BRONZE SERVICES "Lost Wax Casting" PROCESS
Step 1 MODEL MAKING
An artist creates an original model from wax, clay, or another organic type material. Wax and oil-based clay are often preferred because these materials
retain their softness. This original art work will then be molded, so multiple editions can be made.
An artist creates an original model from wax, clay, or another organic type material. Wax and oil-based clay are often preferred because these materials
retain their softness. This original art work will then be molded, so multiple editions can be made.
Step 2 MOLD MAKING
Once the 'original sculpture' is completed by the artist, a mold is made. A high quality silicone rubber mold with a fiberglass or plaster case is made to
capture all the detail of the clay original. The mother (plaster) mold is important because it supports the flexible rubber. Molds are typically 2 parts,
including a shim with keys placed between the two halves during construction so that the mold can be put back together accurately. Sometimes many
molds are needed to recreate the original sculpture, especially for larger pieces. The mother mold is kept in order to make multiple castings, limited only
by the durability of the mold.
Once the 'original sculpture' is completed by the artist, a mold is made. A high quality silicone rubber mold with a fiberglass or plaster case is made to
capture all the detail of the clay original. The mother (plaster) mold is important because it supports the flexible rubber. Molds are typically 2 parts,
including a shim with keys placed between the two halves during construction so that the mold can be put back together accurately. Sometimes many
molds are needed to recreate the original sculpture, especially for larger pieces. The mother mold is kept in order to make multiple castings, limited only
by the durability of the mold.
Step 3 WAX POURING
Once a mold has been made, the foundry begins with the wax pouring. If the mold is extremely detailed, a special layer of wax is painted directly onto
the mold first to capture every detail of the original. Another method is filling the entire mold with molten wax, pouring out the wax, and repeating this
process until the desired thickness of 3/16" is reached. The excess wax is poured out, the mold is turned upside down and the wax layer is left to cool and
harden. After the wax has hardened, the molds are carefully pulled apart and the wax is removed from the mold.
Once a mold has been made, the foundry begins with the wax pouring. If the mold is extremely detailed, a special layer of wax is painted directly onto
the mold first to capture every detail of the original. Another method is filling the entire mold with molten wax, pouring out the wax, and repeating this
process until the desired thickness of 3/16" is reached. The excess wax is poured out, the mold is turned upside down and the wax layer is left to cool and
harden. After the wax has hardened, the molds are carefully pulled apart and the wax is removed from the mold.
Step 4 WAX CHASING
Wax chasing is the next step in the process. Artisans use a heated metal tool to clean up air bubbles and parting lines or flashing where the pieces of
the mold came together. This step is to ensure the wax reproduction is as close to the original as possible. Wax pieces that were molded separately
can be heated and attached; often using registration marks to indicate exactly where they go.
Wax chasing is the next step in the process. Artisans use a heated metal tool to clean up air bubbles and parting lines or flashing where the pieces of
the mold came together. This step is to ensure the wax reproduction is as close to the original as possible. Wax pieces that were molded separately
can be heated and attached; often using registration marks to indicate exactly where they go.
Step 5 SPRUING AND GATES
The waxes then go to the spruing department where tubes of wax are melted to the original wax that will provide paths for molten casting material to
flow and for air to escape. The carefully planned spruing usually begins at the top with a wax "cup" which is attached by wax bars to various points on
the wax copy. Plugs and or core holes are now cut into the wax during sprung to help in the next step of the process which is the shell room.
The waxes then go to the spruing department where tubes of wax are melted to the original wax that will provide paths for molten casting material to
flow and for air to escape. The carefully planned spruing usually begins at the top with a wax "cup" which is attached by wax bars to various points on
the wax copy. Plugs and or core holes are now cut into the wax during sprung to help in the next step of the process which is the shell room.
Step 6 CERAMIC SHELL
Once the waxes are sprued, they are now moved into the shell room. Each piece is then dipped into a slurry of colloidal silica and coated with sand. The
slurry and grit combination is call the the ceramic shell. This shell is allowed to dry, and the process is repeated several times. The bigger the piece, the
thicker the shell.
Once the waxes are sprued, they are now moved into the shell room. Each piece is then dipped into a slurry of colloidal silica and coated with sand. The
slurry and grit combination is call the the ceramic shell. This shell is allowed to dry, and the process is repeated several times. The bigger the piece, the
thicker the shell.
Step 7 BURNOUT/TESTING/PATCHING
The next step is the burnout or dewaxing process. The ceramic shell-coated piece is placed cup-down in a kiln and is fired around 1300 degrees fahrenheit.
The heat hardens the silica coatings into a shell, and the wax melts and runs out leaving a hollow cavity where the wax once was. The melted wax can be
recovered and reused. This is where the term "LOST WAX" casting gets its name. Now all that remains of the original artwork is the negative space, formerly
occupied by the wax, inside the hardened ceramic shell.
Once the ceramic shell is allowed to cool, the pieces are tested to see if water will flow out. Water is used to rinse the shell of any debris. Cracks or leaks can
be patched at this time with thick refractory cartable-mortar.
The next step is the burnout or dewaxing process. The ceramic shell-coated piece is placed cup-down in a kiln and is fired around 1300 degrees fahrenheit.
The heat hardens the silica coatings into a shell, and the wax melts and runs out leaving a hollow cavity where the wax once was. The melted wax can be
recovered and reused. This is where the term "LOST WAX" casting gets its name. Now all that remains of the original artwork is the negative space, formerly
occupied by the wax, inside the hardened ceramic shell.
Once the ceramic shell is allowed to cool, the pieces are tested to see if water will flow out. Water is used to rinse the shell of any debris. Cracks or leaks can
be patched at this time with thick refractory cartable-mortar.
Step 8 PREHEAT AND METAL POURING
Metal pouring begins with the shell being reheated in the kiln to roughly 1700 degrees to harden the patches and remove all traces of moisture. While hot,
the shells are placed cup-upwards into a large tub filled with sand. While the shells are being reheated, bronze ingots have been melted in a silicon carbide
crucible by a natural gas powered furnace to approximately 2000 degrees. Once the molten bronze reaches the desired temperature, it is carefully poured
into each shell. If the shell was not hot, the temperature difference would shatter it. The filled shells are then removed from the sand and allowed to cool.
Metal pouring begins with the shell being reheated in the kiln to roughly 1700 degrees to harden the patches and remove all traces of moisture. While hot,
the shells are placed cup-upwards into a large tub filled with sand. While the shells are being reheated, bronze ingots have been melted in a silicon carbide
crucible by a natural gas powered furnace to approximately 2000 degrees. Once the molten bronze reaches the desired temperature, it is carefully poured
into each shell. If the shell was not hot, the temperature difference would shatter it. The filled shells are then removed from the sand and allowed to cool.
Step 9 RELEASE
After the bronze cools for several hours, the ceramic shell is hammered, chiseled, and sand-blasted to release the hard shell. The sprues, which are also
recreated in metal are cut off to be reused in another casting.
After the bronze cools for several hours, the ceramic shell is hammered, chiseled, and sand-blasted to release the hard shell. The sprues, which are also
recreated in metal are cut off to be reused in another casting.
SteP 10 WELDING
Now the pieces are moved into the welding area. Welding is the process used to join the metal pieces. All the different sections are welded back together
and the resurfacing of all the textures begins. This process is time consuming and requires a lot of patience, precision and skill.
Now the pieces are moved into the welding area. Welding is the process used to join the metal pieces. All the different sections are welded back together
and the resurfacing of all the textures begins. This process is time consuming and requires a lot of patience, precision and skill.
Step 11 METAL CHASING
Just as the wax copies were chased, the casting is worked until the telltale signs of the weld seams and/or flashing are removed with the goal of the piece
looking exactly like the original model. Pits left by air bubbles in the casting, and the stubs of spruing are filed down and polished. Smoothing and/or texturing
the piece is also part of the metal chasing process.
Just as the wax copies were chased, the casting is worked until the telltale signs of the weld seams and/or flashing are removed with the goal of the piece
looking exactly like the original model. Pits left by air bubbles in the casting, and the stubs of spruing are filed down and polished. Smoothing and/or texturing
the piece is also part of the metal chasing process.
Step 12 PATINA AND BASING
The final casting is now ready for patina. Patina is the chemical coloration of the surface of the bronze, depending
on the desired effect. First, the bronze will be sandblasted and then may be wire brushed, rubbed with steel wool and/or an abrasive pad. Then the bronze will
be heated with a torch and chemicals will be applied to the surface. The casting may be coated with a variety of different compounds such as oxides, carbonates,
sulfides, sulfates or even paints. The reaction of the chemicals on the heated bronze will deposit a layer of oxides on the surface of the casting creating different
colors. The use of different chemicals will result in different patinas. After the layer of oxides is complete, a coat of wax and/or lacquer may be applied to seal the
patina from further oxidation. The piece should be waxed at least once a year to extend the life and appearance of the final bronze sculpture.
The final casting is now ready for patina. Patina is the chemical coloration of the surface of the bronze, depending
on the desired effect. First, the bronze will be sandblasted and then may be wire brushed, rubbed with steel wool and/or an abrasive pad. Then the bronze will
be heated with a torch and chemicals will be applied to the surface. The casting may be coated with a variety of different compounds such as oxides, carbonates,
sulfides, sulfates or even paints. The reaction of the chemicals on the heated bronze will deposit a layer of oxides on the surface of the casting creating different
colors. The use of different chemicals will result in different patinas. After the layer of oxides is complete, a coat of wax and/or lacquer may be applied to seal the
patina from further oxidation. The piece should be waxed at least once a year to extend the life and appearance of the final bronze sculpture.
Step 13 DELIVERY AND INSTALLATION
As large pieces are completed they are often delivered to their destination and installed by the foundry.
As large pieces are completed they are often delivered to their destination and installed by the foundry.
Bronze Services of Loveland, Inc.
140 2nd. Street SE, Loveland, CO 80537
970.667.2723
140 2nd. Street SE, Loveland, CO 80537
970.667.2723
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