You’ve seen the blue wax on the workbench as it is transformed from an anonymous cylinder into a finely carved ring. This medium-grade wax is very malleable and retains its integrity when carved down to intricate design detail. It is the wax of choice at the Ornament Studio workbench.
Casting is the process of making molds. It is also the process of transferring molten metal into a mold. The wax serves as the model.
Here’s how it works, in a nutshell: The jeweler carves a wax piece, let’s say a ring, exactly as he wants it to look in its final metal expression. A thin rod of wax is added at the base (the part that would be on the inside of the hand). This is sometimes called the “screw”. In a container called a flask, very fine plaster is poured around this wax model, with screw at the top. Once the plaster has set, the wax is burned off (lost wax casting), revealing its exact shape and details in the plaster.
With the screw melted away, there is now a “funnel” through which molten metal can enter to fill the entire space that was previously occupied by the wax. But molten metal is thick and it cools fast, so there has to be a way to distribute it evenly and thoroughly… hence the slingshot.
Perhaps one of the most intriguing methods for casting jewelry with wax is Sling Casting or the Centrifuge Method. This is also one of the most ancient methods ever used. While it is ancient, however, it is far from being primitive. In fact, it is downright clever and required a sound understanding of science and physics.
The flask is secured into a sling. With molten metal in place in the cavity, it is swung in large, steady arcs, using centrifugal force to distribute the metal perfectly within the shape and textures left behind by the wax. Every piece comes out with a vestige of the screw, which is then filed down and away by the artist. Design and materials vary depending on how far back in time we look, but the principle is always the same.
Today, the equipment that is used to reproduce this method requires a space the size of an industrial warehouse. This is in great part due to the demands of mass production. Thousands of pieces are cast at once.
While this is a necessary evolution to keep in pace with modern-day commerce, it seems rather far removed from the painstaking process of the artist’s workbench. However, it allows the modern jeweler to focus on personal design, and produce custom pieces in a time-efficient manner and often at a more affordable cost to the customer. It also allows him to clone favorite pieces indefinitely, as opposed to starting from wax every time.
Picture a central trunk with hundreds of wax branches each ending in a different ring from various designers. Commercial sling or centrifuge casting also uses powerful vacuums to assist the process. The notion is impressive.
Sketch images source: The Complete Metalsmith, Tim McCreight. Davis Publications.