2: Mold Making
OVERVIEW | MODELING | MOLD MAKING | WAX CASTING | WAX CHASING | CERAMIC SHELL | POURING BRONZE | CHASING | PATINA
Mold making is essentially a process of using a material to make a "mold" of the original model. Once this mold is created it will be used repeatedly to make the required number of castings for the edition. The most common mold making material is rubber. There are many different rubbers available today - silicone, latex, polyurethane and polysulfides. Each rubber has it's own properties (strength, hardness, flexibility, etc..)
Often certain parts of a sculpture will be removed and a separate mold will be made on it. An arm or torso for example might be molded separately in order to make the molding and casting process easier (they will then be reassembled later.) There are several methods for making the rubber mold.
The easiest is a paint-on mold. This involves shimming sheets of metal into the original model so the mold may be separated into precise pieces as it is removed from the sculpture. Rubber is then painted onto the sculpture in successive coats until the desired thickness is reached for the rubber mold. The rubber is then allowed to cure.
Plaster is then applied onto the sections of the rubber mold - a release of Vaseline often is necessary before applying the plaster to keep it from sticking to the rubber. Hemp or burlap is ingested into the plaster for strength, on larger molds steel re-bar or some other type of reinforcement is often used.
The plaster, also known as the mother mold or backup mold, is removed along the shim lines and then the rubber mold is opened along the shim lines. The original sculpture is then removed and the modeling medium is usually recycled for other models . The rubber molds are then cleaned and put back into the plaster mother mold and is now ready for wax casting.