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Molds to Make Bronze Sculptures

Bronze casting through the use of molds has been a traditional form of sculpture making for thousands of years, due to the polish and beauty of finished bronze sculptures. Also, bronze, a mixture of tin and copper and other materials, was stronger than other metals discovered before the Bronze Age. The Riace Warriors (two Greek Classical bronze figures) are an example of the durability of bronze, as they spent centuries lost underwater before being rediscovered in the 20th century. While bronze sculptures had been poured through molds originally by Asian cultures, the Ancient Greeks from 800 B.C. began to have the greatest effect on Western culture through the continued use of the "lost wax method," one of the earliest forms of mold usage.

  1. Bronze Properties

    • This is a Renaissance example of the lost wax method depicting Perseus and Medusa.

      Bronze is a desirable metal to be poured into a mold, partially because of its tendency to expand just before it fully cools and sets. This allows the bronze to fill in the mold completely.

    Ancient Greek Lost Wax Method

    • The Ancient Greeks became masters of the human form through the creation of hollow bronze figures. They began with a clay sculpture, as clay can withstand high levels of heat. This clay sculpture would then be coated with wax. The final layer of clay over the wax would form the mold. This sculpture would be heated, and the wax would melt and flow out of a hole in the bottom of the mold, hence "lost wax." Molten bronze would be poured into the cavity left by the wax, and as the bronze hardened it would form a thin bronze sculpture that was an exact copy of the original. The inner clay could be scraped out through a hole in the bottom of the bronze.

    Modern Lost Wax Method

    • The process must begin with a positive form, or a finished sculpture in wood, plaster, stone or clay. Modern bronze casters have more options regarding the original, because this original piece does not get exposed to high heat. Modern bronze casters coat the original sculpture with a type of polyurethane rubber or silicone rubber, and then they encase it in plaster to create an exact negative (or mold) of the original positive sculpture. This rubber mold can be taken off of the original sculpture and put back together. The mold is used to create wax sculptures that are identical to the original. The wax must be heated to 210 degrees in order to flow into the rubber mold. The wax sculptures, identical to the original sculpture, are coated in plaster to create another mold through which the bronze can be poured, melting the wax in the process and creating the final bronze positive.

    Patina and Detail Work

    • The finished bronzes from Ancient and Modern cultures may have burrs (raised bumps) or supports jutting from them that need to be sanded off. Some fine detailing may be added, such as placing semiprecious stones in the eye sockets (for example, the Greek Charioteer of Delphi). Ancient cultures buried some of their bronzes in order to speed up the chemical process of creating a patina, or green weathered hue, to the bronze. In modern bronze casting, special chemicals may be used to induce this process almost immediately.

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