Fire Bronze Casting by the Numbers
1. Rubber molds are made from the approved master sculpture. Master sculptures are usually made from clay.
2. Waxing involves repeated filling of the rubber mold with hot wax, slushing or otherwise making sure all areas of the mold are covered, and pouring the wax out. Each coat of wax must be allowed to cool so the next coat can be applied over it. Four or more coats of wax are needed to develop the required section thickness. After the waxing is completed, the rubber mold is stripped away from the wax and a hollow pattern is now ready for cleaning.
3. The finished wax is inspected for thin areas that would not accept the bronze and for flash, wax drips, or any other defects caused by removing the rubber mold.
4. The wax pattern is then gated. Additional wax pieces are attached to the pattern at specific points and then attached to a base to provide multiple entry points for the molten metal.
5. The tree is now ready for the shell to be applied. Each tree or assembly is dipped into a slurry, (like cake batter), removed and allowed to drain. Then, a thin coat of sand is applied. Repeated dipping and sanding is required until sufficient strength is achieved to withstand the temperatures and the thermal shock of the hot metal.
6. After the shelling is completed, the tree is placed in an autoclave. Super heated steam penetrates the outer shell and melts the wax. The wax will leave the mold via the tree base and the gates leaving a shell without the wax pattern or tree.
7. The empty mold is placed into a large oven, then baked at 1900° F for four hours to remove any possible trace of wax and to cure the mold.
8. Silicon bronze is melted using the induction process (electric melting) to give the highest quality finish. It takes approximately 8 minutes to melt 75 pounds of bronze at about 1800 - 1900°F. The mold is taken from the oven and the molten bronze is poured into it.
9. The shell is left until it is cool enough to handle. The shell material is removed from the bronze tree, by sandblasting or chipping away of the shell, though care is taken not to touch the sculpture.
10. The tree is cut away from the sculpture, and all areas where the gates were attached to the wax pattern are ground flush.
11. Each piece is polished and any defects are removed. The bronze is assembled to its base and prepared for patina.
12. The patina is applied using chemicals and blow torches. The piece must be heated to 200°F before the chemicals are sprayed on. Repeated heating and applying of chemicals are required to achieve the deep multi - colored finishes.
13. Final polishing and inspection is done and the edition number and name are placed on the sculpture.
14. One more inspection is made prior to each piece being packaged for shipping. Each bronze is logged into an edition book and shipping documents are prepared
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