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Casting from Wax to Bronze
Lost Wax Ceramic Shell
Abstract
Sculpture
Lost-Wax Process |
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Attending a bronze
"pour" can be an exhilarating experience for any artist or collector.
The piece comes alive when the molten bronze is poured into the negative
space of the investment "mother mold." Anticipation is high because if something
goes wrong, all the time, cost, and preparation spent could be for naught.
Presented here is a short explanation of the lost-wax casting process:
Click Here
to see the difference between the lost wax and the ceramic-shell
processes. |
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Wax sprues are attached to the wax image,
Balance,
to ensure that enough liquid bronze gets to all points of the piece, during the pour.
See the finished piece in the last frame.
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Make a "mother mold." The
wax unit (image and sprues) is
placed in a large container that is filled with a mixture of sand and
plaster, called investment. |
Molds are placed upside-down in the
kiln;
wax drips out slowly leaving negative space for the liquid bronze. |
After 3 days in the kiln,
the molds are placed in a sand pit; and
sand is put around each unit, to keep the molds from cracking during the pour.
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The crucible
is filled with bronze ingots, that are melted into hot-liquid. Melting
took place in the green
furnace shown in Step 6. |
The liquid
bronze is slowly poured into each mold, via the hollow openings
created when the wax sprews melted, in Step 3.
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Investment unit must cool, before
the sand mixture can be
cracked, chipped and washed away; sprues are cut off the piece,
Balance. |
Balance,
1982, 15"x16"x8"
Bronze surface is sanded and refined; a patina is applied;
sculpture is affixed to its base. |
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By 1982, Nannette had produced many small bronze-abstract sculptures and
enjoyed the casting process (described above). Her first pieces were
3 to 5 inches tall, making this time-consuming process manageable, and a
perfect learning exercise. With Balance, Nannette tripled
the measurements, and the work involved was daunting, since the sprue network, in Step 1, and the investment unit, in Step 2, needed to be on a much larger scale.
Back to top
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Waves
1980, 2.5"x4"x2"
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Godiva
1982, 5"x5"x3" |
Déjà Vu
1980, 4"x3"x2" |
Aerobic
1982, 5"x4"x4" |
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Ceramic-Shell Process |
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The major difference, between the
ceramic-shell and lost-wax processes, is the investment that creates the
mother mold (steps 1, 2 and 3 in lost-wax process).
The photo to the right, finds Nannette preparing her wax
sculptures for a ceramic-shell pour in 1988, and illustrates the
following:
Step 1: The
system of sprues is much less
complicated. The investment molds are simply a "shell," made of
a silicon
mixture, covering the sculpture and sprues.
Step 2: The shells are placed over a large water pan and heated
with a blow torch; the wax melts in minutes and drips into the pan. This
wax "burn out" creates a negative image inside the investment unit (the
empty spaces in the shape of the sculpture and sprue system).
Step 3:
The silicon shell is then
turned over and put in the kiln on its pouring spout,
to allow the excess wax to evaporate, while keeping it warm for the
pour.
In contrast, the lost-wax process
requires the wax to "burn out" (evaporate) in the kiln for 3 days. The kiln’s temperature
builds slowly to 1,200 degrees Fahrenheit. Then the temperature is
slowly lowered to keep the investment from cracking.
"One can see that conceiving and setting an
artistic design in clay or wax is only 1% of the total time worked on a
finished bronze sculpture. The other 99% is just hard work."
Nannette |
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