It depends- for molds, your best bet it a silicone based one. I'm using the Micromark mould maker 10 to 1 stuff and it's pretty good. Resin is probably your best best for casting material, as it can get good details and is a lot more easily cut for parts and whatnot, but if you feel you must work with metal they do make low-temp casting metal. And if you just want specific small pieces done, you can easily use 2 part molds as press molds for epoxy putty. Hope this helps!