Linda; Hat is exactly what it is, it is a vulcanized rubber mold,
that is used in Lost Wax casting. The mold is pressed between two
plates and held up to a wax injector.
The wax is then forced into the cavity of the rubber mold to form
the wax pattern that will then be set into a slurry of gypsum,
cristobolite and some other stuff.
This then is placed into a kiln, or oven where that wax is allowed
to drip out the bottom then the metal, is cast into the cavity left
in the investment by the melting wax. (Hence, the process called Lost