Bronze Casting

When I was a sculpture major at The Cooper Union in New York City,  I spent several years casting bronze using the lost wax process.  I was enamored with the intricacy of the arcane workmanship, with the beauty of the molten metal flowing out of the crucible, and with the industrial magic of creating  a lustrous piece of art in bronze that would last for eons.

Bronze objects have been cast using the lost wax (cire perdue) process for at least 5,000 years. This alloy of tin and copper is revered for it’s beauty and durability, and is an ideal material for permanent outdoor sculpture.

A one-of-a-kind steel, wood or clay piece is just that, one. After the work that goes into producing a unique piece it gets sold and it’s gone. Casting in bronze enables the artist to duplicate the original piece by producing a limited edition of bronzes.  Much the same as a print maker making an edition of lithographs or etchings.

To create a bronze there is significant labor and cost involved in the mold making and casting process as well as in the finishing work and patina.

A bronze edition can run anywhere from 1-20 bronzes, although I have heard of some artists casting up to 100.  Each sculpture is labeled 1/10, 2/10, etc, to identify both the number within the edition and the total amount of pieces in the edition.

The production process is laborious and complicated.  A silicon or  plaster mold is made from the original piece of sculpture. Then one wax copy is made from the mold for each of the bronzes to be cast.  The wax copy is then gated and vented, which means wax rods are added to provide a way for the molten metal to reach the inside of the mold and an avenue for gases to escape.  The completed wax is now invested inside of a refractory plaster material which completely covers it leaving only a small cup shape on  the top which will become the spot for the molten bronze to be poured into the mold. The entire invested structure now goes into an oven where the wax is melted away leaving a perfect impression in the investment medium. Hence the term, lost wax.

Bronze is melted down in a crucible and once molten, poured into the waiting mold. After the metal cools and hardens, the refractory mold is broken apart and discarded leaving the sculpture surrounded by a web of what are now solid bronze gates and vents which must be cut away and reused on the next pour.

The piece is then chased, meaning the surface is sanded and finished, and a final patina applied using heat and chemicals that form a permanent coloration on the surface.