“Investment” is the process of building a rock-hard like 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. When repeated approximately nine times, allowing for dry times in between dips, a hard shell about 1/2″ thick forms around the wax.

Whether ceramic shell or plaster is used to make the shell, the wax is a “positive” which must disappear in order to create a cavity or “negative” for the bronze to fill. Thus the phrase “lost wax casting” comes from the process of the wax being melted or “lost” from the shell. Ceramic built shells are “de-waxed” in a high-pressure steam chamber known as an autoclave, or in a kiln.