The Art of Bronze Casting
Bronze casting is an ancient art that has been used for thousands of years. Bronze artifacts have been found dating from 3000 B.C. Although casting techniques have been refined over the centuries, the fundamentals of an old and venerable craft remain.
For the sake of brevity and clarity, the procedure is described in extremely simplified terms; however, this outline will provide a general over-view of the casting process.
1. The artist submits his original model. It may be sculpted in one of a variety of media: clay, wax, wood, stone, etc.
2. A FLEXIBLE mold material is carefully applied over the entire surface of the model.
3. A plaster MOTHER mold is poured around the cured FLEXIBLE mold to insure stability in succeeding steps.
4. When dry, the plaster MOTHER mold is removed in sections from the FLEXIBLE mold which is, in turn, removed from the model. At this point, the original model which may have been damaged in the process is set aside and no longer used.
5. The FLEXIBLE mold is re-positioned within the MOTHER mold.
6. Molten wax is poured into the FLEXIBLE mold to produce a duplicate of the original model. From this point, the steps may be repeated as often as is necessary to produce multiple castings.
7. When the MOTHER mold and FLEXIBLE mold have been carefully removed, a wax duplicate of the original remains. At this point, the founder or sculptor repairs any imperfections that appear in the duplicate.
8. To the wax duplicate are added a wax cone called a "gate" and wax rods called "sprues". Later, the "gate" and "sprues" provide cavities in the SHELL mold that will allow for the pouring of molten bronze.
9. The sprued and gated duplicate is repeatedly dipped in a liquid ceramic slurry until a suitable thickness is built up around the wax producing the SHELL mold.
10. When the SHELL mold is completely dry and hard, the wax duplicate is MELTED OUT. The SHELL mold is now ready to receive the molten bronze.
11. The SHELL mold is embedded in sand for support, and the bronze is poured through the "gate" at a temperature of approximately 2,000 degrees F.
12. When the metal is cool, the ceramic SHELL mold is carefully chipped away with a mallet. A bronze cast remains, with the "gate" and "sprues" still connected.
13. The "gate" and "sprues" are removed, and the cast is cleaned and closely inspected for flaws. If the cast is perfect, it is then chemically treated to produce the patina or color of the finished sculpture. The artist is then presented with a perfect replica of his original sculpture, reproduced in bronze.
