known to be, by viewing the globe against the light; the superfluous amalgam may then be poured out, and the outside of the globe cleared.

To silver the Convex Side of Meniscus Glasses for Mirrors.-Take an earthen plate, on which pour some prepared plaster of Paris, mixed with water, of a proper consistence; then immediately, before it grows too stiff, lay the meniscus with its convex side downward in the middle of the plate, and press it until it lies quite close to the plaster; in which situation let it remain until the plaster becomes quite dry; after which, work a groove with your finger round the outside of the meniscus, in order to let the superfluous mercury rest upon it; then cut the tinfoil to a proper size, and press it with the meniscus into the plaster mould, in order to make it lie close; after which cover it with the mercury, and, without a paper (as directed for silvering plain mirrors), slide it over the silvered foil; then place a weight on it, and let it stand two or three days, raising it by degrees, that the mercury may drip off gradually.

After this method common window glass, &c. may be silvered.

To lay Paper Prints on the Inside of Glass Globes.-First, Cut off all the white part of your impression, so that nothing appear but the print; then prepare some strong gum-arabic water or size, with which you must brush over the face side; after which put it into the globe, and with a long small stick, on which a camel's-hair pencil is fixed, stick it even on, and by this method you may put what number of prints you please into the globe; let them dry about twelve hours, then pour some prepared plaster of Paris, either white or tinged, whatsoever colour you please, and turn the globe easily about, so that every part be covered: pour out the superfluous plaster, and it is finished.

TINNING.-Tinning is the art of covering any metal with a thin coating of tin. Copper and iron are the metals most commonly tinned, The use of tinning these metals is to prevent them from being corroded by rust, as tin is not so easily acted upon by the air or water as iron and copper are.

What are commonly called tin-plates, or sheets, so much used for utensils of various kinds, are in fact iron plates coated with tin.

The principal circumstance in the art of tinning, is to have the surfaces of the metal to be tinned perfectly clean and free from rust, and also that the melted tin be perfectly metallic, and not covered with any ashes or calyx of tin.

Tinning of Iron.-When iron plates are to be tinned, they are first scoured, and then put into what is called a pickle, which is oil of vitriol diluted with water; this dissolves the rust or oxyde that was left after scouring, and renders the surface perfectly clean. They are then again washed and scoured. They are now dipped into a vessel full of melted tin, the surface of which is covered with fat or oil, to defend it from the action of the air. By this means, the iron coming into contact with the melted tin in a perfectly metallic state, it comes out completely coated.

When a small quantity of iron only is to be tinned, it is heated, and the tin rubbed on with a piece of cloth, or some tow, having first sprinkled the iron with some powdered resin, the use of which is to reduce the tin that may be oxydated. Any inflammable substance, as

oil for instance, will have, in some degree, the same effect, which is owing to their attraction for oxygen.

Tinning of Copper.-Sheets of copper may be tinned in the same manner as iron. Copper boilers, saucepans, and other kitchen utensils, are tinned after they are made. They are first scoured, then made hot, and the tin rubbed on as before with resin. Nothing ought to be used for this purpose but pure grain tin; but lead is frequently mixed with the tin, both to adulterate its quality and make it lay on more easily; but it is a very pernicious practice, and ought to be severely reprobated.

To whiten Brass or Copper by Boiling.-Put the brass or copper into a pipkin with some white tartar, alum, and grain tin, and boil them together: the articles will soon become covered with a coating of tin, which, when well polished, will look like silver. It is in this manner that pins and many sorts of buttons are whitened.

BRONZING.-Bronzing is colouring plaster, or other busts and figures, with metallic powders, in order to make them appear as if made of copper or other metals. The powders used for this purpose are either fine copper filings, aurum musivum, or copper precipitated from its solution in aquafortis by iron. Having done over the substance to be bronzed with either isinglass size, japanners' gold size, or, in some cases, with drying oil or oil-paint, the powders are rubbed on, taking care that the projecting parts receive more of the powder than the cavities, to imitate the brightness on those parts of bronze which are liable to be rubbed.

SOLDERING.-Soldering is the art of joining two pieces of metal toge, ther by heating them, with a thin piece or plate of metal interposed between them. Thus tin is a solder for lead; brass, gold, or silver, are solders for iron, &c.

To make Silver Solder.-Melt fine silver two parts, brass one part; do not keep them long in fusion, lest the brass fly off in fumes.

Another for coarser Silver.--Melt four parts of fine silver, and three of brass; throw in a little borax, and put it out as soon as it is melted. A Solder for Gold.-Melt copper one part, fine silver one part, and gold two parts; add a little borax when it is just melted, then pour it out immediately.

The Method of soldering Gold or Silver.-After the solder is cast into an ingot, it would be more ready for use if you were to draw it into small wire, or flat it between two rollers; after that cut it into little bits, then join your work together with fine soft iron wire, and with a camel's-hair. pencil dipt in borax finely powdered, and well moistened with water, touch the joint intended to be soldered; placing a little solder upon the joint, apply it upon a large piece of charcoal, and, with a blow-pipe and lamp, blow upon it through the flame until it melts the solder, and it is done.

To cleanse Silver or Gold after it is soldered.-Make it just red hot, and let it cool, then boil it in alum water, in an earthen vessel, and it will be as clean as when new. If gold, boil it in urine and sal-ammoniac

4 Solder for Lead.-Two parts lead and one part tin: its goodness

is tried by melting it, and pouring the bigness of a crown-piece upon the table; if it be good, there will arise little bright stars in it. Apply resin when you use this solder.

A Solder for Tin.-Take four parts of pewter, one of tin, and one of bismuth; melt them together, and run them into narrow thin lengths.

A Solder for Iron.-Nothing here is necessary but good tough brass with borax applied, mixed with water to the consistence of paste.

CHAP. XIV.

MOULDING AND CASTING.

THE art of taking casts or impressions from pieces of sculpture, medals, &c. is of very great importance in the fine arts.

In order to procure a copy or cast from any figure, bust, medal, &c. it is necessary to obtain a mould, by pressing upon the thing to be moulded or copied, some substance, which, when soft, is capable of being forced into all the cavities or hollows of the sculpture. When this mould is dry and hard, some substance is poured into it, which will fill all the cavities of the mould, and represent the form of the original from which the mould was taken.

The particular manner of moulding depends upon the form of the subject to be worked upon. When there are no projecting parts but such as form a right or a greater angle with the principal surface of the body, nothing more is required than to cover it over with the substance of which the mould is to be formed, taking care to press it well into all the cavities of the original, and to take it off clean, and without bending.

The substances used for moulding are various, according to the nature and situation of the sculpture. If it may be laid horizontally, and will bear to be oiled without injury, plaster of Paris may be advantageously employed, which may be poured over it to a convenient thickness, after oiling it to prevent the plaster from sticking. A composition of bees-wax, resin, and pitch, may also be used, which will be a very desirable mould if many casts are to be taken from it. But if the situation of the sculpture be perpendicular, so that nothing can be poured upon it, then clay, or some similar substance, must be used. The best kind of clay for this purpose is that used by the sculptors for making their models with; it must be worked to a due consistence, and having spread it out to a size sufficient to cover all the surface, it must be sprinkled ove with whiting, to prevent it from adhering to the original. Bees-wax and dough, or the crumb of new bread, may also be used for moulding some small subjects.

When there are under-cuttings in the bas-relief, they must be first filled up before it can be moulded, otherwise the mould could not be got off. When the casts are taken afterwards, these places must be worked out with a proper

tool.

When the model, or original subject, is of a round form, or projects so much that it cannot be moulded in this manner, the mould must be

divided into several parts; and it is frequently necessary to cast sevefal parts separately, and afterwards to join them together. In this case, the plaster must be tempered with water to such a consistence that it may be worked like soft paste, and must be laid on with some convenient instrument, compressing it so as to make it adapt itself to all parts of the surface. When the model is so covered to a convenient thickness, the whole must be left at rest till the plaster is set and firm, so as to bear dividing without falling to pieces, or being liable to be put out of its form by any slight violence; and it must then be divided into pieces, in order to its being taken off from the model, by cutting it with a knife with a very thin blade; and being divided, must be cautiously taken off, and kept till dry; but it must be observed, before the separation of the parts be made, to notch them across the joints, or lines of division, at proper distances, that they may with ease and certainty be properly put together again. The art of properly dividing the moulds, in order to make them separate from the model, requires more dexterity and skill than any other thing in the art of casting, and does not admit of rules for the most advantageous conduct of it in every case. Where the subject is of a round or spheroidal form, it is best to divide the mould into three parts, which will then easily come off from the model; and the same will hold good of a cylinder, or any regular curve figure.

The mould being thus formed, and dry, and the parts put together, it must be first oiled, and placed in such a position that the hollow may lie upwards, and then filled with plaster mixed with water; and when the cast is perfectly set and dry, it must be taken out of the mould, and repaired when necessary, which finishes the operation.

In larger masses, where there would otherwise be a great thickness of the plaster, a core may be put within the mould, in order to produce "a hollow in the cast, which both saves the expence of the plaster, and renders the cast lighter.

In the same manner, figures, busts, &c. may be cast of lead, or any other metal in the moulds of plaster or clay; taking care, however, that the moulds be perfectly dry; for should there be any moisture, the sudden heat of the metal would convert it into vapour, which would produce an explosion by its expansion, and blow the melted metal about.

To take a Cast in Metal from any small Animal, Insect, or Vegetable.Prepare a box of four boards, sufficiently large to hold the animal, in which it must be suspended by a string, and the legs, wings, &c. of the animal, or the tendrils, leaves, &c. of the vegetable, must be separated, and adjusted in their right position by a pair of small pincers. A due quantity of plaster of Paris mixed with talc, must be tempered to the proper consistence with water, and the sides of the box oiled. Also a straight piece of stick must be put to the principal part of the body, and pieces of wire to the extremities of the other parts, in order that they may form, when drawn out after the matter of the mould is set and firm, proper channels for pouring in the metal, and vents for the air, which otherwise, by the rarefaction it would undergo from the heat of the metals, would blow it out, or burst the mould. In a short time the plaster will set, and become hard; when the stick and wires may be drawn out, and the frame or coffin in which the mould was cast

taken away; and the mould must then be put, first, into a moderate heat, and, afterwards, when it is as dry as can be rendered by that degree, removed into a greater, which may be gradually increased, till the whole be red hot. The animal or vegetable inclosed in the mould will then be burnt to a coal; and may be totally calcined to ashes, by blowing for some time into the charcoal and passages made for pouring in the metal, and giving vent to the air, which will, at the same time that it destroys the remainder of the animal or vegetable matter, 'blow out the ashes. The mould must then be suffered to cool gently, and will be perfect; the destruction of the substance included in it, having produced a corresponding hollow; but it may nevertheless be proper to shake the mould, and turn it upside down, as also to blow with the bellows into each of the air vents, in order to free it wholly from any remainder of the ashes; or where there may be an opportunity of filling the hollow with quick-silver, it will be found a very effectual method of clearing the cavity, as all dust, ashes, or small detached bodies, will necessarily rise to the surface of the quicksilver, and be poured out with it. The mould being thus prepared, it must be heated very hot, when used, if the cast is to be made with copper or brass, but a less degree will serve for lead or tin. The metal being poured into the mould, must be gently struck, and then suffered to rest till it be cold; at which time it must be carefully taken from the cast, but without force; for such parts of the matter as appear to adhere more strongly, must be softened, by soaking in water till they be entirely loosened, that none of the more delicate parts of the cast may be broken off or bent.

When tale cannot be obtained, plaster alone may be used; but it is apt to be calcined, by the heat used in burning the animal or vegetable from whence the cast is taken, and to become of too incoherent and friable a texture. Stourbridge, or any other good clay, washed perfectly fine, and mixed with an equal part of fine sand, may be employed. Pounded purnice-stone, and plaster of Paris, in equal quantities mixed with washed clay in the same proportion, is said to make excellent moulds.

Method of taking a Cast in Plaster from a Person's Face.-The person whose likeness is required in plaster, must lie on his back, and the hair must be tied back, so that none of it covers the face. Into each nostril convey a conical piece of stiff paper open at both ends, to allow of breathing. The face is then lightly oiled over in every part with salad-oil, to prevent the plaster from sticking to the skin. Procure some fresh burnt plaster, and mix it with water to a proper consistence for pouring. Then pour it by spoonfuls quickly all over the face (taking care the eyes are shut), till it is entirely covered to the thickness of a quarter of an inch. This substance will grow sensibly hot, and in a few minutes will be hard. This being taken off, will form a mould, in which a head of clay may be moulded, and therein the eyes may be opened, and such other additions and corrections may be made as are necessary. Then, this second face being anointed with oil, a second mould of plaster must be made upon it, consisting of two parts joined lengthwise along the ridge of the nose; and in this a cast in plaster may be taken, which will be exactly like the original.

To take Casts from Medals.-In order to take copies of medals, a