Hi Hahawai,
If you are using "silicone j" r.t.v. by Dow Corning;upon release you should see a flash line the thickness of a human hair.I don't use a mold release agent.I simply spray white automotive laquer on the inside of the mold before injecting.Upon release the paint adheres to the foam and not the rubber, giving me a white undercoat to paint over.Colours come up better on a white background.Also the foam should be self skinning after curing; that is a hard plastic outer surface with a honeycombed inner core.If you sand through this outer skin you expose the inner core making it impossible to paint without using putty.Some days I pour up to 50 lures so I can't afford to sand putty each one.Silicone J is expensive but it's the best.
Barramundi