The Casting Process

The Age of Bronze: Lost Wax Method of Casting

In the third millennium B.C., somewhere between the Black Sea and Persian Gulf, an artist created a sculpture in beeswax, covered it in liquid clay and baked it in flames. In the flames the wax was lost, replaced by empty space, surrounded by a clay shell. The artist used copper an tin to make a bronze alloy that the artist poured into the cavity left when the wax melted. After the molten metal within the clay shell hardened, the sculptor knocked the clay from the metal, and the first bronze was cast. Take a look at how a bronze sculpture is cast and see, after thousands of years, how little the process has changed.

ARMATURE

Creating a fine art bronze sculpture is a lengthy process requiring many hours of hard work by skilled artisans. The first step in creating a sculpture requires building an armature, which acts as a skeleton for the basic shape and design of the piece.

CLAY

Once the armature is ready, the clay is applied over it. Gary uses an oil-based clay, which remains soft and pliable for extended periods of time, allowing for all kinds of textures and details.

RUBBER MOLD

After the sculpture is complete, a silicone rubber mold is made over the sculpture. The rubber is so effective at picking up details that fingerprints in the original clay will show up in the mold. A "mother mold" consisting of plaster and hemp is then applied on top of the rubber mold. This plaster mold helps maintain the original shape of the rubber mold once the clay is removed. A seam is cut in the rubber, and the clay is removed, leaving a negative in the mold.

WAX POUR

The mold is then taken to the wax room. Here, wax, melted at 200 degrees Fahrenheit, is poured into the mold. The mold is rotated, and a layer of wax coats the inside of the rubber, while the excess wax gets poured out, leaving a thin coating of wax on the inside. This is repeated three or four times until there is a 3/16-inch-thick wax copy of the sculpture on the inside of the mold.

WAX RETOUCH

The wax copy is then removed from the mold. Whatever imperfections show up in the wax, such as seams, bubbles, or holes, are then fixed, using various hot irons and sculpting tools.

SPRUE SYSTEM

Wax bars called "sprues" are attached to the wax, creating a series of channels. These channels will eventually be the pathways for the bronze to flow through to reach the different parts of the sculpture.

SLURRY

The completed wax is then brought into the "slurry" room, where it is dipped into a ceramic mixture and coated with fine sand; this is repeated about 6-10 times, depending on the size of the piece.

WAX REMOVAL

The ceramic shell is then drilled at the cup base, and the wax on the inside is exposed. The shell is placed in an autoclave and the wax is steamed out, leaving a hollow ceramic shell.

CERAMIC SHELL FIRING

The ceramic shell is then placed in a furnace in the bronze pour area, where it gets fired to 1,500 degrees Fahrenheit.

BRONZE POUR

As the ceramic shell heats up, bronze ingots are melted in a crucible at 2,000 degrees Fahrenheit. The molten bronze is then poured into the ceramic shell.

CLEANING THE METAL

After the bronze cools, the remaining ceramic gets taken off with drills and chisels, and the hard-to-reach places get sandblasted.

METAL ASSEMBLY

Like piecing together a puzzle, metal workers then weld each piece of the sculpture together and, using grinder, drills, and other power tools, clean up seams.

SAND BLAST

Once the piece is completely together, it gets sandblasted to clean the metal and prepare a final finish for the patina.

PATINA

The sculpture is then taken to the patina area, where it gets heated with a torch and sprayed with chemicals, giving the sculpture its unique coloring.

FINISH

After the patina is applied, the sculpture is waxed and polished and may be placed on a marble, wood, or granite base. The completed sculpture is placed in a fine art gallery or shipped directly to you-our greatly appreciated client!