a transparent, brittle, fictitious body, produced by the action of fire upon a fixed salt and sand, or stone, that readily melts.

The chemists hold, that there is no body but may be vitrified, or converted into glass; being the last effect of fire, as all its force is not able to carry the change of any natural body beyond its vitrification.

When or by whom the art of making glass was first found out is uncertain: some will have it invented before the flood; but without any proof. Neri traces the antiquity of this art as far back as the time of Job: but Dr Merret will have it as ancient as either pottery, or the making of bricks: because that a kiln of bricks can scarce be burnt, or a batch of pottery be made, but some of the bricks and the ware will be at least superficially turned to glass; so that it must have been known at the building of Babel, and as long before as the making of bricks was used. It must have been known, consequently, among the Egyptians, when the Israelites were employed by them in making bricks. Of this kind, no doubt, was that fossil glass mentioned by Ferrant. Imperial. to be found under-ground in places where great fires had been. The Egyptians indeed boast, that this art was taught them by the great Hermes, Aristophanes, Aristotle, Alexander Aphroditeus, Lucretius, and John the divine, put us out of all doubt that glass was in use in their days.

Pliny relates, that it was first discovered accidentally in Syria, at the mouth of the river Belus, by certain merchants driven thither by a storm at sea, who, being obliged to continue there, and dress their victuals, by making a fire on the ground, where there was great plenty of the herb kali; that plant burning to ashes, its salts mixed and incorporated with sand, or stones fit to vitrify, and produced glass: that this accident being known, the people of Sidon, in that neighbourhood, assayed the work, improved the hint, and brought it into use; and that this art has been improving ever since.

Venice, for many years, excelled all Europe in the fineness of its glasses; but of late the French and English have excelled in the Venetians, so that we are no longer supplied with this commodity from abroad.

Nature and characters of Glass. Naturalists are divided in what class of bodies to rank glass: some making it a concrete juice; others a stone; others again rank it among semi-metals; but Dr Merret observes, that these are all natural productions, whereas glass is a fictitious compound, produced by fire, and never found in the earth, but only the sand and stone that form it; that metals are formed by nature into certain species; and that fire only produces them, by its faculty of separating heterogeneous, and uniting homogeneous bodies; whereas it produces glass, by uniting heterogeneous matter, viz. salt and sand, of both which it evidently consists; 100 lb weight of sand yielding above 150 lb of glass.

The same learned doctor gives us a precise and accurate enumeration of the several characters, or properties of glass, whereby it is distinguished from all other bodies, viz. 1. That it is an artificial concrete of salt and sand, or stones. 2. Fusible by strong fire. 3. When fused, tenacious and coherent. 4. It does not waste nor consume in the fire. 5. When melted, it cleaves to iron. 6. When it is red hot, it is ductile, and may be fashioned into any form; but not malleable; and capable of being blown into a hollowness, which no mineral is. 7. Fragile when thin, without annealing. 8. Friable, when cold. 9. Diaphanous, whether hot or cold. 10. Flexible and elastic. 11. Dissoluble by cold and moisture. 12. Only capable of being graven or cut with a diamond, or other hard stone and emery. 13. Receives any dye or colour both externally and internally. 14. Not dissoluble by aqua fortis, aqua regia, or mercury. 15. Neither acid juices nor any other matter extract either colour, taste, or any other quality from it. 16. Admits of polishing. 17. Neither loses weight nor substance by the longest and most frequent use. 18. Gives fusion to other metals, and softens them. 19. The most pliable thing in the world, and that which best retains the fashion given it. 20. Not capable of being calcined. 21. An open glass being filled with water in the summer-time, will gather drops of water on the outside, just so far as the water on the inside reaches; and a person's breath blown on it will manifestly moisten it. 22. Little glass balls filled with water, mercury, and other liquor, and thrown into the fire, as also drops of green glass being broken, will fly asunder with a great noise. 23. Neither wine, beer, nor any other liquor, will make it musty, or change its colour, or rust it. 24. It may be cemented, as stones and metals. 25. A drinking glass, partly filled with water, and rubbed on the brim with a wet finger, yields musical notes, higher or lower as the glass is more or less full, and will make the liquor frisk and leap.

Materials for making of Glass. The materials whereof glass is made, we have already mentioned to be salt and sand, or stones. The salt here used, is procured from a sort of ashes, brought from the Levant, called pulverine, or rochetta; which ashes are those of a sort of water-plant, called kali, cut down in summer, dried in the sun, and burnt in heaps, either on the ground, or on iron grates; the ashes falling into a pit, grow into a hard mass, or stone, fit for use.

To extract the salt, these ashes, or pulverine, are powdered and sifted, then put into boiling water, and there kept till one third of the water be consumed; the whole whole being flirred up, from time to time, that the ashes may incorporate with the fluid, and all its salts be extracted: then the vessel is filled up with new water, and boiled over again, till one half be consumed; what remains is a sort of lea, strongly impregnated with salt. This lea, boiled over again in fresh coppers, thickens in about twenty-four hours, and shoots its salt; which is to be ladled out, as its shoots, into earthen pans, and thence into wooden fats to drain and dry. This done, it is groly pounded, and thus put in a sort of oven, called calcar, to dry. It may be added, that there are other plants, besides kali, which yield a salt fit for glass: such are the alga, or sea-weed, the common way-thistle, bramble, hops, wormwood, weed, tobacco, fern, and the whole leguminous tribe, as peas, beans, &c.

The sand or stone, called by the artists Tarso, is the second ingredient in glass, and that which gives it the body and firmness. These stones, Agricola observes, must be such as will fuse; and of these such as are white and transparent are best; so that crystal challenges the precedence of all others.

At Venice they chiefly use a sort of pebble, found in the river Tefino, resembling white marble, and called cuogolo. Indeed Ant. Neri assures us, that all stones which will strike fire with steel, are fit to vitrify: but Dr Merret shews, that there are some exceptions from this rule. Flints are admirable; and when calcined, powdered, and searched, make a pure white crystalline metal: but the expense of preparing them makes the masters of our glasses houses sparing of their use. Where proper stones cannot be so conveniently had, sand is used; which should be white, and small, and well washed, before it be applied: such is usually found in the mouths and sides of rivers. Our glasses houses are furnished with a fine sand for crystal, from Maidstone; the same with that used for sand boxes, and in scouring; and with a coarser for green glasses from Woolwich. For crystal glasses, to 200 lb of tarso, pounded fine, they put 130 lb of salt of polverine; mix them together, and put them into the calcar, a sort of reverberatory furnace, being first well heated. Here they remain baking, frying, and calcining, for five hours, during which the workman keeps mixing them with a rake, to make them incorporate: when taken out, the mixture is called frit, or bolito.

It may be further observed, that glasses might be made by immediately melting the materials without thus calcining, and making them frit: but the operation would be much more tedious.

A glass much harder than any prepared in the common way may be made by means of borax, in the following manner. Take four ounces of borax, and an ounce of fine white sand, reduced to powder, and melt them together in a large close crucible set in a wind furnace, keeping a strong fire for half an hour: then take out the crucible, and, when cold, break it; and there will be found at the bottom a hard, pure glass, capable of cutting common glasses almost like a diamond. This experiment duly varied, says Dr Shaw, may lead to some considerable improvements in the art of glasses, enamels, and artificial gems. It shows us an expeditious method of making glasses without the use of fixed salts, which has generally been thought an essential ingredient in glasses, and which is the ingredient that gives common glasses its softness; and it is not yet known, whether calcined crystal, or other substances being added to this salt, instead of sand, it might not make a glass approaching to the nature of a diamond.

Kinds of Glass. Of these materials we have many sorts of glasses made, which may principally be distinguished according to their beauty: as the crystal flint glasses, the crystal white glasses, the green glasses, and the bottle glasses. Again these several sorts are distinguished by their several uses: as plate or coach glasses, looking-glasses, optic glasses, &c., which are made of the first sort. The second sort includes crown-glasses, toys, phials, drinking-glasses, &c. The third sort is well known by its colour, and the second by its form.

Balas coloured Glass is made thus: Put into a pot crystal frit, thrice washed in water; tinge this with manganese prepared into a clear purple: to this add alum cativum fitted fine in small quantities, and at several times; this will make the glasses grow yellowish, and a little reddish, but not blackish, and always dissipates the manganese. The last time you add manganese, give no more of the alum cativum, unless the colour be too full. Thus will the glasses be exactly of the colour of the balas-ruby.

Red Glass. A blood-red glass may be made in the following manner: Put six pounds of glasses of lead, and ten pounds of common glasses, into a pot glazed with white glasses: when the whole is boiled and refined, add, by small quantities, and at small distances of time, copper calcined to a redness, as much as, on repeated proofs, is found sufficient: then add tartar in powder by small quantities at a time, till the glasses become as red as blood; and continue adding one or other of the ingredients till the colour is quite perfect.

Yellow Glass. It is a necessary remark in glasses-making, that the crystal glasses made with salt that has an admixture of tartar will never receive the true gold yellow, though it will all other colours: for yellow glasses, therefore, a salt must be prepared from polverine, or pot ashes alone, to make the glasses.

Furnaces for the making Glass. In this manufacture, there are three sorts of furnaces; one, called calcar, is for the frit; the second is for working the glasses; the third serves to anneal the glasses, and is called the leer. See Furnace.

The calcar (Plate XCVII, fig. 1.) resembles an oven ten feet long, seven broad, and two deep: the fuel, which in England is sea coal, is put into a trench on one side of the furnace; and the flame reverberating from the roof upon the frit, calcines it. The glasses furnace, or working furnace B, is round, of three yards diameter, and two high; or thus proportioned. It is divided into three parts, each of which is vaulted. The lower part C is properly called the crown, and is made in that form. Its use is to keep a brisk fire of coal and wood, which is never put out. The mouth of it is called the bocca. There are several holes in the arch of this crown, through which the flame passes into the second vault, or partition, and reverberates into the pots filled with the ingredients above mentioned. Round the indies are eight or more pots placed, and piling pots on them. The number of pots is always double that of the bocca D, or mouths, or of the number of workmen, that each may have one pot refined to work out of, and another for metal to refine in while he works out of the other. Through the working holes the metal is taken out of the pots, and the pots are put into the furnace; and these holes are stopped with moveable covers made of lute and brick, to screen the workmen's eyes from the scorching flames. On each side of the bocca, or mouth, is a bocarella, or little hole, out of which coloured glasfs, or finer metal, is taken from the piling pot. Above this oven, there is the third oven or leer, about five or six yards long, where the vessels, or glasfs, is annealed, or cooled: this part consists of a tower, besides the leer F, into which the flame ascends from the furnace. The tower has two mouths, through which the glasfs are put in with a fork, and set on the floor or bottom: but they are drawn out on iron pans, called fraches, through the leer, to cool by degrees; so that they are quite cold by the time they reach the mouth of the leer, which enters the sarofel, or room where the glasfs are to be flowed.

But the green glasfs furnace is square; and at each angle it has an arch for annealing, or cooling glasfs. The metal is wrought on two opposite sides, and on the other two they have their colours, into which are made linen holes, for the fire to come from the furnace to bake the frit, and to discharge the smoke. Fires are made in the arches to anneal the work, so that the whole process is done in one furnace.

These furnaces must not be of brick, but of hard sandy stones. In France, they build the outside of brick, and the inner part to bear the fire is made of a sort of fuller's earth, or tobacco-pipe clay, of which earth they also make their melting-pots.

Mr Blancourt observes, that the worst and roughest work in this art, is the changing the pots, when they are worn out, or cracked. In this case the great working hole must be uncovered; the faulty pot must be taken out with iron hooks and forks, and a new one must be speedily put in its place, through the flames, by the hands only. For this work, the man guards himself with a garment made of skins, in the shape of a pantaloons, that covers him all but his eyes, and is made as wet as possible: the eyes are defended with a proper sort of glasfs.

Instruments for making of Glass. The instruments made use of in this work, may be reduced to these that follow. A blowing pipe, made of iron, about two feet and a half long, with a wooden handle. An iron rod to take up the glasfs, after it is blown, and to cut off the former. Scissors to cut the glasfs when it comes off from the first hollow iron. Shears to cut and shape great glasfs, &c. an iron ladle, with the end of the handle cased with wood, to take the metal out of the refining pot, to put it into the workmen's pots. A small iron ladle, cased in the same manner, to skim the alkaline salt that swims at top. Shovels, one like a peel, to take up the great glasfs; another, like a fire-shovel, to feed the furnace with coals. A hooked iron fork, to stir the matter in the pots. An iron rake for the same purpose, and to stir the frit. An iron fork, to change or pull the pots out of the furnace, &c.

Working or blowing round Glass. The tools thus provided, the workman dips his blowing pipe into the melting-pot; and by turning it about, the metal sticks to the iron more firmly than turpentine. This he repeats four times, at each time rolling the end of his instrument, with the hot metal thereon, on a piece of iron G, over which is a vessel of water which helps to cool, and so to consolidate, and to dispose that matter to bind more firmly with what is to be taken next out of the melting-pot. But after he has dipt a fourth time, and the workman perceives there is metal enough on the pipe, he claps his mouth immediately to the other end of it H, and blows gently through the iron tube, till the metal lengthens like a bladder about a foot. Then he rolls it on a marble stone I, a little while; to polish it, and blows a second time, by which he brings it to the shape of a globe of about eighteen or twenty inches diameter. Every time he blows into the pipe, he removes it quickly to his cheek, otherwise he would be in danger, by often blowing, of drawing the flame into his mouth; and this globe may be flattened by returning it to the fire, and brought into any form by stamp-irons, which are always ready. When the glasfs is thus blown, it is cut off at the collet, or neck, which is the narrow part that stuck to the iron. The method of performing this is as follows: the pipe is refted on an iron bar, close by the collet; then a drop of cold water being laid on the collet, it will crack about a quarter of an inch, which, with a slight blow, or cut of the shears K, will immediately separate the collet.

After this is done, the operator dips the iron rod into the melting-pot, by which he extracts as much metal as serves to attract the glasfs he has made, to which he now fixes this rod at the bottom of his work, opposite to the opening made by the breaking of the collet. In this position the glasfs is carried to the great bocca, or mouth of the oven, to be heated and scalded, by which means it is again put into such a soft state, that, by the help of an iron instrument, it can be pierced, opened, and widened without breaking. But the vessel is not finished till it is returned to the great bocca; where it being again heated thoroughly, and turned quickly about with a circular motion, it will open to any size, by the means of the heat and motion. And by this means we come to learn the cause why the edge of all bowls and glasfs, &c. are thicker than the other parts of the same glasfs; because in the turning it about in the heat, the edge thickens; and the glasfs being as it were doubled in that part, the circumference appears like a selvage. If there remains any superfluities, they are cut off with the shears L; for till the glass is cool, it remains in a soft, flexible state. It is therefore taken from the bocca, and carried to an earthen bench, covered with brands, which are coals extinguished, keeping it turning; because that motion prevents any settling, and preserves an evenness in the face of the glass, where, as it cools, it comes to its consistency; being first cleared from the iron rod by a flight stroke by the hand of the workman.

If the vessel conceived in the workman's mind, and whose body is already made, requires a foot, or a handle, or any other member or decoration, he makes them separate; and now assays to join them with the help of hot metal, which he takes out of the pots with his iron rod: but the glass is not brought to its true hardness, till it has passed the leer, or annealing oven, described before.

Working, or blowing, of window or table Glass. The method of working round glass, or vessels of any sort, is in every particular applicable to the working of window or table-glass, till the blowing iron has been dipt the fourth time. But then, instead of rounding it, the workman blows, and so manages the metal upon the iron plate, that it extends two or three feet in the form of a cylinder. This cylinder is put again to the fire, and blown a second time, and is thus repeated till it is extended to the dimensions required, the side to which the pipe is fixed diminishing gradually till it ends in a pyramidal form; so that, to bring both ends nearly to the same diameter, while the glass is thus flexible, he adds a little hot metal to the end opposite the pipe, and draws it out with a pair of iron pinchers, and immediately cuts off the same end with the help of a little cold water, as before.

The cylinder being now open at one end, is carried back to the bocca, and there, by the help of cold water, it is cut about eight or ten inches from the iron pipe or rod; and the whole length at another place, by which also it is cut off from the iron rod. Then it is heated gradually on an earthen-table, by which it opens in length, while the workman, with an iron tool, alternately lowers and raises the two halves of the cylinder, which at last will open like a sheet of paper, and fall into the same flat form in which it serves for use; in which it is preserved by heating it over again, cooling it on a table of copper, and hardening it twenty-four hours in the annealing furnace, to which it is carried upon forks. In this furnace an hundred tables of glass may lie at a time, without injury to each other, by separating them into tens, with an iron sliver between, which diminishes the weight by dividing it, and keeps the tables flat and even.

This was the method formerly made use of for blowing plate-glass, looking-glasses, &c.; but the workmen, by this method, could never exceed fifty inches in length, and a proportional breadth, because what were larger were always found to warp, which prevented them from reflecting the objects regularly, and wanted substance to bear the necessary grinding. These imperfections have been remedied by an invention of the Sieur Abraham Thevart, in France, about the year 1688, of casting or running large plates of glass in the following manner.

Casting, or running of large looking-Glass plates. The furnace G, fig. 2, is of a very large dimension, environed with several ovens, or annealing furnaces, called carquaffes, besides others for making of frit, and calcining old pieces of glass. This furnace, before it is fit to run glass, costs £3500. It seldom lasts above three years, and even in that time it must be refitted every six months. It takes six months to rebuild it; and three months to refit it. The melting-pots are as big as large hogheads, and contain about 2000 weight of metal. If one of them bursts in the furnace, the loss of the matter and time amounts to £250. The heat of this furnace is so intense, that a bar of iron laid at the mouth thereof becomes red hot in less than half a minute. The materials in these pots are the same as described before; and A is the man breaking the frit for that purpose. When the furnace is red-hot, these materials are put in at three different times, because that helps the fusion; and in twenty-four hours they are vitrified, refined, settled, and fit for calting. H is the bocca, or mouth of the furnace; K is the cistern that conveys the liquid glass it receives out of the melting-pots in the furnace to the casting table. These cisterns are filled in the furnace, and remain therein six hours after they are filled; and then are hooked out by the means of a large iron chain, guided by a pulley marked I, and placed upon a carriage with four wheels marked L, by two men P P. This carriage has no middle piece; so that when it has brought the cistern to the casting-table M, they slip off the bottom of the cistern, and out rushes a torrent of flaming matter O, upon the table: this matter is confined to certain dimensions by the iron rulers N, N, N, which are moveable, retain the fluid matter, and determine the width of the glass; while a man R, with the roller Q resting on the edge of the iron rulers, reduces it as it cools to an equal thickness, which is done in the space of a minute. This table is supported on a wooden frame, with trusses for the convenience of moving to the annealing furnace; into which, strewed with sand, the new plate is shoved, where it will harden in about ten days. After this, the glass needs only be ground, polished, and foliated for use.

Grinding and polishing of plate-Glass. Glass is made transparent by fire, but it receives its lustre by the skill and labour of the grinder and polisher, the former of whom takes it rough out of the hands of the maker.

In order to grind plate glass, they lay it horizontally upon a flat stone-table, (fig. 2,) made of a very fine-grained free-stone; and for its greater security they plaster it down with lime, or stucco: for otherwise the force of the workmen, or the motion of the wheel with which they grind it, would move it about.

This stone-table is supported by a strong frame A, made of wood, with a ledge quite round its edges, rising about two inches higher than the glass. Upon this glass to be ground, is laid another rough glass not above half so big, and so loose as to slide upon it; but cemented G L A

G L A

remented to a wooden plank, to guard it from the injury it must otherwise receive from the scraping of the wheel, to which this plank is fastened; and from the weights laid upon it, to promote the grinding, or friture, of the glasses. The whole is covered with a wheel, B, made of hard light wood, about six inches in diameter; by pulling of which backwards and forwards alternately, and sometimes turning it round, the workmen who always stand opposite to each other, produce a constant attrition between the two glasses, and bring them to what degree of smoothness they please, by first pouring in water and coarse sand; after that, a finer sort of sand, as the work advanceth, till at last they must pour in the powder of smalt. As the upper or incumbent glass polishes, and grows smoother, it must be taken away, and another from time to time put in its place.

This engine is called a mill by the artists, and is used only in the largest size glasses; for in the grinding of the lesser glasses, they are content to work without a wheel, and to have only four wooden handles fastened to the four corners of the stone which loads the upper plank, by which they work it about.

When the grinder has done his part, who finds it very difficult to bring the glass to an exact plainness, it is turned over to the care of the polisher, who with the fine powder of tripoli-stone, or emery, brings it to a perfect evenness and lustre. The instrument made use of in this branch, is a board, c, c, furnished with a felt, and a small roller, which the workman moves by means of a double handle at both ends. The artist in working this roller, is assisted with a wooden hoop or spring, to the end of which it is fixed: for the spring, by constantly bringing the roller back to the same points, facilitates the action of the workman's arm.

Painting in Glass. The ancient manner of painting in glass was very simple; it consisted in the mere arrangement of pieces of glass of different colours in some sort of symmetry, and constituted what is now called Mosaic.

In process of time they came to attempt more regular designs, and also to represent figures heightened with all their shades: yet they proceeded no farther than the contours of the figures in black with watercolours, and hatching the draperies after the same manner on glasses of the colour of the object they designed to paint. For the carnation, they used glasses of a bright red colour; and upon this they drew the principal lineaments of the face, &c. with black.

But in time, the taste for this sort of painting improving considerably, and the art being found applicable to the adorning of churches, basilicas, &c., they found out means of incorporating the colours in the glass itself, by heating them in the fire to a proper degree; having first laid on the colours. The colours used in painting or staining of glass are very different from those used in painting either in water or oil colours.

For black, Take scales of iron, one ounce; scales of copper, one ounce; jet, half an ounce; reduce them to powder, and mix them. For blue, Take powder of blue, one pound; sal nitre, half a pound; mix them and grind them well together. For carnation, Take red chalk, eight ounces; iron scales and litharge of silver, of each two ounces; gum arabic, half an ounce; dissolve in water; grind altogether for half an hour as stiff as you can; then put it in a glass and stir it well, and let it stand to settle fourteen days.

For green, Take red lead, one pound; scales of copper, one pound; and flint, five pounds; divide them into three parts; and add to them as much sal nitre; put them into a crucible, and melt them with a strong fire; and when it is cold, powder it, and grind it on a porphyry. For gold colour, Take silver an ounce; antimony, half an ounce; melt them in a crucible; then pound the mass to powder; and grind it on a copper plate; add to it yellow ocher, or brick-dust calcined again, fifteen ounces; and grind them well together with water. For purple, Take minium, one pound; brown stone, one pound; white flint, five pounds; divide them into three parts, and add to them as much sal nitre as one of the parts; calcine, melt, and grind it as you did the green. For red, Take jet, four ounces; litharge of silver, two ounces; red chalk, one ounce; powder them fine, and mix them. For white, Take jet, two parts; white flint, ground on a glass very fine, one part; mix them. For yellow, take Spanish brown, ten parts; leaf silver, one part; antimony, half a part; put all into a crucible, and calcine them well.

In the windows of ancient churches, &c., there are to be seen the most beautiful and vivid colours imaginable, which far exceed any of those used by the moderns, not so much because the secret of making those colours is entirely lost, as that the moderns will not go to the charge of them, nor be at the necessary pains, by reason that this sort of painting is not now so much in esteem as formerly. Those beautiful works which were made in the glass-houses were of two kinds.

In some, the colour was diffused through the whole substance of the glass. In others, which were the more common, the colour was only on one side, scarce penetrating within the substance above one third of a line; though this was more or less according to the nature of the colour; the yellow being always found to enter the deepest. These last, though not so strong and beautiful as the former, were of more advantage to the workmen, by reason that on the same glass, though already coloured, they could show other kind of colours where there was occasion to embroider draperies, enrich them with foliages, or represent other ornaments of gold, silver, &c.

In order to this, they made use of emery, grinding or wearing down the surface of the glass, till such time as they were got through the colour to the clear glass. This done, they applied the proper colours on the other side of the glass. By these means, the new colours were hindered from running and mixing with the former, when they exposed the glasses to the fire, as will appear hereafter.

When indeed the ornaments were to appear white, the glass was only bared of its colour with emery, without tinging the place with any colour at all; and this was the manner by which they wrought their lights, and heightnings, on all kinds of colour.

The first thing to be done, in order to paint or stain glass, in the modern way, is to design, and even colour the whole subject on paper. Then they choose such pieces of glass as are clear, even, and smooth, and proper to receive the several parts, and proceed to distribute the design itself, or papers it is drawn on, into pieces suitable to those of the glass; always taking care that the glasses may join in the contours of the figures, and the folds of the draperies; that the carvings, and other finer parts, may not be impaired by the lead with which the pieces are to be joined together. The distribution being made, they mark all the glasses as well as papers, that they may be known again; which done, applying every part of the design upon the glass intended for it, they copy or transfer, the design upon this glass with the black colour diluted in gum water, by tracing and following all the lines and strokes as they appear through the glass with the point of a pencil.

When these strokes are well dried, which will happen in about two days, the work being only in black and white, they give a slight wash over with urine, gum arabic, and a little black; and repeat it several times, according as the shades are desired to be heightened, with this precaution, never to apply a new wash till the former is sufficiently dried.

This done, the lights and risings are given by rubbing off the colour in the respective places with a wooden point, or the handle of the pencil.

As to the other colours above-mentioned, they are used with gum water, much as in painting in miniature; taking care to apply them lightly, for fear of effacing, the outlines of the design; or even, for the greater security, to apply them on the other side; especially yellow, which is very pernicious to the other colours, by blending therewith. And here too, as in pieces of black and white, particular regard must always be had not to lay colour on colour, or lay on a new lay, till such time as the former are well dried.

It may be added, that the yellow is the only colour that penetrates through the glass, and incorporates therewith by the fire; the rest, and particularly the blue, which is very difficult to use, remaining on the surface, or at least entering very little. When the painting of all the pieces is finished, they are carried to the furnace, or oven, to anneal, or bake the colours.

The furnace here used is small, built of brick, from eighteen to thirty inches square. At six inches from the bottom is an aperture to put in the fuel, and maintain the fire. Over this aperture is a grate, made of three square bars of iron, which traverse the furnace, and divide it into two parts. Two inches above this partition, is another little aperture, through which they take out pieces to examine how the coddling goes forward. On the grate is placed a square earthen pan, six or seven inches deep; and five or six inches less every way than the perimeter of the furnace. On the one side hereof is a little aperture, through which to make trials, placed directly opposite that of the furnaces destined for the same end. In this pan are the pieces of glass to be placed, in the following manner. First, the bottom of the pan is covered with three strata, or layers, of quick lime pulverized; those strata being separated by two others of old broken glass, the design whereof is to secure the painted glasses from the too intense heat of the fire. This done, the glasses are laid horizontally on the last or uppermost layer of lime.

The first row of glasses they cover over with a layer of the same powder, an inch deep; and over this they lay another range of glasses, and thus alternately till the pan is quite full; taking care that the whole heap always end with a layer of the lime powder.

The pan being thus prepared, they cover up the furnace with tiles, on a square table of earthen ware, closely luted all round; only leaving five little apertures, one at each corner, and another in the middle, to serve as chimneys. Things thus disposed, there remains nothing but to give the fire to the work. The fire for the first two hours must be very moderate, and must be increased in proportion as the coddling advances, for the space of ten or twelve hours; in which time it is usually completed. At last the fire, which at first was charcoal, is to be of dry wood, so that the flame covers the whole pan, and even issues out at the chimneys.

During the last hours, they make essays, from time to time, by taking out pieces laid for the purpose through the little aperture of the furnace, and pan, to see whether the yellow be perfect, and the other colours in good order. When the annealing is thought sufficient, they proceed with great haste to extinguish the fire, which otherwise would soon burn the colours, and break the glasses.

Glass of lead. See Chemistry, p. 136.

Glass porcelain, the name given by many to a modern invention of imitating the china-ware with glass.

The method of making it, as given by Mr Reamur, who was the first that carried the attempt to any degree of perfection, is as follows.

The glass vessels to be converted into porcelain, are to be put into large vessels, such as the common fine earthen ditches are baked in; or into sufficiently large crucibles: the vessels are to be filled with a mixture of fine white sand, and of fine gypsum; or plaster stone, burnt into what is called plaster of Paris; and all the interstices are to be filled up with the same powder, so that the glass vessels may nowhere touch either one another, or the sides of the vessels they are baked in.

The vessel is to be then covered down, and luted, and the fire does the rest of the work: for this is only to be put into a common potter's furnace, and when it has stood there the usual time of taking the other vessels, it is to be taken out, and the whole contents will be found no longer glass, but converted into a white opake substance, which is a very elegant porcelain, and has almost the properties of that of china. GLASS of antimony. See Chemistry, p. 87.