Step 11 - The Wax Positive
It is necessary to have a hollow wax positive model of the original sculpture made. This wax positive will be used to eventually create the final ceramic mold into which the molten bronze alloy will be poured.
The hollow wax positive is created by pouring or painting successive layers of hot wax into the mold that was created from the clay sculpture. The wax positive will be the same thickness as the final bronze, so careful consideration is taken when creating the wax positive. Each edition of a bronze sculpture must have its own wax positive.
Step 12 - Wax Chasing
After the wax positive is removed from the mold it is cleaned or "chased" by the foundry's wax artist, who pays close attention to details. Ms. Mongeon also likes to work on her own waxes. She will often spend many additional hours adding intricate detail to the waxes. After the wax positive is signed and numbered it is ready for “gating.”
Step 13 - Gating the Wax Positive
The foundry's artisans must pay close attention to how the bronze alloy will be poured and how trapped gases will escape. The wax is "sprued" with wax "gates" [tubes] that form a system of channels that allow the molten bronze to flow evenly. Degassing vents and a pouring cup are also added. This is a very important step because it will determine the quality of the bronze cast.
Step 14 - The Slurry
The wax positive, sprued with gates and a pouring cup, is now dipped into a ceramic slurry. The slurry builds a hard ceramic shell made of silica and sand, that covers both inside and the outside of the wax positive. The gated wax positive is dipped several times into the slurry and then into a bath of sand and must dry completely before each dip.
Step 15- The Wax Burnout
The ceramic shell (with the wax positive still inside) is then placed in a hot furnace with temperatures at approximately 2000°F. The wax is burned out (or lost, hence the name Lost Wax Process) of the ceramic shell cavity. Later molten bronze alloy is poured into the cavity.
Continue to pouring and finishing the bronze.
(More about the mold making process can be found on the artist's forum and in the online Newsboy Journal.)