Make a bronze casting by creating a clay sculpture, then making a rubber mold for the wax sculpture, followed by a ceramic mold to produce the bronze casting. The whole process can take several days or longer to complete.
- Create a pattern
The original clay sculpture that is copied is often called a pattern. Create a pattern out of oil or water based clay, which are the easiest to work with when making the molds.
- Make a rubber mold
Spray the clay sculpture with a silicone spray that helps to release the rubber mold. Apply two thin layers of silicone or rubber mold. Insert plastic shims with buttons along the seam line; these help to rejoin the mold once it has been released. To make the shell for the rubber mold, apply plaster, resin or epoxy to create the "mother mold." Once dry, cut the mold along the seam.
- Create a wax sculpture
Pour melted wax into the mother mold. Rotate the mold to coat the inside. Pour out the excess. Repeat these steps until the wax reaches a thickness of 1/8 - 1/4 inch. Once cooled, remove the mold, which leaves a hollow wax casting of the pattern.
- Chase the wax
Using a soldering iron and small wood or metal tools, remove the seam lines, air bubbles and any imperfections from the wax casting.
- Weld sprues to the wax sculpture
Insert wax rods, known as sprues, into the wax casting. Sprues allow for the metal to flow through all parts of the mold as well as allow for gas to escape. Weld sprues with sticky wax and a soldering iron.
- Create the ceramic mold
Dip the wax replica into a slurry, a ceramic slip made from colloidal silica and silica flour. Let the excess drip back into the tank. Pour silica sand over the wet slurry, and let the mold dry for several hours. Repeat this process at least six to eight times for smaller molds and as many as 20 times for larger molds.
- Burn out the wax
Once the ceramic shell is complete, place it upside down into a heated kiln or autoclave to remove the wax.
- Casting the bronze sculpture
Melt bronze ingots in a furnace to 2200 degrees Fahrenheit. Pour the molten metal into the mold which has also been heated in a kiln to about 1500 degrees Fahrenheit.
- Finish the bronze sculpture
Once the metal has cooled, remove the ceramic shell with a hammer and chisel. Cut the sprues with an angle grinder, and sand the remaining bits. Sand blast the surface of the casting to make it smooth. To create the patina, apply chemicals in layers that oxidize the surface. Finally, heat the surface with a torch, and coat with carnauba wax.