Before Christ, somewhere between the Black Sea and the Persian Gulf, an artist crafted a vision in beeswax, covered it in liquid clay and cooked it in a fire. In the flames the wax was lost, replaced by empty space. Tin and copper alloys of bronze – were gathered and heated. Once melted, the metal was poured into the cavity of the fire-hardened clay. The metal cooled and the sculptor knocked the clay from the metal. The first bronze was cast.
Certain elements of the “Lost Wax” process have indeed been refined, yet today bronze casting remains essentially the same as it was in 2,000 BC during the Akkadian period.
Wax chasing is the delicate process of joining the wax pieces back together to form a complete “positive” of the sculpture (including removing seams and repairing imperfections with heated customized soldering irons or tools: dental tools being ideal). Artists are very involved at this juncture, checking the integrity of the wax and, after approving it, signing the piece.
Investment is the process of building a rock-hard shell around the wax sculpture. Later in the process, when the wax has been melted out, the investment will serve as a mold for the molten bronze. For most of history, an investment consisting of plaster, sand and water was used to accomplish this task.
In the last 15 years, a new technology called ceramic shell has become the industry standard.The ceramic shell technique begins by dipping the gated wax into vats of slurry followed immediately by a bath of sand. This process builds a very thin wall of silica around the wax.
Devesting is the process during which the investment is removed from the metal. Approximately one hour after the pour, the piece is cool enough to handle. Skill and strength are combined with hammers and power chisels to knock the investment off the freshly solidified metal. The gates and sprues must also be removed with a high intensity electric arc that can cut through the bronze like butter. The final step is to sandblast the fine investment from the bronze. When clean, the sculpture advances to the metal shop.
Like wax chasing, bronze must also be chased or cleaned to address the slight imperfections that may result from the casting or shell building process. On larger sculptures, where assembly of cast sections is required, chasing is essential to take down weld line formed by the joining of two planes. Metal chasing usually starts with large electric or pneumatic grinders to remove the bulk of the unwanted metal.
Many larger bronze statues are analyzed by a structural engineer who recommends an inner support structure that can reinforce the piece to withstand earthquakes and high winds.
Patination is enhancement of bronze by the chemical application of color. Three water soluble compounds form the basis for most patinas: Ferric Nitrate produces reds and browns, Cupric Nitrate creates the greens and blues and Sulphurated Potash produces black.
There you have it, a brief history of many different sculpting methods and how they came to be. Next time your embark on your newest project, you will remember what all these unique methods are and maybe have more appreciation for them.