The Bronze Foundry Process, Part 2

11. Bronze pins are inserted through the walls of the wax duplicate to hold the ceramic that will fill the wax sculpture's interior, preventing the ceramic from falling within the cavity created when the wax is melted out. Eventually, they will simply become part of the surface of the sculpture.

12. The wax duplicate, sprue system and gate are repeatedly coated inside and out in ceramic slurry and progressively coarser ceramic sand, building up a thick layer that dries to a hard investment or shell, with only the open end of the wax gate left exposed.

16. The cooled ceramic shell is chipped away, exposing raw bronze, which appears a dull gold. As much as possible of the shell remaining in the sculpture's core is removed to reduce the total weight, but often much is left inside. The bronze pins have become fused into the surface of the sculpture and are invisible.

18. The patina is applied; either a polychrome patina that is handpainted by the artist or a chemical patina that is applied at the foundry under the artist's direction. This is essentially an artificial rust that stabilizes the surface metal and gives a beautiful finish. Bronze is mostly copper and would turn a raw green if not patinated. Finally the sculpture receives a coat of wax for protection and is attached to its base. The only care required by a bronze sculpture is a very occasional cleaning and reapplication of wax polish, and it could last literally for centuries. Bronze sculpture is one of the best investments an art collector can make.

CASTING, PAGE 1



				10. A system of wax bars or sprues are attached to the wax duplicate, creating a web of channels around the sculpture which will quickly distribute the molten bronze to all parts of the sculpture, and through which molten wax and gases will escape. A large wax gate is attached into which the bronze will eventually be poured. These large-to-small channels increase the pressure on the liquid bronze, forcing it into every detail.



	11. Bronze pins are inserted through the walls of the wax duplicate to hold the ceramic that will fill the wax sculpture's interior, preventing the ceramic from falling within the cavity created when the wax is melted out. Eventually, they will simply become part of the surface of the sculpture. 12. The wax duplicate, sprue system and gate are repeatedly coated inside and out in ceramic slurry and progressively coarser ceramic sand, building up a thick layer that dries to a hard investment or shell, with only the open end of the wax gate left exposed.



				13. The ceramic shell is then heated with steam to melt out the wax duplicate, sprues and gate, leaving a hollow cavity into which the bronze will be poured. This de-waxing phase gives the procedure its name: The Lost Wax process, a technique which has not changed in its essentials in 5000 years. The shell is then furnace cured, hardened and preheated in preparation for casting.he walls a thick coat of plaster is thrown to make the outer or mother mold. Usually the mother mold is in several interlocking pieces, so separator must be used in the seams so that the edges of the plaster mold sections do not bind.



	14. The ceramic shell is buried in sand, with only the opening of the gate exposed, and molten bronze is quickly poured into it at a temperature of over 2000 C. Gases escape into the system of sprues, preventing bubbles from forming in the bronze.



				5. Silicon rubber is poured in liquid form at room temperature into15. The bronze casting in its shell is allowed to slowly cool over several days to prevent cracking, before being removed from the ceramic investment.



	16. The cooled ceramic shell is chipped away, exposing raw bronze, which appears a dull gold. As much as possible of the shell remaining in the sculpture's core is removed to reduce the total weight, but often much is left inside. The bronze pins have become fused into the surface of the sculpture and are invisible.



				17. The bronze sprues and gate are sawn off, and if the sculpture was cast in several pieces, they are welded together. Bolt holes are drilled to attach a base of wood or marble. The surface of the bronze is chased by hand to remove the scars where the gate and sprues were attached, and is then sandblasted to a fine finish.



	18. The patina is applied; either a polychrome patina that is handpainted by the artist or a chemical patina that is applied at the foundry under the artist's direction. This is essentially an artificial rust that stabilizes the surface metal and gives a beautiful finish. Bronze is mostly copper and would turn a raw green if not patinated. Finally the sculpture receives a coat of wax for protection and is attached to its base. The only care required by a bronze sculpture is a very occasional cleaning and reapplication of wax polish, and it could last literally for centuries. Bronze sculpture is one of the best investments an art collector can make. CASTING, PAGE 1