The Lost Wax method of bronze casting – what exactly is it?
It is a centuries old method of making a duplicate copy of any solid object. The object needs only to be sturdy enough to allow it to be covered, without damage, by another medium – usually a viscous, room-curing rubber, and/or a wet, air-drying plaster.
Bronze sculptures typically begin with the artist creating the original sculpture out of clay, although many other materials (wood, plaster, wax, etc.) may be used. The art casting foundry then makes a mold of the sculpture, from which it creates a hard wax duplicate. To this duplicate are attached various wax rods which become the sprue system for the sculpture. This assembly is then immersed into a vat of a liquid ceramic material, removed, and while still wet, sprinkled with silica sand and then set aside to dry. This process is repeated several times to build up a strong ceramic shell.
The ceramic shell, with the wax duplicate and wax sprue system inside, is put into a furnace, which causes the shell to vitrify and harden, and the wax to melt and evacuate the shell. It is into this now hollow shell that the molten bronze is poured, where the sprue system allows the bronze to fill the space once occupied by the wax. When cooled, the ceramic is broken away and the rough bronze duplicate is exposed. Various tools and techniques are then utilized by foundry artisans to remove any imperfections in the bronze sculpture, to perform any assembly required, and to prepare it for patination. There, under heat, it is subjected to various acids which react with the copper in the bronze alloy to create the desired colorization.
