Many years ago I made several RTV molds of belt buckles. Being
inexperienced at cutting molds I tried another way of doing the job.
I set up the buckle on modeling clay which was in a frame. I pressed
holes in the clay, around the buckle, which would act as locks. I
poured 1/2 of the mold on top of the buckle and the clay. Once the
first part of the mold was set I turned it over, removed the clay,
and painted a separation agent on the RTV. The second part of the
mold was then poured. The mold separated nicely where the separation
agent had been painted. It took twice as long to make a mold in this
fashion but it saved an inexperienced person from having to cut it
open. Unfortunately I do not remember what I used as a separation
agent. Maybe someone out there can enlighten us.