This piece was modeled in an oil based clay before a wax positive was created. Before modeling the clay, a wire armature must be constructed. The armature I used was built with baling wire and galvanized pipe and provided a frame for the clay to be modeled upon.
Once an armature had been constructed clay was added and modeled. This stage of the process is by far the most extensive.
after the clay bust was completed molds were taken off the surface. A parting line is defined on the piece using playing cards. This wall of cards will provide a seam in the mold components so it can be released off the form. With a shim line in place, a two part rubber is applied in coats until roughly a quarter inch thick throughout. The rubber is then sprayed with a release agent, and a two part plastic is applied in the same way. This mold making process allows for a flexible rubber to be peeled off the clay and then replaced into a rigid plastic shell.
when the plastic mother mold has dried it needs to be prepped to accept wax. The shim line created with cards was drilled out so hardware can be installed to rejoin the mold components, and the excess material was ground off the edges. Once the edge of the cards is visible between layers of rubber and plastic, the mold could be split. Clay was removed, and the rubber surface was scrubbed clean.
Once the mold was sufficiently cleaned, the components were bolted back together, leaving an opening at the bottom where the hollow space could be accessed. Hard wax is then melted down and poured into the mold; the filled mold is rolled around so the liquid wax coats every surface. This process was repeated four times, each time with slightly cooler wax, as to create a hollow copy of the clay form, with walls less than half an inch thick.
After the Wax had solidified, it was removed from the mother mold and cleaned to remove bubbles and other imperfections. A hole was cut out of the skull, to convert the bowl like wax form to a tube form to make the following steps easier. The two components are then attached to a series of wax rods which converge to a single pyramid. These rods are called sprues and vents, and they provide a pathway for molten bronze.
the sprued wax form was then dipped in a glue like substance called slurry. The slurry-coated piece was covered completely with a silica sand and then set out to dry. This part of the process is repeated ten times - the initial three in a fine sand that better captures fine details, and the final seven in a coarser sand that builds thickness. After ten coats with sand, one final seal coat of slurry was applied to finish the ceramic shell mold. The hole cut in the head of the wax form allows slurry and sand to pass completely through the form, and accelerates the dry time of each layer.
Edges of the dried ceramic shell mold were cleaned with a diamond blade, and the piece was placed into a burnout kiln. The kiln melts the wax out of the mold leaving a hollow negative of ceramic shell. The hollow ceramic shell mold is able to withstand the heat of molten metal.
The bronze was loaded into a small gas kiln and the ceramic shell mold wired into a cage for preheating. As the bronze began to approach an appropriate viscosity the ceramic shell was heated with a propane burner to reduce the risk of cracking from temperature shock.
When the molds and metal are both at the right temperature, the bronze can be poured. Two people pull the crucible out of the furnace and scrape the impurities off the surface of the molten metal. Using a two person ladle, the bronze was poured into the molds - one person controlling the angle of the crucible and then other maintaining a standard height.
As the metal cooled it began to shrink slightly, creating hairline fractures in the ceramic shell. The shell was broken off the surface of the bronze and thrown out, leaving nothing but the bronze figure and a series of sprues that had been cast into the piece. These rods were cut away and ground flush with the edges of the piece. The panel cut out of the skull of the figure along with a pin for mounting the piece were TIG welded into place.
With the piece completely welded together, it was time to clean the surface of the bronze. a series of sanding disks and grinding tools are used to remove any imperfections from the surface of the metal and completely hide the areas that had been welded. The metal surface is finished with a thorough sandblast.
Once the bronze is cleaned, it was colored and sealed. The bronze patina i used was a two part traditional patina. a cold patina of liver of sulfur was applied first, completely blackening the piece. Highlights in the piece are brought forward with a Scotch-Brite or a Brillo pad.
When the shadows have been established, the hot patina is applied. A solution of Ferric Nitrate suspended in water is sprayed onto the piece, after the piece has been heated. The piece is heated so the water in the solution evaporates on impact. The final color of the patina is altered by the rate of this evaporation. If any spot on the piece is too cold splotchy yellow spots will form.
While the piece was still warm, several coats of wax were applied as a sealant. The wax is applied, allowed to reconstitute, and then polished back. When the piece is completely waxed it is ready for a base.