The origin of the lost-wax process of metal casting, called cire perdue, dates back to the Bronze Age. This process was introduced over four thousand years ago and is enlisted to capture the original clay sculpture in bronze. Although materials have improved and new technology is employed, each step of the process of casting bronze today is the same as that used thousands of years ago, and requires uniquely skilled professionals to execute.

Creating the Sculpture in Clay

The first step involves creating the initial sculpture in clay. Teresa typically uses oil-based clay in the creation of a bronze work of art. The timing for sculpting a piece in clay is dependent on factors such as size, specific details of the project and client input.

Making the Mold

The original sculpture is coated with rubber supported with plaster, which is done by encasing the original sculpture in rubber applied in layers. Most sculptures require several parts to the mold. For instance, the head might be one part of the mold, and an arm another. The original is now removed from the mold leaving the negative space inside.

Pouring and “Chasing” the Wax

Wax is poured into the mold and then poured out evenly coating the interior walls of the mold. About three coats of wax will make a hollow wax replica of the original sculpture. After cooling, this hollow wax replica is removed from the mold and any surface imperfections in the wax are corrected. This part of the process is referred to as “wax chasing”.

Making the Ceramic Shell

The wax replica is then sprued and gated. In this step a wax pouring cup, wax rods or “sprues” that will later serve to guide molten metal into the piece, and air vents to release air when the metal is poured, are attached to the wax replica. This engineering process is to prepare the piece for the bronze pour.   Now an investment, or a “ceramic shell”, is applied to each wax by dipping it into a heat resistant liquid, or “slurry”, and then coating it with a heat resistant sand or “stucco”. Each of the 6 to 12 coats must be completely dry before the next coat is applied. Extremely fine sand is used in the initial coats to capture small detail.

Pouring the Bronze

After the ceramic shell is fully dry, the piece is inverted and placed in a kiln at 1800 degrees, which hardens the shell. The wax melts and pours out of the ceramic shell. This empty ceramic shell is placed in a sand pit with the pouring cup at the top. Molten bronze heated to 2200 degrees is poured into the cup and down through the “sprues” into the cavities of the shell.

The Welding and “Metal Chasing”

After a cooling period the shell is broken away revealing the bronze casting. The next stage is metal chasing out any imperfections. During this “metal chasing” step sprues are cut off, and the sculpture is sand blasted. Any parts that were cast separately are welded back together.

Coloring the Bronze or “Patina”

The final step is coloring the bronze. Various compounds are brushed or sprayed onto the metal to create the “patina”. Different formulations are applied using hot and cold techniques used to create a variety of colors.

This multi-step intricate process takes approximately twelve weeks.  Each step is important to make certain that goals outlined in the beginning are met with accuracy and precision. As a result every piece is a unique combination of the Teresa’s creative skills and the work done by the professionals at the foundry.