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The lost wax process is the oldest casting method for most metals, including of course bronze. First developed during the bronze age this casting method is more efficient than the traditional, and less expensive sand casting process. The lost wax method preserves more of the tradition involved with the artistic making of fine arts crafted from metal, thus giving more importance to the intricate detail of the pieces. This process is composed of several steps, which are very briefly explained here.
Making The Mold
The original sculpture should be made of a material such as clay, plaster, stone, or wood. The mold maker examines the sculpture and decides how to divide the master. The number of divisions depends on the complexity of the design.
The mold most often used involves applying rubber onto the original, building to a ¼ ” thickness. Then covering the flexible mold with a rigid material called a mother mold made of plaster or fiberglass. Once the mold is prepared, the original sculpture is removed and a hollow wax replica is poured.
Preparing the wax
The wax original is prepared following de-molding by chasing seam lines, touching up the surface and checking detail. Since the wax will serve as the pattern for the finished bronze it is important to check it carefully before moving on to the next step. At this point the casting is etched with an edition number. Having an edition allows the artist to spread the mold costs over the whole series.
Then the gating system is fitted, which is the system of channels through which the molten metal flows. Constructed correctly the gating system ensures a quick, smooth flow of the molten metal. This structure is also necessary to allow gasses and air to escape. Attaching sprees to the wax with a hot metal tool and attaching a wax-pouring funnel make the gating system.
The prepared wax, complete with the pouring gate and cup, is evenly coated with a slurry made of colloidal silica and silica flour, then left to dry and harden in a controlled atmosphere.
The first layer picks up all the detail. Subsequent layers of ceramic shell are then applied, including large particles of fused silica, which eventually build up to a stucco like appearance. Each application must be allowed to dry and harden before another coat is applied.
When the desired wall thickness has been achieved, the entire piece can be prepared for de-waxing.