Sculpture From Clay To Bronze : Part Four

Pouring a wax replica from the mold. With the mother mold complete, positive forms can now be generated by pouring a wax replica. Pouring a wax is usually done in four stages or coats. The first coat is applied by heating the wax to a temperature of approximately 220 degrees fahrenheit. While the wax is quite hot, the mold is rotated about, in an attempt to coat the entire internal surface of the mother mold through a hole. The second coat of wax is applied slightly cooler, at around 200 degrees. The final two coats go on at approximately 180 to 185 degrees. A completed wax should be approximately 1/4″ thick, or just slightly thinner. When the wax cools and the mold is removed, a wax positive of the sculpture emerges. If the sculpture is a bas relief, or if it has a large mold that opens wide, it is usually much easier to brush on the wax. Following the same temperature guidelines per coat as above, the wax must be brushed on beginning in the deepest hollows of the mold to avoid any drips. Wax chasing is the procedure of repairing all of the imperfections that were created during the pouring process of the wax to maintain the original details with in the mold. There will most always be a few air bubbles, seams, and mold lines which will need to be removed from the surface of the wax positive. Wax chasing is usually preformed at the foundry by a professional wax chaser. However if the sculptor prefers, they can do the wax chasing themselves. The wax chasing procedure is done with small, delicate tools for scraping, and with a hot tool for filling in the imperfections within the wax. Once the wax is back to a perfectly finished state, the sculptor inspects the wax. If the wax receives the sculptor’s approval, it is ready to go to the foundry for spruing. Spruing a wax : The finished wax is a positive replica of the original clay. A network of wax rods, called sprues and gates, are next attached to the positive wax model. These sprues will serve as a type of channel system, which will feed the molten metal to all of the areas of the sculpture, as well as allow gases and air to escape. Also, a wax funnel is attached to the gates for use during pouring. During the spruing process, special care is given to areas such as the tips of a rabbit ear, or the fingers of a frog, to ensure that these fine areas will not short pour. Once the spuring is completed, the wax is ready to go on to the shelling process. The ceramic shell process requires a series of dipping the wax positive into a mixture called slurry to create a hard shell. This ceramic shell, once dry, becomes a hard, durable shell around the entire sculpture that is going to receive, hold , and shape the molten metal to produce the bronze figure. The wax is first dipped into a solvent, which cleans any loose particles or debris from the surface of the wax. the shell process is about to begin. The clean wax is dipped into a solution called prewet, followed by two coats of a very fine grained slurry. This is known as the primary coating. this is where all the fine detailing in the piece is picked up. It is almost like grained silicon flour. The shell then progresses through the slurry process, into different slurry mixtures, which are various grades, gradually becoming courser with each coating. Each time the wax is coated with the ceramic slurry mixture, it is allowed to dry thoroughly. Each coat adds support to the overall strength of the shell. The ceramic shell process consists of seven to nine coats of slurry mixture. Once all of the coats have dried, the ceramic shell is then sent to be dewaxed.

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