The lost wax process of casting bronze follows a series of careful steps. First, the artist models the art work in clay. Then, she delivers it to a foundry and works with a team of fabricators. They create a mold over the clay. The mold may be plaster or a rubbery material covered with plaster. When plaster covers a softer material, it's called the mother mold.
Next, they break open the mold and paint the inside with a layer of wax. Then, they put the mold back together and pour in more wax. They swish the wax around so it covers the entire inner surface of the mold. When the wax is cooled, the hollow wax from is removed from the mold. It is important to examine the wax shape very carefully at this point and correct any flaws. The final casting will look exactly like the wax.
Now the fabricators attach a funnel with gates on it to the open end of the wax form. They dip the form in a tank of liquid clay about ten times. The clay covers the form inside and out, making a shell around the wax.
Next, they place the piece in an oven, also called as a burn-out kiln. As the wax melts, it pours out of the funnel through the gate. This is why the process is called lost wax. The clay shell bakes for several hours until it becomes really hard.
While the clay or ceramic shell is still glowing hot, the molten bronze is poured in to the shell, filling in the space left by the lost wax.
Finally, the fabricators chip away the ceramic shell, remove the gates and the funnel. The bronze sculpture is hollow and about 1/4 inch thick.
The sculpture is chase or finished using files and sand papers. A special surface treatment called a patina is created using chemicals and a blow torch.
The artwork has finished its journey from clay, plaster and wax to a metal form that will last for centuries.