There is actually a higher likelihood of air remaining in an RTV
mold if it is an opaque material, than in a heat cured mold rubber.
If you use a clear RTV, you can usually move a bubble away from the
model with a straightened paper clip to reach down in the mold before
it starts to cure.
If you find pinholes or voids in other kinds of mold rubbers, you
have not trapped air in the mold. You have not packed enough rubber
in the mold frame.
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