Our masks start with a bandage-plaster face casting...

...which is then slip-cast in clay and released from the plaster mold.  Once dry, the clay mold is coated with a kiln-wash-release and kiln-fired to "bisque" hardness

An appropriate glass is chosen...

The glass is generally shaped by scoring, snapping and grinding edges.  Intricate shapes can be created with my glass saw.

If the mask is intended to be one layer of glass, it can now be slumped over the clay face mold.

The kiln that makes it happen

If the mask is to be decorated, its layers are fused on the flat in another firing...

...and then slumped over the clay mold in yet a third firing.

...and maybe decorated further.