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The Household Cyclopedia


To Manufacture Glass.

Glass is a combination of sand, flint, spar, or some other silicious substances, with one or other of the fixed alkalies, and in some cases with a metallic oxide. Of the alkalies, soda is commonly preferred; and of the silicious substances, white sand is most in repute at present, as it requires no preparation for coarse goods, while mere washing in water is sufficient for those of a finer quality. The metallic oxide usually employed, is litharge, or some other preparation of lead. Iron is used in bottle-glass.

The silicious matter should be fused in contact with something called a flux. The substances proper for this purpose are lead, borax, arsenic, nitre, or any alkaline matter. The lead is used in the state of red-lead; and the alkalies are soda, pearlash, sea-salt, and wood-ashes. When red-lead is used alone, it gives the glass a yellow cast and requires the addition of nitre to correct it. Arsenic, in the same manner, if used in excess, is apt to render the glass milky. For a perfectly transparent glass, the pearlash is found much superior to lead; perhaps better than any other flux, except it be borax, which is too expensive to be used, except for experiments, or for the best looking-glasses.

The materials for making glass must first be reduced to powder, which is done in mortars or by horse mills. After sifting out the coarse parts, the proper proportions of silex and flux are mixed together, and put into the calcining furnace, where they are kept in a moderate heat for 5 or 6 hours, being frequently stirred about during the process. When taken out the matter is called frit. Frit is easily converted into glass by only pounding it, and vitrifying it in the melting pots of the glass furnace; but in making fine glass, it will sometimes require a small addition of flux to the frit to correct any fault. For, as the flux is the most expensive article, the manufacturer will rather put too little at first than otherwise, as he can remedy this defect in the melting pot. The heat in the furnace must be kept up until the glass is brought to a state of perfect fusion; and during this process any scum which arises must be removed by ladles. When the glass is perfectly melted, the glass-blowers commence their operations.

For the best flint-glass, 120 lbs. of white sand, 50 lbs. of red-lead, 40 lbs. of the best pearlash, 20 lbs. of nitre, and 5 oz. of manganese; if a pound or two of arsenic be added, the composition will fuse much quicker, and with a lower temperature.

For a cheaper flint-glass, take 120 lbs. of white sand, 35 lbs. of pearlash, 40 lbs. of red-lead, 13 lbs. of nitre, 6 lbs. of arsenic, and 4 oz. of magnesia.

This requires a long heating to make clear glass, and the heat should be brought on gradually, or the arsenic is in danger of subliming before the fusion commences. A still cheaper composition is made by omitting the arsenic in the foregoing, and substituting common sea-salt.

For the best German crystal-glass, take 120 lbs. of calcined flints or white sand, the best pearlash, 70 lbs, saltpetre, 10 lbs.; arsenic, 1/2 lb., and 5 oz. of manganese. Or, a cheaper composition for the same purpose is 120 lbs. of sand or flints, 46 lbs. of pearlash, 7 lbs of nitre, 6 lbs. of arsenic, and 5 oz. of manganese. This will require a long continuance in the furnace; as do all others where much of the arsenic is employed.

For looking-glass plates washed white sand, 60 lbs.; purified pearlash, 25 lbs.; nitre, 15 lbs.; and 7 lbs. of borax. If properly managed, this glass will be colorless. But if it should be tinged by accident, a trifling quantity of arsenic, and an equal quantity of manganese, will correct it; an ounce of each may be tried first, and the quantity increased if necessary.

The ingredients for the best crown-glass must be prepared in the same manner as for looking-glasses, and mixed in the following proportions: 60 lbs. of white sand, 30 lbs. of pearlash, and 15 lbs. of nitre, 1 lb. of borax, and 1/2 lb. of arsenic.

The composition for common green window-glass is, 120 lbs. of white sand, 30 lbs. of unpurified pearlash; woodashes, well burnt and sifted, 60 lbs.; common salt, 20 lbs.; and 5 lbs. of arsenic.

Common green bottle-glass is made from 200 lbs. of wood-ashes and 100 lbs. of sand, or 170 lbs. of ashes, 100 lbs. of sand, and 50 lbs. of the slag of an iron furnace; these materials must be well mixed.

The materials employed in the manufacture of glass, are by chemists reduced to three classes, namely, alkalies, earths, and metallic oxides.

The fixed alkalies may be employed indifferently; but soda is preferred in this country. The soda of commerce is usually mixed with common salt, and combining with carbonic acid. It is proper to purify it from both of these foreign bodies before using it. This, however, is seldom done.

The earths are silica (the basis of flints), lime, and sometimes a little alumina (the basis of clay). Silica constitutes the basis of glass. It is employed in the state of fine sand or flints; and sometimes for making very fine glass, rock crystal is employed. When sand is used, it ought, if possible, to be perfectly white, for when it is colored with metallic oxides, the transparency of the glass is injured. Such sand can only be employed for very coarse glasses. It is necessary to free the sand from all the loose earthy particles with which it may be mixed, which is done by washing it well with water.

Lime renders glass less brittle, and enables it to withstand better the action of the atmosphere. It ought in no case to exceed the 20th part of the silica employed, otherwise it corrodes the glass pots. This indeed may be prevented by throwing a little clay into the melted glass; but in that case a green glass only is obtained.

The metallic oxides employed are the red oxide of lead or litharge, and the white oxide of arsenic.

The red oxide of lead, when added in sufficient quantity, enters into fusion with silica, and forms a milky hue like the dial-plate of a watch. When any combustible body is present, it is usual, in some manufactories, to add a little white oxide of arsenic. This supplying oxygen, the combustible is burnt, and flies off, while the revived arsenic is at the same time volatized.

There are several kinds of glass adapted to different uses. The best and most beautiful are the flint and the plateglass. These, when well made, are perfectly transparent and colorless, heavy and brilliant. They are composed of fixed alkali, pure siliceous sand, calcined flints and litharge, in different proportions. The flint glass contains a large quantity of oxide of lead, which by certain processes is easily separated. The plate glass is poured in the melted state upon a table covered with copper. The plate is cast 1/2 an inch thick or more, and is ground down to a proper degree of thickness, and then polished.

Crown-glass, that used for windows, is made without lead, chiefly of fixed alkali fused with silicious sand, to which is added some black oxide of manganese, which is apt to give the glass a tinge of purple.

Bottle-glass is the coarsest and cheapest kind, in this little or no fixed alkali enters the composition. It consists of alkaline earth and oxide of iron combined with alumina and silica. In this country it is composed of sand and the refuse of the soap-boiler, which consists of the lime employed in rendering this alkali caustic, and of the earthy matters with which the alkali was contaminated. The most fusible is flint-glass, and the least fusible is bottleglass.

Glass for Looking-glass Plates, No. 1.

Take of white sand, cleansed, 60 lbs.; of purified pearlash, 25 lbs.; of saltpetre, 15 lbs.; and of borax, 7 lbs.

This composition should be continued long in the fire, which should be for some time strong and afterwards more moderate, that the glass may be entirely free from bubbles before it is worked. It will be entirely clear of all color, unless in case of some accident; but if any yellow tinge should, nevertheless, unfortunately infect it, there is no remedy except by adding a small proportion of manganese, which should be mixed with an equal quantity of arsenic, and after their being put into the glass, giving it a considerable heat again, and then suffering it to free itself from bubbles in a more moderate one, as before. If the tinge be slight, an ounce of manganese may be first tried, and if that prove insufficient, the quantity must be increased, but the glass will always be obscure in proportion to the quantity that is admitted.

Looking-glass Plates, No. 2.

Take of the white sand, 60 lbs.; of pearlash, 20 lbs.; of common salt, 10 lbs.; of nitre, 7 lbs.; and of borax, 1 lb.

This glass will run with as little heat as the former, but it will be more brittle and refract the rays of the light in a greater degree.

Crown or Best Window-glass, No. 1.

Take of white sand, 60 lbs.; of purified pearlash, 30 lbs.; of saltpetre, 15 lbs,; of borax, 1 lb.; and of arsenic, 1/2 lb.

This will be very clear and colorless if the ingredients be good, and will not be very dear. It will run with a moderate heat; but if it be desired to be yet more fusible and soft, 1/2 a lb. or a pound more of arsenic may be added.

If the glass should prove yellow, the manganese must be used as above directed for the looking-glass.

Cheaper kind of Window-glass, No. 2.

Take of white sand, 60 lbs.; of unpurified pearlash, 26 lbs.; of common salt, 10 lbs.; of nitre, 5 lbs.; of arsenic, 2 lbs.; and of manganese, 1 1/2 oz.

This will be inferior to the above kind, but may be improved, where desired, by purifying the pearlash.

Common or Green Window-glass, No. 3.

Take of white sand, 60 lbs.; of unpurified pearlash, 30 lbs.; of common salt, 10 lbs.; of arsenic, 2 lbs.; and of manganese, 2 oz.

This is a cheap composition and will not appear too green nor be very deficient in transparency.

Common or Green Window-glass, No. 4.

Take of the cheapest kind of white sand, 120 lbs.; of unpurified pearlash, 30 lbs.; of wood-ashes well burnt and sifted, 60 lbs.; of common salt, 20 lbs.; and of arsenic, 5 lbs.

This composition is very cheap, and will produce a good glass with a greenish cast.

Best Phial-glass, No. 1.

Take of white sand, 120 lbs.; of unpurified pearlash, 50 lbs.; of common salt, 10 lbs.; of arsenic, 5 lbs.; and of manganese, 5 oz.

This will be a very good glass for the purpose and will work with a moderate heat, but requires time to become clear, on account of the proportion of arsenic; when, however, it is once in good condition, it will come very near to the crystal glass.

Cheapest Green or Common Phial-glass, No. 2.

Take of the cheapest kind of white sand, 120 lbs.; of wood-ashes, well burnt and sifted, 80 lbs.; of pearlash, 20 lbs.; of common salt, 15 lbs; and of arsenic, 1 lb.

This will be green, but tolerably transparent and will work with a moderate fire, and vitrify quickly with a strong one.

Green or Bottle glass.

Take of wood ashes, 200 lbs.; and of sand, 100 lbs. Mix them thoroughly by grinding together.

This is the due proportion where the sand is good and the wood-ashes are used without any other addition.

The same, with the addition of scoria.

Take of wood-ashes, 170 lbs.; of sand 100 lbs.; and of scoria. or clinkers, 50 lbs. Mix the whole well by grinding them together.

The clinkers should be well ground before they are used, if they admit of it; but frequently they are too hard, and in that case they should be broken into as small bits as can be done conveniently and mixed with the other matter without any grinding. The harder they are, the less material will be the powdering of them as they will the sooner melt of themselves in the furnace, and consequently mix with the other ingredients.

The most Perfect kind of Flint-glass, No. 1.

Take of white sand, 120 lbs.; red-lead, 50 lbs.; the best pearlash, 40 lbs.; nitre, 20 lbs.; manganese, 5 oz.

If this composition be fused with a very strong fire, and time be given to it, a glass will be produced that will have the play of the best flint-glass, and yet be hard and strong. It is not so cheap as the compositions given below, where arsenic or common salt is introduced, or where more of the pearlash are used; in either of which cases, savings may be made by diminishing proportionally the quantities of nitre. But the qualities of this glass will be found to come nearer to the standard of perfection, which is to unite the lustre and hardness together in the greatest degree they are compatible with each other.

If this composition be, however, desired to flux with less heat, and quicker, a pound or two of arsenic may be added, which will be found effectually to answer the purpose.

Flint-glass, No. 2.

Take of sand, 120 lbs.; the best pearlash, 54 lbs.; red-lead, 36 lbs.; nitre, 12 lbs.; manganese, 6 oz.

This will require much the same heat as the other, but will be harder in its texture. If it be desired to be made more yielding to the fire, arsenic may be added, or the quantity of sand may be lessened. In these cases the glass will be softer and weaker.

White Flint-glass, No. 3.

Take of white sand, 120 lbs.; the best pearlash, 35 lbs.; arsenic, 6 lbs.; manganese, 4 oz.

This glass will require a considerable time in the fire to become clear, and must not, if it can be avoided, be strongly urged at first. This glass will not be so hard as those of the above compositions, but it will be very clear, and may be employed for large vessels, where a sufficient thickness can be allowed to give it strength.

Cheaper Composition of Glass, No. 4.

Take the proportions of the other ingredients given in the last, and omitting the arsenic, add in its stead 15 lbs. of common salt.

This will be more brittle than the last, and therefore cannot be recommended, unless for the fabrication of such kind of vessels, or other pieces, where the strength is of little moment.

Cheapest Composition of White Flint-glass, No. 5.

Take of white sand, 120 lbs., red-lead, 30 lbs.; the best pearlash, 20 lbs.; nitre, 10 lbs.; common salt, 15 lbs.; arsenic, 6 lbs.

This glass will fuse with a moderate heat, but requires time, like the last, to take off the milky appearance of the arsenic; it is yet softer than the last, and may therefore be deemed the worst kind of flint that can be made.

Best German Crystal-glass, No. 6.

Take of calcined flints, or white sand, 120 lbs.; the best pearlash, 70 lbs.; saltpetre, 10 lbs.; arsenic, 1/2 lb.; manganese, 5 oz.

If the pearlash be pure and good, this glass will equal the best of this kind that ever was made. Borax has been frequently used also in the compositions of this sort of glass, but its great price, without any equivalent advantage, will deter from the employing it in large manufactures, as there is no sort of transparent glass (plate excepted), that can bear the expense of it.

German Crystal-glass, No. 7.

Take of calcined flints, or white sand, 120 lbs.; pearlash, 46 lbs.; manganese, 5 oz.

This composition requires a long continuance of heat, on account of the arsenic, for the reason before given. It produces a glass equally or more transparent and colorless than the preceding, but somewhat more brittle. The arsenic is, however so disagreeable an ingredient, from the deleterious qualities of the fumes, which will necessarily rise copiously till the fusion of the other ingredients check it, that, where the advantage is not more considerable than the saving arising from the difference of these two recipes, it is scarcely worth while to submit to the inconvenience of it.

To Anneal Glass.

"Nealing," as it is called by the workmen, is a process in the glass-houses, and consists in putting the glass vessels, as soon as they are formed, and while they are yet hot, into a furnace or an oven, not so hot as to re-melt them, and in which they are suffered to cool gradually. This is found to prevent their breaking easily, particularly on exposure to heat.

A similar process is used for rendering cast-iron vessels less brittle, and the effect depends on the same principles.

To Polish and Grind Glass.

To grind plate-glass, lay it horizontally upon a flat stone table, made of a very fine grained free-stone; and for its greater security, plaster it down with mortar or stucco. The stone table is supported by a strong wooden frame, with a ledge all round its edges, rising about 2 inches above the glass. Upon the plate to be ground is laid another rough glass, not above half as big, and so loose as to slide upon the former, but cemented to a wooden plank, to guard it from the injury it must otherwise receive from the scraping of the wheel whereto the plank is fastened, and from the weights laid upon it to promote the triture or grinding of the glasses. The whole is covered with a wheel made of hard light wood, about 6 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 whatever degree of smoothness they please, by first pouring in water and coarse sand; after that, a finer sort of sand, as the work advances, till at last they pour in the powder of smalt. As the upper or incumbent glass becomes smooth it must be removed, and another, from time to time, substituted for it.

The engine just described is called a mill by the workmen, and is employed only in grinding the largest-sized glasses. In grinding lesser glasses, they usually work without a wheel, having four wooden handles fastened to the corners of the stone that loads the upper plank, by which they work it about. The grinders' part done, the glass Is turned over to the polisher, who, with 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 furnished with a felt and small roller, which the workman moves by means of a double handle at both ends. The artist, in working this roller, is assisted by 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.

To make Frit.

Frit, in the glass manufacture, is the matter or ingredients of which glass is to be made, when they have been calcined or baked in a furnace. There are three kinds of frit: the first, crystal frit, or that for crystal or clear glass, is made with salt of pulverine and sand. The second and ordinary frit is made of the bare ashes of the pulverine or barilla, without extracting the salt from them. This makes the ordinary white or crystal-glass. The third is frit for green glasses, made of common ashes, without any preparation. This last frit will require 10 or 12 hours' baking. The materials in each are to be finely powdered, washed and searced; then equally mixed, and frequently stirred together in the melting-pot.

To bring Pearlash, or any other Fixed Alkaline Salt, to the Highest Degree of Purity.

Take of the best pearlash 3 lbs., and of saltpetre 6 oz. Pound them together in a glass or marble mortar, till they are thoroughly well mixed, and then put part of them into a large crucible, and set it in a furnace, where it may undergo a strong heat. When the part of the matter that was first put into the crucible is heated red hot, throw in the rest gradually, and if the crucible will not contain the whole, pour part of the melted matter out on a moistened stone, or marble, and having made room in the crucible, put in the rest and let it continue there likewise till it be red hot. Pour it out then as the other, and afterwards put the whole into an earthen or very clean iron pot, with 10 pts. of water, and heat it over the fire, till the salts be entirely melted. Let it then be taken off the fire, stand till it is cold, and afterwards filter it through paper in a pewter colander. When it is filtered, return the fluid again into the pot, and evaporate the salt to dryness which will then be as white as snow, the nitre having burnt all the combustible matter that remained in the pearlash after its former calcination.

To Polish Optical-glasses.

The operation of polishing optic-glasses after being properly ground, is one of the most difficult points of the whole process. Before the polishing is begun, it is proper to stretch an even, well-wrought piece of linen over the tool, dusting upon it some very fine tripoli. Then taking the glass in the hand, run it round 40 or 50 times upon the tool, to take off the roughness of the glass about the border of it. This cloth is then to be removed, and the glass to be polished upon the naked tool, with a compound powder, made of four parts tripoli mixed with one of fine blue vitriol, 6 or 8 grains of which mixture are sufficient for a glass 5 in. broad. This powder must be wetted with 8 or 10 drops of clear vinegar in the middle of the tool, being first mixed and softened thoroughly with a very fine small muller. Then, with a nice brush, having spread this mixture thinly and equably upon the tool, take some very fine tripoli, and strew it thinly and equably upon the tool so prepared, after which take the glass to be polished, wiped very clean, and apply it on the tool, and move it gently twice or thrice in a straight line backwards and forwards, then take it off, and observe whether the marks of the tripoli, sticking to the glass, are equably spread over the whole surface; If not, it is a sign that either the tool or glass is too warm, in which case wait awhile and try it again, till the glass takes the tripoli everywhere alike. Then begin to polish boldly, there being no danger of spoiling the figure of the glass, which in the other case would infallibly happen.

To Purify Pearlash for the manufacture of Mirrors.

Take any quantity of the best pearlash, and dissolve it in 4 times its weight of water boiling, which operation may be best performed in a pot of cast iron. When they are dissolved, let the solution be put in a clean tub, and suffered to remain there 24 hours or longer. Let the clear part of the fluid be then decanted off from the dregs or sediment, and put back into the iron pot, in which the water must be evaporated away till the salts be left perfectly dry again. They should then, if not used immediately, be kept in stone jars, well secured from moisture and air, till such time as they are wanted.

Great care should be always taken in this treatment of the salts to keep the iron pot thoroughly clean from rust, which would give a yellow tinge to the glass, not to be removed without greatly injuring it.

To Ornament all kinds of Glass in Imitation of Engraving, etc.

The method heretofore known for engraving on glass, has been by means of a machine with wheels, of different substances, which have been employed with sand, etc., to grind off some parts of the surface of the glass which is to be engraved on, and then by means of grinding and polishing different parts on the rough surface, the different figures are formed according to the designs given. By this invention, instead of grinding or taking off any part of the surface of the glass, the patentee lays on an additional surface or coating of glass, prepared for the purpose, which, when subjected to a proper degree of heat, will incorporate with the glass to be operated upon, so as to produce an effect similar to that which has hitherto been obtained by means of grinding. When it is required to ornament glass, then, previously to the heat being applied, with an etching or engraving tool such parts are to be taken out as will produce the required effect, and that in a much superior way to the effect produced by the usual mode of grinding, polishing, etc. The materials used are to be melted in a crucible, or other pot, and they are to be made up in the same manner as if used for the making of the best flintglass, broken glass, or, as it is usually denominated, "cullitt", being the principal ingredient in it. Several mixtures are given, of which the first is 160 parts of cullitt, 10 of pearlash, 40 of red-lead, and 10 of arrence.

The second is 120 parts of cullitt, 160 of red-lead, 60 of sand, and 60 of borax.

The third is 70 parts of red-lead, 22 1/2 of sand, and 410 of calcined borax.

When these are subjected to such a heat as to be thereby completely fused, take equal parts of each mixture and grind them to an impalpable powder, for the purpose of being mixed with a menstruum proper for coating the glass.

The menstruum consists of 1 part of refined loaf sugar dissolved in 2 parts of pure water, to which is added, at the time of mixing the powder, about 1/3 part of common writingink; the effect, we are told, produced by this addition of oxide of manganese, used in a small quantity by the glassmakers in making their best flint-glass, because without such an addition the specimens would be of a cloudy or milky appearance. A quantity of this menstruum is used sufficient to render the ground-mixture of a proper consistence for laying on with a thin, smooth surface. When the coating or mixture is thus prepared, the glass is to be coated by means of a camel's-hair brush, or squirrel's-foot, etc. It is then to be exposed to a heat sufficient to produce a semivitrification of the coaty surface, and to incorporate it with the substance or body of glass so coated. But the heat must not be carried higher than this, because in that case a complete vitrification would ensue, and the desired effect of having a surface in imitation of the rough surface produced by grinding would not be obtained; the article must, under such circumstances, be re-coated and submitted again to the fire. If, after the coating has been applied, any borders, cyphers, or other ornaments, are wanted to be executed thereon, then, previously to the heat being applied with an etching or engraving tool, such parts of the coated surface must be chased out as will produce the desired effect, after which the requisite degree of heat is to be applied.

This invention is not only applicable to all kinds of useful and ornamental articles of glassware on which the common methods of engraving have been practised, but may be applied to window-glass and plate-glass of every description, in place of grinding for the purpose of making window-blinds. It is also said to be peculiarly adapted to produce beautiful specimens of art for the windows of altar-pieces, libraries, museums, coach-windows, and for the glass used in ornamental buildings of all descriptions. This invention has another advantage over the common method of the work wearing much cleaner than the work of ground glass, the surface of which being fractured by the action of the wheel, etc., is therefore liable to gather dirt on the rough, unpolished parts of the borders, etc.

To make the Bologna Phial.

The Bologna, or philosophical phial, is a small vessel of glass which has been suddenly cooled, open at the upper end, and rounded at the bottom. It is made so thick at the bottom that it will bear a smart blow against a hard body without breaking, but if a little pebble or piece of flint is let fall into it, it immediately cracks, and the bottom falls into pieces; but unless the pebble or flint is large and angular enough to scratch the surface of the glass, it will not break.

To make Prince Rupert's Drops.

Prince Rupert's drops are made by letting drops of melted glass fall into cold water; the drop assumes by that means an oval form, with a tail or neck resembling a retort. They possess this singular property, that if a small portion of the tail is broken off, the whole bursts into powder, with an explosion, and a considerable shock is communicated to the hand that grasps it.

To Break Glass in any Required Way.

Dip a piece of worsted thread in spirits of turpentine, wrap it round the glass in the direction required to be broken, and then set fire to the thread, or apply a red hot wire round the glass, and if it does not immediately crack, throw cold water on it while the wire remains hot. By this means glass that is broken may often be fashioned and rendered useful for a variety of purposes.


The Best and Hardest Glass for Receiving Colors, No. 1.

Take of the best sand, cleansed by washing, 12 lbs.; of pearlash, or fixed alkaline salt, purified with nitre, 7 lbs.; of saltpetre, 1 lb.; and of borax, 1/2 lb.

The sand being first reduced to powder in a glass or flint mortar, the other ingredients should be put to it, and the whole well mixed by pounding them together.

Best Glass, but not so Hard, No. 2.

Take of the white sand, cleansed, 12 lbs.; of pearlash, purified with saltpetre, 7 lbs.; of nitre, 1 lb.; of borax, 1/2 lb.; and of arsenic, 4 oz.

Proceed as in the last; but if the glass be required to melt with yet less heat, 1 lb. of borax may be used instead of the 1/2 lb., and 1 lb. of common salt may be added. But this last is apt to make the glass more brittle, which is an injury done to such as is to be cut into very small pieces, and ground with so many angles in the figure, in imitation of jewels.

Soft Glass or Paste for Receiving Colors. No. 3.

Take of white sand, cleansed, 6 lbs.; of red-lead 3 lbs.; of purified pearlash, 2 lbs.; and of nitre 1 lb.

Proceed with the mixture as with the foregoing.

Glass or Paste, Softer than the above, No 4.

Take of white sand, cleansed, 6 lbs.; of red-lead and purified pearlash, each 3 lbs.; of nitre, 1 lb; of borax, 1/2 lb.; and of arsenic, 3 oz.

This is very soft and will fuse with a very gentle heat, but requires some time to become clear, on account of the arsenic. It may even be prepared and tinged in a common fire without a furnace, if the pots containing it can be surrounded by burning coals, without danger of their falling into it. The borax, being a more expensive ingredient than the others, may be omitted where a somewhat greater heat can be applied, and the glass is not intended for very nice purposes, or 1 lb. of common salt may be substituted in its place, but the glass will be more clear and perfect, and free itself much sooner from bubbles, where the borax is used.

This glass, will be very soft, and will not bear much water, if employed for rings, buckles, or such imitations of stones as are exposed to much rubbing; but for ear-rings, ornaments worn on the breast, or such others as are but seldom put on, it may last a considerable time.

In all these soft compositions care should be taken that part of the sand be not left unvitrified in the bottom of the pot, as will sometimes happen, for in that case the glass, abounding too much with salt and lead, will not bear the air, but, being corroded by it, will soon contract a mistiness and specks in the surface, which will entirely efface all the lustre of the paste.

Hard Glass of a full Blue Color. No. 1.

Take of the composition of hard glass, No. 1 or 2, 10 lbs.; zaffre, 6 dr.; and of manganese, 2 dr. Proceed as with the above.

If this glass be of too deep a color, the proportion of the zaffre and manganese to the glass may be diminished, and if it verge too much on the purple, to which cast it will incline, the manganese should be omitted. If a very cool or pure blue be wanted, instead of the manganese, half an ounce of calcined copper may be used, and the proportion of zaffre diminished by one-half.

Paste of a Full Blue Color, No. 2.

Take of the composition for paste, No. 1 or 2, 10 lbs., and proceed as with the foregoing.

Hard Glass, Resembling the Sapphire, No. 3.

Take of the composition for hard glass, No. 1 or 2, 10 lbs.; of zaffre, 8 drs. and 1 scr.; of purple of Cassius, 1 dr. Proceed as with the above.

Cheaper Hard Glass for Resembling the Sapphire, No.4.

As the foregoing, only, instead of the purple of Cassius, use 2 drs. and 2 scr. of manganese.

If this be well managed, the color will be very good, and the glass, when set and cut, will not be easily distinguishable from the true sapphire; but the preceding will be a finer color, as there is a foulness in the tinge of the manganese, which will always diminish, in some degree, the effect of brighter colors, when with them.

Paste Resembling the Sapphire, No. 5.

Take of the composition for paste, No. 3 or 4, and proceed as with the foregoing.

It is not worth while to bestow the expense of coloring paste with the gold, and it is therefore more expedient, in the case of such, to use the other method.

Hard Glass and Paste for Sapphire, by means of Smalt, No. 6.

Take of the compositions for hard glass and paste, any quantity, and mix with them one-eighth of their weight of smalt, the brightest and most inclining to purple that can be procured.

If it be desirable to give a more purple tinge, manganese may be added in the proportion required.

Hard Glass Resembling Eagle Marine, No. 7.

Take of the composition for hard glass, No. 1 or 2, 10 lbs.; of oxide of copper, highly calcined with sulphur, 3 oz.; and of zaffre, 1 scr. Proceed with the foregoing.

Paste for Eagle Marine, No. 8.

Take of the composition for paste, No. 1 or 2, 10 lbs., and proceed as with the above.

Hard Glass of a Gold or Yellow Color, No. 1.

Take of the composition for hard glass, No. 1 or 2, 10 lbs., but omit the saltpetre, and for every pound add 1 oz. of calcined borax, or, if that do not render the glass sufficiently fusible, 2 oz.; of red tartar, the deepest color that can be procured, 10 oz.; of manganese, 2 oz.; of soft charcoal, 2 drs. Proceed as with the rest.

Paste of a Gold or Yellow Color, No. 2.

Take of the composition for paste, No. 3 or 4 prepared without the saltpetre, 10 lbs.; of colcothar, strongly calcined, 1 1/2 oz. Proceed as with the others.

The crude tartar and the charcoal must not be used where lead enters into the composition of the glass, and the nitre may be spared, because the yellow tinge, given to the glass by the lead, on account of which the nitre is used, is no detriment in this case, but only adds to the proper color. This color may also be prepared by crude antimony, as well as the colcothar, but it is more difficult to be managed, and not superior in its effect.

Hard Glass Resembling the Topaz, No. 3.

Take of the composition for hard glass, No. 1 or 2, 10 lbs. and an equal quantity of the gold-colored hard glass. Powder and fuse them together.

As there is a great variety in the color of the topaz, some being a deeper yellow, and others slightly tinged, the proportions of the yellow glass to the white may be accordingly varied at pleasure, the one here given being for the deepest.

Paste Resembling the Topaz, No. 4.

This may be done in the same manner as the preceding, but the saltpetre may be omitted in the original composition of the glass, and for the resemblance of the very slightly colored topazes neither the gold-colored paste nor any other tinging matter need be added, that of the lead being sufficient, when not destroyed by the nitre.

Glass Resembling the Chrysolite, No. 5.

Take of the composition for hard glass, No. 1 or 2, 10 lbs.; of colcothar, 6 drs. Proceed as with the above.

Paste Resembling the Chrysolite, No. 6.

Take of the composition for paste, No. 3 or 4, prepared without saltpetre, 10 lbs.; and of colcothar, 5 drs. Proceed as with the rest.

Hard Glass Resembling the Emerald, No. 1.

Take of the composition for hard glass, No. 1 or 2, 9 lbs.; of oxide of copper, 3 oz.; and of precipitated oxide of iron, 2 drs.

Paste Resembling the Emerald. No. 2.

Take of the composition for paste, No. 1 or 2 and proceed as with the above, but if the saltpetre be omitted in the preparation of the paste, a less proportion of the iron will serve.

Hard Glass of a Deep and very Bright Purple Color. No. 1.

Take of the composition for hard glass, No. 1 or 2, 10 lbs.; of zaffre, 6 drs.; of purple of Cassius, 1 dr. Proceed as with the rest.

Hard Glass of a Deep Purple Color, No. 2.

Take of the composition for hard glass, No. 1 or 2, 10 lbs.; of manganese, 1 oz.; and of zaffre, 1/2 oz. Proceed as with the other.

Paste of a Deep Purple Color, No. 3.

Take of the composition for pastes, No. 3 or 4, 10 lbs., and treat them as the foregoing.

Hard Glass of the Color of the Amethyst. No. 4.

Take of the composition of hard glass, No. 1 or 2, 10 lbs.; of manganese, 1 1/2 oz.; and of zaffre, 1 dr. Proceed as with the rest.

Paste of the Color of the Amethyst, No. 5.

Take of the composition for paste, No. 1 or 2, 10 lbs., and treat it as the preceding.

Paste Resembling the Diamond.

Take of white sand 6 lbs.; of red-lead, 4 lbs.; of pearlash, purified as above directed, 3 lbs.; of nitre, 2 lbs.; or arsenic, 5 oz.; and of manganese, 1 scr. Proceed as with the others, but continue the fusion for a considerable time on account of the large proportion of arsenic.

If this composition be thoroughly vitrified, and kept free from bubbles, it will be very white, and have a very great lustre; but if, on examination, it appears to incline to yellow, another scruple or more of the manganese may be added. It may be rendered harder by diminishing the proportion of lead, and increasing that of the salts, or fusing it with a very strong fire, but the diminution of the proportion of lead will make it have less of the lustre of the diamond.

Hard Glass, Perfectly Black.

Take of the composition for hard glass, No. 1 or 2, 10 lbs.; of zaffre, 1 oz.; of manganese and of colcothar, strongly calcined, each, 7 drs. Proceed as with the rest.

Paste, Perfectly Black.

Take of the composition for paste, No. 1 or 2, prepared with the saltpetre, 10 lbs.; of zaffre, 1 oz.; of manganese, 6 drs.; and of colcothar, 5 drs. Proceed as with the others.

White Opaque Glass, No. 1.

Take of the composition for hard glass, No. 1 or 2, 10 lbs.; of horn, ivory, or bone, calcined perfectly white, 1 lb. Proceed as with the others.

Paste of an Opaque Whiteness, No. 2.

Take of the composition No. 8 or 4, 10 lbs.; and make the same addition as to the above.

Glass of an Opaque Whiteness Formed by Arsenic, No. 3.

Take of flint-glass 10 lbs., and of very white arsenic, 1 lb. Powder and mix them thoroughly, by grinding them together, and then fuse them with a moderate heat till they be well incorporated, but avoid liquefying them more than to make a perfect union.

This glass has been made in great quantities, and has not only been formed into a variety of different kinds of vessels, but, being very white and fusible with a moderate heat, has been much used, as a white ground, for enamel in dial-plates, and other pieces which have not occasion to go several times into the fire to be finished. It will not, however, bear repeated burnings, nor a strong heat continued for any length of time, when applied to this purpose, without becoming transparent, to which likewise the smoke of a coal fire will also greatly contribute; but it answers the end very well in many cases, though even in those, enamel of the same degree of whiteness would be preferable, as this is always brittle, and of less firm and tenacious texture.

Hard Glass, or Paste., Formed by Calx of Tin or Antimony, No. 4.

Take of any of the compositions for hard glass or pastes, 10 lbs.; of oxide of tin (commonly called putty), or of antimony, or tin calcined by means of nitre, 1 1/2 lbs.; mix them well by grinding them together, and then fuse them with a moderate heat.

The glass of this kind made with the composition for pastes, differs in nothing from white enamel, but in the proportion of the calx of tin and antimony.

Semi-transparent White Glass and Paste Resembling the Opal, No. 5.

Take of any of the compositions for hard glass or paste, 10 lbs.; of horn, bone, or ivory, calcined to a perfect whiteness, 1/2 lb. Proceed as with the rest.

This white hard glass is much the same with the German glass formerly brought here in porringers, cream pots, vinegar cruets, and other such pieces, of which we frequently meet with the remains.

Fine Red Glass Resembling the Ruby, No. 1.

Take of the hard glass, No. 1 or 2, 1 lb.; of the purple of Cassius, 3 drs. Powder the glass, and grind the calx of gold afterwards with it in a glass, flint, or agate mortar, and then fuse them together.

This may be made of a stronger or more diluted color, by varying the proportion of the gold, in adjusting which, proper regard should be had to the application of the glass when made; for where this glass is set in rings, bracelets, or other close work, where foils can be used, a great saving may be made with regard to the color of it, without much injury to the effect; but for ear-rings, or other purposes where the work is set transparent, a full strong color should be given, which may be effected by the proportions directed in the composition

Paste Resembling the Ruby, No. 2.

Take of the paste No. 3 or 4, 1 lb., and of calx caffei, or precipitation of gold by tin, 2 drs. Proceed in the mixture as with the above.

This will be equally beautiful with the above, and defective only in softness; but as that greatly takes away the value for some purposes, such as is appropriated to them may be tinged in a cheaper manner by the following means.

A Cheaper Paste Resembling the Ruby, No. 3.

Take of the composition for paste No. 3 or 4, of glass of antimony, each 1/2 lb., and of purple of Cassius, 1 1/2 dr. Proceed as with the others.

This will be considerably cheaper and will have much the same effect, except that it recedes more from the crimson to the orange.

Hard Glass Resembling the Garnet, No. 4.

Take of the composition for hard glass, No. 1 or 2, 2 lbs.; of glass of antimony, 1 lb.; of manganese, and of purple of Cassius, each 1 dr.

This composition is very beautiful, but too expensive, on account of the gold, for the imitation of garnets for common purposes; on which account the following may be substituted.

Hard Glass Resembling the Garnet, No. 5.

Take of the composition, No. 1 or 2, 2 lbs.; of the glass of antimony, 2 lbs.; and of manganese, 2 dr.

If the color be found too dark and purple in either this or the preceding composition, the proportion of manganese must be diminished.

Paste of the Color of Garnet, No. 6.

Take of the composition for paste, No. 1 or 2, and proceed as with the above.

Hard Glass Resembling the Vinegar Garnet, No. 7,

Take of the composition, No. 1 or 2, 2 lbs.; of glass of antimony, 1 lb.; of colcothar, 1/2 oz. Mix the colcothar with the uncolored glass, and fuse them together till the mass be perfectly transparent, then add the glass of antimony, powdered, stirring the mixture with the end of a tobacco-pipe, and continue them in the heat till the whole be perfectly incorporated.

Paste Resembling the Vinegar Garnet, No. 8.

Take of the composition for paste, No. 3 or 4 and proceed as with the foregoing.

Fictitious or Counterfeit Lapis Lazuli.

Take of any of the preceding compositions for hard glass, or paste, 10 lbs.; of calcined bones, horn, or ivory, 3/4 lb.; of zaffre, 1 oz. Fuse the uncolored composition with the zaffre and manganese, till a very deep transparent blue glass be produced. The mass being cold, powder it, and mix it with the calcined matter, by grinding them together. After which fuse them with a moderate heat till they be thoroughly incorporated, and then form the melted mass into cakes, by pouring it on a clean bright plate of copper or iron.

Another. - If it be desired to have it veined with gold, it may he done by mixing the gold powder with an equal weight of calcined borax, and tempering them with oil of spike, by which mixture, the cakes being painted with such veins as are desired, they must be put into a furnace of a moderate heat, and the gold will be cemented to the glass as firmly as if the veins had been natural.

Another. - If the counterfeit lapis lazuli be desired of a lighter hue, the quantity of zaffre and manganese must be diminished; or, if it be required to be more transparent, that of the calcined horn, bone, or ivory, should be lessened.

To make Glass Resembling Red Cornelian.

Take of the composition for hard glass, No. 1 or 2, 2 lbs.; of glass of antimony, 1 lb.; of colcothar, 2 oz.; and of manganese, 1 dr.

Fuse the glass of antimony and manganese with the other glass first together, and then powder them well, and mix them with the colcothar, by grinding them together, and afterwards fuse the mixture with a gentle heat, till they are incorporated, but the heat must not be continued longer than is absolutely required to form them into a vitreous mass.

If it be desired to have the composition more transparent, part of the colcothar must be omitted.

Paste Resembling the Red Cornelian.

Take of the composition for paste, No. 1 or 2, 2 lbs.; and proceed as with the above.

Hard Glass Resembling White Cornelian.

Take of the composition for hard glass, No. 1 or 2, 2 lbs.; of yellow ochre, well washed, 2 dr.; and of calcined bones, each 1 oz. Mix them well by grinding them together, and fuse them with a gentle heat till the several ingredients he well incorporated in a vitreous mass.

Paste Resembling White Cornelian.

Take of the composition for pastes, No. 1 or 2, 1 lb.; and proceed as with the foregoing.

Hard Glass or Paste Resembling the Turquoise Stone.

Take of the composition for blue glass or paste, No. 7 or 8 (being those resembling the eagle marine), 10 lbs.; of calcined bone, or ivory, 1/2 lb. Powder and mix them well, and then fuse them in a moderate heat till they are thoroughly incorporated.

If the color be not so deep as may be desired, a small proportion of smalt may be added.

Brown Venetian Glass with Gold Spangles.

Take of the composition for hard glass, No. 2, and the composition for paste, No. 1, each 5 lbs.; and of colcothar, 1 oz. Mix them well, and fuse them till the iron be perfectly vitrified, and have tinged the glass of a deep transparent yellow brown color. Powder this glass, and add to it 2 lbs. of powdered glass of antimony, and mix them well by grinding them together. Take part of this mixture and rub into it 80 or 100 leaves of Dutch metal; and when the particles of the leaf seem sufficiently divided, mix the powder containing it with the other part of the glass. Fuse the whole then with a moderate heat till the powder runs into a vitreous mass fit to be wrought into any of the figures or vessels into which it is usually formed; but avoid a perfect liquefaction, because that destroys, in a short time, the equal diffusion of the spangles, and vitrifies, at least, part of the matter of which they are composed, converting the whole into a kind of transparent olive-colored glass.


To paint upon glass is an art which has generally appeared difficult, yet there is no representation more elegant than that of a mezzotinto painted in this manner, for it gives all the softness that can be desired in a picture, and is easy to work, as there are no outlines to draw, nor any shades to make.

The prints are those done in mezzotinto; for their shades being rubbed down on the glass, the several lines, which represent the shady part of any common print, are by this means blended together and appear as soft and united as in any drawing of Indian-ink.

Provide such mezzotintos as are wanted; cut off the margin, then get a piece of fine grown-glass the size of the print, and as flat and free from knots and scratches as possible; clean the glass, and lay some Venice turpentine, quite thin and smooth, on one side, with a brush of hog's hair. Lay the print flat in water, and let it remain on the surface till it sinks; it is then damp enough; take it carefully out, and dab it between some papers, that no water may be seen, yet so as to be damp.

Next lay the damp print with its face uppermost upon a flat table, then hold the glass over it, without touching the turpentine, till it is exactly even with the print; let it fall gently on it. Press the glass down carefully with the fingers in several parts, so that the turpentine may stick to the print; after which take it up, then holding the glass towards you, press the prints with the fingers, from the centre towards the edges, till no blisters remain.

When this is done, wet the back of the paint with a sponge, till the paper will rub off with the fingers; then rub it gently, and the white paper will roll off, leaving the impression only upon the glass; then let it dry, and, with a camel's hair pencil, dipped in oil of turpentine, wet it all over, and it will be perfectly transparent, and fit for painting.

Improved Method.

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

When these strokes are well dried, which will be in about 2 days (the work being only in black and white), give it a slight wash over with urine, gum-arabic, and a little black, and repeat this 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 color in the respective places with a wooden point, or by the handle of the pencil.

The colors are used with gum-water, the same 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 colors, by blending therewith. And here too, as in pieces of black and white, particular regard must always be had not to lay color on color, till such time as the former is well dried.

When the painting of all the pieces is finished, they are carried to the furnace to anneal, or to bake the colors.

Colors Proper to Paint with Upon Glass.

The several sorts of colors, ground in oil for this purpose, may be had at all the color shops, etc.

Whites. - Flake white, podium.

Blacks. - Lampblack, ivory-black.

Browns. - Spanish brown, umber, spruce ochre, Dutch pink, orpiment.

Blues. - Blue bice, Prussian blue.

Reds. - Rose-pink, vermilion, red-lead, Indian-red, lake cinnabar.

Yellows. - English pink, masticot, English ochre, Saunders blue, smalt.

Greens. - Verdigris, terra vert, verditer.

The ultramarine for blue, and the carmine for red, are rather to be bought in powders, as in that state they are less apt to dry; and as the least tint of these will give the picture a cast, mix up what is wanted for present use with a drop or two of nut-oil upon the pallet with the pallet knife.

Then lay a sheet of white paper on the table, and taking the picture in the left hand, with the turpentine side next you, hold it sloping (the bottom resting on the white paper), and all outlines and tints of the prints will be seen on the glass; and nothing remains but to lay on the colors proper for the different parts, as follows:

To Use the Colors.

As the lights and shades of the picture open, lay the lighter colors first on the lighter parts of the print, and the darker over the shaded parts; and having laid on the brighter colors, it is not material if the darker sorts are laid a little over them; for the first color will hide those laid on afterwards. For example:

Reds. - Lay on the first red-lead, and shade with lake or carmine.

Yellows. - The lightest yellow maybe laid on first, and shaded with Dutch pink.

Blues. - Blue bice, or ultramarine, used for the lights, may be shaded with indigo.

Greens. - Lay on verdigris first, then a mixture of that and Dutch pink. This green may be lightened by an addition of Dutch pink.

When any of these are too strong, they may be lightened, by mixing white with them upon the pallet, or darken them as much as required by mixing them with a deeper shade of the same color.

The colors must not be laid on too thick - but if troublesome, thin them before using them, with a little turpentine oil.

Take care to have a pencil for each color, and never use that which has been used for green, with any other color without first washing it well with turpentine-oil, as that color is apt to appear predominant when the colors are dry.

Wash all the pencils, after using, in turpentine oil.

The glass, when painted, must stand 3 or 4 days free from dust before it is framed.

To Draw on Glass.

Grind lampblack with gum-water and some common salt. With a pen or hair-pencil, draw the design on the glass, and afterwards shade and paint it with any of the following compositions:

Color for Grounds on Glass.

Take iron-filings and Dutch yellow beads, equal parts. If a little red cast is wanted, add a little copper filings. With a steel muller grind these together on a thick and strong copper plate, or on porphyry. Then add a little gum Arabic, borax, common salt, and clear water. Mix these with a little fluid, and put the composition in a phial for use.

When it is to be used there is nothing to do but, with a hair pencil, to lay it quite flat on the design drawn the day before; and having left this to dry also for another day, with the quill of a turkey the nib unsplit, heighten the lights in the same manner as with crayons on blue paper. Whenever there are more coats of the above composition put one upon another, the shade will naturally be stronger; and when this is finished, lay the colors for garments and complexions.

To Prepare Lake for Glass.

Grind the lake with water impregnated with gum and salt; then make use of it with the brush. The shading is operated by laying a double, treble, or more coats of the color, where it is wanted darker.

Blue Purple for the same.

Make a compound of lake and indigo, ground together with gum and salt water, and use it as directed in the preceding article.


Mix with a proportionable quantity of gamboge ground together as above.


Grind gamboge with salt water only.


Heighten much the white parts with a pen.

To Transfer Engravings on Glass.

Metallic colors prepared and mixed with fat oil, are applied to the stamp on the engraved plate. Wipe with the hand in the manner of the printers of colored plates; take a proof on a sheet of silver paper, which is immediately transferred on the tablet of glass destined to be painted, being careful to turn the colored side against the glass; it adheres to it, and as soon as the copy is quite dry, take off the superfluous paper by washing it with a sponge; there will remain only the color transferred to the glass; it is fixed by passing the glass through the ovens.

The bases of all the colors employed in painting on glass, are oxidized metallic substances.

In painting on glass, it is necessary that the matter should be very transparent.

To Prepare Metallic Oxides and Precipitates of Gold.

A solution of gold in aqua-regia, which is evaporated to dryness, leaves gold, which is used for glass, enamel, and porcelain gilding; or by precipitating the solution with green vitriol dissolved in water, a similar powder is produced. This powder is mixed with some essential oil, as oil of spike and calcined borax, and the whole made to adhere to the surface of the glass by a solution of gum Arabic. It is then applied with a fine pencil, and burnt in under a muffle.

To Prepare Oxide of Cobalt.

When regulus of cobalt is exposed to a moderate fire in the open air, it calcines; and is reduced to a blackish powder.

This oxide vitrifies with vitrifiable matters and forms beautiful blue glasses. Cobalt is, at present, the only substance known which has the property of furnishing a very fine blue that is not changed by the most intense heat.

To Prepare Zaffre.

Zaffre is the oxide of cobalt, for painting pottery ware and porcelain of a blue color. Break the cobalt with hammers into pieces about the size of a hen's egg; and the stony gangue, with such other foreign matters, separate as much as possible. Pound the chosen mineral in stamping-mills, and sift it through brass-wire sieves. Wash off the lighter parts by water, and afterwards put it into a large flatbottomed arched furnace resembing a baking-oven, where the flame of the wood reverberates upon the ore, which stir occasionally, and turn with long-handled iron hooks or rakes; and the process is to be continued till its fumes cease. The oven or furnace terminates by a long horizontal gallery, which serves for a chimney, in which the arsenic, naturally mixed with the ore, sublimes. If the ore contains a little bismuth, as this semi-metal is very fusible, collect it at the bottom of the furnace. The cobalt remains in the state of a dark gray oxide, and is called zaffre. This operation is continued four, or even nine hours, according to the quality of the ore. The roasted ore being taken out from the furnace, such parts as are concreted into lumps, pound and sift afresh. Zaffre, in commerce, is never pure, being mixed with two, or rather three parts of powdered flints. A proper quantity of the best sort of these, after being ignited in a furnace, are to be thrown into water, to render them friable and more easily reduced to powder; which, being sifted, is mixed with the zaffre, according to the before-mentioned dose; and the mixture is put into casks, after being moistened with water. This oxide, fused with 3 parts of sand and 1 of potassa, forms a blue glass which, when pounded, sifted and ground in mills (included in large casks), forms smalt.

The blue of zaffre is the most solid and fixed of all the colors employed in vitrification. It suffers no change from the most violent fire. It is successfully employed to give shades of blue to enamels, and to crystal-glass made in imitation of opaque and transparent precious stones; as the lapis lazuli, the turquoise, the sapphire, and others.

Purple of Cassius.

Dissolve some pure gold in nitro-muriatic acid; add either acid or metal, until saturation takes place. Now dissolve some pure tin in the same kind of acid; observe the same point of saturation as with the gold, and pour it into the solution of gold. A purple powder will be precipitated, which must be collected and washed in distilled water.

This beautiful purple color, as before mentioned, is extremely useful to enamellers and to glass-stainers.

When brought into fusion with a clear, transparent glass, it tinges it of a purple, red, or violet color. Hence the method of making false rubies and garnets.

To Paint Colored Drawings on Glass.

This art is exercised two ways. 1. Plates of stained glass are cut into the shape of figures and joined by leaden outlines. On these plates a shading is afterwards traced by the painter, which gives features to the face and folds to the drapery.

2. Vitrifiable colors are attached to plates of white glass, which are afterwards placed in the oven, and thus converted into a transparent enamelling. The first sort is cheaper, but the shading wears off by the insensible corrosion of the atmosphere. The second sort defies every accident except fracture; but the color of the figures suffers in the oven. For small objects, the first sort, and for large objects, the second, as far as art is concerned, seems best adapted.

Flux for Staining Glass.

1. When the colors used are not affected by lead, 100 parts powdered quartz, 125 red-lead, 50 of bismuth.

2. When the flux is required free from lead, 100 parts quartz, 75 glass of borax, 12 1/2 saltpetre, 12 1/2 powdered statuary marble.

Colors for Staining Glass.

To 6 cwt. of flux or flint-glass are to be added as follows:

White (soft), 24 lbs. white arsenic, 6 lbs. antimony.

White (hard), 200 lbs. putty-powder.

Blue (transparent), 2 lbs oxide of cobalt.

Azure, 6 lbs. protoxide of copper.

Ruby, 4 oz. oxide of gold.

Amethyst, 20 lbs. oxide of manganese.

Common Orange, 12 lbs. iron ore, 4 lbs. oxide of manganese.

Emerald Green, 12 lbs. copper scales and 12 lbs. iron ore.

Gold Topaz (canary glass), 3 lbs. oxide of uranium.

The colors will vary with the degree of heat to which the glass is subjected. The whole glass may be colored, or the mixture of flux and oxide may be laid on the surface, and then vitrified.