Diagram depicting a version of the lost-wax slush-molding process combined with ceramic shell casting:
1) a flexible silicone two-piece mold is created from the model (in this example made of clay); the layer of silicone is backed with a rigid mother mold;
2) this reusable mold is disassembled and the model removed;
3) to form the inter-model, molten wax may first be brushed into the interior of the piece mold to ensure that the wax reaches all areas and captures the fine details;
4) the mold is reassembled; the molten wax is poured in and slushed around in order to coat the interior;
5) excess molten wax is poured out; this “slush molding” is repeated until the desired thickness is achieved;
6) the hollow wax inter-model is removed from the mold, imperfections repaired, and details refinished;
7) core pins are pushed through the wax walls and the wax sprue system is fused to the inter-model;
8) an internal core support (armature) is inserted into the hollow wax, which is then filled with refractory core material (note: in ceramic shell casting, the core can be a plaster-based investment or the same ceramic shell materials as the outer mold);
9) the inter-model is then coated with a liquid ceramic slurry followed by grains of fused ceramic to provide bulk and a textured surface that will ensure that the next layer of slurry adheres well; once this first layer is dry, the process is repeated (eight to ten times) to create the desired thickness of ceramic shell;
10) when the refractory mold has dried, it is placed upside down and heated rapidly to burn out all traces of wax; it is then placed in a kiln to dry the plaster investment core and sinter the ceramic shell into a sturdy, unified body that can withstand the pressure of the molten bronze;
11) the hot mold is removed from the kiln, turned with the casting cup facing up, and the molten bronze poured into the mold;
12) when the metal has cooled, the ceramic shell casing is broken off of the cast and remains are removed by sandblasting; the bronze sprue system is cut off and the core pins and plaster core removed along with the internal armature;
13) chasing includes polishing, burnishing, and the addition of textures and sharpening of details as needed;
14) as a final step, a chemical patina and/or a coating may be applied.
Diagram based on Andrew Lacey (British, b. 1969), The Anatomy of Bronze, cast by the artist in 2019, Devon, UK, H. 45 cm (artist’s collection). See Case Study 7.