Okay, from reading more, it seems that you are pouring the RTV mold
entirely in one piece and then cutting it apart? You are making it SO
much harder on yourself! Some of you have talked about clay and
similar things, but I was taught to simply take some very thin
cardboard or very stiff, thick paper (Iused things like sketchbook
covers; I always have something like that laying around) to make my
box to form my mold inside of. Much cheaper and easier I think. I
would figure out how big I needed it to be, and then cut out a strip
that was the height I would need (for the thickness of the final
mold, but plus some to give me some leeway) and the length that
equaled the total of all sides (or two strips if the mold was too big
for me to make that way), score where the corners would be, then tape
the two cut ends together, and I’d have a rectangle that I would then
tape to a backing piece (just make sure your tape covers all gaps).
My actual method for pouring the molds is similar to what is on
Micro-Mark’s website here:
I don’t suspend the item like they suggest, though - my professor
taught me to pour some RTV mold into the bottom first, let it set,
and use that to keep the item from sinking all the way to the bottom.
Then I pour the rest of the half of the mold and place the item in
that. The rest is basically the same, tho, with the addition of how I
already described making the “keys” in a previous post.
As far as the liquid I use to keep the two halves from sticking, I
actually got that from Micro Mark (I ordered all of my RTV mold
supplies through them) - it’s called “Rubber to Rubber Mold Release”.
I used this method to make all of the cast fossils in my fossil
series on my website (see the link in my signature).