I’ve talked at length about one of the materials commonly used for creating prosthetic appliances, but only as it applies to mold making: silicone. Appliances made of silicone look and feel remarkably like real skin. They certainly can, anyway. And they’re made mostly using platinum RTV silicone because platinum silicone cures significantly faster than tin silicone, though both will cure in a shorter time with the application of heat. Many platinum silicones, unlike all tin silicones, are safe for application directly to the skin. Something else that’s true about platinum silicone is that the more platinum it contains, the faster it will kick and the more expensive it becomes. Last time I checked, platinum was pretty expensive.
The good news is that there are also some wonderful tin RTV silicones available for prosthetics, particularly tin silicone gels; they just take longer to cure. They can be accelerated, but as you’ll recall, a fast catalyst will weaken the silicone. Perhaps not that won’t happen quickly enough to be a problem for your application if it’s immediate, but most silicones have a negligible shrink factor, and if you make multiples of a piece with the intention of storing them over time, they may become unusable, even brittle, if the cure is accelerated. This can happen within a matter of days, especially if you use only a fast catalyst and none of the regular catalyst. I’ve seen it happen with some of my tin RTV mold rubber; I am making a presumption that it will be true for other silicones as well. I’m sure I will be quickly corrected if I am mistaken about that.
Silicone appliances can be cast in a number of types of molds, including Ultracal, Hydrocal, fiberglass, Forton MG, urethane, and even silicone, provided it’s supported by a jacket mold. However, remember that platinum silicone cannot be cast into a tin silicone mold; it will not cure. Platinum into tin is not okay. Tin into platinum is okay; tin into tin is okay; platinum into platinum is okay. But the molds must be released well to prevent the new silicone from permanently bonding to the silicone of the mold.