MOLTEN BRONZE AND THE MOMENT OF TRUTH
The wax burnout leaves a hollow mold, completely devoid of wax and ready to accept the molten bronze. After close examination for any cracks, and patching if necessary, the ceramic shell mold is returned to the kiln and brought up to approximately 1400 degrees Fahrenheit. At Studio Foundry, this is a time of reverence and concentration. The work of art has been through numerous, complicated and time-consuming steps to reach this one, critical moment in time. After the wax burnout and before the bronze pouring, the sculpture no longer exists, as an object, and is defined only by its absence in the casting mold.
While the casting molds are being heated in the kiln, the forced air, gas fired furnace is lit. A silicon carbide graphite crucible, inside the furnace is charged with bronze ingots. The composition of bronze used at Studio Foundry is 95% copper, 4% silicon and 1 % manganese. It is called Everdure Silicon Bronze. In order to know what quantity of metal is required for this pouring, a wax weight to metal weight formula is used. The ratio for bronze is approximately ten pounds for every one pound of wax.
As the bronze ingots in the furnace begin to melt, more ingots are added, charging the crucible until the desired amount is achieved. Fluxing agents, which enhance the pour and trap impurities, are added toward the end of the melt. The metal is then watched closely as it reaches the appropriate temperature for pouring, which for Everdure bronze is between 1940 and 2050 degrees Fahrenheit. The desired pouring temperature is estimated for each mold, based on various characteristics unique to each sculpture to be poured. When the bronze reaches the required temperature, the ceramic shells are removed from the hot kiln, and carefully placed on a bed of sand, stabilized with the pouring cups straight up.