CASTING OF BRONZES, is thus performed : The figure to be cast from must have a mould made on it, consisting of a mix ture of plaster-of-paris and brick-dust, in the proportion of not more than one-third of the former, to two-thirds of the latter. The thickness of this mould must be according to its length and breadth, in order to be sufficiently strong. Little channels, tending upwards, should be cut in various parts of the joints, to give vent to the air forced out by the metal as it runs into the mould. After the mould is made, a thin layer of clay is spread smoothly and uniformly over its inner surthce, of the intended thickness of the bronze ; the mould is then closed, and its cavity filled with a composition of two-thirds brick dust and one-third plaster, nixed with water, to form the core; previous to which, should the work be of any magnitude, it will be necessary to insert strong irons bars within the mould, to secure it from accidents, and to facilitate the removal of the core. The mould being then opened, and the clay removed, is with the core thoroughly dried ; to effect which more perfectly, they are exposed to the action of a charcoal fire or lighted straw ; great attention is required to this part of the process, for should the least moisture be suffered to remain, the mould will burst, and the cast be blown to pieces, to the great danger of the lives or limbs of the workmen.
When the mould is finally closed, the cord must be supported in its place by short bars of bronze, running from the mould into the core. The whole then is bound round with iron bars, proportioned in strength to the weight of the east, and laid in a proper situation for receiving the metal, supported by dry materials, as sand-stones, &c., to prevents accidents. In placing the mould, due care must be taken to connect its mouth with the reservoirs, by means of a channel on an inclined plane, that the liquid metal may run freely. The form of the furnace, and mode of running, are similar to those practised in bell-founding.