Explanation of Dewax stage preceding firing of shell

Dewaxing is removing from inside the shell the wax casting from upon which the shell was built.

A shell is formed on a wax casting by dipping in slurries and granular "stuccos".

If the wax can be removed without damaging the built-up shell, molten metal poured into the shell will take up the form of the prior wax casting. Hence "Lost Wax Casting".

The wax is removed from inside the shell with a high-pressure steam autoclave. Steam has the property of supplying a lot of heat while at a strictly limited maximum temperature will does not degrade the wax in the process. Sudden melting of the surface of the wax casting enables wax infiltration into the shell or flow down escape paths out of the shell to relieve any wax expansion which could otherwise burst the shell. It is not trivial to extract the wax without bursting the shell formed upon it!