The Making of a Bronze
This shows the steps involved in the long process of turning a clay sculpture into a bronze using the "lost wax" process. The subject is Lioness and Cub. The basic steps are listed below the images.
- Create a sculpture using one of a variety of materials - water clay (in this case), oil clay, plaster, super sculpey, etc.
- Make a mold. To pick up detail, silicone painted or poured over the clay and allowed to vulcanize. It will be soft and pliable, picking up detail but flexible enough to be pulled off the complex shapes of the was without distorting it. The silicone mold is surrounded by a tough plaster mother mold to give it support.
- Pour melted wax into the mold a little at a time till a 1/4 inch thick layer covers the silicone. All of the concave areas of the silicone mold must be filled, or gaps will occur.
- Separate the mold to extract the delicate wax copy. The wax copy can be worked on if necessary. Gaps that the liquid was did not fill can be repaired, edges can be sharpened, parts that were separated into different molds can be joined.
- The foundry then builds a new mold around the delicate wax, using layers of increasingly dense sand, ending with a ceramic like case, which is the mold for the bronze. Before this can be done, wax tubes are added around the wax sculpture that will allow the liquid bronze to flow evenly throughout the piece filling all nooks and crannies.
- The new mold is heated, the melted wax is drained, and the liquid bronze is poured in until it fills the area vacated by the wax.
- The mold is broken apart, and the bronze remains. The tubes that were added, now filled with bronze, need to be ground off. If the sculpture was cast in pieces, these need to be welded together and the metal needs to be ground and cleaned, called chasing, until it matches the original clay. Imperfections in the casting might also need to be addressed, where bronze is welded on to gaps and then ground down and smoothed.
- Using chemicals and fire, the patina is applied. A lot of artistry can occur here. A skilled craftsman can apply a variety of acids in layers to create rich colors above the regular french brown and classic green.