Alginate is a very good moulding compound, Kronos, but it's fragile. During the production of special effects appliances, life-casts, etc., it's great for detail reproduction but is usually reinforced with a couple of plaster of paris coats for stability. (You can't apply plaster of paris directly to skin because of the exothermic reaction when it sets.)
My compromise, which might actually work in this case, is liquid latex. The appliances that I'm wearing in my avatar, for example, are made by that process. I used a positive mould of my head (okay, it was a wig dummy), sculpted plasticine into the shape that I wanted, then applied 3 coats of latex. When it was cured, I used that as a negative mould and brushed 5 or 6 coats of latex on the inside. Once that was cured, I just glued it onto my face and applied standard theatrical makeup and fake hair.
It might be applicable to KingNothing's situation, as long as the mould doesn't have to survive very high temperatures. At the very least, it will peel off of anything coated with paste wax, WD40, etc. with no deformation.
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