ORIGINAL: sidgates

rcpete,
I make most of my molds out of styrofoam (blue preferred). You can see some of my construction on my personal web site http://gates-sid.com (go to models and F-94C)
For parting on larger molds I use Johnson's wax and one coat of Partall. For some very small ones I use the packing film which will stretch around corners and is very thin.