Archeologists have uncovered bronze sculptures from Ancient Greece and Rome, the Shang Dynasty period in China, as well as from the Chola Dynasty in South India. Just about every major civilization in history created bronze sculptures at one point or another, using a process known as lost wax casting to create small and intricate pieces like jewelry and vases, all the way to life-size statues and replicas. For instance, The Victorious Youth is a bronze statue cast in Ancient Greece in approximately 300 BC. It was found on the ocean floor and is one of the few full-size bronze statues to survive from Ancient Greece. There are thousands of bronze sculptures, statues, mausoleums, and even cathedral doors scattered around the world that are several centuries, if not millennia, old.
But bronze sculpture casting is not some ancient art; it’s alive and well in today’s culture and bronze sculptures can be seen in cities all over the world. For instance, a bronze statue of hockey legend Wayne Gretzky carrying the Stanley Cup is outside the Edmonton hockey arena. What’s even more amazing is that most bronze sculptures today are made the same way as they were 5,000 years ago, with the same lost wax casting process.
Here are the basics steps of the lost wax casting process, an art form which has hardly had to change in thousands of years:
Model-making. The artist creates an original model from wax, clay, or another material that retains its softness, making it easy to shape and form.
Mold-making. A mold is made of the original wax model or sculpture. This mold becomes the inner mold, which is an exact negative of the original wax model. Inner molds are usually made of latex, polyurethane rubber or silicone. The inner molds are then supported by the outer mold made from plaster or fiberglass. Most molds are made of at least two pieces, and a shim with keys is placed between the parts during construction so that the mold can be put back together accurately, which is essential if the artist intends to make multiple copies of their bronze sculpture.
Wax. Once the inner-outer mold is finished, molten wax is poured into it, covering the inner surface of the mold. Different thicknesses of wax can be achieved by pouring less or more wax into the mold. Eventually the hollow wax copy of the original model is removed from the mold.
The Chasing. Each hollow wax copy is then “chased”: the artists use a heated metal tool to rub out the marks that show the lines of where the pieces of the mold came together. The wax ends up looking like the finished piece.
Spruing. The wax copy is “sprued” with a treelike structure of wax that creates paths for the molten bronze casting material to flow into the mold and for air to escape so there are no air pockets in the finished product. The spruing usually begins at the top with a wax “cup,” which is attached by wax cylinders to various points on the wax copy. This ensures that the molten bronze is evenly distributed throughout the mold.
Slurry. A sprued wax copy is dipped into a slurry of silica, then into a sand-like stucco, or dry crystalline silica. This shell is allowed to dry, and the process is repeated until at least a half-inch coating covers the entire piece. Only the inside of the cup is not coated.
Burnout. The ceramic shell-coated piece is placed into a kiln, where the extreme heat hardens the silica coatings into a shell, and the wax melts and runs out, leaving a hollow space in the shape of the final sculpture.
Pouring. Bronze is melted in a crucible in a furnace and then poured carefully into the shell using those sprue lines.
Release. The shell is hammered or sand-blasted away, releasing the rough casting. The sprues, are also cut off.
Metal-chasing. Pits left by air bubbles in the casting and the stubs of the spruing are filed down and polished so the final product is a smooth and beautiful bronze sculpture.