Glass

and the word calls up so many varied associations, that I must here at the very beginning make clear w

an anomaly of the English language, whose vocabulary for matters connected with the arts is so strangely deficient, we have come to understand by the term 'glass,' when used without further explanation, what is called in the trade 'hollow ware,' the verrerie of the French; in other words-vessels of glass. The term may also be extended to

department, with artistic problems only incidentally connected with the material in which they work. In other words, the art element in both these crafts only becomes prominent at a stage when the actual preparation of the glass is

tances of similar composition. They may all probably be traced back to a common origin, so that from an evolutionary point of view we have here an instance of the development of the complex and varied from the simple and single. Looking at the question in another way, the art of the enameller, using the term in a restricted sense, may be held to be subsidiary both to that of the potter and of

ance for them. The Romans, on the other hand, who in the first centuries of our era first fully appreciated and developed the capacities of glass, produced little pottery of artistic interest. In the sixteenth century, in Umbria and Tuscany, where the finest majolica was made, we hear nothing of

r Eastern lands, by a primitive process, although it only became an article of general use after the discovery of the blowing-iron. When and where this discovery was made we do not know-perhaps somewhere in Syria or Mesopotamia, in the third or second century before Christ. The art of blowing glass was known, no doubt, if not fully developed, at the time when the kingdoms of the Ptolemies and of the Seleucid? fell under the rule of the Romans. By them it was before long brought to perfection and carried into every corner of the West, so that by the second or third century of our era the production of glass in Europe was prob

nterval, in one direction only, in the West, was any advance made. Within this period falls the great development of stained glass: we must turn to the glorious windows of the cathedrals of France and other Western lands, to see what the glass-workers of the time were capable of producing. In the East, on the other hand, in the lands ruled from

iterranean)-except it be the inlaid metal work-there is nothing that now interests us so much as the enamelled glass, the beautiful ware that culminated in the magnificent Cairene mosque lamps of the thirteenth and fourteenth centuries. The art of enamelling on glass passed over to Venice in the fifteenth century, perhaps earlie

mountain fringe of Bohemia' held the premier position, but towards the end of the eighteenth century this place was taken by the facetted flint-glass of England. It is certainly remarkable that it is only of quite recent years that any such prominent position could be claimed for France, which heretofore

more than three thousand years, there is no need to linger for any time except at a few of the more important étapes. Indeed such a procedure is forced upon us, for mu

e first centuries of the Roman Empire, the enamelled glass of the Saracens, and the Venetian glass of the Renaissance-this exhausts all that we find either of commanding historic interest or of superlative artistic merit. What follows-the German and the Netherlandish glass o

hat can claim an Assyrian origin, of the glass pastes of the Mycen?an age, and of the few examples of glass that can be strictly classed as Greek of the classical age. So again of the second long hiatus-the interval of nearly a thousand years between the period of the Rom

oduction-these latter centres, I may note, until comparatively recent times are mostly to be found in close connection with the basin of the

time of the Middle Empire in Egypt-of beads, I mean, and other allied applications of glass, included in the French term verroterie. But, however great the claims to attention of such objects, their interest

and Composi

lt and sand or stones. 'Tis artificial. It melts in a strong fire. When melted 'tis tenacious and sticks together.... When melted it cleaves to iron, etc. 'Tis ductile whilst red-hot, and fashionable into any form, but not malleable, and it may be blown into a hollowness' (Art of Glass, 1662). Here we have briefly expr

e rod upon which the mass is gathered is hollow, the glass may be blown out into a vesicle or bulb, the starting-point from which an endless variety of objects, bottles, cups, tubes, or even flat sheets of glass, may be subsequently formed. Until advantage was taken of this remarkable property of glass-its capabili

se from the point of view of the time and country. But as, on the one hand, for classical times, our sources of information for these practical details are but scanty, and as, on the other, I am not concerned with the industrial developments of the nineteenth c

ical and physical properties of gla

t of potash or soda. Such a glass-a simple alkaline silicate-would indeed be transparent, but it would be difficult to work and very fragile. In all cases there is need of a second base, and this, to speak generally, should be either lime or oxide of lead. The latter base we may for the present neglect; speaking generally, it is the presen

potash, it is remarkable how little difference of composition we find in examples of glass of the most divergent origin. Let us

Lime. Iron O

ymatory 71·

ate-glass

ies. A sample of Saracenic glass of the fourteenth or of Venetian glass

s possible the native rock crystal (itself pure silica), but which at the same time shall be not only fusible, but after fusing pass on cooling through a plastic condition when it may be expanded into a vesicle and otherwise worked up into various shapes? Long practical experience has shown that

ned have a high combining number-and this is especially the case with lead-the percentage of silica may fall below the former figure. Thus, in a bottle glass with 12 pe

r the heads of crown-glass, bottle-glass, broad-glass, plate-glass, flint-glass, etc.

ortant-I have indeed regarded such glass as the normal type-may, it would seem, be placed not only the 'primitive' glass of the Eastern Mediterranean, but probably all the glass of the Romans. To it belongs also the glass of the Saracens and the greater part of the artistic glass of the Renaissance, including the Venetian glass, although in this last the soda is often in part replaced by an appreciable quantity of potash. The potash group, on the other hand

fall between the fifth and sixth divisions of that scale. In other words, it would be difficult to find a specimen of glass on which a crystal of apatite (phosphate of lime) would make any impression, whereas all glass in ordinary use is readily scratched by felspar. It is possible, however, that some kinds of Bohemian glass may equal the latter mineral in hardness; it is indeed a common statemen

er its dispersive power on the light that passes through it. Hence the

2·4 and 2·8. That of flint-glass, on the other hand, varies from 3 to 3·8; indeed in some optical glasses containing a larg

ss, makes them invaluable in the laboratory of the chemist. On the other hand, the ready fusibility of glass con

glass containing lead are soft and easily fusible, and at the same time they combine a high specific gravity with a wide dispersive power. What we may call the maritime or sod

and secondly an alkali, in each case as pure as possible, and in a convenient form for mixing a

the form of rock crystal or of the white pebbles from the beds of Alpine river

h tribe, and we find among them various species of Salsola, Chenopodium, Salicornia, etc. These plants were all included in old days under the vague name of kali. The roughly lixiviated ashes exported from Spain were known in the trade as barilla; those from the Levant as roq

lants. This 'potash' was obtained by lixiviating the ashes of various trees and bushes-in Ge

f lime, to say nothing of the iron oxide and alumina, that they contained, rendered unnecessary in many cases the addition of any further basic material; even the comparat

alt with in the next chapter-almost exclusively concerned with vessels of 'hollow ware' made by a blowing process, it may be well to indicate, in this introductory chapter, the nature of this process, and to give the names of the principal too

metimes by swinging it over the workman's head), and then by shaping it by means of certain simple tools, the paraison is started on the course by which it will finally be converted into a bottle or into a bowl-shaped vessel. I will here only dwell on one point. It is evident that so long as the glass is attached to the blowing-iron, although a simple bulb-shaped vessel may be formed, there is so far no means of shaping or finishing the upper portion. Before this can be done the further extremity of the paraison must be attached by means of a small gathering of molten glass to a light tapering rod of iron, the 'punto' or 'pontil.' The vessel-for so the paraison may now be called-is at this stage removed from the blowing-iro

say, a flask of simple shape, I have only dwelt upon such instrume

cay of

changes are in the main due to the moisture and carbonic acid contained either in the soil or in the atmosphere. Perhaps what is most striking in this action is on the one hand t

hen, the carbonic acid or the ammonia salts contained in the air or soil find, in the presence of moisture, a secure lodgment, and the work of decay proceeds rapidly. Thus in the case of the little flasks of primitive glass of which I shall have to speak in the next chapter, in one example it may be found that the sm

ace, especially in the disintegration of the granitic rocks. It depends upon the power possessed by carbonic acid, in the presence of moisture, of decomposing the silicates of the alkalis. The soluble carbonate of soda or of potash thus formed is then

t iron-this complicated formation is in part revealed, for it is evident that upon it the lines taken by the decay are in a measure dependent. On blown glass especially, the disintegration of the surface tends to result in a scaly formation resembling that of the shell of an oyster. As a result of the decomposition of light in its passage through these fine superficial films, and of the partial reflection

t where in such glass decay has once set in, the whol

this change has been fully developed we get a true crackle-glass, not to be confounded with the frosted glass of Venice mentioned in Chapter XIII. This fissuring of the glass-mass in

anese, is above all liable to assume in the course of time a purple tint under the action of sunlight. Again, if sulphur be present in glass, as is the case where sulphate of soda has been employed as a source of the

ndows of our Gothic churches-the flesh-tints, which we know were produced in early day