THE PROCESS OF CASTING BRONZE
|welding the iron structure to be able to work on it with plastiline and model the sculpture
Jan Willem Tuytel in the foundry for the project of Menken
melted bronze which is going to poured in the investment
The particular process I used to cast is called Cira Perdu or "Lost Wax". First a plaster, silicone, gelatin or rubber moulds is made from the original statue. The negative mould is then removed and all that remains is the wax that will be "lost" once the sculpture is cast. The wax model is hollow and about 3 to 4 mm thick like the bronze statue eventually poured in its place, the best quality castings are light. The wax is then surrounded with liquid clay or ceramic shell to make a mold. A pouring hole is left open at the top. After the investment hardens, this entire thing is put into a big oven and the wax is melted out, then molten bronze is poured into the remaining cavity. Bronze, alloys of copper mixed with zinc, tin, and lead, is fired to a temperature of 1100\170C approx when it becomes liquid and is then poured into the mold. If everything has gone to plan the shape should be in bronze inside when the mold is broken open. When a piece is cast in components, the parts need to be welded together. The sculpture is then chased: the metal surface is worked and polished. Finally, the statue is colored with a patina. The patina is made with sulfur liver and ammonia-salt and other chemicals, a methodology that will be able to provoke in the time chromatic variations with the oxidation.