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Lost Wax
Casting Process Most detailed are cast using the “Lost Wax”
process. This is the most precise metal casting technique in existence,
ensuring accurate reproductions of the original sculpture and exquisite
detail. All bronze pieces are cast from a wax model regardless of
the original material the model was sculpted in usually in clay
or wax. “Lost wax” casting method was found in thousand years ago.
Even though, modern methods and materials have improved the technique.
It is still an extremely labor intensive and expensive process.
Step 1:
Making the mold from original sculpture
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This step
is the most critical. The mold is cut into sections for casting,
depending on the size and design of the sculpture. All detail
of the original must be captured and transferred in the mold,
if not, it will be difficult to replace the detail in any other
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We create rubber
mold by covering the original with a layer silicone or latex. When
the rubber is completely set, we make fiberglass or resin shell,
called “Mother Mold”, in order to support the rubber for the wax
pouring process. Fiberglass mold is durable and light. Now, it is
ready to receive the wax.
Step 2: Making the wax
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First
layer of wax is applied by painting into the rubber mold to
capture fine detail.
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| The mold is
put together and more hot wax is poured in. It is then rotated
until wax is achieved a thickness of 1/8 to 3/8 of an inch all
over the mold.Then, the excess wax is poured out. |
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After
the wax has completely cooled, the rubber mold is pulled away
from the wax. Wax casting will have some imperfections such
as seam lines or bubbles.
Then wax duplicate is to be repaired and finished to the sculpture’s
specifications. Using a variety of tools and hot soldering
irons, mold lines will be removed and any parts reattached.
The wax is will look exactly like the original work.
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Step 3:
Gates
Wax rods,
called “gates” or “sprues”, are attached to critical points on the
piece and the entire gated piece is affixed to a central wax “cup”.
Prior to creating a ceramic shell, vents are attached within the
wax model. These vents are necessary in difficult areas where gas
may accumulate such as hips, limbs, and neck. When the wax is “lost”,
these gates will become the avenues for the molten metal to flow
into the piece. The vents allow the gas to escape when the molten
bronze is poured and will prevent air pockets from forming and exploding
the ceramic shell.
Step 4:
Casting the Shell (Investment)
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The Plaster
shell is one of the few materials that can withstand the heat
of molten bronze.
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The wax
casting is dipped into the powder plaster sand. After this
first layer, several layers will be applied, called “Investment
Casting”. This repeated step increases the coarseness of the
material to create the shell. Between each dip, the layer
must dry before another layer can be applied.
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Step 5: Burn-out
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The shell
is placed up side down in fired. The shell bakes and the wax
is melted from the shell (“Lost wax”). This creates a hollow
shell mold.
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Step 6:
Casting
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The shell
is removed from the fire and immediately the molten bronze
is poured into the shell.
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Step 7:
Break-out
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After
the casting has cooled several hours, the shell will be carefully
removed with hammer. The shell is chipped off and a rough
casting is removed.
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Step 8:
Assembly
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Spures
will be cut off and extensive sand blasting will be performed
in order to weld it all back together. Reassemble will take
place in the welding area by carefully realigning and refitting
the pieces.
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| The
bronze must now be repaired and finished. All the weld marks
are chased and re-detailed to transforms the rough casting into
a finished work of art. Any imperfections such as air pockets
or pits must be brazed with bronze rod, as in welding. |
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Step 9: Finishing and coloring
(Patina)
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The raw
bronze sculpture is now hand polished in preparation for the
“Patina”. The natural bronze has a dull finish. Since bronze
comes in a variety of alloys, the patina requires different
chemicals and techniques to achieve variety color and look.
Chemicals, pigments, heat, and a lot of experience are involved.
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a coating of wax is applied to the surface while it is hot in
order to ensure durability of color and finish. This serves
to protect the surface from oxidation and also gives the finished
bronze its luster. |
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