I make my molds from POP mostly. I seal my masters with rattle can paint, several coats with steel wool between coats 1 and 2. Make sure that you use gloss paint, this will give a better detail transfer.
Never had a problem getting the master out of the mold; even in a two-piece mold.
When I make an open mold with a complicated shape, I will make it in two pieces. This way you can get the wooden master out quite easily. Then if you still only want a one piece mold all you do is epoxy it back together.
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