Sculpture From Clay to Bronze : Part 5

When the ceramic shell is complete, it is placed in a high pressure sealed oven, known as an autoclave. High temperatures 1500 to 1800 degrees Fahrenheit and pressure force the wax from the shell and the wax melts out, thus becoming lost. This is where the name Lost Wax Process has been derived. The wax has now left the shell, leaving the detailed impression within the shell, which will soon become filled with the molten bronze. This step also hardens the ceramic shell in order to prepare the shell for the extreme temperature of the molten bronze which it is about to receive. When the ceramic shell is empty of wax, it is then re-fired and made ready to have the molten bronze poured into it. All of the hot ceramic shells are taken to the pouring floor, where they are either placed in sand to stand by themselves, or they are wired to a support frame to be held in place. The solid blocks of bronze, meanwhile, are heated to a temperature of approximately 2250 degrees Fahrenheit so that liquid bronze is created. The liquid bronze is stirred and prepared for the pour. When the molten bronze is ready, the foundry workers very carefully lift the crucible, containing the liquid bronze, out of its heating furnace. The workers must wear protective face shields, clothing, gloves and boots. Moving quickly and very precisely, the foundry workers pour the liquid bronze into each awaiting ceramic shell. When the ceramic shells are all full with the poured bronze, they are then left to cool for several hours. The negative space within the ceramic shells have now become bronze positives. Once the bronze and ceramic shells has cooled, the ceramic shell is broken off to separate the bronze metal from the shell. This is done with hammers, tools, power tools and sand blasters. This process needs to be done very cautiously, though , in order not to cause unwarranted damage to the metal surface. Once the entire ceramic shell has been removed, the sprues which have now become metal must also be cut away or sawed off. At this stage, the uncovered bronze is considered a raw metal.              To be continued :