Modern Bronze Sculpture - The Process
LOST WAX | CASTING PROCESS
An original sculpture is first created using a material such as wax or clay.
A rubber mould is made from the original sculpture in order to create duplicates of the original design. The mould captures every detail from the original sculpture. Molten wax is poured into the rubber mould to form a wax copy of the original sculpture. The hot wax cools and hardens. The wax casting is removed from the mould and further work performed by hand to produce an exact pattern of the original sculpture. Wax rods ("gates") are attached to the wax pattern to allow the even flow of molten metal avoiding the trapping of air and gas.
The wax is then coated with several layers of a liquid refectory ceramic ("investment") and allowed to cure for several days The hard heat-resistant shell with the wax inside is fired in a kiln. The ceramic shell is baked and the wax melts away to leave a cavity (hence the term "lost wax") Molten bronze is heated to a very high temperature and is poured into the cavity. Once cooled, the ceramic shell is broken away to reveal a bronze sculpture.
Traces of ceramic shell are removed from the bronze by sandblasting. The sprues (a sprue is the passage through which molten material is introduced into a mould) and gates are cut away and further work is performed by chasing, sanding and polishing to achieve an exact copy of the original sculpture.
A patina finish is created on the bronze surfaces. A chosen colour is applied with the use of chemicals and is heated with the flame of a torch to add colour and shading to the sculpture. The patina is sealed under a wax coating.