The lost wax method of bronze casting is at least 6,000 years old. In 1847 the first bronze castings were done in America.
1. The first step begins with the artist creating an original sculpture, usually made of wax or clay.
2. For clay models, a plaster or rubber mold is made from the artist's original sculpture. This mold is used to create duplicates (editions) of the original design.
3. Melted wax is poured into the mold, creating a wax casting.
4. The wax casting is removed from the mold, and hand finished.
5. Wax "gates" or "sprues" and a pouring cup are added to the wax casting or wax model to provide channels for the wax to melt out and the bronze to flow into the sculpture.
6. The wax model is then coated with many layers of liquid ceramic shell and sand, creating a stable mold.
7. The wax model, now coated in ceramic shell, is fired in a kiln. This bakes the ceramic shell and eliminates the wax, leaving a cavity in its place. Thus, the term "Lost Wax".
8. The ceramic shell is removed from the kiln and molten bronze, heated to about 2,100 deg F, is poured into the cavity of the hard ceramic shell.
9. After the bronze cools, the ceramic shell is broken away, revealing the bronze sculpture.
10. Fine sand particles are blasted under strong air pressure to remove the last traces of ceramic shell.
11. The gates are removed, and the bronze sculpture is hand finished. By grinding, chasing, sanding, and polishing, all areas are blended to make the bronze look exactly like the artist's original wax sculpture. A sculpture that cannot be cast in one piece may be cast in two or more pieces and welded or brazed together to create the finished work.
12. The chased (raw metal) bronze is then treated with chemicals to give it its color. This is called the patina, which is a permanent part of the sculpture. A wax coating is applied to seal the finished bronze sculpture.
