Glassmaking

“ Silica{10} is fusible only at a very high temperature, but readily combines with alkaline substances to form soluble silicates, which are known in commerce as soluble glass, or water-glass, because it dissolves readily in hot water. Water-glass is used in making artificial stone, in coating stone surfaces, e.g. walls of buildings, etc., to preserve the stone from decay under the weathering influence of the atmosphere, and in the manufacture of cement.
Ordinary glass has many valuable properties which make it of great importance in the arts and manufactures. ”

“ MANUFACTURE OF GLASS.
The first object in glass making is to obtain suitable materials. The sand which is employed for window glass differs from that which is required for flint glass, in that the latter should be as pure as possible. The maker can correct the impurities in the window glass sand, provided they be not present in too great quantities; but it is far more difficult, in the case of flint glass, to chemically counteract the influence of those substances which might impair its tint. ”

“ From the mixing of the crude materials to the annealing of the finished product, the glass-maker must be alert and intelligent. It is a very easy matter simply to make glass. Sand, metallic bases, and heat are the only elements needed. But to make good glass—glass that is clear, transparent, colorless; that simulates the purest water of a mountain-stream—this requires skill and patience. From beginning to end the process is one of painstaking and delicate manipulation.
In the genesis of a pane of glass, the first step is naturally the provision of such stuff as it is made of. ”

“ They were chemists, glaziers, artists, colorists, and glass manufacturers, all in one. The heritage was passed on in those days, when the great key of science which opens all portals had not yet become common property. Some of the oldest glass is merely a crude mosaic inlay of small bits and must date back to early thirteenth century. Coloring glass by partial fusion was then first practised and soon followed by the introduction of figures and themes in the glass, and the acquisition of a lovely, homogeneous opalescence in place of the purely geometrical patterns. ”

“ Of late years each country has been learning so much from the others that the newest effort is very much in one direction. It seems to be agreed that the art of the window-maker begins with glazing, that the all-needful thing is beautiful glass, that painting may be reduced to a minimum, and on occasion (thanks to new developments in the making of glass) dispensed with altogether. A tendency has developed itself in the direction not merely of mosaic, but of carrying the glazier’s art farther than has been done before and rendering landscapes and even figure subjects in unpainted glass. ”

“ The word glass-blower, generally speaking, signifies a workman who occupies himself in making of glass and enamel, the instruments, vessels, and ornaments, which are fabricated on a larger scale in the glass-houses: but the domain of the sciences having laid the art of glass-blowing under contribution, the artists of the lamp have divided the labours thereof. Some apply themselves particularly to the construction of philosophical and chemical instruments; others occupy themselves with little ornamental objects, such as flowers, &c. ”

“ Between the period when it was glazier’s work eked out by painting and when it was painter’s work with the aid of the glazier lies the entire development of stained and painted window-making. With the eventual endeavour of the glass painter to do without the glazier, and to get the colour by painting in translucent enamel upon colourless glass, we have the beginning of a form of art no longer monumental and comparatively trivial. ”

“ The malleability of glass is still a secret.
DESCRIPTION OF A GLASS-HOUSE.
Dismissing history and theory, we will now step into the glass-house itself, where the practical work of converting sand into goblets, vases, mirrors, and window-panes is going forward with a celerity and accuracy of hand and head that can not fail to excite wonder and admiration. As the whole agency employed is that of heat, the interior of the manufactory consists of furnaces specially constructed for the progressive processes to which the material is subjected before it is sent out perfected for use. ”

“ This is mixed with oil or gum and water in order to apply it, and then the glass is placed in a kiln and "fired" till the enamel is fused on and, if well fired, becomes part of the glass itself. This is the only "painting" involved in the production of a stained-glass window, and its effect, in the hand of an artist, besides enabling him to express more than could be done merely with glass and lead, is to decorate and enrich what would otherwise be somewhat crude and papery in effect. ”

“ As a consequence, it is probably not too much to claim that the modern workers in coloured glass have materials at their disposal which are at least as suitable for the purpose as those that were available in the best days of the ancient art. ”

“ In all processes for the production of hollow glass-ware, the glass or “metal” is taken from the pot by the process of gathering which has already been described; where blown articles are to be produced, as distinct from pressed goods, the initial stage is always the formation of a small hollow globe or bulb at the end of the glass-blower’s pipe. The subsequent manipulations depend upon the nature of the article to be produced. ”

“ When the glass is made, and its temperature so reduced that it is in a doughy or pasty state, it is then worked off by the blowers into either sheets or tables, as is desired. The blowing of sheet and crown glass is a work of considerable difficulty and labour, and one which cannot be successfully performed, except by a workman who has been brought up from boyhood in a glass-house. A quantity of the soft glass is collected or gathered on the end of a blowpipe, and the workman then blows into it, and distends it into a globular form. ”

“ It is lamentable to think of the quantities of old glass that have been, and are in process of being, wholly lost through neglect alone. An ancient glass painting is composed of many pieces of glass, of various sizes, held together by means of leads, i. e. narrow strips of that metal, having a groove on either side sufficiently wide to receive the edges of the glass. From age, and other causes, the leads become decayed; a piece of glass drops, or is blown out of the leads by the wind; the leads, deprived of its support, become gradually relaxed in other parts ”

“ The cutting and putting together of the glass is called glazing, and it is this that gives the window colour; while the enamel work is spoken of as painting, and gives detail, richness, and texture.
I shall presently show that the glazing and painting are really two separate crafts, having separate origins and development, and that stained glass as we know it, or as it should be called in strict accuracy "stained-and-painted" glass, is the product of their union. ”

“ The island owes its chief renown to its glass-works. It was a famous discovery to make glass that should vie with crystal in clearness. Since then the nimble wit of the workmen and the never-resting care to find something new have led them to apply to the material a thousand various colours and shapes without number. Hence the calices, the flasks, the canthari, the ewers, the candelabra, the animals of every race, the horns, the beads (segmenta) , the bracelets, etc. ”

“ This hasty sketch of the history of glass-making will help us to understand why it is that in following the development of the art in so many lands, and for a period of more than three thousand years, there is no need to linger for any time except at a few of the more important étapes. ”

“ When in succeeding centuries painters invaded the realms of glass they would appear to have ignored the obvious requirements of the new medium in which they were to work. Experimentally and intuitively the mediæval glazier, on the other hand, must have studied the whole question of radiation as it affected his task. And the result is, that for the most superb effects of stained glass we have to go, not to the pictures burnt on the large sheets of glass by famous painters, but to the designs of the thirteenth-century anonymous monkish craftsmen. ”

“ The quality of pot-metal glass is all important. It should never be mechanically flat and even. The mechanically imperfect material made in the Middle Ages is so infinitely superior to the perfect manufacture of our day, that we have had deliberately to aim at the accidents of colour and surface which followed naturally from the ruder appliances and less accurate science of those days. There are legends about lost secrets of glass making, to which much modern produce gives an appearance of truth. ”

“ There is a choice collection of fragments of millefiori and banded glass in the British Museum, [25] and a still larger one in the Industrial Museum at Vienna.
52 A broken fragment of glass will indeed often tell us more than a complete vase. We can, for example, see from it whether the pattern passes continuously through the whole thickness of the glass, or whether it has been inlaid, or perhaps pressed into the surface when hot. In one case we have a process that reminds us of mosaic work; in the other there is some approach to a champlevé enamel, only with a base of glass instead of metal. ”

“ If, therefore, we want the qualities of deep, rich, luminous and translucent colour, which glass better than any other medium can give, we must resort to the use of pot-metal—that is to say, to glazing—assisted more or less by brown paint, used, not to get colour, but to stop it out, or to tone it down. ”

“ But for the most part—above all after the end of the century—the facetting runs wild; sometimes it covers the whole surface, and even where there are no facets the ground is marked out by rectangular divisions. The decoration as a whole is mechanically executed. But even this machine-made work is better than the cheap imitations of later days produced by pressing the glass into moulds of metal. ”

“ The design is produced, for the most part, of pure pot-metal, while white glass is introduced here and there to heighten the effect in draperies and in ornaments. Each piece of glass is of one even colour, another piece has to be inserted wherever a different colour is wanted, and each separate piece is encompassed by its sustaining framework of lead. ”

“ In the seventeenth century, however, the history of glass in France centres round the manufacture of plate-glass by the new process of coulage or casting. After the middle of the century a demand arose in France for large sheets of clear glass, not so much for windows, it would seem, as for the tall mirrors that were now coming into fashion, and again for the portières of the ‘glass-coaches’ of the nobility. ”

“ What one would like to have would be a pigment whose own fusing-point was the same, or about the same, as that of the glass itself, so that the surface, at least, of the piece of glass softens to receive it and lets it right down into itself. You should never be satisfied with the firing of your glass unless it presents two qualifications: first, that the surface of the glass has melted and begun to run together; and second, that the fused pigment is quite glossy and shiny, not the least dull or rusty looking, when the glass is cool. ”

“ The purity of glass, its adaptability to colour, and its remarkable ductility while hot for blowing, twisting or drawing into threads, differentiates it from all other materials and methods of treatment. Its tradition dates from the remote past, for glass-blowing is represented on the tombs at Thebes, B.C. 2500. It was also used in Egypt for vitreous pastes for bronze and gold cloisonné jewellery, and for the small bottles or Stibium, with chevron patterns, in yellow, turquoise and white on a coloured ground. ”

“ To make a glass, melt it well and grind it, to every twenty pounds of which add six pounds of white lead, adding a small portion of smalt to clean the colour; mix it well and glaze the ware, which is done by dipping in the vessell and setting it on to dry, when it must be put in cases and burned as above with wood, till the surface of the ware is clear and shining, and it is finished. ”

“ Both sheet and crown glass owe their origin to the blower's breath. Though they are less brilliant than the plate, their methods of fabrication are much more interesting, since they involve a far greater amount of manual dexterity on the part of the artisans. It is, indeed, difficult to know which to admire the more, the chemistry or the physics of the operation; the nicety with which the glass-maker regulates the proportions of his charge so as to produce this beautifully clear substance, or the skill with which he subsequently handles the finished glass and adapts it to our uses. ”

“ THE GLASS-BLOWER.
1. Glass is a substance produced from a combination of silicious earths with alkalies, and, in many cases, with metallic oxydes. The basis of every species of glass is silex, which is found in a state nearly pure in the sands of many situations. It is also found in the common flints and quartz pebbles.
2. When quartz pebbles or flints are employed, they must be first reduced to powder. This is done by grinding them in a mill, after they have been partially reduced, by heating them in the fire, and plunging them into cold water. ”