5: Ceramic Shell
OVERVIEW | MODELING | MOLD MAKING | WAX CASTING | WAX CHASING | CERAMIC SHELL | POURING BRONZE | CHASING | PATINA
The now chased and gated wax casting is ready to be covered by a ceramic shell. The wax is first coated with ceramic shell "slurry" - whether by dipping or pouring it over the wax casting. You are making both an inside mold and an outside mold. This allows you to cast a hollow bronze, you are just coating the wall thickness of the wax.
After coating the wax with slurry it is then stuccoed with a refractory material, fused silica. These stuccos come in a fine, medium, and coarse grain. Each slurry coat and stucco must dry before the next one is applied, which is about 12 hours. It takes an average of 4-5 days, mostly drying time, to create the ceramic shell.
The mold is then put into a high temperature dewaxing oven. The wax then melts out, thus being "lost." This is where the bronze casting technique known as "lost wax casting" got its name. In our times this wax is actually recycled and used again. At this point, after the wax has been melted out of the ceramic shell, it is inspected for any cracks or leaks in its surface and is patched accordingly with refractory cement.
The ceramic shell is now ready to have bronze poured into it.