1. For fine work the Lost Wax process is used –
A rough model of the statue to be cast is formed slightly smaller than the work to be cast. This model is coated over with beeswax; and the sculptor then touches up the surface for the finished form. The whole surface then receives two or three coatings of a potter’s slip or fine cream of ground brick, clay and ashes, which forms a closely adherent skin around the wax. Then the mould is built up of clay, packed around all the parts to form a solid mass, which is clamped up within a strong iron framework. At certain intervals iron pins are stuck through the clay and wax into the central core, and suitable ‘gates’ are made for pouring in the bronze and allowing the wax to escape. The clamped-up mass is now placed in the furnace, and slowly heated until the wax runs out, and the clay of both mould and core are dried and sufficiently baked. The space occupied by the wax is now vacant, and it only remains to pour in the molten bronze to occupy that space and assume the thickness of the original wax.
2. The Sand Method
This was used for less delicate and smaller castings –
The shape of the model was pressed by sections into specially prepared sand boxes and then cast. In simple relief the model could be taken in one cast, but when it came to making undisturbed impressions in the sand the variations were infinite, and the craftsmen had to choose the least destructive sections and then join and finish the pieces with greatest care. On completion, the components were finished by being dipped in a series of acid baths of various strengths, including one which boiled and then buffed and polished.