The Bronze Medium: Lost-Wax Bronze Sculpture Method
This ancient lost-wax method of creating bronze sculptures requires many tedious steps. Along with the original inspiration and talent of the sculptor, the perfection of the final piece relies on the artistic skill of the foundry workers. Learn more about lost-wax bronze casting at Wikipedia.
McEwen, the bronze sculptor, began the process by fashioning a rough foundation. For the Willis Whitfield statue, a larger-than-life piece, he started with a metal rod armature and added styrofoam to develop the general size and shape of the piece. Then he began applying clay to the structure. McEwen continued building up the clay until it became the recognizable form of a man. Using his artistic skills, McEwen carved the clay to bring out the intricate details that transformed the generic man into Willis Whitfield. When satisified with his work, McEwen carefully transported his sculpture to a foundry.
At the foundry, a mold was made by meticulously painting a thin coat of silicone rubber over the clay. Increasingly thicker rubber coats were applied. For large sculptures like this, there were numerous sections in the mold which allowed it to be pulled away from the clay sculpture. Plaster was applied to strenthren and stabilize the rubber mold.
The mold sections were taken to the wax room where hot wax was poured into and out of each several times, building up a wax coating. The wax coating was allowed to cool. Then a wax chaser cleaned up the seams and imperfections and attached wax vents and feeder tubes called sprues and a wax cup base. The wax sections were submerged in a liquid ceramic called slurry, and sand was added to create a shell. This was repeated six or seven times, and the cup base was drilled to allow the wax to melt out later.
The shells were then heated in a furnace to harden and the wax was melted out, leaving an exact replica of the artist's original clay sculpture. The shells were allowed to dry and tested for leaks. When ready, the shells were heated again to prevent shattering when the bronze was added. Bronze ingots were melted and the molten bronze was poured into the shells. Then the shells were allowed to cool.
The slurry shell was chipped away revealing the bronze sections, and the sprues were cut off. Metal workers welded the bronze pieces together and used a variety of bits to smooth the welds and make the piece match the look and texture of the original artwork. The statue was then polished until shiny with no trace of the joints or casting.
To finish with the artist's chosen color, the sculpture was treated with sulfur, scrubbed and rinsed. Then ferric nitrate was added with a brush and heated with a blow torch to create the final patina. The competed bronze sculpture was then coated with lacquer and wax for protection and was ready for placement at Sandia Labs, in Albuquerque, New Mexico.