By Gavin McCalden
Sorrel Sky Gallery has an extremely large collection of bronze artwork and one of the most common questions is “how do they do it?” The art of bronze making is an extended and very complex process.
Bronze is one of the oldest metal alloys known to man, with a history dating back as far as 3300 BC. In it’s molten state it has the ability to creep and fill the smallest crevices, allowing artists the ability to create immaculately detailed sculptures.
Composed primarily of copper and tin, bronze is a unique metal alloy that is harder and more durable than stone or copper. It is also resistant to corrosion and proved to be quite useful for everything from tools to architecture to artwork. A low melting point allowed bronze to be developed far before iron or steel, and continues to be used today.
There are various techniques used in the casting of bronze, the oldest and most common being the Lost Wax Technique. The Lost Wax Technique has changed surprisingly little since antiquity, and continues to be the method of choice for most modern bronze artists.
Typically, an artist will begin a sculpture by creating a full-scale model of the sculpture using a non-drying oil-based clay. The clay sculpture is coated with a urethane rubber, after which it is coated with plaster to create what is called the “plaster master mold”. The master mold is saved for multiple editions of a sculpture to be made years after the original clay sculpture was formed.
Larger works are often created with a series of “studies” to determine the desired composition, and then sculpted around a wood or foam armature to save on weight. The plaster mold is cut into smaller pieces for assembly after the final bronze casting.
Next, hot wax is poured into the mold and sprues are attached – sprues being the passage through which the molten bronze will flow into mold from bottom to top. Once the wax has cooled, the wax mold is removed from the master plaster mold and dipped in a clay-like substance and coated with silica. Once the wax mold is coated several times in the ceramic material, it is then heated in a kiln to about 1500 degrees, melting the wax and leaving a hard ceramic shell of the sculpture mold, sprues and all.
Once the ceramic mold has been hardened, liquid bronze is poured through the sprues to fill the mold from the bottom to the top. After the bronze has cooled, the ceramic mold is chipped and sandblasted away, the sprues are cut off to reveal the sculpture, and any incomplete voids, tool marks, or other imperfections are finished through welding, carving, filing and finally polishing the sculpture to the desired detail. It is at this time that a large work will be assembled through welding.
The final step is the addition of the tarnish that forms the surface of the bronze otherwise known as the patina. The patina if generated by heating the sculpture and applying an acid or other corrosive material to generate a desired color. The bronze is then waxed for protection and shipped off for the world to enjoy.