If made in a hard alloy or silver, a rubber mould is made by surrounding the master model with sheet rubber in a mould frame. Placing it in a heated press and vulcanizing it. On cooling, it is cut with a scalpel into halves, thus releasing the master model.
The rubber mould is used to make many copies of the master model in wax, by use of a wax injector which injects molten wax, often under a vacuum to remove air from the mould, into the mould cavity. On cooling, the wax is removed to give an exact copy of the original master model in wax.
The waxes are assembled into a ‘tree’ around a central feeder or sprue. This tree is cleaned of dust, and placed in a metal cylinder, known as a ‘flask’. Special investment powder is mixed with water to a slurry