CASTING, in foundery, the running of liquid metal into a mould prepared for that purpose. See Foundery. Casting in Sand or Earth, is the running of metals between two frames or moulds, filled with sand or earth, in which the figure that the metal is to take has been impressed en creux, by means of the pattern.

Casting, among sculptors, implies the taking of casts and impressions of figures, busts, medals, leaves, or the like.

The method of taking casts of figures and busts is most generally by the use of plaster of Paris, that is, alabaster calcined by a gentle heat. The advantage of using this substance in preference to others is, that notwithstanding a slight calcination reduces it to a pulverized state, it becomes again a tenacious and cohering body, by being moistened with water, and afterwards suffered to dry; by which means either a concave or a convex figure may be given by a proper mould or model to it when wet, and retained by the hardness it acquires when dry; and, from these qualities, it is fitted for the double purpose of making both casts, and moulds for forming casts. The particular manner of making casts depends on the form of the subject to be taken. Where there are no projecting parts, it is very simple and easy; as likewise where there are such as form only a right or any greater angle with the principal surface of the body; but where parts project in lesser angles, or form a curve inclined towards the principal surface of the body, the work is more difficult.

The first step to be taken is the forming of the mould. In order to this, if the original or model be a bas-relief, or any other piece of a flat form, having its surface first well greased, it must be placed on a proper table, and surrounded by a frame, the sides of which must be at such a distance from it as will allow a proper thickness for the sides of the mould. As much plaster as will be sufficient to cover and rise to such a thickness as to give the necessary strength to the mould, as also to fill the hollow betwixt the frame and the model, must be moistened with water, till it be just of such consistence as will allow it to be poured upon the model. This must be done as soon as possible; or the plaster w ill concrete or set, so as to become more troublesome in the working, or unfit to be used. The whole must then be suffered to remain in this condition till the plaster has attained its hardness; and then the frame being taken away, the preparatory cast or mould thus formed may be taken off from the subject entire.

Where the model or original subject is of a round or erect form, a different method must be pursued, and the mould must be divided into several pieces; or if the subject consists of detached and projecting parts, it is frequently most expedient to cast such parts separately, and afterwards join them together.

Where the original subject or mould forms a round or spheroid, or any part of such round or spheroid, more than one half the plaster must be used without any frame to keep it round the model, and must be tempered with water to such a consistence that it may be wrought with the hand like very soft paste; but though it must not be so fluid as when prepared for flat-figured models, it must yet be as moist as is compatible with its cohering sufficiently to hold together; and being thus prepared, it must be put upon the model, and compressed with the hand, or any flat instrument, that the parts of it may adapt themselves in the most perfect manner to those of the subject, as well as to be compact with respect to themselves. When the model is so covered to a convenient thickness, the whole must be left at rest till the plaster be set and firm, so as to bear dividing without falling to pieces, or being liable to be put out of its form by slight violence; it must then be divided into pieces, in order to its being taken off from the model, by cutting it with a knife having a very thin blade; and being divided, it must be cautiously taken off, and kept till dry; but it must be always carefully observed, before the separation of the parts be made, to notch them across the joints or lines of the division, at proper distances, that they may with ease and certainty be properly conjoined again; which would be much more precarious and troublesome without such directive marks. The art of properly dividing the moulds, in order [7:6:231] to make them separate from the model, requires more ' dexterity and skill than any thing else 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 curved figure.

The mould being thus formed and dried, and the parts put together, it must be greased, and placed in such a position that the hollow may lie upwards, and then filled with plaster mixed with water, in the same proportion and manner as was directed for the casting of the mould; and when the cast is perfectly set and dry, it must be taken out of the mould, and repaired where it is necessary; which finishes the operation.

This is all that is required with respect to subjects where the surfaces have the regularity above mentioned; but where they form curves which intersect each other, the conduct of the operation must be varied with respect to the manner of taking the cast of the mould from off the subject or model; and where there are long projecting parts, such as legs or arms, they should be wrought in separate casts. The operator may easily judge from the original subjects what parts will come off together, and what may require to be separated. The principle of the whole consists only in this, that where under-workings, as they are called, occur, that is, wherever a straight line drawn from the basis or insertion of any projection would be cut or crossed by any part of such projection, this part cannot be taken off without a division, which must be made either in the place where the projection would cross the straight line, or, as that is frequently difficult, the whole projection must be separated from the main body, and divided also lengthwise into two parts; and where there are no projections from the principal surfaces, but the body is so formed as to render the surface a composition of such curves, that a straight line being drawn parallel to the surface of one part would be cut by the outline in one or more places of another part, a division of the whole should be made, so as to reduce the parts of it into regular curves, which must then be treated as such.

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

This core may be of wood where the forming of a hollow of a straight figure or a conical one with the basis outward will answer the end; but if the cavity require to be round, or of any curve figure, the core cannot then be drawn while entire, and consequently should be of such matter as may be taken out piece-meal. In this case the core is best formed of clay, which must be worked upon wires to give it a tenacity, and suspended in the hollow of the mould by cross wires lying over the mouth; and when the plaster is sufficiently set to bear handling, the clay must be picked out by a proper instrument.

Where it is desired to render the plaster harder, the water with which it is tempered should be mixed with parchment size properly prepared, which will make it very firm and tenacious.

In the same manner, figures, busts, and the like, may be cast of lead or any other metal in the moulds of plaster, only the expense of plaster, and the tediousness of its becoming sufficiently dry, when in a very large mass, to bear the heat of melted metal, render the use of clay, compounded with some other proper materials, preferable where large subjects are in question. The clay in this case should be washed over till it be perfectly free from gravel or stones, and then mixed with a third or more of fine sand to prevent it cracking; or, instead of sand, coal ashes sifted fine may be used. Whether plaster or clay be employed for the casting in metal, it is extremely necessary to have the mould perfectly dry, otherwise the moisture, being rarefied, will cause an explosion that will blow the metal out of the mould, and endanger the operator, or at least crack the mould in such a manner as to frustrate the operation. Where the parts of a mould are large, or project much, and consequently require a greater tenacity of the matter they are formed of to keep them together, flocks of cloth, prepared like those designed for paper hangings, or fine cotton plucked or cut till it is very short, should be mixed with the ashes or sand before they are added to the clay to make the composition for the mould. The proportion should be according to the degree of cohesion required; but a small quantity will answer the end if the other ingredient of the composition be good, and the parts of the mould properly linked together by means of the wires above directed.

There is a method of taking casts in metals from small animals, and the parts of vegetables, which may be practised for some purposes with advantage, particularly for the decorating of grottos or rock works, where nature is imitated. The proper kinds of animals are lizards, snakes, frogs, birds, or insects, the casts of which, if properly coloured, will be exact representations of the originals.

This is to be performed by the following method: A coffin or proper chest for forming the mould being prepared of clay, or four pieces of boards fixed together, the animal or parts of vegetables must be suspended in it by a string, and the leaves, tendrils, or other detached parts of the vegetables, or the legs, wings, and other parts of the animals, properly separated and adjusted in their right position by a small pair of pincers; a due quantity of plaster of Paris and calcined talc, in equal quantities, with some alumen plumosum, must then be tempered with water to the proper consistence for casting, and the subject from which the cast is to be taken, as also the sides of the coffin, moistened with spirit of wine. The coffin or chest must then be filled with the tempered composition of the plaster and talc, putting at the same time a piece of straight stick or wood to the principal part of the body of the subject, and pieces of thick wire to the extremities of the other parts, in order that they may form, when drawn out after the matter of the mould is properly set and firm, a channel for pouring in the melted metal, and vents for the air, which otherwise, by the rarefaction it would undergo from the heat of the metal, would force its way out or burst the mould. In a short time the plaster and talc 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 it can be rendered by that degree of heat, removed into a greater, which may be gradually increased till the whole be red hot. The animal or part of any vegetable which was included in the mould will then be burnt to a coal, and may be totally calcined to ashes, by blowing for some time gently into the channel 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 of the animal or vegetable having produced a hollow of a figure correspondent to it; but it may be nevertheless 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 [7:6:232]of filling the hollow with quicksilver without expense, 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 be made with copper or brass; but a less degree will serve for lead or tin; and the matter being poured in, 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 the least 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.

Where the alumen plumosum cannot easily be procured, the plaster may be used alone; but it is apt to be calcined by the heat used in burning the animal or vegetable from which the cast is taken, and to become of too incohering and crumbly a texture; or, for cheapness, Stourbridge or any other good clay, washed over till it be perfectly fine, and mixed with an equal portion of sand, and some flocks cut small, may be employed. Pounded pumice-stone and plaster of Paris, taken in equal quantities, and mixed with washed clay in the same proportion, is said to make excellent moulds for this and similar purposes.

Casts of medals, or such small pieces as are of a similar form, may be made in plaster by the method directed for bas-reliefs. Indeed nothing more is required than to form a mould by laying them on a proper board, and having surrounded them by a rim made by a piece of card, or any other pasteboard, to fill the rim with soft tempered plaster of Paris; which mould, when dry, will serve for several casts. It is nevertheless a better method to form the mould of melted sulphur, which will produce a sharper impression in the cast, and be more durable than those made of plaster. Casts are likewise frequently made of sulphur, which being melted, must be treated exactly in the same manner as plaster.

For taking casts from medals Dr Lewis recommends a mixture of flowers of brimstone and red lead. Equal parts of these are to be put over the fire in a ladle till they soften to the consistence of pap; then they are to be kindled with a piece of paper, and stirred for some time. The vessel being afterwards covered close, and continued on the fire, the mixture grows fluid in a few minutes. It is then to be poured on the metal, previously oiled and wiped clean. The casts are very neat; and their colours sometimes a pretty deep black, sometimes a dark gray. They are very durable; and when soiled, may be washed clean in spirits of wine.

Dr Lettsom recommends tin-foil for taking off casts from medals. The thinnest kind is to be used. It should be laid over the subject from which the impression is to be taken, and then rubbed with a brush, the point of a skewer, or a pin, till it has perfectly received the impression. The tin-foil should now be pared close to the edge of the medal, till it be brought to the same circumference. The medal must then be reversed, and the tin-foil will drop off into a chip box or mould placed ready to receive it. Thus the concave side of the foil will be uppermost, and upon this plaster of Paris, prepared in the usual manner, may be poured. When dry the whole is to be taken out, and the tin-foil sticking on the plaster will give a perfect representation of the medal, almost equal in beauty to silver. If the box or mould is a little larger than the medal, the plaster running round the tin-foil will give the appearance of a white frame or circular border; and hence the new made medal will appear neater and more beautiful.

Casts may likewise be made with iron prepared in the following manner: “Take any iron bar, or piece of a si milar form, and, having heated it red hot, hold it over a vessel containing water, and touch it very slightly with a roll of sulphur, which will immediately dissolve it, and make it fall in drops into the water. As much iron as may be wanted being thus dissolved, pour the water out of the vessel, and pick the drops formed by the melted iron from those of the sulphur, which contain little or no iron, and will be distinguishable from the other by their colour and weight.” The iron will by this means be rendered so fusible that it will run with less heat than is required to melt lead, and may be employed for making casts of medals, and many other such purposes, with great convenience and advantage.

Impressions of medals having the same effect as casts may be made also of isinglass-glue, by the following means: Melt the isinglass, beaten, as when commonly used, in an earthen pipkin, with the addition of as much water as will cover it, stirring it gently till the whole is dissolved; then with a brush of camel’s hair cover the medal, which should be previously well cleansed and warmed, and then laid horizontally on a board or table, greased in the part around the medal. Let them rest afterwards till the glue be properly hardened; and then, with a pin, raise the edge of it, and separate it carefully from the medal. The cast will be thus formed by the glue as hard as horn; and so light that a thousand will scarcely weigh an ounce. In order to render the relief of the medal more apparent, a small quantity of carmine may be mixed with the melted isinglass; or the medal may be previously coated with leaf-gold by breathing on it, and then laying on the leaf, which will by that means adhere to it; but the use of leaf gold is apt to impair a little the sharpness of the impression.

Impressions of medals may likewise be taken in putty; but it should be the true kind, made of calx of tin and drying oil. These may be formed in the moulds, previously taken in plaster or sulphur; or moulds may be made in its own substance, in the manner directed for those of the plaster. These impressions will be very sharp and hard; but the greatest disadvantage that attends them is their drying very slowly, and being liable in the mean time to be damaged.

Impressions of prints or other engravings maybe taken from copperplates, by cleansing them thoroughly, and pouring plaster upon them; but the effect in this way is not strong enough for the eye; and therefore the following method is preferable, where such impressions on plaster are desired: Take vermilion, or any other coloured pigment, finely powdered, and rub it over the plate. Then pass a folded piece of paper, or the flat part of the hand, over the plate, to take off the colour from the lights or parts where there is no engraving; the proceeding must then be the same as where no colour is used. This last method is also applicable to the making of impressions of copperplates on paper with dry colours; for the plate being prepared as here directed, and laid on the paper properly moistened, and either passed under the rolling press, or any other way strongly forced down on the paper, an impression of the engraving will be obtained.

Impressions may likewise be taken from copperplates, either on plaster or paper, by means of the smoke of a candle or lamp; if, instead of rubbing them with any colour, the plate be held over the candle or lamp till the whole surface become black, and then wiped off by the flat of the hand, or paper.

These methods are not, however, of great use in the case of copperplates, except where impressions may be desired on occasions where printing ink cannot be procured. But as they may be applied likewise to the taking of impressions from snuff-boxes, or other engraved subjects, by which means designs may be instantly borrowed by [7:6:233]artists or curious persons, they may in such instances be very useful.

The expedient of taking impressions by the smoke of a candle or lamp may be employed also for botanical purposes in the case of leaves, as a perfect and durable representation not only of the general figure, but of the contexture and disposition of the larger fibres, may be extemporaneously obtained at any time. The same may be nevertheless done in a more perfect manner by the use of linseed oil, either alone, or mixed with a small proportion of colour, where the oil can be conveniently procured; but the other method is valuable on account of its being practicable at almost all seasons, and in all places, within the time that the leaves will keep fresh and plump. In taking these impressions it is proper to bruise the leaves, so as to take off the projections of the large ribs, which might prevent the other parts from plying to the paper.