LOST WAX PROCESS
LOST WAX PROCESS
Generations old, the “Lost Wax” process dates back approximately six thousand years. Because of the durability and longevity of this art form, we like to say that one never really owns a bronze, but rather acts as a caretaker on its long journey through time and linage.
ADMIRAL CHESTER WILLIAM NIMITZ CAST IN BRONZE BY RIP CASWELL AND OUR TEAM
1. CREATION OF THE ORIGINAL
The Admiral Nimitz sculpture began with Caswell’s contact with the Naval Order of the United States. The design began to formulate in Caswell’s mind during the early discussions with the client and as he studied Nimitz’s life and images.
As usual with his monument work, Caswell worked from the inside out. He used foam to create the armature onto which the sculpting clay would be applied. Once the armature was constructed, the artist built up layers of clay and created every detail and every gesture through carving and sculpting. As a result he was able to reflect the Admiral’s personality and physical character. As the clay shape was refined, the fine surface features were sculpted into the clay, such as veins, stitching and uniform emblems. This process took Caswell several months to complete.
2. MAKING THE MOLD
In preparation for the casting process, the Admiral’s final clay figure had to be cut into multiple sections to be individually molded and cast. The number of sections into which a monument sculpture is divided depends on the size and complexity of the artwork. In this case, the sculpture was cut into more than a dozen pieces for the molding process.
The Admiral’s metamorphosis from clay to bronze began by applying a silicon rubber mold in two hemispheres to each cut section of the Nimitz sculpture. The liquid rubber, applied by the mold maker, captured all of the sculpture’s details, even fingerprints left by the artist, into a negative impression.
This mold was then encased in a plaster “mother” mold. This enabled the form to be held in place without distortion by the flexibility of the rubber. This two part mold was crafted to be used more than once. The two copies of the sculpture could then be cast; one for Pearl Harbor and one for Fredericksburg, Texas.
3. PULLING WAX PATTERS AND CHASING
After removing the mold from the original clay sculpture pieces, wax was than heated to approximately 200 degrees Fahrenheit. It was then poured into the rubber mold, creating a thin coating. This first “hot” layer filled in the fine details. The subsequent layers of slightly cooler wax (160-180 degrees) were poured in to bulk up the wax pattern until it was 1/8 to 3/16 of an inch thick. After the cooled positive wax patterns were pulled from the mold, the foundry’s skilled artisans hand finished or “chased” the patterns. As a result each of the sculpture’s originally sculpted details and textures were revealed.
4. CREATING THE GATING SYSTEM
After the wax was chased, a gating system was engineered to provide the channels in which the molten bronze traveled when poured. This was done with sprues, or branches, that were attached to the wax patterns pulled from the mold. This gating system, which when completed is called “trees”, was designed to aid in the efficient flow of molten bronze and to allow gases to escape. A unique gating system must be specifically designed for each individual piece of the sculpture.
5. CREATING THE CERAMIC MOLD
The next step in the process of casting Admiral Nimitz was to then invest the gated wax “trees” into ceramic shells. This was done by dipping the trees into a vat of ceramic slurry, coating both the inside and the outside of the hollow waxes. Immediately after the dipping, the pieces were bathed in silica sand. These steps were repeated eight to ten times, drying between each layer, in order to encase the waxes in thick ceramic shells.
6. BURNING OUT THE WAX
Once the ceramic molds were dried and cured, they were placed into a burnout oven and heated to melt the wax out…hence the term, “lost wax.” Once the wax was melted, hollow cavities were then present where the wax pattern and gating system once were solid. These hollow cavities and channels then acted as arteries in which the molten bronze would be carried into each section within each shell.
7. POURING THE BRONZE
The bronze alloy used in creating the Admiral Nimitz monument and which is currently used in fine art foundries today, consists of mainly copper, silicon and manganese. This bronze is referred to as “silicon bronze.” If this bronze had been poured into the hollow shells at room temperature, the molds would have cracked and the bronze would have cooled too quickly, hardening and blocking the narrow portions of the molds. To avoid this, the ceramic shells were preheated while bricks of bronze are melted at over 2000 degrees in a large ceramic crucible.
As typical for this type of fine art casting, three foundry artisans were involved in the bronze pour. The “lead pour” directed the hand-held crucible to the awaiting shells, while the “dead man” maintained its balance. The third member kept the surface of the molten bronze clear of any impurities or “slag.” Because of safety concerns and for the success of the pours, team work was essential.
8. REMOVING THE SHELL OR DE-VESTING
De-vesting is the process of removing the ceramic shell. In order to retrieve the castings done for the Nimitz monument, each ceramic shell, once cooled, was broken away from the bronze pieces. Once the shells were removed, the engineering gates or trees were cut and removed. The surface of the visible artwork was then sandblasted, which freed the crevices from ceramic residue. As a result, every detail sculpted by Caswell in the original clay was revealed.
9. REASSEMBLING THE BRONZE
After the bronze pieces were freed from the ceramic material, foundry artisans then referred to photographs and measurements taken of the original clay sculpture to reassemble the sections of the casting. The seams were tig welded using a rod of the same bronze alloy used in casting. Like the wax pattern, the bronze had to be chased and cleaned to ensure that excess metal was ground off and any remaining pits in the bronze filled.
10. SANDING AND POLISHING
The weld lines were then sanded down. This was done using carbide tipped grinders. The surface texture was added back in to blend with the rest of the sculpture. As in all fine art bronze casting, the weld seams on the Nimitz monument are undetectable.
11. APPLYING THE PATINA
Caswell’s patina artist achieved the patina he desired on the sculpture’s surface by first applying heat to the bronze. The next step included applying a variety of metal salts, causing a chemical reaction. Each of the metal salts used, which were mostly nitrates, caused a different reactive color.
To protect the patina, wax was applied while the bronze was still hot. As it melted, the wax sealed the metal’s pores and then, once cooled several more layers were applied by hand and then buffed to give the sculpture its final luster. Through the hands of Caswell and his patina artist, the Nimitz monument was brought to life.