I've only done this a few times. The first time I used wax from a new toilet ring,(I switched to using gaskets in the apartments, so I have a few of these lying around) It worked fine when applied liberally. Lately, after reading it here somewhere, I've simply used a liberal coating of axil grease. That also worked fine and is probably easier for me to work with. Probably anything that the resin won't stick to that can be smoothed over the mold will work. I guess if you were looking for fine detail in the mold, you might need a less viscous or thinner layer of release agent. Hope this helps, Rich Hagen