Investment Casting the Sculpture in Bronze
The life-size clay model
was finally moved to the art casting foundry at Beacon Fine Art Foundry, where the standard processes of invest- ment casting were followed from mold creation, wax pat- tern
creation and rework,
through to final casting and shakeout. While the general steps of the lost-wax casting process are universal to most investment
casting profes-
sionals, there are some adap- tations to each that are unique to art casting.
Making the Mold Using the life-size clay
model as the core around which the mold would be fit- ted, the bronze casting arti- sans at Beacon Foundry and I began to fabricate the mold that would later be used to create the wax pattern. The clay model itself is gently coated with a silicone coat- ing, then followed by either additional silicone layers or a heavier semi-liquid rubber that later solidifies to a soft but self-supporting consis- tency. The outer molds are typically made of hard plaster (as in this case) and serve to contain and support the soft- er “inner mold” layers that come into direct contact with
the clay model inside. Once the soft inner mold layers of silicone and rubber have suf- ficient time to “set,” the en- tire mold is gently opened to remove the clay model core. This creates a “negative” or void of the sculpture which will then be used to fashion the wax pattern.
Wax Pouring and Rework
Into this first mold, mol-
ten pattern wax is painted across the entire inner surface of the mold to ensure the in- tricate details of the figure are evenly coated. After the first layer of wax is applied, the follow-on additions of molten pattern wax are more
liberally applied. Wax contin- ues to build in layers until the desired thickness is reached. This hollow wax copy of the original clay model is care- fully removed from the mold and re-worked. Re-working is fixing any imperfections in the wax pattern that may have occurred in the first mold cre- ation, so that the wax pattern ultimately matches the clay model sculpture in exact de- tail.
Gating A carefully planned and
calculated gating system made up of wax-tubing is attached to the wax sculpture, typically focused on the shortest travel distance for molten cast metal to flow while the air displaced by the incoming molten met-
Figure 5 – Partial Wax Pattern 20
Figure 6 – Bronze figure before patina September 2012
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