Statue-founding
Whether the model from which bronze cast is to be taken be of wax, clay, plaster, or any other material, the customary mode of constructing the mould by the cire-perdue or waste wax-process is substantially as follows: The outside mould or matrix is first obtained in convenient plaster sections. The sections, either separate or together, according to convenience, are thicknessed with wax, and secured in their respective positions to form the mould, into which a core composition, usually consisting of a creamy paste made from 2 parts of brick-dust and 1 part plaster of Paris, with water, is introduced. Should the core be massive or complicated, a skeleton core-iron is constructed, and such other preparations are made as may be needed to convey away the gases therefrom at the time of casting. When the core composition has set, the sections of mould are carefully taken off, leaving the wax thickness adhering to the core--a true representation of the original model, which, when made perfect at such parts as may have been injured, is then ready to receive a thin coat of very fine composition, usually applied with a brush, over which another coat more porous than the first is laid, and again a subsequent backing of a very open nature is applied until the requisite stiffness is acquired. Coarse composition alone serves this purpose when the objects are small, for larger ones bricks, loam, etc., are often employed. When core and matrix have been thus constructed, heat is applied, and the wax forthwith evacuates the mould, escaping at the lowest points of every portion of the figure through holes previously provided for that purpose. When the mould has been thoroughly dried, the space originally occupied by the wax is filled with metal by means of gates which are suitably disposed when the outer mould is constructed. Small statuettes and other figures are very easily made in the foundries by first carving a composition core, around which the sculptor lays a wax thickness and models his figure. A wire or perhaps two wires are then thrust through the figure, leaving the ends projecting; it is then placed within an iron frame or box, and the surrounding space filled with composition. When this has become hard, the wax is made to pass out by the application of heat, as before explained, the core remaining as a permanent fixture by reason of the projecting wires, which are firmly imbedded in the matrix.
Hollow casts in zinc, lead, and tin are obtained by filling sectional brass moulds with molten metal at the open end, and allowing sufficient time for a shell to congeal on the surface, when the remainder is allowed to escape by inverting the mould.
For statuary, as above described, the sculptor produces his casting alone; but when the metal employed is cast iron, he must secure the services of a competent moulder, who first builds a core in loam, around which the sculptor fashions his figure in clay.
The moulder then proceeds to form a cope in as many divisions as are needed for obtaining a perfect impression of the figure, by the processes common to loam or sand moulding. These several divisions being lifted away, the thickness is removed, core and cope duly finished and dried, and subsequently closed together again, and the mould cast.
Many colossal statues are made in sections and pinned together over a stout iron or steel frame, and numbers of large plaster models are now sawn into convenient sections for moulding in sand, and cast either green or dry, according to circumstances. See PLASTER-CAST; CIRE-PERDUE; MODELLING; STATUARY-BRONZE.