My Bronze Limited Editions are cast using Silicon Bronze; an alloy composed of 94% copper, 4% silicon, 1% manganese and traces of other elements such as iron. Since it’s development in the 1920’s, Silicon Bronze has been the discerning artist’s choice for fine art sculpture castings because of its resistance to corrosion, its strength and its resilience. My editions are cast from the original clay sculptures using the “Lost Wax” casting process. The steps are as follows:
- Obtaining The Source Rubber Mold
- First, a high quality rubber mold is made of my original clay sculpture by the application of multiple layers of rubber to the sculpture over several days. When the rubber dries, a reinforced plaster mold is made around it to prevent distortion and damage when it is removed from the clay sculpture. For my sculptures, the clay original usually does not fare as well and is destroyed during this process. The rubber mold is a “negative” of the original which was a “positive”, and is used to create a wax positive for each item in the edition. When all items of the edition have been cast the rubber mold is destroyed.
- Creating The Wax Positive
- For each sculpture in an edition, hot wax is poured into the rubber mold and slushed around until it evenly coats the interior of the mold. This process is repeated a number of times, using cooler wax each time so that the previous coat of wax is not melted. This results in a near perfect reproduction of the original sculpture. The edition item number (as item number/edition total) is carved into each wax positive, any imperfections are repaired and finishing touches may be sculpted here and there using heated tools – making each item of the edition unique.
- Investment is the process by which a rock-hard ceramic shell is built around the wax positive. First, the wax positive is alternately dipped into slurry followed by a bath of sand and allowed to dry. This process is repeated about 9 times. Then the wax is melted out in a high pressure steam chamber (autoclave). Hence the name “lost wax” process.
- The Pour
- A crucible, fired by a furnace is filled with bronze ingots which are then melted. Concurrently, the ceramic shell is heated up so that there is no cooling of the bronze during the pour. The molten bronze is then poured into the heated shell.
- Devestment and Finishing
- After the item has cooled, the ceramic shell is removed by hammer and chisel, with a finishing sand blasting step. The sculpture is left to cure for about two weeks.
- Patination is the enhancement of bronze by the torch enhanced chemical application of color. The patina of each edition has been carefully chosen such that it enhances the lines and mood of the piece. The patina is applied after the curing step.
As you can see, bronze casting is a labor intensive process. Depending upon the edition, it can take from four to six weeks.