Mould Making Process

A mould is usually constructed of two layers or the outer and inner mould. The rigid outer mould contain the softer inner mould, which is the exact negative of the original model. The inner mould is usually made of latex, polyurethane rubber or silicone, which is supported by the outer mould. The outer mould can be made from plaster, but can also be made of fiberglass or other materials. Most moulds are at least two pieces, and a shim with keys is placed between the pieces during construction so that the mould can be put back together accurately. The process below describes the constroction of a two piece silicone rubber inner mould supported by a 4 piece plaster mother mould

•  Building A Wall. A wall of clay is built around the original which forms the line where the two halves of the mould can come apart. The positioning of this wall is critical, as the mould has to be able to come away from the original and later the wax copy easily without getting stuck in crevices and deep undercuts. Dimples are cut to form bumps in the mould that lock the two parts together precisely.

•  First silicone Rubber Inner Mould. The upper part of the silicone rubber inner mould is applied. When cured it is trimmed to form a neat edge.

•  Upper Mother Mould. The plaster mother mould is then applied over the silicone mould. In this case I made the upper part of the mother mould in two parts. As it would have been impossible to remove it off the tail if it was just one part. Dimples are cut into the plaster to. This allows the two parts of the plaster mould to lock together accurately.

•  Removal of Wall and Cleaning. The piece is turned onto its back and the clay wall is removed. You can now see the bumps that have formed around the edge of the mould by the silicone that had flowed into the dimples cut into the clay wall.

•  Second Part of Inner silicone Mould . The lower part of the silicone rubber inner mould is then applied. Firstly as a runny layer that easily gets into all the crevices . Then as a thickened layer to build up the thickness of the mould. Again the silicone is trimmed and dimples cut around the edge of the plaster mother mould .

•  Lower Sections of Mother Mould . The lower part of the mother mould is then built in the same way as the upper part . Again the lower part was constructed in two sections for ease of removal.

•  Removal of Original . The sections of the mould are then separated and the original removed. The mould is cleaned of bits of clay and put back together with the entrance pointing up. Elastic bands are used to hold the parts of the mould in place .

•  Pouring the Wax. Wax is then poured in and sloshed around. After a couple of minutes, depending on the size of the mould , it is poured out. This process can be repeated a number of times to build up the layers of wax coating the inside of the mould.

•  Removal of Wax Copy. When the wax has cooled, the mould is taken apart and the hollow wax copy removed. The wax copy is then used in the next stage - ceramic shell application and casting.