Sculpture From Clay To Bronze : Part 3

Making a Mold of the Clay Original : When the clay sculpture is completely smooth and finalized, a mold must be made of the original clay. Excellent surface replication of the original can be achieved with a polyurethane mold compound or a high quality silicon rubber. The most common material used to produce a mold today is a material known as Smooth On. It is a latex rubber that is carefully formulated to be able to pick up the minutest details in a work. The rubber mixture is applied directly to the surface of the clay, using a brush to actually paint it onto the surface. Special attention needs to be given to avoidance of air bubbles that may be trapped within the rubber mixture. Once the first coat of rubber has been applied to the surface, it must be allowed to dry before the next coat is applied. All of the details from the original clay are now picked up within the rubber material that has been painted on. A mold most generally consists of three to five coats of rubber applied over the course of several days. One the final coat of rubber has dried, a firm outer jacket is made to help retain the shape of the more flexible rubber mold for pouring the wax replica. This jacket is usually made out of plaster, Hydrocal, resin, or epoxy, and is called the mother mold. When all of this is complete and it is all dry, the outer jacket is removed, and the rubber is then cut away from the clay, on what is called a parting line. The sculpture has now gone from a positive form to a negative form. If the sculpture is large or complex, it will usually have to be divided into smaller pieces, with each piece needing its own individual mold. The pieces will be rejoined later, after the sculpture is cast in bronze, to make the complete sculpture whole again. The learning process for making an excellent multiple piece rubber mold can take years. A novice should hire a professional, or make a plaster waste-mold of the original and make a plaster cast, a positive. From this solid positive a rubber mold can be made without risk of losing the original. The highest quality mold will save much time and money in production.

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