Can you release a stone positive from a stone mould?

CaitG

I have an ultracal positive from an alginate life cast that I would like to mold and then run in silicone.
Is it possible to release a stone positive from a stone mould? If I seal the ultracal would I lose detail? If not, what should I use to seal it?
I'd like to do a stone mold if possible to use up material I already have, and because I have never worked with epoxy before. 
(I want to a core which will probably require a 3 part mould, so the more I think about it the more I think I should do an epoxy mould.) But still curious!

Chris Ellerby

Normally you want to avoid casting rigid pieces from a rigid mold or making a rigid mold around a rigid piece, as things can lock together mechanically.  If the piece is designed with enough of a draft and no areas that will lock, it is possible with the right mold release.  But even the smallest overhang could lock things together forever.

You are better off using a flexible material like silicone.

If you are certain there are no overhangs, you have a good draft, etc. then you could use a brush on paste wax and/or vaseline, and design the mold to have pry points.  With both pieces being rigid it could be very difficult to pry them apart, as the model release will create a seal and that suction will have to be broken.  The more surface area the pieces have, the more force will be needed.  I would strongly advise against it in most cases.

/Chris