The primitive bronze-workers, before they arrived at the knowledge of casting, began by hammering solid metals into shapes. The _toreutic_ art, although not definitely known at present, was probably that of hammering, punching, and chiseling plates of metal, either separately or with a view of fixing them upon stone or wood. Both the solid hammered work and the hollow-plate work is mentioned by the authorities. The hollow statues were built up in pieces, fastened together with nails, rivets, and dove-tails, and it is not improbable that some system of welding was practiced.
The casting of metals in moulds must have followed the discovery that they could be melted. As the sculptor improved in his art of modeling he would be able to make better moulds. He would soon observe that the solid statue was not only very costly, but so very heavy that the whole figure would collapse from sheer weight.
This trouble was corrected by the discovery of a contrivance for casting metals in a hollow mould. It was done pretty much as it is at the present day, by fixing within the mould a _core_, which did not touch the sides, except at certain small points necessary for support. The space between this and the surface of the mould was to be filled by the molten metal.
There is still another method, less common in modern times, but employed by the ancients, for some of their smaller works. This is when a wax model is encased in clay or plaster of Paris and the molten metal then poured into it to melt the wax, and take the form of the work precisely as it left the hand of the sculptor. The original model is thus destroyed and the bronze takes its place. Some very large and important works have recently been cast in this method, but with the core. In bronze casting with a core, this contrivance must be made with great care. The mould, which is obliged to be formed of pieces fitted together, in order that the model may be taken out, is first well soaked in oil, then melted wax is applied to the inner side of the moulded parts in such thickness as may be required in the metal of the completed statue. But as a hollow metal statue would not be strong enough to support its own weight, a sort of skeleton of iron bars is made to take the general form of the figure, and this strong frame-work is firmly fixed within the mould. We have then the mould, with its wax lining, enclosing the iron skeleton, or _armature_, as it is called, with an opening left in the proper place to allow of pouring in the liquid plaster of Paris mixed with pounded brick, which fills the space about the armature. Therefore, if at this stage, the mould were taken to pieces again, the sculptor would behold his statue as one of apparently solid wax. Practically this is done in order that he may satisfy himself of the success of his work, and correct it where necessary. The model is then again placed in the mould preparatory to casting.