How Fine Art Sculpture is Made

The Investment Casting (lost wax method)

To begin, a rubber or plaster mold is made of the original sculpture, which is usually made of on oil based clay plastesine wax or other material.

This “ mother mold” is produced by brushing on successive layers of thick rubber that, when dry, is surrounded by a heavy application of plaster.

When the plaster dries, the “mother mold” is opened and the original is destroyed. If a successful mold is not made from the original, all of the sculptor’s work has been lost.

With a successful and now hollow mother mold, the process continues. Hot, liquid wax is poured into the mother mold. The outside layer cools first, when desired thickness is achieved the excess wax is poured out of the mold. When cooled becomes a hollow positive of the original.

Care is now taken to “flash” the wax replica; that is, to smooth out any discrepancies that occur while pouring the wax. The wax flashing is integral to the final outcome, because how the wax looks at this stage will determine the final look of the metal.

At this point, an experienced foundry man ( or even the sculptor) will authorize the spruing. These are the gates or vents that the liquid metal will follow. Once the wax replica is sprued, a series of dippings into a ceramic slurry is applied. Each of the six to eight layers of ceramic liquid is allowed to cure thoroughly.

The wax replica is now encased in a thick ceramic shell and placed in a “burn-out” oven. The oven is heated to 1,600 degrees Fahrenheit and the wax purged from the shell. Thus the name “lost wax process”.

When both the metal and the now empty ceramic shell are ready, the molten bronze is poured into the hollow shell and allowed to cool. Once cooled, the brittle ceramic is carefully chipped off, concealing the metal inside. An experienced metal “chaser” can then cut off the now metal sprues and weld any imperfections. After this, the bronze is sand-blasted to remove any remaining pieces of ceramic and prepare it for the final step.

The patination process is simply the quickening or coloring of the metal. The bronze is heated with a torch to open the pores of metal while different chemicals are either sprayed or brushed on, which produces different lustrous and colors. Finally, wax is brushed over the still warm bronze to lock in their colors forever.

Sandor Monos