Techniques and Processes
Lost-Wax Bronze Casting
The Finished Bronze
The finished bronze is then waxed or lacquered to protect the surface from any further oxidation, keeping the patina stable for many years to come
The Original Sculpture
The original sculpture can be made of any material, but most sculptors prefer to work in oil based clay or wax.
Mold Making
In order to prepare the sculpture for molding, it is usually cut into pieces. Those pieces are then painted with several layers of liquid rubber to capture the surface detail, and then covered with a plaster shell material in order to preserve the form.
The Wax Pattern
The original sculpture is then removed from the finished mold. By building several layers of hot wax inside the rubber mold, and pouring out the excess wax between layers, a hollow wax copy of the original is made.
Wax Chasing
Thorough attention is given to refining the wax pattern so that it exactly matches the original. This process is referred to as "wax chasing".
spruing
The wax pattern is then sprued and mounted on a wax cup. The red sprues (solid wax rods) serve as gates and vents later in the casting process.
The Ceramic Shell
The wax is then dipped into a slurry tub and coated with ceramic slurry. While still wet, it is then coated with sand to build up the layer of ceramic shell. This process is repeated, and between each of the coats, the shell must dry.
Burn Out
The dry shell is then placed into a burnout kiln where the shell is cured and the wax pattern is melted out. This is where the term "lost wax" comes from. Each time a piece is cast, a new wax pattern must be pulled from the rubber mother mold.
The Bronze Pour
The shell is then ready to receive the molten bronze. It is poured at a temperature of about 2000 degrees Fahrenheit.
Removing the Shell
Once the bronze is cooled, the shell is manually removed from the metal, usually by sandblasting.
Metal Chasing
The now bronzed gates, vents and cup are then removed and the cast parts are welded back together. The weld lines are tooled out and any imperfections in the metal are corrected.
Sandblasting
The reassembled and tooled sculpture is then sandblasted to clean the surface and prepare it for patina.
Patina
The completed metal sculpture is then heated with a torch and the patina is chemically applied to the surface, sometimes in many layers. The color achieved through this subsurface oxidation is referred to as "patina".
The Finished Bronze
The finished bronze is then waxed or lacquered to protect the surface from any further oxidation, keeping the patina stable for many years to come
The Original Sculpture
The original sculpture can be made of any material, but most sculptors prefer to work in oil based clay or wax.