound of the precise nature re- 
quired, thus : 

Slag. Additions. Glass. 

Silica, 40 Ferruginous sand 60 = 100 or 57.14 % 

Lime 35 = 35 or 20.00 % 

Alumina 16 = 16 or 9.14 % 

Magnesia 6 = 6 or 3.43 % 

Alkali 1 Soda 10 = 11 or 6.29 % 

Oxide of iron 2 From the sand. . . 5 = 7 or 4.00 % 

100 175 100 


The natural tint of the glass thus produced is greenish in col- 
or, but by "fining" and bleaching it can be made almost colorless 
With some ores the slag contains silica enough, and with the addi- 
tion of soda and arsenic becomes perfectly transparent. The con- 
stituents of slag are common to all green glass, and by dilution 
with purer materials, decolorizers, etc., slag glass can be brought 
up to almost any desired standard, consistent with the iron and 
other impurities in its constituency. However, without at- 
tempting to predict the possibilities of its manufacture in the fu- 
ture, so far its use has been confined to the ordinary black, dark 
green and amber colored bottle glass. 









10 uj SSS us 



! s 


g ;oo :oo 

| * s . 
1 °° 

| : 8SS : ! 

1 !"" 




* :§3 :§§ 









"* 11 1111 


" tubes 

Under the caption of flint, or crystal glass, many varieties of 
glass may be properly classed ; and while there are different 
grades of flint glass, yet it is important to recommend the use of 
the best materials for the finer grades. Of course for the manu- 
facture of ordinary hollow ware, a glass made from cheaper ma- 
terials may be entirely satisfactory. Such titles as "lead flint," 
"lime flint/' "tank flint," "German flint," etc., are applied to 
glasses graded according to materials used and circumstances con- 
tingent to their manufacture. It. hardly seems necessary to 
specially define any of them, but rather remark a few especial fea- 
tures in their manufacture, and refer the reader to a list of well se- 
lected recipes. Old recipes for crystal glass called for less lime 
than is in use in present day practice ; as a result the glass now 
has a higher polish and more resistance ; but it must be remem- 
bered that an excess of lime retards fusion, and renders glass re- 
fractory and liable to devitrification. To avoid repetition we refer 
the reader to the data given in preceding pages regarding the ma- 
terials in use, and their respective actions and effects in glass. 

As a basis for a good soda-lime glass, it is said that the com- 
position must approach: Lime I, soda i, sand 6. Benrath recom- 
mends the following: Sand Jj, soda 14, lime 9, but circum- 
stances modify conditions and must govern the proportion of all 
materials. In lead glass the yellowish tint imparted by the lead 
must be neutralized with decolorizers, as manganese, oxide of 
nickel, cobalt, etc. The same applies to the bluish green tint im- 
parted by soda. 

Lead (Crystal) Glass Recipes. 
English. (Pellat.) 

Sand 336 Potash 112 

Lead 224 Saltpetre 14 to 28 

Manganese *4 to J4 


— 2 — 

Sand 100 Borax 0.1 

Soda (90%) 39 Nickelous carbonate.0008 to .01 

Minium (red lead) 51 Red cobaltous oxide 0005 

Nitre 3 Cullet 100 


English Crystal* 

— 3— 

Sand 300 Cullet 300 

Lead .200 Saltpetre 48 

Potash 80 Manganese ji 

Arsenic 1 

English Crystal. 

Sand 100 Cullet 100 

Lead 80 Saltpetre 0.5 

Potash 40 Manganese 0.4 

French Crystal. 

Sand 150 Cullet 100 

Lead 90 Borax 6 

Potash 40 Manganese 1-10 

Arsenic ., 1-10 


Sand 100 Potash 35 to 40 

Lead 80 to 85 Nitre 2 to 3 

Manganese 0.5 . r ' | ' I- ' ' ' J 


— 7— 

Sand 300 Potash no 

Lead 215 Saltpetre 10 

Borax 12 ! 

German Crystal. 

Sand 300 Cullet 100 

Lead 160 Manganese 1 J4 

Potash 105 Lime 60 

American Crystal. 

Sand 1500 Saltpetre 150 

Lead 600 Manganese 1 y% 

Potash 500 Arsenic 1 y 2 


Soft with Cullet. 

Cullet 400 Lead 10 

Sand 10 Pearl ash 10 

— 11 — 

Sand : 336 Nitre 28 

Lead 224 Manganese 5-32 

Pearl ash 112 Arsenic 1-16 

Best Flint. 

— 12 — 

Sand 450 Nitre 38 

Lead 250 Manganese Y% 

Pearl ash 125 Arsenic J^ 

Borax 1 J4 


Sand 900 Nitre 100 

Lead 600 Manganese 1-16 

Pearl ash, 300 to every cwt. of 


Saiid 500 Nitre 75 

Lead 160 Manganese % 

Pearl ash 150 Phosphate of calcium J4 


Sand 600 Lead 400 

Pearl ash 130 Nitre 75 

Manganese $4 

Sand 100 Pearl ash 18 

Lead 48 Soda 16 

Nitre 6 Arsenic 9-64 

Manganese 1-16 Antimony 1-64 



Sand 2100 Lead 750 

Pearl ash 600 Manganese 2 

Nitre 250 Arsenic 2 



Sand 200 Nitre 10 

Pearl ash 75 Borax % 

Lead 80 Arsenic 1 

Manganese J4 

— 1< 

Sand 270 Nitre 10 

Lead 200 Arsenic % 

Pearl ash 90 Antimony % 

Manganese % 

Good sand 3000 Ground limestone 260 

Potash (90 %) 1000 Nitre no 

Minium (red lead) 1500 Manganese 3 

Cullet 3000 


— 21 — 

Sand 360 Nitre 30 

Lead 150 Arsenic 1 

Pearl ash 125 Manganese % 

— 22 — 

Sand 500 Pearl ash 150 

Lead 350 Nitre 30 

Manganese 7-16 


Sand 100 Nitre 20 

Lead 100 Arsenic J4 

Pearl ash 100 Manganese . - y 2 

— 24 — 

Sand 650 Nitre 22 

Lead — 250 Phosphate of sodium 6 

Pearl ash 300 Phosphate of calcium 1 j£ 

Manganese .. . J4 

Three-fourths Kiln Metal. 

' —25— 

Sand 720 Nitre 60 

Lead 470 Borax * 5 

Pearl ash 240 Manganese £4 


Lead, Soda. 


Sand 252 Nitrate of sodium 56 

Litharge 140 Manganese 5-16 

Soda 98 Arsenic J /% 

Baryta, Lead. 


Sand ;. .260 Carbonate of barium 400 

Potash 160 Oxide of lead 200 

Baryta, Soda, Lead. 


Sand 350 Oxide of lead 230 

Carbonate of barium 300 Soda 100 

Baryta, Potash. 


Sand 500 Potash 200 

Carbonate of barium 300 



Sand 500 Cullet 450 

Lead 200 Saltpetre 40 

Potash 160 Manganese 1 


Sand 200 Carbonate of calcium 30 

Lead 25 Cullet 90 

Manganese 1 

Optical Glass. 

Optical glass is difficult to make and its processes are care- 
fully guarded, so but little can be said regarding it except that the 
glass must be perfectly homogeneous and absolutely free from all 
stratification, as difference in density creates corresponding differ- 
ences in the light refracting powers of the glass. 


Optical Glass Recipes. 

123 123 

Sand 100 100 100 Potash 30 25 26.66 

Lead 67 128 105 Saltpetre 3^ 2 4.8 


Sand 100 Borax 1.75 

Lead 100 Manganese 0.45 

Potash (pure) 23 Arsenic 0.45 

Saltpetre 1.33 Cullet 22 


— 3— 

Sand 100 Cullet 30 

Lead 100 Borax 



— 4— 

Sand 100 Potash 23 

Lead 100 Borax 6.5 


— 5— 

Sand 100 Potash 26 

Lead 100 Saltpetre 6.75 





Lime Flint. Glass Recipes. 

Sand ioo Nitre 1.25 

Potash 35 Green nickel carbonate . .0.007 

Burned lime 19 Cullet 100 

— 2 — 

Sand 100 Cullet 100 

Potash 25 Soda 5 

Burned lime 20 Minium 32 

Arsenic 0.75 

— 3— 
Sand 100 Cullet 100 

Potash 25 Soda 10 

Burned lime 17 Arsenic 1.5 

Nitre 0.5 Manganese 0.05 

— 4— 
Sand 100 Arsenic 0.5 

Soda 42 Borax 0.5 

Limestone 25 Carbonate of nickel 010 

Nitre 2 Red oxide of cobalt 0006 

Cullet 100 


— 5— 
Quartz sand ^ . 100 Chalk 8 

Carbonate of potassium ... 60 Manganese 75 


Sand 300 Lime ,.75 

Carbonate of sodium 170 Charcoal 10 


Sand 100 Lime 18 

Carbonate of potassium ... 30 Manganese 0.5 


Sand 100 Carbonate of calcium 24 

Soda (95%) 32 Charcoal 2.5 

Sand •. . . . 100 Carbonate of calcium 24 

Soda (95%) 46 Charcoal 2.5 

. 108 

American Practice, 

Sand 400 Lime • • 35 

Soda 155 Manganese '. . . . . 2 

Saltpetre 20 Arsenic 2 

— 11 — 

Sand 550 Lime 35 

Soda 170 Manganese 1 

Saltpetre 35 Arsenic 24 

— 12 — 

Sand 560 Lime 55 

Soda 190 Manganese J4 

Saltpetre 20 Arsenic 1 


Sand 100 Lime 43 

Soda 37 Arsenic 0.5 

Nitrate of sodium . 8 Manganese 0.15 



Sand 100 Ground lime 25 

Soda 25 Potash 8.5 

Cullet 50 


— 15— 

Sand 100 Potash 33 

Soda 33 Ground lime 25 

Cullet 115 

Gas Belt. 

Sand 1500 Arsenic 5 

Soda 550 Manganese 2 

Nitrate of sodium 80 Powdered blue 5-32 

Bone ash ' 4 



Sand 1500 Nitrate of sodium 1 

Soda 500 Arsenic 2 

Ground lime 150 Manganese 2 

Smalt % 


— 18— 

Sand 1500 Antimony (needle) i}4 

Soda 550 Manganese 2 

Ground lime 150 Smalt % 

Nitrate of sodium 100 Borax 2 

Sand 120 Cullet 50 

Soda ash 60 Arsenic }i 

Carbonate of calcium 30 Manganese J4 


Sand 200 Arsenic J4 

Nitrate of sodium 2 Manganese 1 

Cullet 60 Sulphate of sodium 120 

Ckarcoal 2 


— 21 — 

Sand 180 Manganese % 

Nitrate of sodium 10 Sulphate of sodium 75 

Arsenic J4 Charcoal J4 

Common salt 20 


— 22 — 

Sand 1400 Nitre 100 

Soda 530 Arsenic 24 

Lime 230 Manganese J4 

Gray zaffre ^ 

With Potash. 


Sand 300 Lime 50 

Potash 90 Nitre 6 

Manganese 1 }4 

With Potash. 

— 24— 

Sand 500 Lime 60 

Potash 165 Nitre 5 

Manganese 1 


Baryta, Potash, Lime. 

Sand 520 Lime 70 

Potash 70 Oxide of lead 100 

Carbonate of barium 100 

Baryta, Soda, Lime. 

— 26— 

Sand 600 Carbonate of barium 210 

Soda 1 10 Lime 80 

Cheap Flint Glass Recipes for Hollow Ware. 

Sand 300 Quicklime 75 

Soda ash 150 Cullet 275 

Arsenic J4 

— 2 — 

Sand 240 Carbonate of calcium 50 

Soda ash 120 Arsenic ^ 

Nitrate of sodium 2 Manganese *H$ 

With Potash. 

— 3— 

Sand 100 Saltpetre 2 

Potash 50 Manganese 02 

Lime 20 Cullet : . . 100 

— 4— 

Sand 100 Manganese J4 

Potash 40 Cullet 100 

Slacked lime 40 Arsenic 2 

Saltpetre 8 Salt 16 

With Soda. 

— 5— 

Sand 100 Saltpetre 1 J4 

Ground lime 36 Manganese y 2 

Soda 30 Cullet 100 

Sand 100 Arsenic 2 

Ground lime 34 Manganese 1 J£ 

Soda 34 Cullet 100 


With Salt Cake. 


Sand ioo Charcoal 3 

Salt cake 35 Arsenic 1 

Ground lime 32 Manganese j/2 

Cullet 100 

Sand 100 Charcoal 6 

Salt cake 40 Arsenic 2 

Ground lime 38 Manganese 1 J4 

Cullet 100 





Light and Colon 

As light is the source of color, it is necessary to examine its 
constitution to obtain an understanding of the fundaments of 
color. When a sunbeam shines through a prism the ray is not 
only bent from its course, but it is spread out fanlike into what 
is called the solar spectrum, showing six prominent colors, viz.: 
violet, blue, green, yellow, orange and red. If we pass the spec- 
trum through a convex lens it will show a white spot ; we there- 
fore conclude that white light is composed of six colors. They 
are separated in the spectrum because the prism bends them un- 
equally, violet being refracted most, red least. These colors are di- 
vided into three primary, or simple, colors: red, blue and yellow; 
and three secondary or mixed colors : orange, green and violet. 
Orange is the result of a combination of red with yellow, green, of 
blue with yellow, and violet, of blue with red. 

The primary colors are pure and cannot be produced by mix- 
ing other colors ; their color may vary in intensity, but it cannot 
vary in hue ; while the secondary colors may vary in hue indef- 
initely, according to the primary colors of which they are formed. 
The analysis goes further : Two colors, which by their mixture 
produce white light, are termed complementary to each other, and 
herein arise the complementary colors. Thus, if we sift the red 
out of a beam of light, and bring the remainder to a focus, a green 
image will be formed ; hence red is termed the complementary 
of green. We assume that white light is composed of but three 
colors : Red, blue and yellow ; the absent color from the com- 
pound is termed the complementary ; and this complementary of 
any primary color is the secondary or mixed color composed of 
the two primary colors. Thus, the complementary of red is green, 
(blue and yellow) ; the complementary of blue is orange, (red and 
yellow) ; the complementary of yellow is violet, (red and blue). 
Any given color may be modified and appear very different, ac- 
cording to the circumstances under which it is seen ; contrast of 
tone ; the glazed surface of the colored substance ; form of ob- 
ject containing the color ; quality of the light by which it is illu- 
minated, (if light be added to a color it is tinted ; if taken from 
a color it is shaded; thus — yellow tinted, would be light yel- 
low, while a yellow shade would be a dark yellow). As an 
illustration take red, and its tone and intensity may be modified 
by placing it in contact with other colors. Placed in contact with 
white it appears lighter ; with grey it appears brighter ; with 
black, duller ; with blue, yellower ; with yellow, bluer, and with 
green, purer and brighter, as a color is always heightened by being 
placed near to, or in contact with its complement. 


When light passes through a transparent substance if all its 
vibrations are transmitted in the same proportion in which they 
exist in white light, the body appears colorless; but if some of the 
vibrations are absorbed or extinguished, the transmitted light 
and consequently the transparent body possesses the color pro- 
duced by the combination of the unchecked vibratidhs, and inten- 
sity of color depends upon the amplitude of the vibrations. When 
a body absorbs all the colors of the spectrum except blue, but re- 
flects that to the eye, we call it a blue body ; when it absorbs all 
but green, we call it a green body ; if it absorbs all the colors we 
call it black. 

Thus arises color in glass, by the combination of the oxides 
of certain metals with the ingredients producing the glass, which 
become dissolved in the resultant product and possess the power 
to retard or extinguish certain of the vibrations of white light, and 
transmit corresponding colors. Thus colors may be produced 
simple or compound, by the use of a single oxide, a combination 
of oxides, or by a mixture of their products. 

The nature of the metal, quantity present and state of oxida- 
tion, however, modify the power of extinction or absorption, 
which is illustrated by experiments with borax beads holding 
metallic oxides in solution and exposed to the action of a blow- 
pipe flame. Some metals, copper for instance, form two series of 
compounds, and give different colors to the bead when present in 
either the higher or lower state of oxidation, assuming a blue color 
while Containing the copper in the cupric, and a red color when in 
the cuprous form. Iron in the oxidizing flame gives a deep 
orange color ; manganese a violet ; nickel a reddish brown ; 
cobalt a purple blue ; and chromium an emerald green or yellow. 
While in the reducing flame the orange of iron becomes a dull 
green ; the violet of manganese disappears ; the brown of nickel 
changes to a turbid grey, while the colors of cobalt and chro- 
mium remain unchanged. Opacity, or total extinction of light, is 
generally obtained by an infusible and insoluble excess present in 
the substance of the glass, by which all of the vibrations of light 
are absorbed. The black opacity is obtained by the excessive use 
of manganese and iron ; and white opacity by a like use of 
arsenic, tin, calcium phosphate, fluor-spar, cryolite, etc. 

Generally the coloring agents are incorporated directly with 
the batch. The former practice was how r ever, that labor-entailed 
process, of first melting a pure flint batch, which was removed 
from the pot, cooled and pulverized ; the coloring agents were 
then thoroughly mixed with the pulverized glass and it was re- 
melted. This practice, for obvious reasons, has been superseded 
by that of the direct incorporation of the coloring agents with the 


The Principal Coloring Agents Used in Glass. 


Some oxides, as gold, silver, copper and iron, require special 


Gold is used in glass to produce a red or so-called ruby color, 
which may be said to be difficult to obtain. Primarily in a ruby 
batch all ingredients must be of great purity, and the gold must be 
intimately incorporated with the batch. The temperature of the 
furnace must be sufficiently high, and the melt well regulated, as 
the color develops anywhere from red heat to point of fusion, and 
is aided in development in proportion to greater amount of gold 
used. Any batch producing salt water or "glass gall," must be 
avoided, as the gold will not distribute itself so long as these im- 
purities are present. Two dangers are to be avoided ; first the 
super-oxidation of the gold, which forms auric oxide, and does 
not color glass ; second, the conversion of the oxide into metal- 
lic gold by reduction, which gives the glass the property of trans- 
mitting a blue color, while reflecting a dull brown. Hence it is 
very important to avoid an excessive use of reducing agents, and 
neutral agents must be added to the batch to regulate and limit 
the oxidation of the metal. 

Gold distributes itself in the glass uniformly only at a very 
high temperature. Mueller claims that one part of gold will im- 
part a red or ruby tint to 50,000 parts of glass, remain visible up 
to 100,000 parts, and entirely vanish at 200,000 parts. 

Gold is added to the batch in the form of "purple of cassius," 
which is prepared (according to Pelletier) by dissolving 20 
grammes of gold in 100 parts of "aqua regia," (20 parts nitric acid, 
and 80 parts of commercial hydrochloric acid,) aqua regia being 
the only true solvent of gold. Evaporate the solution to dryness 
and dissolve the residue in water ; filter and dilute with about 7 
or 8 deciliters (about i l / 2 pints) of water, and place in con- 
tact with tin filings. The liquid will then undergo a vigorous ac- 
tion and become brown, when a purple precipitate is thrown down, 
which is then washed and dried at a moderate heat ; this consti- 
tutes "purple of cassius/' and is composed about as follows: 

Stannic acid 32.746 

Protoxide of tin 14.618 

Protoxide of gold 44-772 

Moisture 7.864 



American colormakers however, have dispensed with the use 
of tin, and simply dissolve the gold in equal parts of nitric and 
muriatic acids, and facilitate the dissolution by means of the sand 
bath, and as soon as dissolution is complete, the liquid holding the 
gold in solution is poured over the sand entering the batch, or on 
the batch itself, and thoroughly mixed with it. 


The oxide of silver yields a color from light yellow to orange. 
The silver is not mixed with the batch in the ordinary method and 
then fused, as it is invariably reduced and is found at the bottom of 
the crucible. Silver added to the batch produces a pale yellow 
glass, and by attempting to intensify the color by increased quan- 
tity of silver, brings about an iridescent surface to the glass, in- 
stead of a deeper color, by that part of the silver over and above 
what is sufficient to saturate the glass, being superficially sep- 
arated and producing other light effects. But if the chloride of 
silver be mixed with any convenient medium, say powdered clay, 
and applied to the surface of the glass with a brush as a pigment 
and the glass exposed to a moderate heat in a muffle, a yellow 
tint or stain will be imparted by penetration. By experiment 
Lemal demonstrated that by baking five minutes the color pene- 
trated to a depth of 0.17 m, m ; after one hour 0.34 m, m ; after 
eighteen hours 1.6 m, m. By this means a lace pattern can be 
transferred to the glass by dipping the lace in a 0.00 1 per cent, so- 
lution of silver nitrate, and then in potassium sulphide. The rate 
of penetration depends upon the nature of the glass and its atomic 
volume. But glass so stained should contain alumina to get a 
good effect. 

The chloride of silver can be prepared by taking one part of 
nitric acid, and three parts boiling water, which forms "aqua 
fortis" and will dissolve one-third of its weight of silver before the 
acid is perfectly saturated. To precipitate the solution dilute it 
with five times its quantity of water, and add a portion of common 
salt ; stir well continually. A white powder will be precipitated ; 
decant the liquor, and continue adding boiling water until the 
water becames quite insipid. 

Silver is rarely introduced with the batch, because : First, it 
does not readily unite with oxygen ; second, it loses its oxygen 
at a high temperature and becomes reduced to the metallic state, 
in which condition it exercises no coloring effect and is conse- 
quently worthless in that capacity. 


Copper forms two oxides ; the peroxide or black oxide col- 
ors glass green ; the sub-oxide or red oxide, red or ruby. Cop- 
per imparts its color at a fair red heat, and in making ruby glass 


especially, much that has been said regarding gold, in many in- 
stances applies to the use of copper, inasmuch as it must be incor- 
porated thoroughly with the batch ; the temperature of the furn- 
ace must be carefully regulated ; ingredients generating "glass 
gall" must be avoided; and the oxide of copper must be associated 
with reducing agents of sufficient strength to prevent its super-ox- 

Copper colors glass deeper than gold because of its greater 
fusibility. For the purpose of holding copper at its lower state of 
oxidation, oxidizing agents are avoided, and reducing agents, as 
oxide of tin, iron scales, etc., are substituted. 

To prepare oxide of copper, mix copper filings or small pieces 
of copper, with sulphur, in a crucible and burn until the whole is 
reduced to a cinder. When cool reduce to a powder (copper 
scales). Muspratt's method of procuring the sub-oxide of copper 
is to boil acetate of copper in four parts of sugar. The sugar as- 
sumes a portion of the oxygen from the cupric acetate, and it is 
reduced to the sub-oxide, which is precipitated as a brilliant red 
powder. Boil moderately about two hours, settle, decant liquid, 
wash and dry. 

The use of commercial copper scales imparts a cheap blue 
color, which can be varied according to quantity of copper scales 


Iron colors glass green, yellow or red. The pure oxide of 
iron imparts an orange-red color to glass. For this purpose it may 
be prepared by heating the nitrate. The protoxide of iron imparts 
a green color, which however lacks brilliancy. Care must be taken 
to prevent the conversion of the protoxide into sesqui-oxide, as the 
sesqui-oxide colors glass orange. 

An orange yellow can be obtained by combining iron, anti- 
mony and minium. 


Manganese besides being a decolorizer yields, proportionate 
to quantity, a color varying from rose to violet, purple, brown and 
black. But manganese when exposed to intense and prolonged 
heat parts with a portion of its oxygen and becomes manganous 
oxide, and glass containing the oxide in this form is colorless. 

Manganese used in connection with the oxides of copper and 
iron produces the color termed "London smoke" ; (this same ef- 
fect is produced by the combination of blue and amber colors). 



The oxide of cobalt yields a very rich color. It is very posi- 
tive in its results, and is exceedingly easy to handle, and colors 
glass a deep, rich blue. A small amount of iron or copper oxide 
in connection with cobalt aids in preventing the hue from verging 
to violet, when used for intensity of color ; while nickel or zinc 
brightens a cobalt blue. 

Zaffre, an impure cobalt oxide, may be used, but there is no 
economy in its use. 


The oxide of uranium produces the peculiar yellow color 
verging on green known as canary. It is too expensive except 
for the finest grades of yellow. 


The oxide of chromium produces an emerald yellow, passing 
into a grass green. Used in excess the surplus remains dissem- 
inated through the glass in sparkling crystals. 


»Minium, or oxide of lead, used in excess yields a pale yellow 


Antimony sulphide roasted to a state of antimonious acid, 
and melted with from three to five per cent, of undecomposed 
antimony sulphide produces a fine yellow. 


Selenium is added directly to the ingredients in the pot, and 
imparts a rose tint to the glass. The depth and intensity of the 
tint depends upon the character of the glass to a certain extent, 
soft glass assuming more depth of color than hard glass. The 
tint however depends more especially upon the quantity of selen- 
ium used. By combining cadmium sulphide with the selenium, 
an orange-red color is the result, the intensity of the orange-yel- 
low being proportionate with the quantity of cadmium sulphide, 
which should be mixed with the selenium before introducing it to 
the material to be colored. 



Oxide of nickel imparts a bluish tint to potash glass ; a hy- 
acinth tinge to soda glass, and, used in excess, imparts a violet 
tint. The tints imparted by nickel are constant. Nickel is gen- 
erally used in the form of nickelous oxide or protoxide of nickel, 
a powder of dull green color. 


The oxide of zinc, as a rule, imparts a yellow color. 


Carbon occurs in many forms, and is used for coloring glass 
from a straw color to a dark amber. Any carbon, or carbonaceous 
substance effects this purpose. It is generally used in the form 
of powdered charcoal, anthracite, cannel coal, coke, birch bark, 
burned animal hoofs, corn, oats, etc. 

Calcium Phosphate. 

Calcium phosphate, generally in the form of bone-ash, is used 
to impart opal color or opacity to glass. Bone-ash glass however, 
is brittle and difficult of fusion. Used in excess it increases liabil- 
ity to oxidation if exposed. Calcium phosphate used in moderate 
quantities imparts opalescence to the various colored glasses, 
which is developed in proportion to the amount of lime used, and 
temperature to which it is re-heated. 


Cryolite is a brilliant mineral, sub-transparent to translucent 
substance found in Greenland, that is sometimes used in the manu- 
facture of opal glass. Its composition is about as follows : 

Aluminium 13.0 

Sodium 32.8 

Fluorine 54.2 

It. is fusible in the flame of a candle. The use of cryolite is 
objectionable on account of its vigorous attack on the melting pot. 
When used it is proportioned about 14 pounds of cryolite to 100 
pounds of sand. 

Sodium Seleniate. 

Seleniate of sodium is used to replace oxide of gold in the 
production of ruby colored glass. One to two pounds of selen- 
iate of sodium to 1,000 pounds of sand, is recommended to pro- 
duce a very fine red color. 


Fluor-Spar— Feldspar. 

Fluor-spar and feldspar (feldspar contains about 14 per cent, 
of potash), are used principally as substitutes for cryolite, etc., in 
the manufacture of opal glass. While their action on the pot is 
even more vigorous than that of cryolite, yet glass in which they 
enter can be melted at a much lower temperature than cryolite 
glass. The proportion of these ingredients used is generally 
large — 40 fluor-spar to 100 of sand \ 20 feldspar to 100 of sand. 

Tin Oxide. 

Tin oxide imparts a white opacity to glass, but is expensive ; 
hence its use has been to a certain extent discontinued. 


Guano seems to be the only substance which will impart a 
white opacity to glass, and yet be economical in cost and effect on 
pots. For these reasons foreign glassmakers have long since 
adopted it. Prof. Draper, of New York, gives the following 
analysis of Baker's Island and Jarvis' Island guano, which show 
the constituents to be : 

Baker's Island. Jarvis' Island. 

Moisture 4.50 7.50 

Organic matter 11.00 4.00 

Soluble salts 2.50 

Calcium sulphate 7.00 5.00 

Calcium phosphate 76.80 81.00 

Carbonates and silica 1.50 

Guano is always calcined before use to remove organic mat- 


Borax is sometimes used in colored glass to intensify the 


Taking into consideration the foregoing we summarize as 
follows : 

Red is produced by manganese, oxide of iron, sub-oxide of 
copper, gold and sodium seleniate. 

Blue is produced by cobalt, zaff re and copper scales. 

Green is produced by protoxides of iron, peroxide of copper 
and oxide of chromium. 

Black, by oxides of manganese, iron and cobalt. 


Violet, by oxide of manganese. 
Yellow, by oxide of uranium, antimony and silver. 
Orange, by oxide of iron, antimony and minium combined. 
White opal, by bone-ash, cryolite, oxide of tin or guano. 
In making colors much must be determined by experiment, 
as no two glassmakers use precisely the same formulas, or work 
under similar conditions ; and all effects must be determined by 
such circumstances as crude materials, oxides, furnaces, fuels, 
pots, etc. 

We have assumed to outline in the preceding pages, the basis 
of the fixed and more prominent colors. Other colors may be 
produced indefinitely by blending different colors, hues and 
densities into new colors modified in tone and intensity. It is 
perfectly reasonable to suppose, that as the artist blends his pig- 
ments, so may a glassmaker blend his batches, to a dfertain extent 
of course, in the production of compound colors. Good judg- 
ment and ingenuity figure largely in this particular. 

If a color is intense it may be toned down by the addition of 
clean flint glass cullet of the same composition, as the founda- 
tion of the average colored glass is simply a good crystal flint 
batch to which the oxides productive of the different colors have 
been added. The intensity of a color varies in proportion with 
the quantity of the oxide used, and it is very important that the 
materials composing the entire batch are as pure as possible. Pel- 
lat in his "Curiosities of Glassmaking," recommends for a good 
flint batch : 

Carbonate of potash ioo 

Red lead, or litharge 200 

Sand 300 

Saltpetre 14 to 28 

Oxide of manganese J4 to ^ 

The American practice in many instances is to substitute an 
equivalent of soda for potash, except when lead is used. 

As lead glass assumes a finer, fuller color it is preferable to 
lime glass in making fine colors, besides a smaller amount of col- 
oring matter can be used. But while lime glass requires a larger 
quantity of the oxides, the addition of a small quantity of lead en- 
hances the color and improves the quality of the glass. 

The use of salt cake is never advised in the finer grades of col- 
ored glass, as the carbon required to remove the salt water and 
like impurities would radically impair the coloring power of the 
oxides ; hence it is advisable to not add the oxides, when salt 
water does occur, until it has been thoroughly removed, and 
then add them to the fluid glass. In such cases it is best to mix 
the coloring agents with pulverized glass, and thus add them to 
the metal. As the pulverized glass melts it envelops the oxides, 
prevents their evaporation, decreases their liability of reduction to 


the metallic state, and holds them in suspension in the glass, as, 
on account of their greater specific gravity, they have a tendency 
to sink to the bottom of the pot. This is especially so where they 
have been added to the fluid glass instead of being mixed with the 

Red Glass. (Ruby.) 
Gold Red. 

The use of a rich lead batch is recommended, to which add 
one ounce of gold to every sixty pounds of batch. This is the 
usual American practice. Pellat recommends the use of four 
ounces of gold to every six hundred (600) pounds of batch. 
Kohn recommends 0.115 kilograms of gold to every 100 kilo- 
grams of sand. 

When a pot of metal is plain it should be "worked out" at 
once, and the color developed in a hot lehr. If the metal turns 
muddy or thick while working it, ladle it into clean water. 

ipes for Gold Red. 

Sand 62 lbs v Antimony 6 oz 

Lead 76 lbs Manganese 3 oz 

Nitre 22 lbs Gold 1 oz to 80 lbs batch 

— 2 — 

Sand 56 lbs Antimony 4 oz 

Lead 63 lbs Manganese 2 oz 

Nitre 18 lbs Gold 1 oz ioj^ drams 


Sand 60 lbs Nitre 7 lbs 

Lead 34 lbs Arsenic 1 oz 

Pearl ash 25 lbs Gold 1 oz 

Note. — Must be filled, melted, ladled and refilled three 
times, and has the appearance of dirty flint until after annealing. 

Sand 32 lbs White oxide of antimony . . 2 oz 

Lead 36 lbs Manganese 1 oz 

Nitre : . . 16 lbs Gold 1 oz 

— 5— 

Sand 12 lbs Pearl ash 1 lb 

Lead 14 lbs White oxide of antimony . Y\ oz 

Nitre 5 lbs Manganese ]/ 2 oz 

Gold y 2 oz 


Sand 16 lbs White oxide of antimony . . I oz 

Lead 18 lbs Manganese $4 oz 

Nitre 8 lbs Prepared gold J^ oz 

— 7— 
Sand ioo lbs Oxide of tin 13 oz 

Lead 80 lbs White oxide of antimony. 13 oz 

Potash 32 lbs Red oxide of iron 2 oz 

Saltpetre 4 lbs Manganese . . . . '. 13 J^ oz 

Regulus antimony ia^ lbs Gold \]/ 2 oz 

Sand 102 lbs Oxide of tin 13 oz 

Potash 32 lbs Red oxide of iron 2 oz 

Lead 80 lbs Manganese 12 oz 

Nitre 4 lbs Powdered slate J4 oz 

Black oxide of antimony.i^ lbs Gold 1V2 oz 

Belgian; rose-red. 

Sand 100 Tin . .0.4 dissolved in aqua regia 

Potash 32 Gold 0.04 dissolved in aqua regia 

Red lead 40 Mix solution with three or four 

Nitrate of potash 15 quarts of water and moisten 

Borax 15 the sand with it. 

To retain rose-red, avoid an excess of lead, which has a ten- 
dency to lead the color to violet. Per-oxide of tin adds warmth 
to color. 

Copper Red. 

Copper reds are more difficult to make than gold reds. The 
reduction of the copper must not be carried beyond a certain lim- 
it, as the copper will return to the metallic state and give the 
glass, instead of a ruby color, a spangled effect ; hence it often 
happens when trying to obtain copper reds the so-called adven- 
turin glass is the result, and vice versa. Again, when the reduc- 
tion is carried too far the glass assumes an opaqueness that re- 
sembles a coral or sealing wax red color. 

Copper Red Recipes. 

Sand 100 Gullet 100 

Carbonate of sodium 28 Oxide of copper 4 

Slacked lime 24 Oxide of iron 4 

Lead 8 Nitrate of potassium 8 


— ±— 

Sand ioo Oxide of copper 7 

Soda 38 Oxide of tin 7 

Lead 66 Nitrate of potassium 10 

Oxide of iron 4 


— 3— 

Copper cullet 15 lbs 

When melted add copper calcined to redness, 4 to 6 ozs ; let 
it settle and add powdered red tartar ; let all refine, and then 
work out and anneal until the color assumes sufficient depth. 

Wax Red. 

—■ 4— 

Flint batch 2 tbs Tartar salts 2 oz 

Calcined copper 4 oz Oxide of iron j4 oz 

— 5— 

Sand 9 Pearl ash 3 

Lead 6 Raw brass 1 

Crocus martis 12 oz 

Flint batch 30 Brown glass metal 30 

Calcined copper 1 

Belgian for Flashing. 

Sand 100 Borax 12 

Potash 32 Carbonate of calcium 10 

Red lead .* 40 Peroxide of copper 2 

Nitrate of potassium 12 Peroxide of tin 2 

Iron fillings 0.5 


Sand  . . 100 Melt, cast, grind to fragments 

Carbonate of sodium 75 and add per 100 parts: 

Lime 20 Sand 80 

Equal parts of copper scales Carbonate sodium 30 

and sulphateof iron heated Lime 14 

to red heat 10 Cast and grind as before, and 

Stannic acid 10 add 35 parts of sand and re- 



Sand 25 Melt, stir, cast, grind and re- 
Red lead 50 melt three successive times. 

Oxide of copper 1.2 At second color is light yel- 

Stannic acid 3 low, at third the color is an 

orange yellow. 

After third casting mix with 25 parts of crystal glass com- 
posed as follows : 

Sand 100 These 25 parts of cullet are 

Carbonate of potassium ... 36 melted with above. Add 30 

Lime . . . . : 18 to 40 grains of tartar or tin 

Red lead 3 chips and remelt. 




Amethyst Glass. 

Flint batch 1 12 Manganese 8 oz 

Crude antimony 1 oz 

Blue Glass Recipes. 
Deep Azure. 

Sand 40 Nitre 15 

Lead 50 Arsenic 3 

Zaffre 4 oz 

— 2 — 

Flint batch 600 Zaffre 9 

Flint cullet 600 Manganese , 1 

— 3— 
Flint batch 560 Zaffre 9 

— 4— 

Flint batch 600 Zaffre 6 

Manganese 3 

— 5— 

Flint batch 800 Zaffre 2 

Manganese 1 }4 

Deep Opaque. 

Sand 49 Phosphate of calcium 9 

Lead 39 Arsenic 1 

Nitre 11 . . Zaffre 8 oz 

Brass filings 3 oz 

— 7— 

Sand 300 Nitre 50 

Lead . . . . 200 Manganese 8 

Soda 100 Borax 4 

Oxide of cobalt 3 

Sand 260 Nitre 20 

Lead 212 Zaffre 4 

Ash 85 Manganese 1 % 

Flint batch 120 Nitre 10 

Cullet '. 220 Zaffre 3 

Manganese 1 


Flint batch 200 Nitre 6 

Flint cullet 200 Zaffre 2 

— II — 

Flint batch 250 Oxide of nickel 2 

— 12 — 

Flint batch 112 Blue cullet 112 

Zaffre 1 



Sand 44 Nitre 8 

Lead 44 Zaffre ,-...... 2^4 

Ash 20 Manganese 4 

Opaque Sky-Blue. 


Opal batch 28 Phosphate of calcium 1 

Arsenic 4 oz Zaffre ij4 02 

Calcined brass }£ oz 

Sky-Blue. ' 

— 15— 

Sand 40 Nitre 15 

Lead 50 Arsenic 5 

Zaffre 4 oz 

Waterloo Blue. 

Flint batch 40 Cullet 40 

Zaffre 3 oz 


Sand 1000 Manganese 10 oz 

Soda , 360 Arsenic 10 oz 

Lime 125 Cobalt . . 10 oz 

Cheap Blue. 


Sand 100 Nitre 7 

Soda 35 Manganese 2}i oz 

Lime 18 Arsenic 2]/ 2 oz 

Cobalt 1 oz 


Cheap Blue. 

— 1< 

Window glass ioo Zaffre i 

Sulphate of sodium 6 Manganese }4 


Flint batch 1 12 Black oxide of copper 3 oz 

Oxide of iron 3 oz 

— 21 — 

Sand . . ., 100 Oxide of cobalt J4 

Potash 25 Salt 2 

Borax 4 Arsenic J4 

Slacked lime 12 Blue cullet 100 

Blue Sheet. 

— 22 — 

Sand 100 Zaffre y 2 

Soda 35 Arsenic 1 

Lime , ... 10 Oxide of zinc 1 

Bone dust 10 

For Casing. 


Sand 100 Bi-carbonate of sodium 50 

Lead 1 Cobalt 1 

Nitrate of sodium 10 Manganese y 2 

Arsenic J4 Cullet 100 

For Casing. 

Flint batch to be cased 100 Best cobalt 1 



Sand 100 Oxide of cobalt 0.400 

Soda . ; 36 Oxide of copper 7 

Carbonate of calcium 25 Saltpetre 6 

Lead . ; 10 Flint cullet 200 

Belgian; Light. 

Sand . . . 100 Black oxide of copper 0.01 

Soda 32 Black oxide of cobalt 0.04 

Carbonate of calcium 24 Borax 1 

Charcoal 2.5 


Belgian; Dark. 


Sstnd 100 Black oxide of copper 1.5 

Soda 32 Copper sulphate 1.5 

Carbonate of calcium 24 Black oxide of cobalt o. 1 5 

Charcoal 2.5 Borax 1 

# 1 

Belgian for Flashing. 


Sand 100 Oxide of copper. 4 

Soda 32 Oxide of cobalt 0.3 

Carbonate of calcium 24 Borax 5 

Charcoal 2.5 




Green Glass Recipes. 

Flint batch 500 Copper scales .2254 

— 2 — 

Flint batch 1000 Copper scales 15 

Red ochre 14 



Flint batch 500 lbs Calcined copper 7 lbs 

Iron scales powdered, washed 
and dried 8 oz 

Light Blue-Green. 

— 4— 

Flint batch 108 lbs Peroxide of iron 3 oz 

Carbonate of copper. .2 lbs 4 oz 

Dark Green. 

— 5— 

Flint batch 100 lbs Black oxide of copper 1 lb 

Crocus martis 12 oz 

Light Yellow-Green. 

Flint batch .28 Bi-chromate of potassium .... 2 


— 7— 
Flint batch 224 Brass filings 8 

Light Emerald-Green. 

Sand 120 Pearl ash 40 

Lead 60 Nitre 20 

Iron filings I 

Green for Muffs. 

Flint batch . . .380 Flint cullet 320 

Nitre 10 Brass filings 30 

Manganese 2 



Flint batch 280 Iron filings 2lbs 8 oz 

Flint cullet 250 Borax 2 

Antimony .8 oz 

Light Green for Muffs. 

— 11 — 

Flint batch 100 lbs Iron finings 4 oz 

Borax 6 oz 


— 12 — 

Sand 100 lbs Nitre 7 lbs 

Soda . . ., 35 lbs Manganese 21/2 oz 

Lime 18 lbs Arsenic 2% oz 

Copper scales 6 oz 



Flint batch 50 lbs Yellow arsenic 3 lbs 2 oz 

Crocus martis* 3 lbs 2 oz Brass filings 1 lb 9 oz 



Flint batch 260 Green yellow cullet .550 

Flint cullet 100 Brass 34 

Iron 16 

Saxon Green. 


Sand 135 Nitre 36 

Lead 100 Oxide of copper 6 

Opaque Green. 

— 11 

Sand 18 lbs Arsenic 3 

Nitre 14 lbs Brass filings 3 oz 

Oxide of copper 2 oz 



Flint batch 126 lbs Iron filings 11 oz 

Oxide of copper 5 oz 


Bohemian Aqua-Marine. 

Sand ioo Oxide of copper 8 

Soda 38 Oxide of iron 4 

Lime 12 Salt . . . . . 3 

Arsenic % 

Yellowish-Green Sheet Glass. 

Sand 100 Bone ash . . 10 

Salt cake 38 Yellow or red chromate of 

Carbonate of calcium 25 potassium 3 

Plain cullet 100 

Chromate dissolved and poured over the sand. 


Sand 100 Sulphate of copper 2 4 

Soda 3q Arsenic T /% 

Lime 22 Uranium 1 

Green for Casing. 

— 21 — 

Sand 100 Nitrate of sodium 3 

Potash 38 Oxide of copper 8 

Lead 58 Oxide of iron 3 

Bi-carbonate of potassium . . 1 

Bontemps Yellow Tinted. 

— 22 — 

Sand 100 Nitrate of potassium 7 

Carbonate of sodium 33 Oxide of iron 3 

Chalk 20 Oxide of copper 5 

Bi-chromate of potassium. . 1.4 

Belgian Green; Yellowish. 


Sand 100 Charcoal 2.5 

Soda 32 Black oxide of copper 8 

Carbonate of calcium 24 Bi-chromate of potassium . . 1 

Borax 1 


Belgian Bluish-Green. 


Sand 100 Black oxide of copper 1 

Soda 32 Bi-chromate of potassium . .0.5 

Carbonate of calcium 24 Borax 1 

Chafcoal 2.5 Smalt r 1 

Belgian Dark Green. 


Sand 100 Black oxide of copper 1.5 

Soda 32 Bi-chromate of potassium . . 1 

Carbonate of calcium 24 Borax 1 

Charcoal 2.5 Smalt , q.i 

Red oxide of iron (crocus 
martis) 1 

Oriental Green. 


Sand 36 lbs Nitre 16 lbs 

Lead 29 lbs Oxide of uranium 9 oz 

Carbonate of copper. . . .2}4 oz 

Olive Green. 


Flint batch 1 12 Red ochre 4 

Brass 2 

Pea Blossom Green. 

Flint batch 100 Zaffre 1 lb 8 oz 

Manganese 12 oz 

Note. — Uranium imparts a greenish fluorescence to glass, 
Copper-green should always be melted in covered pots. The use 
of chromium oxides has been abandoned, and red and yellow 
chromates of potassium have been substituted, and should be used 
in a finely pulverized condition. 




Turquois Glass Recipes. 

Sand 5op Nitre 64 

Lead 400 Phosphate of calcium 90 

Pearl ash 160 Arsenic 15 

Calcined brass 15 

Sand 24 lbs Phosphate of calcium.3 lbs 12 oz 

Lead 19 lbs Arsenic 1 lb 4 oz 

Pearl ash 6 lbs Zaffre 3 lbs 4 oz 

— 3— 

Sand •. 50 lbs Nitre 6 oz 

Lead 50 lbs Phosphate of calcium 9 oz 

Pearl ash 16 lbs Arsenic 1 lb 8 oz 

Brass filings 1 lb 8 oz 

— 4— 

Flint batch 5 lbs Green cullet 3 lbs 

Blue cullet 5 lbs Enamel white 1 oz 

— 5— 

Sand 160 lbs Pearl ash 28 lbs 

Lead 80 lbs Phosphate of calcium .... 18 lbs 

Nitre 28 lbs Arsenic 3 lbs 

Brass filings 1 lb 8 oz 

Very Good. 

Sand 100 lbs Pearl ash 40 lbs 

Lead 80 lbs Phosphate of calcium. ... 18 lbs 

Nitre .-. 20 lbs Arsenic 3 lbs 

Brass filings 1 lb 8 oz 

Note. — Turquois batches must be thoroughly mixed. Add 
sulphate of copper to batch to raise color ; phosphate of calcium 
to lower color. 




Black Glass Recipes. 

Green cullet ioo Manganese 8 

Soda 38 Oxide of iron 6 

Lime 18 Pulverized coke 4 

Arsenic 2 


Sand 100 Oxide of copper 10 

Potash 36 Oxide of iron 10 

Lime 13 Manganese . . ; 10 

Zaffre 10 

' — 3— 
Sand 100 Oxide of copper 4 

Potash 15 Oxide of iron 4 

Soda 24 Manganese 5 

Lime 18 Zaffre 2 



Sand 100 Black oxide of copper 3 

Soda 31 Manganese 4 

Carbonate of calcium 24 Smalt 4-10 

Charcoal . . , 2.5 Peroxide of nickel 3-10 

Borax 1 


Sand 100 Charcoal 2.5 

Soda 32 Manganese 2 

Carbonate of calcium 25 

Flint batch 560 Manganese 20 

Flint batch 100 Zaffre iq 

Manganese .'754 Calcined iron 6 oz 2 drams 

Flint glass 200 Black cullet 100 

Flint chest cullet 100 Manganese 50 

Flint batch 600 Manganese 40 

Black cullet 700 Oxide of iron 40 


Flint batch 112 Oxide of iron 7 

Manganese 12 Zaffre 4 oz 

•11 — 

Window glass .1500 Manganese 64 

Nitrate of sodium 75 Zaffre 1 

A grey glass is obtained by neutralizing the violet color im- 
parted by manganese with the oxides of iron and copper. The 
same effect may be obtained by the use of oxide of nickel. 

Brown Glass Recipes. 

Flint batch 30 Red lead 42 

Manganese 12^ 


Flint batch 53 Manganese 20 

Flint cullet , 50 Zaffre 2 




Amber Glass Recipes. 

Flint cullet 12 lbs Nitre 8 oz 

Lead 4 lbs Tin ash 2 oz 

Sand 2 lbs Oxide of silver 3 dr 

Oxide of copper y 2 oz 

Flint batch 56 Nitre 16 

Lead 64 Amber 2 

— 3— 

Flint batch 112 Manganese 4 

Red ochre 20 Arsenic .1 

— 4— 

Flint batch 30 lbs Red oxide of iron 5 oz 

Flint cullet 50 lbs Manganese 8 oz 

Antimony 1 oz 


Flint batch 112 Crocus martis 6 

Manganese 2 

Rich Color. 

Flint batch 112 Peroxide of iron 

Manganese , 1 


Amber cullet 448 Red oxide of iron 63 

Flint cullet 784 Manganese 14 

Flint batch 124 Arsenic 1 

Rich Dark. 

Sand 12 lbs Nitre 2 lbs 

Lead 10 lbs Oxide of iron 2 lbs 

Pearl ash 4 lbs Manganese 4 oz 

Flint batch 20 lbs Yellow arsenic 10 oz 

Crocus martis 10 oz Coal dust 7 oz 


Western Practice. 

Sand 900 Lime 120 

Soda 340 Cannel coal 6 

Sulphur 2 

— 11 — 

Flint batch 100 lbs Coal dust 1 lb 1 oz 

Crocus martis 3 lbs 2 oz Yellow arsenic 1 lb 9 oz 


Sand 100 lbs Lime 28 lbs 

Soda 40 lbs Fine salt 10 lbs 15 oz 

Pulverized charcoal. 3 lbs 15 oz 




Purple Glass Recipes. 

Flint batch ioo lbs Manganese 10 oz 

Zaffre 5 oz 

— 2 — 


Flint batch ioo lbs Manganese 16 oz 

Zaffre i J4 oz 

— 3— 

Flint batch 560 lbs Manganese 12 lbs 

Cullet 50 lbs Antimony 1 oz 

— 4— 

Flint batch 220 Borax 6 

Manganese 2 Cullet 260 

— 5— 

Flint batch 560 Manganese 12 

Arsenic 1 

Broken window glass 1000 Manganese 32 

Nitrate of sodium 50 Zaffre 4 oz 

Note. — The commonest kind of material will do for purple 
glass ; even black, or window glass, fluxed with nitrate of sodium. 

Violet Glass Recipes. 

Flint batch 84 lbs Calcined copper 5 lbs 8 oz 

Strong smalt 4 lbs 6 oz Antimony 6 oz 

— 2 — 

Flint batch 100 Calcined brass 1 

Zaffre ij4 

— 3— 

Sand 56 Nitre 4 

Lead 28 Calcined copper 4 

Pearl ash 14 Strong smalt 3 

Antimony 2 

Opaque Violet. 

— 4— 

Sand 40 lbs Nitre 15 lbs 

Lead 45 lbs Arsenic 2 lbs 

Oxide of nickel 7 oz 



— 5— 

Sand ioo Carbonate of calcium 90 

Soda 100 Nitrate of potassium 90 

Potash . . . . r 20 Manganese 22 

Lead 90 Nitrate of sodium 12 

Cullet 90 

Violet Sheet. 

Sand 100 Slacked lime 15 

Soda 35 Manganese 10 

Lead 2 Saltpetre 2 

Ground glass 100 


— 7— 

Sand 100 Charcoal 2.5 

Soda 30 Manganese 3 

Limestone 25 Smalt 0.1 

Borax 1 

For Flashing. 

Sand 100 Charcoal 2.5 

Soda 30 Manganese 6 

Limestone 25 Oxide of cobalt 0.2 

Borax 1 




White Glass Recipes. 
White Enamel. 

Sand ioo lbs Soda 70 lbs 

Lead 100 lbs Arsenic 16 lbs 

Antimony 8 oz 

White Enamel. 

— 2 — . 

Sand 300 lbs Arsenic 24 lbs 

Lead ., 300 lbs Alabaster or chalk 8 lbs 

Nitrate of sodium 25 lbs Manganese 3 oz 

Antimony 2 oz 

White Enamel. 

— 3— 
Sand 120 lbs Nitrate of sodium 40 lbs 

Lead 130 lbs Arsenic 15 lbs 

Antimony 6 oz 

White Enamel. 

Sand 15 lbs Arsenic i 1 ^ lbs 

Lead 16 lbs Manganese 1 oz 

Nitrate of sodium 4 lbs Antimony 1 oz 

White Enamel. 

Sand 100 lbs Lead 120 lbs 

Nitrate of sodium 24 lbs Arsenic 10 lbs 

Antimony 6 oz 

White Enamel. 

Sand . . . ., 37 Pearl ash 1 

Lead 28 Arsenic 4 

Nitre 24 Sulphate of calcium 1 

Antimony .1 

White Enamel. 

Sand 60 lbs Pearl ash , 10 lbs 

Lead 48 lbs Arsenic , 6 lbs 

Nitre 29 lbs Phosphate of calcium 3 lbs 

Antimony 2 oz ' 

j _ — 


White Enamel. 

Sand 336 lbs Arsenic 24 lbs 

Lead 336 lbs Chalk 81bs 

Nitre , 20 lbs Antimony 2 lbs 

Manganese 3 oz 

White Enamel. 

Sand 180 Arsenic 12 

Lead 160 Antimony 4 

Nitre 20 

White Enamel. 

— 10— 

Sand 112 Arsenic 8 

Lead 112 Antimony }i 

Nitre 20 Manganese 1 

Note. — To every pound common flint batch in Nos. 6, 7, 8, 
9 and 10, add: Arsenic 1 oz., chalk % lb., lead 1 oz. 


— 11 — 

Sand „. ... 20 lbs Arsenic 1 J4 oz 

Potash 10 lbs Manganese ; 4 oz 

Quicklime 4 lbs 2 J4 oz Nitre 6 lbs 

Phosphate of calcium 4 oz 


— 12 — 

Sand 20 lbs Quicklime 3 lbs 9 oz 

Potash 6 lbs Arsenic 1 oz 

Phosphate of calcium .... 
1 y 2 to 3 lbs 



Sand 40 lbs Arsenic .2 oz 

Potash 44 lbs Manganese 2 oz 

Quicklime 9 lbs Nitre 2 oz 

Phosphate of calcium. 4 lbs 8 oz 


— 14— 

Flint batch 500 Arsenic 4 

Bone ash 60 Borax v . 15 


— is— 

Flint batch 1 12 lbs Soda , 30 lbs 

Lead , 84 lbs Nitre 32 lbs 

Bone ash 23 lbs Arsenic 2 lbs 

Antimony ,. 2 oz Manganese 2 oz 


Sand 40 Nitre 15 

Lead .45 Arsenic 3J4 


Sand 1 14 lbs Nitrate of sodium 30 lbs 

Lead 75 lbs Sulphate of calcium 16 lbs 

Soda 30 lbs Arsenic 6 lbs 

Antimony 3 oz 


Sand 204 Nitrate of sodium 140 

Lead 172 Arsenic 12 

Antimony J4 

— 19— 

Sand 20 Nitrate of sodium 8 

Lead 25 Arsenic 1 }i 

— 20 — 

Sand 1800 Lead 160 

Nitrate of sodium 10 Arsenic 12 

— 21 — 

Flint batch 400 Burnt bones 25 

Arsenic 7 Zaffre 1 oz 

Note. — To every pound flint batch Nos. 21 and 22 add : Ar- 
senic % oz. and nitre j4 oz. 

— 22 — 

Sand 100 Phosphate of calcium 20 

Lead 80 Arsenic ? 3 

Nitrate of sodium 30 Antimony 4 oz 

Potash 28 

Will Turn in Working. 

Sand 90 Arsenic 2 

Lead 60 Antimony % 

Phosphate of calcium 15 Potash 30 

Will Turn in Working. 


Sand 56 Arsenic 1 }£ 

Lead 44 Antimony J4 

Phosphate of calcium 10 Potash 24 


Will Turn Without Cooling. 


Flint batch 112 Phosphate of calcium 10 

Lead 4 Arsenic 1 

Antimony 1-32 

Sand 49 Nitre 11 

Lead 39 Phosphate of calcium 9 

Arsenic 1 lb 8 oz 

Note. — For turquois add 10 ounces calcined brass. 

Bright Opal. 


Sand 100 Fluor-spar 25 

Lead , 38 Potash 19 

Bi-carbonate of potassium . . 10 Borax 1 

Feldspar 35 Manganese % 

Bright Opal. 

Sand 100 Fluor-spar 22 

Soda 35 Feldspar 38 

Lime 10 Nitre 4 

Oxide of tin 5 Manganese % 

German Lead Opal. 

Sand 100 Cryolite 14 

Soda 10 Lead 6 

Feldspar 13 Saltpetre 3 

German Without Lead. 

Sand 100 Bone ash 18 

Slacked lime 16 Soda 45 

Arsenic 3 

Bontemps' French Opal. 


Sand 100 Bone ash 14 

Lead 120 Borax 4 

Potash 30 Oxide of zinc 9 

Arsenic 4 


Lime Opal. 


Sand 100 Nitre 9 

Soda 33 Feldspar A . 15 

Lime 8 Arsenic 6 

Bone 5 

Note. — Oxide of tin is seldom used. Lead increases smooth- 
ness and luster. Bone ash glass on account of brittleness and 
hardness endures a high temperature without losing shape ; hence 
is suitable for decorating in the muffle. Opalescence is imparted 
to glass by the use of less phosphate of calcium than is necessary to 
render it opaque when first taken from the pot ; and as opal glass 
is easily colored with the various metallic oxides, opalescence may 
be imparted by reheating the glass. A glass, colored or crystal, 
may be made opalescent, semi-opaque or opaque in proportion to 
amount of phosphate of calcium used and amount of heat to which 
the glass is exposed while being manipulated. The coloring pow- 
er of the oxides is modified by opalescence, and the tints may be 
made to vary in intensity according to the amount of heat to 
which they are exposed. 




Yellow Glass Recipes. 
Yellow Sheet. 

Sand ioo Charcoal 4 

Soda 45 Arsenic I 

Carbonate of calcium 40 

French Yellow. 

— 2 — 

Sand 100 Lime , 25 

Potash 40 Sulphur i}i 

Arsenic % 

Flint batch 150 lbs Crocus martis 2 lbs 5J^ oz 

— 4— 

Flint batch 100 lbs Crocus martis 6% oz 

Soft Yellow. 

— 5— 
Flint batch 3 lbs Red lead 6 oz 

Naples yellow 1 lb 

Green Yellow. 

Flint batch 16 lbs Crocus martis 48 grains 

Lead 16 lbs If too green increase the quan- 

Oxide of copper 6 oz tity of crocus martis. 

Gold Yellow. 

— 7— 
Flint batch 50 Purified tartar 1 

Flint cullet 50 Manganese 1 

Victoria Yellow. 

Flint batch 350 Oxide of uranium 2 y 2 

Claret Yellow. 

Flint batch 100 Red oxide of iron 7 oz 

Yellow for Lamps. 

— 10— 

Flint batch 112 Manganese 2 J4 

Arsenic 2^4 Oxide of iron 15 


Victoria Yellow or Topaz. 

— ii — 

Sand 125 Potash 37 

Lead 52 Nitre 7 

Uranium 2 

Note. — To impart to any of the above yellows a green tinge, 
shading green one way and yellow the other way, add carbonate 
of copper 1 to 5 ounces. 

Gold and Silver Yellow— Fachblatt. 

— 12 — 

Pure quartz sand 74 kilogrammes 

Potash made up with molasses 6)4 kilogrammes 

Saltpetre 15 kilogrammes 

Red lead 19 kilogrammes 

Crystallized (humid) borax 30 kilogrammes 

Silver dissolved in nitric acid 27 and 45 grammes. 
Gold dissolved in aqua regia 5 franc piece. 

Belgian Yellow for Plashing. 


Sand 100 Borax \ ... 10 

Potash 32 Saltpetre 10 

Red lead 20 Carbonate of calcium 12 

Chloride of silver 0.3 





The ancients secretly prosecuted the manufacture of artificial 
gems, but in the decline of the art of glass the secrets were lost. 
Joseph Strasser, a Viennese jeweler, rediscovered the ancient 
method of imitating precious stones ; hence the glass which forms 
the base of all imitations is called "Strass." This is a glass very 
rich in lead, to which the coloring materials are added. Lead 
ranks first in importance by imparting the great specific gravity 
and refractive power essential in imitating the products of nature. 
In making this glass the greatest care is necessary; all ingredients 
must be chemically pure to obtain good results, and be carefully 
pulverized and thoroughly mixed. Specially manufactured pots 
are used, and in Austria and France, where a specialty of this 
glass is made, the pots are about one-quarter of an inch thick, and 
hold about six gallons, and are highly burned and glazed with 
loam, which makes the clay hard and dense. The melting tem- 
perature varies between i,ooo° and 1,500° centigrade. Great care 
is necessary during the melt. After the glass has been carefully 
melted it is allowed to cool very slowly and annealed in the pots. 
Profitable results in working up the glass are only obtained by 
careful cooling, which insures homogeneity and avoids disinte- 
grating by cracks, splintering, etc. When cool the glass and pots 
are separated with hammer and chisel, and the glass reworked into 

Recipes for Artificial Gems. 
Venetian Adventurin— Fremy-Clemandot. 

Pulverized lead flint . . 300 parts Iron scales 80 parts 

Copper scales 40 parts 

Spangled Glass— American Practice. 

— 2 — 

Flint batch (rich) melted until plain. Add copper filings; 
stir thoroughly; reheat until the glass has settled and all air ex- 
pelled. The reheating requires both tact and care to be success- 

Yellow Adventurin. 

— 3— 
Plate glass 2000 Iron scales 125 

Nitrate of potash 200 Peroxide of iron 60 

When fused add 38 grains of iron filings, stir, and cool very 


i 5 8 

Yellow Adventurin. 


White sand 250 Calcined iron scales 112 

Carbonate of sodium 100 Copper scales 23 

Carbonate of calcium 50 

Green Adventurin. 

— 5— 
White sand 250 Carbonate of calcium 50 

Carbonate of sodium 100 Bi-chromate of potassium. . .40 

Strass'— Donald-Wieland. 

Rock crystal 300 Arsenious acid 1 

Slacked lime 163 Red lead 470 

Calcined borax 22 

Strass'— Donault-Wieland. 

— 7— 
White sand 300 Arsenious acid 1 

Slacked lime 96 White lead 514 

Calcined borax 27 

Strass' Bastenaire. 

Sand 100 Borax 20 

Lead 40 Saltpetre 12 

Potash 24 Manganese 04 

Opal— Bastenaire. 

Sand 25 Saltpetre 2 

Lead 25 Oxide of tin 16 

Potash 10 

Topaz— Donault-Wieland. 

— 10— 

White strass 1000 Purple of cassius 1 

Clear yellowish orange red 
glass of antimony 40 


— 11 — 

White colorless strass. . . . 1000 Oxide of chromium 0.2 

Pure oxide of copper 8 



— 12 — 

Colorless strass iooo Oxide of cobalt 5 

Oxide of manganese 8 Purple of cassius; .0.2 



Colorless strass 1000 Purple of cassius 4 

Glass of antimony 500 Oxide of manganese 4 

Imitation Ruby. 

Strass 80 parts Oxide of manganese. . .2 parts 

Paste Resembling the Diamond. 

— is— 

White sand 900 parts Nitre 300 parts 

Red lead 600 parts Arsenic 50 parts 

Pearl ash 450 parts Manganese J4 part 

Imitation Gold. 

Platinum 16 parts Zinc 1 part 

Copper 7 parts 

Put in a crucible with powdered charcoal, or : 

Platinum 4 oz Copper 1 oz 

Silver . . . 3 oz 





Enamels constitute easily-fused glasses, colored by the same 
metallic oxides as the colored glasses. The art of enameling 
lent a charm to the works of past ages, but it has fallen into disuse. 

Lead predominates largely in enamels, which are generally a 
silicate of lead, potash and soda, mixed with tin and antimony salts 
of the same elements ; the silicates are also sometimes mixed with 
the borates. The object of the enamel applied to glass is to con- 
vey the idea of a metallic lustre, but owing to the low fusing point 
of glass the ordinary metallic lustres applied thereto have lacked 
stability ; the low temperature at which they are fired, on account 
of the fusibility of the glass, is insufficient to convert the boracic 
acid and silica, for instance, into stable compounds of a definite re- 
sistance. G. Alefeld suggests the conversion of the metallic 
oxides into a durable condition by adding to the lustres before use, 
substances that will transform the oxides into saturated and stable 
compounds, as phosphates, titanates, molybdates, tungstates or 
vanadates, which will be applicable to even a very fusible ground. 

1 62 



Containing Miscellaneous Recipes and 
Information Pertaining to Glass. 

Cost of Glass Per Pound. 

When the materials constituting the different varieties of 
glass have been melted into glass and it is ready to be worked the 
cost per pound of the different varieties does not vary greatly, 
possibly excepting lead-flint. The cost of the melted glass in the 
pot averages from 10 to 20 per cent, of the cost of the finished 
product ready to ship, and it is the labor required to put the glass 
into commercial forms that entails the cost. Even a large portion 
of the above 10 to 20 per cent, involves considerable labor in the 
form of mixer, teaser, furnace builder, potmaker, etc. The fol- 
lowing approximate estimates of cost per pound were computed 
in 1892: 

Flint Bottles. 

Sand .000503 

Soda ash 004510 

Lime 000269 

Glass 000039 

Manganese 000069 

Nitrate of soda 000896 

Arsenic 000088 

Lamp Chimneys. 

Sand .000358 

Soda ash 001009 

Potash 003300 

Lime 000018 

Lead 007407 

Glass 003181 

Other materials 000348 

Other materials 000018 V A11 labor except skilled 

All labor except blow- 
ing 007998 

Officials and clerks. . . .002993 
Supplies and. repairs. . .001734 

Fuel 004866 

Taxes 000334 

and boys 01 1359 

Officials and clerks. . . .002816 
Supplies and repairs... . .002010 

Fuel 006127 

Taxes 000206 

Total 024317 

Green Glass. 

Sand 000721 

Soda ash 003747 

Burnt lime or limestone .000196 

Glass 000872 

Other materials 000005 

All labor except blow- 
ing 005739 

Officials and clerks . . . .000390 
Supplies and repairs . . .000537 

Fuel 001033 

Taxes 000027 

Total 038139 



Total .013267 


Recipes for Silvering Glass. 
Liquid Foil for Silvering. 

Lead 1 part 

Tin 1 part 

Bismuth 1 part 

Melt, and just before it sets add mercury. . . .10 parts; 
pour into globe and turn rapidly. 

— 2 — 

Nitrate of silver ; . . . . I oz Liquid ammonia I oz 

Distilled water 3 oz Alcohol 3 oz 

Let mixture stand one hour and filter. To each ounce of 
above solution add one-fourth ounce of grape sugar, dissolved in 
equal quantities of water and alcohol. The surface to be silvered 
is covered with liquid and heated to a temperature of 160 F, until 
the deposit of silver is complete ; when dry give the surface a 
covering of mastic varnish. 

— 3— 

Partly dissolve one ounce of nitrate of silver in one-half pint 
of distilled water ; when dissolved and stirred well, pour off about 
one and one-half ounces of the solution. Then add liquid am- 
monia to the larger portion of the solution until it is clear ; pour 
back the portion taken out ; this will produce a muddy appear- 
ance in the solution ; filter through cotton. For sugar solution 
take best white sugar or rock candy, one pound ; water, one gal- 
lon ; tartaric acid, one scruple ; boil the whole 20 minutes. 

— 4— 

Dissolve one ounce of silver in one quart of water, add one 
ounce of caustic potash, and clear solution with ammonia. For 
sugar solution take sugar, one pound ; water, one gallon ; boil 20 
minutes ; add tartaric acid, one ounce, and boil again 20 minutes. 
Use one ounce of silver solution to 15 to 20 drops of sugar solu- 

To Solder Glass to Metals. 

Make an alloy composed of 95 per cent, of tin and 5 per cent, 
of copper ; melt tin first, and pour in copper while stirring well 
with a wooden spatula. This should be poured granulated, and 
remelted. One-half to one per cent, of lead or zinc makes this 
alloy, as hard, or fusible, as desired. The melting point of the 
above composition is about 6oo° C. 


Solder for Glass. 

Take 95 parts of tin, 5 parts of zinc ; has a beautiful metallic 
lustre, adheres firmly to glass and melts at 200 . 

To Stick Glass Letters to Windows. 

Take one part pure India rubber (not vulcanized), three parts 
mastic and thirty parts chloroform ; let it stand two or three days 
and dissolve ; then apply rapidly, as it does not take it long to 
get thick. 

Ink for Writing on Glass. 

Dissolve on water bath, to parts bleached shellac and 5 parts 
Venice turpentine in 15 parts oil of turpentine ; incorporate in 
the solution 5 parts of lamp black. 

Pencil for Writing on Glass. 

Stearic acid 4 parts, mutton suet 3 parts, wax 2 parts ; melt 
together and add 6 parts of red lead and 1 part purified carbonate 
of potassium, previously triturated together. Set aside for an hour 
and then pour into hollow reeds or glass tubes. 

Ink for Writing on Glass. 

Dissolve 300 grains of brown lacquer in 5 ounces of alcohol 
without the aid of heat ; then mix drop by drop with a solution of 
borax 2 ounces, in distilled water 8 ounces ; color to suit with ani- 
line dyes. 

Acid Proof Cements. 

Quick Setting. 

Silicate of potassium 2 parts 

Asbestos 2 parts 

Sulphate of barium '. 3 parts 

Slow Setting. 

Silicate of sodium (50 Baume) 2 parts 

Fine sand 1 part 

Asbestos 1 part 


Water Proof Cement. 

Dissolve 10 parts mastic in 60 parts absolute alcohol, 20 parts 
isinglass in 100 parts water, 10 parts grain brandy. Mix first and 
second thoroughly, and add third. 

To Drill Glass. 

1. Use a hardened steel drill, driven at a high velocity, 
moistened with camphor and turpentine. 

2. Use a copper drill and emery. 

3. To turn glass in a lathe use a good mill file and camphor 
and turpentine drip. 

4. Dip a steel drill, heated to white heat, into quicksilver, 
which hardens it ; then sharpen it on a whetstone. When drilling 
moisten drill with a saturated solution of camphor and oil of tur- 
pentine ; keep bore hole also moist, and glass can be drilled like 
wood. . 

To Clean Glassware and Bottles. 

Break a few raw egg-shells in the article to be cleaned, with a 
little cold water (use warm water if the article is greasy) ; shake 
well and rinse with water, and the glass will shine as nothing else 
will make it. 

Setting Plaster of Paris. 

Where it is important to have it set quick, mix it with a 5 
per cent, solution of sodium chloride, which may be made roughly 
by adding a tablespoon full of salt to one pint of water. 

Home-made Fire Extinguishers. 

Handy about a factory is a simple fire extinguisher. M. Ray- 
mond gives the following recipe : 

Water 1,000 parts 

Borax 40 to 60 parts 

Anhydrous soda 80 to 120 parts 

Sodium hydrate 150 to 200 parts 

Ammonium carbonate 75 to 100 parts 

Ammonium chloride 200 to 280 parts 

This liquid thrown on or about a fire is caused to evaporate 
quickly, generating gases free from oxygen, which displace the 
air and extinguish the fire 


To Mount Photographs on Glass. 

Clean the glass thoroughly. Pour on gelatine dissolved in 
boiling water, lay the picture on and pour on gelatine again until 
everything swims ; neatly remove what is superfluous, avoiding 
blisters, and allow to dry. 

No. 2. 

Gelatine 16 parts by weight 

Glycerine I part by weight 

Water 32 parts by weight 

Methylic alcohol 12 parts by weight 

Prepare the mixture by swelling the gelatine in water ; dis- 
solve it by moderate heat ; add the glycerine and stir thoroughly 
and pour the whole in a thin stream into the alcohol. 

Order of Expansion of Different Substances. 

1 — Diamond. 1 5. — Brass. 

2 — ISne. 16 — Silver. 

3 — Graphite. 17 — Tin. 

4 — Marble. 1 8 — Aluminum. 

5 — White glass. 19 — Lead. 

6 — Platinum. 20 — Zinc. 

7 — Untempered steel. 21 — Sodium chloride. 

8 — Cast iron. 22 — Ice. 

9-^-Sandstone. 23 — Sulphur. 

10 — Wrought iron. 24 — Ebonite. 

11 — Tempered steel. 25 — Paraffin. 

12 — Gold. 26 — Gutta-percha ; nearly 500 

13 — Copper. times as much as the dia- 

14 — Bronze. mond. 


Bright iron becomes yellow 435 degrees F 

Bright iron becomes red 500 degrees F 

Bright iron becomes indigo 550 degrees F 

Bright iron becomes grey 750 degrees F 

Tin melts 445 degrees F 

Mercury boils 660 degrees F 

Lead melts 612 degrees F 

Zinc melts 775 degrees F 

Silver melts : i>775 degrees F 

Copper melts 1,885 degrees F 

Gold melts 1,900 degrees F 

Iron bar becomes red in dark room 950 degrees F 


Iron bar becomes red in open air i,45° degrees F 

Annealing malleable iron 1,600 to 1,750 degrees F 

Annealing glassware 800 to 1,000 degrees F 

Siemens-Martin Process. 

Deg. C. Deg. F. 

Gas from producers 720 1,328 

Glass furnace between pots 1,375 2,507 

Glass in the pots refining 1,310 2,390 

Glass in the pots working 1,045 I ,9 I 3 

Glass melted for casting 1,310 2,390 

Method of Conducting Flame Tests. 

As the analytical reactions of most raw materials respoad to 
a "flame test," for convenience we give herewith a synopsis of 
methods adopted in testing by flame. (Simon's Manual of Chem- 
istry) : 

"A platinum wire is cleaned by washing in hydrochloric acid 
and water and heating it in the flame until the latter is no longer 
colored, when it is dipped into the substance to be examined, and 
again held in the lower part of the flame, which then becomes 
colored. A colorless flame must be used, as an alcohol lamp or 
Bunsen burner, and one end of the platinum wire is fused in a 
short piece of glass tubing, the other end bent into a loop. 

"There is a second method of showing flame reactions by 
mixing the substance to be examined with alcohol in a small dish ; 
the alcohol upon being ignited shows a colored flame, especially 
in the dark." 

Another test is called the "borax bead" test: "The compounds 
of some metals when fused with glass impart to it characteristic 
colors ; this is demonstrated by the use of borax. Dip the loop of 
the platinum wire in powdered borax and heat it in the flame (di- 
rectly or by means of a blow-pipe) until all water has been expelled 
and a colorless transparent bead has been formed. To this color- 
less bead a little of the finely powdered substance is added and the 
bead is strongly heated. The metallic compound is chemically 
acted upon by the boric acid, a borate being formed which colors 
the bead more or less intensely, according to the quantity of the 
metallic compound used. Some metals (copper for instance), 
forming two series of compounds, give different colors to the bead 
when present in either the higher or lower state of oxidation. By 
modifying the blow-pipe flame so as to either oxidize (by supply- 


ing an excess of atmospheric oxygen) or de-oxidize (by allowing 
some unburnt carbon to remain in the flame), the metallic com- 
pound in the bead may be made to assume the higher or lower 
state of oxidation. Thus a copper bead may be changed from 
blue to red; or red to blue, the blue bead containing the copper in 
cupric, the red bead in cuprous form." 

Paste for Iron Molds. 

Take lard oil and linseed oil equal parts, say one-half pint of 
each ; boil down to about one-half, or until it becomes good and 
thick, so that when you remove some on a stick and let it cool 
a little while it will draw in a string like melted wax when you 
touch it fo anything ; then let it cool and add enough painter's 
red lead to make it about the color of mahogany, as that gives it 
body. Now make some sawdust from apple wood or maple by 
putting the wood in a lathe and holding a tile against it. 

Get the mold clean and just a little warm, so the paste will 
spread easily ; put the paste on thin with a brush, then dust it 
with sawdust as long as any will stick ; put the mold up to heat — 
where it is not too hot — and bake paste until it becomes brown in 
color; then let it cool and blow one piece of ware in it before dip- 
ping it in water, and blow first one very easy. The best utensil to 
boil paste in is a small iron pot with a cover, so that when the oil 
ignites it can be smothered and extinguished. 

Chemical Names and Their Common Versions. 

Common — Chemical — 

Aqua fortis Nitric acid 

Aqua regia . ; .Nitric and hydrochloric acids 

Blue vitrol Sulphate of copper 

Chalk Carbonate of calcium 

Salts of tartar , Carbonate of potassium 

Caustic potash .Hydrate of potassium 

Common salt Chloride of sodium 

Copperas — or green vitrol Sulphate of iron 

Glauber's salt Sulphate of sodium 

Iron pyrites Bi-sulphide of iron 

Lime Oxide of calcium