Yes, cornstarch works as a mold release agent. I’ve used to
make separation molds (vulcanized). I’m sure I read about that
somewhere – Untracht or McCreight.
I use talc or cornstarch (baby powder) for venting a mold. If
there are undercuts or other difficulties in removing waxes I 'd
use silicone on the mold area I need to lubricate. I spray a
little onto some scrap and brush it where I want it.