The Clay Used for Bronze Molding
Bronze molding is the art of creating a bronze replica from a clay model of a statue. The procedure for bronze molding, known as lost-wax casting or industrial casting, involves first creating a wax model of the sculpture and then creating a hollow clay cast of the model using slurry clay and shell clay. When the clay is baked, the wax melts away, yielding a hollow cast for creating a new sculpture.
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Slurry Clay
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A thin layer of clay known as slurry clay is mixed with water and painted onto a wax model of the to-be-cast figure. Also known as China clay or kaolin, slurry clay has a particularly thin consistency and is capable of capturing the finer-grained features shown by the wax model. Typically the slurry is painted on twice using a toothbrush or other fine-toothed brush.
Shell Clay
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The next layer that is painted onto the wax model is a thin layer of stucco or heavier, pasty clay. To mimic ancient techniques, a mixture of rice husk, sand and clay can also be used. This process produces a layer that is referred to as a ceramic shell mold, although this is a misnomer given the lack of ceramic used. At least two coats must be applied to create a ceramic shell mold; the resulting shell should be 1/2 inch or greater in depth.
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Baking the Clay
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After the ceramic shell mold has dried, it is baked in a kiln. During the baking process the outer clay coating is hardened in the kiln, while the coated wax model melts to leave a hollow cast.
Testing the Clay
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It is important to test the integrity of the new ceramic mold before pouring liquid bronze into the cast to create a new statue. First the cast is drilled to determine the thickness of the shell. These holes are then patched if the thickness is deemed adequate. When the shell is cooled, water is poured along the shell to determine if there are any cracks; these cracks are then patched with a thick paste.
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References
- Photo Credit sculpture 3 image by thierry planche from Fotolia.com
