I use silicone grease for a great release. I make my own toroids from iron powder and epoxy resin. I use a donut maker and coat it with silicone grease inside of the mold, then wipe it off. Nothing will Ever stick to it if you do this. The mold if silicone rubber or similar will release from it anyway, however, when the next batch is poured , then one or two more, the mold releases easily.
I regrease within 4 or 5 uses total and it works great.. you just have to wipe the goo off and go lightly with it.. A little goes a long way and the grease wipes off completely with a damp terrycloth washcloth lather on without seeing one bit on the mold. It is smoother than a donut and they work well too.
Good Luck To Anybody Trying.. I'm guessing the agent used to mold will matter most.. rubber releases well with silicone, however, certain things may not.. depends on the mold too, especially with the shape of the mold. That could always make release tough if it wasn't beveled or rounded..