September 26, 2011 Part 4: The Process of Bronze – Casting
Now we’ve made it to actual bronze casting, the most intriguing step in the foundry process, where the term “lost wax casting” comes from. To read earlier installments, click here:
Bronze ingots are placed in a large crucible.
The crucible is placed in a furnace where the ingots will be melted to a temperature of approximately 1900 ° F.
The wax, encased in ceramic shell, is heated in a kiln (below). The wax is melted out, leaving an empty ceramic mold ready to receive the molten bronze.
The ceramic molds are placed in sand beds that keep the molds upright.
A highly choreographed and careful team sets up to pour the molten bronze.
The bronze will cool inside the ceramic mold.
As the bronze cools, the mold will even begin to split due to the change in temperature.
Bronze hammers and mallets are used to carefully chip away the ceramic shell.
Everything that was wax is now bronze, including the sprues or channels shown below on the left. This is an example of Man I (a tall sculpture), which is about 6′ tall once assembled.
The rough bronze casting is fully revealed and sprues are carefully removed. Below, chasing tools are used on a medium size sculpture, Man Study. “In the finishing area, opaque barriers shield the eyes from welding torch sparks. This is where pieces are meticulously matched to the original, and any deviations are carefully reworked to reconcile the finished piece to the artist’s initial intent. In this way, every piece, even in a series, is truly an original.” (an excerpt from Tom Corbin The Inevitable Artist by Beverly Bellinger).
Most sculptures larger than about 20″, depending on the form, are cast in several parts. Skilled artisans at the foundry will carefully weld the pieces together leaving no visible seam.
Woman I is being assembled below.
Once the sculpture is fully assembled and chased to replicate the original, the next step is to get a completely uniform surface so that the surface can accept the patina.
Man on Diving Board Study is shown below.
Using small beads (like sand), the surface will be blasted to remove any dirt or oil.
Read the full excerpt from our book HERE.
See the finished work featured in this post by clicking below. The final step, Patina, will be revealed next time.
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