CASTS. These are impressions, figures, or statues, formed of plaster of Paris, sulphur, metals, or other substances.
Sculptures of every description arc so tedious and expensive, that a more speedy and economical method is adopted, of obtaining resemblances in plaster of Pa ris. This is attended with the convenience of the mate rials being easily procured in a state of preparation for immediate use as all linpallialik pOwdCu; and nothing in( re is required than an addition of water to reduce it to t consistence of thin paste or cream.
A mould is always necessary for a cast, in whatever subst.ea a it is made, and it is formed according to the mune or figure of the subject. In taking a cast from a medal, for example, it is to be laid on a smooth surface, and encircled by a hoop of card or paper, of the breadth desired l'or the thickness of the mould. The plaster, reduced to the consist( ',cc or thick cream, is then to be poured over the medal, and allowed to dry. Thus a mould is formed, which is hollow, to receive the cast. its surface must be brushed over with a camel-hair pencil, dipped in olive-oil ; observing if there arc ally bo,es, previously to fill them up by a similar expedient, with thin plaster, which will also prevent hole s in the cast. The mould is next to be surrounded with a card or paper hoop, as broad as the thickness of the cast, and the plaster, reduced almost to a fluid, poured in. By allowing it to dry, the cast is formed, and many succes sive casts may be obtained from the same mould.
If the subject be larger than a medal, we must use a wooden frame, within W. jell the subject is laid, as a certain degree or strength is necessary to resist the prtssure of the hold plaster. It is essential to observe, that immediately after being reduced to the proper con sistence. the plaster must be poured on the subject, as by standiog it becomes unfit for use.
This, owever, is a method adapted only to the most simpi impressions, and where none but one side or sur face is to be tal.,cit off. If here are several surfaces, the mould must be divided into such a number of parts as circumstances may require. Supposing a cast of a round
or ai,gmar subject is desired, the plaster must not be reduced nearly to Nudity as before, but to the consist ence of paste. This is to be applied bv the hand as a coating on the subject, and slightly pressed, so as to be adapted to all its different parts, and then cut through in se% erid places with a very thin-edged knife. After be ing of such consistency as to retain the impression, the pieces arc allowed to become completely dry, having, precious to the division, received various pencil marks, that they may be more easily united for the cast. Con •iderable dexterity is necessary in dividing the pieces of the mould asunder, and in properly adapting them for the cast they are to receive, After being completely dried, they are to be well greased and united, and the plaster, as before, reduced almost to a fluid state, pour ed in so as to fill the whole cavity. The mould is then taken off, and the cast appears.
Large casts are generally hollow, both to be lighter and to save the materials. In that case. a wooden core is suspended within the mould, with the thicker end outwards, so as to be more easily' withdrawn. If the cavity be of an irregular figure, the core may consist of clay, also suspended within the mould by cross wires, or and afterwards picked out by' a shin p pointed or hooked implement.
In casting a bas-relief from wax, or to obtain another cast of the saint substance, the figure desired is first to be modelled on NVOOd or glass, and being surround ed by a frame, plaster is poured over it. This is al lowed to dry, and when removed, serves to receive the cast. If dipped in water, and suddenly withdrawn, the wax poured in will not adhere, and comes out quite clean.
Delicate and beautiful casts are obtained in sulphur. which, of hue years t. daily, ha be• n sh it employed to re ehel.tatitolAS 01 the most el( gait sculptures of antigun). 'The inc,uld for a cast of this de scription being formed of plaster, is repeatedly dippi d into half a pint of boiled lintseed oil, mix( d y. ith al, 011110: of spirit of turpentine, by which the sou r hat (lc lied.