While studying resin casting I was told that no release agent will be needed when making Silicone Rubber molds. Release agents are used to create a thin layer between mold and master(usually fluid) so that it will make it easier to remove the master from the mold once it has hardened. Most of the time however I've noticed that with tight or small spaces of the master, the Silicone Rubber has a tendency to stick to it. It could be a case of just incorrect mixing with the hardener and Silicone Rubber, but the best way to ensure this from not happening is to use a release agent.
For a backyard resin casting hobbyist with a limited budget, release agents are an added burden. You can try using petroleum jelly but the uneven spreading of the wax on the surface of the master will lead to an unsmooth Silicone Rubber Mold. What would be ideal would be to use a liquid release agent.
Luckily while googling I found out that you can make a cheap alternative to a liquid release agent by first diluting Petroleum jelly in some thinner. mixing it evenly, then applying it generously on the master with a brush. Works for me and I can say that I've had success in disengaging my mold from the silicon rubber. Take care though to watch out for globs of Petroleum jelly that could form up that could result in an imperfect mold.
