When the mold is complete, a wax copy of the original master needs to be developed. Liquid heated wax is poured into the prepared mold. Once it has hardened, the wax can easily be released from the mold. The unfinished wax copies are carefully reworked by me or a foundry wax worker with sculpting tools to take out any imperfections.
Once the waxes are to my satisfaction, I send them to the foundry. They attach the sprues (channels the bronze is poured through into the molds) and dip them into a ceramic mixture until a shell of about and inch has built up.
Next, they add the waxes in their shell to the kiln. The wax is molten out and the negative is retained in the ceramic shell mold. Then the liquid bronze (2,250 degrees Fahrenheit!) is poured into this second mold. After a slow cooling time the ceramic shell is destroyed and the raw bronze is sandblasted. The sprues are roughly cut with a plasma cutter by the metal worker. They also do some welding to fill in holes in the metal, referred to as “cutting and chasing”, and generally working and sanding details in the bronze.
The raw bronze is sandblasted again and carefully cleaned. To get the desired finished look, acids and chemicals are applied to create the coloration called “patina”.
Finally certain surfaces like the faces and knees of the finished bronze sculpture are highlighted by polishing and a protective coating of wax is applied that prevents further oxidation.