Polymer clay itself makes a great molding agent. Here’s a quick tutorial for making a basic 2 part mold (front and back) with polymer clay. Barbara, the tutorial creator, uses baby powder as a release agent but I prefer corn starch since it’s less scented. For Premo or Sculpey 3, water works well too.
My luck with 2 part molds is somewhat limited but for basic pieces without a lot of details this process is great to speed up product work. You may need to do individual tweaking but the rough pull is done quickly.
Oooh thanks for this! I’ve been looking into how to do molds for awhile.