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Casting from Wax to Bronze
Lost Wax Ceramic
Shell
Abstract Sculpture
Reclining Nude
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Lost-Wax &
Ceramic-Shell Processes: Click Here
to see the difference between lost wax and ceramic shell.
"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 runs high, because
all of the time, cost, and preparation could be for naught, if even
one of the steps goes array.
Conceiving and setting an artistic design in clay or
wax is only 1% of the total time taken to finish a bronze sculpture.
The other 99% is just hard work." Nannette
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Lost-wax process in 8
steps.
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1) Affix wax sprues to
a wax image. Many sprues are use to ensure that, during the pour, the liquid bronze
reaches all areas of the piece. Above, is
Balance, in wax; see the finished bronze in the last frame. |
2)
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. This thick coating must harden before going
into the kiln. |
3) Molds are placed upside-down in the
kiln;
the kiln's temperature is adjusted and watched for three days, while the
melting wax slowly drips out, leaving negative space for the liquid bronze
to flow. |
4) After 3 days in the kiln,
the molds are taken out, turned right-side up, and
immediately placed in a sand pit; extra sand is added and packed around each unit, to keep the molds from cracking,
during the pour. |
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5) The crucible
is filled with solid-bronze ingots, that are melted in the green
furnace, shown in Step 6. The ingots melt to a hot-liquid. |
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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7) The investment needs to cool, before
the sand mixture can be
cracked, chipped, and washed away; sprues are cut off the piece,
Balance. |
Balance,
1982, 15"x16"x8"
8)
The 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 sucess using the lost-wax 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. The complicated sprue network, in Step 1, and the
larger investment unit, in Step 2, were challenging.
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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
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 a simple thin "shell," made of
a silicon
mixture, covering the sculpture and sprues.
Step 2: The shells are heated
with a blow torch, and the wax melts out in minutes, dripping into a
receptical. This
wax "burn out" creates the needed negative image (the
empty spaces in the shape of the sculpture and sprue system) inside the investment
shell.
Step 3: The
empty-silicon shell is then
placed upside-down and put in the kiln on its pouring spout,
to allow any 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.
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