The first step begins with the artist creating an original sculpture. The sculptor makes his “original” (a positive form) out of clay or plastiline.
From the original sculpture a negative rubber mold is made. This flexible mold captures every detail put into the artist’s original work, and is one of the most critical phases in the bronze process. This mold is used to create duplicates of the original design.
From the rubber mold a transitory wax sculpture is made.
The wax casting is removed from the mold and retouched to conform to the original in every way.
The wax model is then equipped with wax rods, called gates and vents to allow the even flow of molten metal and to alleviate the trapping of air and gas. A sprue cup is placed onto the wax to receive the molten bronze.
The wax is then coated with an “investment”, a liquid refractory ceramic, creating the final mold. The entire wax sculpture gates and vents included, is covered inside and out, with a ceramic slurry liquid, and then covered with successive coats of ceramic sand and stucco.
The piece now coated in a ceramic shell, is placed in an autoclave. Under steam and pressure the wax is eliminated from the shell thus the term “lost wax”. The de-waxed shell now becomes the final mold into which the molten bronze will be poured. The molds are then placed into a kiln. This bakes the shell and eliminates the excess wax.
The molds are removed from the kiln while they are still hot and molten bronze is immediately poured into the form. Bronze is poured at a temperature of 2100 Fahrenheit. (Bronze is an alloy of 85% copper, and 15% nickel, zinc, and tin.)
After cooling for several hours, the ceramic shell is carefully broken away, revealing the bronze sculpture within.
Sand blasting is now used to remove any ceramic still adhering to the bronze.
The gates and sprues are cut off. Parts are welded together and then by grinding, chasing, sanding and polishing, all areas are blended back to make the casting look exactly like the artist’s original sculpture.
The chased bronze is now treated with chemicals and heat to give it the chosen color according to the artist’s specifications. The patina is sealed under a wax coating and becomes a permanent part of the sculpture