Ground glass

“ The plain electric glass shades through which the source of light is plainly seen are practically nil. They absorb more light than a good reflector and do no good—unless to look a wee bit better than a bare lamp. Ground glass is a better thing but poor enough. ”

“ To inlay glass in glass involves little difficulty, if ground and inlay are as it were fused together; but to produce a ground apparently in glass, and to inlay it with so fine a pattern, both "au froid," is a perfect marvel in vitreous manufacture.
The only way in which I can imagine that such an effect could be produced is as follows, but in offering any such explanation I desire to do so with all due deference to practical glass-workers. I believe that two metal-moulds were made, one with the ornament in relief, and the other with the same ornament sunk in intaglio. ”

“ Thus on the same piece of glass he could depict among the grass white daisies and yellow buttercups and bluebells blue as nature, he could give even the yellow eye of the daisy and its green calyx; and, by judicious modification of his stain, he could make the leaves of the flowers a different shade of green from the grass about them. The drawing of the flowers and leaves and blades of grass, it need hardly be said, he would get in the usual way, tracing the outline with brown, slightly shading with half tint, and painting out only just enough of the ground to give value to his detail. ”

“ To grind glass. Rough edges of glass can be ground smooth by means of emery paper. For example, to smooth the edges of the glass bottle you have just cut in two, use the file for the rough work, then lay a piece of emery paper on a plate of glass, emery side up, pour a little kerosene on it and rub the rough surface on the emery with a rotary motion (Fig. 91) . ”

“ When removed from the annealing kiln the plates or discs of optical glass are taken to a grinding or polishing workshop, where certain of their faces or edges are ground and polished in such a way as to permit of the examination of the glass for bubbles, striæ and other defects in the manner indicated in the previous chapter. As the amount of sorting that can be done while the glass is still in rough fragments is necessarily very limited, it follows that a considerable proportion of the glass which has been moulded and annealed must be rejected as useless when thus finally examined. ”

“ In painted glass, on the other hand, the colour is not in the glass but upon it, more or less firmly attached to it by the action of the fire. A metallic colour which has some affinity with glass, or which is ground up with finely powdered glass, is used as a pigment, precisely as ceramic colours are used in pottery painting. The painted glass is then put into a kiln and heated to the temperature at which it is on the point of melting, whilst the colour actually does melt into it. ”

“ 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. ”

“ A very crude form of ground-in stopper may be made by drawing out the neck and the mass of glass which is intended to form the stopper to approximately corresponding angles, wetting the surfaces with a mixture of the abrasive material and water, and grinding the stopper in by hand. ”

“ Allusion has been made (page 2) to the Roman practice of making glass in strata of two colours, which they carved cameo-fashion in imitation of onyx and the like; at least, one tour de force of this kind is familiar to every one in the famous Portland vase, in which the outer layer of white glass is in great part ground away, leaving the design in cameo upon dark blue. The mediæval glass-blower seems from the first to have been acquainted with this method of coating a sheet of glass with glass of a different colour. ”

“ In a general way we may say that there has always been a distinction between the mechanical processes of grinding and polishing and the more delicate and artistic work of the engraver. In the latter case the work is done by pressing the glass against the edge of a minute copper wheel. On the other 284 hand, the glass is ground down on a wheel of iron from three to eighteen inches in diameter, it is smoothed upon a stone wheel and finally polished upon one of wood, with the assistance in each case of suitable abrading mediums, whether emery, quartz sand, tripoli, or putty-powder. ”

“ This led me to the adoption of the ridge-and-furrow principle for glass roofs, which places the glass in such a position that the rays of light in the mornings and evenings enter the house without obstruction, and present themselves more perpendicularly to the glass at those times when they are the least powerful; whereas at mid-day, when they are most powerful, they present themselves more obliquely to the glass. ”

“ Don't you think it's worth while spending half-an-hour to paint false lead lines on the back of the plate? A ha'p'orth of lamp-black from the oil-shop, with a little water and treacle and a long-haired brush, like a coach-painter's, will do it for you (see Plate XIII.) .
Another thing: when the window is in its place, each light will be surrounded with stone or brick, which, although not so black as the lead lines, will tell as a strong dark against the glass. See therefore that while you are painting, your glass is surrounded by dark, or at any rate not by clear, glittering light. ”

“ As to the slab-glasses—"Early-English," "Norman," or "stamped-circles"—which are chiefly affected by this question, the texture and surface upon which their special character depends is sometimes a very useful resource in work seen against, or partly against, background of trees or buildings; while against an entirely "borrowed" light perhaps, sometimes, it can almost dispense with any painting. The grey shadows that come from the background play about in the [Pg 228] glass and modify its tones, doing the work of painting, and doing it much more beautifully. ”

“ The glass with which windows are generally glazed, is called Crown glass. It is formed of different materials in different manufactories. In some instances the materials consist of fine white sand, carbonate of lime, carbonate of soda, and clippings or waste pieces of old glass; while in other cases they consist of white sand, pearl-ash, saltpetre, borax, and arsenic, in certain proportions. On this point we shall not dwell, for almost every manufacturer has a favourite receipt of his own. Whatever substances are employed, they are intimately mixed before being melted. ”

“ 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 property does not belong to the glass containing lime, to anything like the same extent. Lead glass, too, is much heavier than lime glass, and is therefore unsuited to many of the purposes for which the latter is generally used, the principal of which is for the glazing of windows. ”

“ Rough, ribbed, or prismatic glass throws the rays much further into the room, hence they strike so much larger an area of wall, ceiling, and floor that in being reflected again and again the light is well diffused, and but little is sent forth again into outside space. ”

“ How easy it would be, if things were thought of from the beginning and the place built for the work, to have such width of bench and space of window that, along the latter, easily and comfortably within reach, should run stages, tier above tier, of strong sheet or thin plate glass, sloping at such an angle that the cuttings might lie along them against the light, with a fillet to stop them from falling off. ”

“ 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. ”

“ It is by their aid we get those mosaics of pot-metal, the depth and richness of which to this day, with all our science of chemistry, we cannot approach by any process of enamelling. Moreover, though merely constructional leads, taking a direction contrary to the design, may at times disturb the eye, (they scarcely ever disturb the effect) they add to the richness of the glass in a way its unlearned admirers little dream. ”

“ 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. ”

“ When proofs, taken as just described, have shown that the glass is free from bubbles, the extreme heat of the furnace is allowed to abate, and the fire-clay slabs in front of the mouth of the pot are removed. ”

“ Now the side you first looked at is the side to cut on, and the side to paint on, and it is the side placed inwards when the window is put up.
The reason is this. Glass is made into sheets by being blown into bubbles, just as a child blows soap-bubbles. If you blow a soap-bubble you will see streaks playing about in it, just like the wavy streaks you notice in the glass. ”

“ An effort at producing a similar brilliance of surface on moulded and pressed articles is often made by exposing them, after they have attained their final form, to the heat of a furnace to such an extent as to soften the surfaces and allow the glass to re-solidify under the undisturbed influence of surface-tension much as it would do in solidifying freely in the first place. ”

“ In France, Germany and the United States it is rare to find a piece of table-ware which has not received its shape in a mould. The old and the new systems of making a wine-glass illustrate almost all the ordinary processes of glass working. Sufficient glass is first “gathered” on the end of a blowing iron to form the bowl of the wine-glass. The mere act of coiling an exact weight of molten glass round the end of a rod 4 ft. in length requires considerable skill. The mass of glass is rolled on a polished slab of iron, the “marvor,” to solidify it, and it is then slightly hollowed by blowing. ”

“ For this reason sheet-glass, works such as those of Belgium and some parts of Germany, which have large deposits of pure sand close at hand, possess a very considerable advantage over those in less favoured situations, since sand in particular forms so large151 a proportion of the glass, and the cost of carriage frequently exceeds, and in many cases very greatly exceeds, the actual price of the sand itself. ”

“ It does not give the effect of actual flesh, and it does not help the effect of the window. Since you cannot get actual flesh tones it is as well to accept the convention of white flesh, which gives breadth [Pg 107] and dignity to the glass. There is a sort of frivolity about enamelled flesh-pink. It is, in a way, pretty, but out of key with the monumental character of a window. Glass lends itself best to strong, large work. The quality of pot-metal gives the colour chord. The leads give the key to the scale of design—the pitch, as it were, of the artist’s voice. ”

“ The softness of lead which makes it the only practicable metal for joining pieces of glass of complicated shapes, has the disadvantage that a stained-glass window when leaded up has a considerable degree of flexibility, and, if held by the edges alone, would be quite unable to resist the pressure of the wind, which on a big window is enormous,—think of the power even of a fresh breeze on a boat's sail. ”

“ 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. ”

“ On the other hand, when falling upon a piece of glass having an irregular surface, and containing all manner of irregularities such as striæ, air-bells, and even pieces of enclosed solid matter, the light is scattered, refracted, and deflected into all manner of directions until it almost appears to emanate from the body of the glass itself, which thus appears almost to shine with an internal light of its own; the eye can hardly perceive the presence of external objects, and the whole window appears as a brilliant self-luminous object. ”

“ Every one who wants to study glass should go to York Minster. Go to the extreme west end, the first two windows are of plain quarries most prettily leaded, and showing how pleasant "plain-glazing" may be, with silvery glass and a child-like enjoyment of simple patterning, unconscious of "high art." But look at the second window on the north side. ”

“ Glass is made into vessels, as most people know, by "blowing." The workman takes a dab of molten glass on the end of a long metal pipe, and putting his mouth to the pipe blows the glass—soap-bubble fashion—into a hollow bulb. Then by a rapid and dexterous series of alternate and repeated heating, blowing, and spinning, and 15 manipulation with tools, most fascinating to watch, he shapes it into the form required. If a flat sheet be required for window glass it may be run out flat when liquid, or blown as described above, and worked into a cylindrical form, split open, and unrolled. ”