Sculpting can take anywhere from days to months to complete. After I have sculpted the original work from clay it is either fired and painted with acrylics, cast in cold cast bronze (resin mixed with bronze powder) or cast in foundry bronze. A silicone rubber mold is made for any work being cast. Layers of liquid rubber are applied to the original sculpture to capture the fine detail. After the rubber has set, a thick plaster mixture is applied and given time to harden to create a rigid "mother mold" to help preserve the firm shape. If the work is being cast in foundry bronze, I then ship the entire mold to the foundry.
There are a lot of steps that take place during the process of creating a foundry bronze. I use Baer Bronze Fine Art Foundry for my castings. The process they use is described below.
Wax Pour
Using the rubber mold made from the original piece, molten sculpting wax is poured into the hollow interior of the mold. The wax is allowed to cool before it is carefully pulled out of the mold. Now we have a highly detailed positive wax copy of the original sculpture!
Wax Chase
Now that we have a detailed wax copy of the original sculpture, trained wax chasers clean up the wax. Using many of the same tools that the artist uses to sculpt the original, the wax chasers clean up air bubbles, seams (from connecting areas of the mold), and any imperfections so as to match the texture and essence of the original sculpture.
Wax Sprue
After the wax is cleaned, a circulatory system must be created and attached to support the wax model and leave passageways or tunnels through which the melted wax escapes from the slurry shell to permit the molten metal to enter the pattern chamber of the casting flask. This system is created by attaching sprues (wax bars) and a pouring cup to the wax pattern to insure the proper flow of metal and to control the metal solidification. Spruing is more important to casting than is generally realized. In fact, it is essential that sprues are properly engineered to each individual sculpture in order to create a flawless casting.
Slurry/Shell
The sprued wax copy & cup are then dipped in several layers of a liquid "slurry" mixture and sand to encase the wax, which then dries and hardens. This ensures that the wax pattern & sprues are fortified by an outer ceramic shell that becomes the final mold after the shell is fired and the wax has melted out.
Shell Burnout or Flashing
The flashing/burn-out stage eliminates all wax and moisture from the ceramic shell. The shells are placed into the furnace and heated to a point where the wax is melted away, leaving a hollow ceramic shell that is ready to accept the molten bronze. The shells are now ready for casting!
Bronze Casting
After the ceramic shells have been hollowed out, ingots of bronze are placed into a crucible and melted into a liquid state. The red-hot crucible is hooked to a movable crane and hoisted up to pour the molten bronze into the ceramic shells at 2000 degrees.
Metal Prep
After the molten bronze has cooled, the ceramic shell is removed through chipping and sandblasting to reveal the detailed, raw bronze copy of the original sculpture. The sprue gates that were attached in wax (now converted to bronze) are cut off so that the metal chasing can begin!
Metal Chase
Once the metal has been prepped, the metal chasers re-assemble the art piece by welding the cast pieces together. Then, significant time is taken to chase away the weld and replace the texture in the sculpture. Pneumatic tools are used to restore detail, resulting in an exact representation of the artist's original sculpture.
Patina
The final stage is patina, which is the coloration of the bronze brought about by the oxidation of the metal surface. This is achieved by applying various chemicals and finishes to the surface of the bronze to ensure they create the desired color effect that the artist desires.