Lost-wax casting is a process by which the duplicated metal sculptures are cast from original sculptures. Depending on the skill of the sculptor, more intricate works are achieved with this method. Though today, the process varies and differs from each foundry, steps that are used in the casting of small bronze sculpture is highly standardized. To start with the process, most sculptors make the original, out of clay mold. Multitudes of clay varieties are available for sculpting. Most artists prefer to do their work with the oil based clay as it never hardens or dries. The main advantage is that they can be softened and can be reworked on, if at all there is a change. Usually the clay should be chosen such that they are hard enough for working in detail and then to use the heat in softening the clay to a build-up. Small sculptures that are very small are more often modeled directly in the wax which although is very difficult to be modeled but allows to get maximum details.
The armature in the sculpture is the material used in supporting the clay's weight. It is necessary when a figure is portrayed in standing posture or in motion. When working for large sculptures, sculptors use"fillers" like aluminium foil or Styrofoam to fill out the form and reduce the clay used. Then the clay sculpture is formed on and around the armature. Once final touches are made in the original sculpture of clay, delicate details and smoothing is done so as to avoid many imperfections, as they may get copied in the molding process and may appear in the subsequent stage.
When the clay sculpture is smoothened completely, a mold is made of the original clay. Excellent replication of the surface is achieved with polyurethane mold or silicon rubber with high quality. Smooth On, the latex rubber mixture is then applied onto the surface of clay directly with a brush. Usually 3 to 5 coats of it is done. When the coat dries, it is cut and there emerges a " mother mold". Positive forms are then generated by pouring the wax replica. Then the repairing procedure called " wax chasing" is done to maintain all the details originally found in the mold. This procedure is done with delicate and small tools.
Finished wax is the positive replica of the original clay. Sprues are attached to the wax model through which all molten metal is fed to all of the areas of the sculptures. After spruing the wax goes on to shelling process. In the selling process, the wax positives are dipped in a slurry mixture which creates a hard shell which helps in shaping and holding the bronze sculpture. Once the ceramic shell and the bronze has cooled, the bronze is separated from the casing of the shell. "Metal chasing" is done to finish the metal to its original appearance. When all final pieces are welded together, making it shiny and smooth, the sculpture is sand blasted to get the final sculpture. The main advantage of the lost-wax casting is that they create true and unique sculptures.
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