How do you write on silicon RTV molds?
Two methods I’ve used. With clear silicon RTV, I write/type/print
the number on a slip of paper and put it into the rubber facing a
side, near the end where it will be imbedded, but out of the way. You
can also cut a slit into the rubber after it cures and imbed a slip,
but then it can also come out, or get dirty, etc. With non-clear
types including vulcanized rubbers, I took a sheet of thin aluminum
and some number/letter stamps and made a bunch of small bits of
aluminum with letters and numbers stamped into them. I used "reverse"
stamps, so they read “wrong” looking at the tags themselves. Now,
pack the mold or pour it, with the intended number or label spelled
out with those tags. For a vulcanized mold, just insert them between
the mold frame or mold plate (clear stamped image facing the rubber)
and the rubber before vulcanizing. With poured molds stick the tags
to the frame or mold plate with a bit of sticky wax so they don’t
float away.
After the mold is cured or vulcanized, those tags can be removed
from the rubber and saved for reuse with the next mold, and they
leave an impression in the rubber that now reads correctly. Not
written, so no ink to come off, but permanently “embossed” into the
rubber.