How can one make a silicone mold?
Tape up all the cracks on a cardboard box, and use that as an
enclosure for the mold. If you intend to make a one-sided mold,
simply mix the silicone, pour it into the box, and coat the item to
be molded with mold release and press it into the silicone, and let
it cure. To make a two-sided mold, you'll need to create a tube for
the casting material to enter, and another tube to vent the
displaced air. You can easily create these by securing two pencils
to the item with some putty. Coat the whole thing with mold
release, even the first silicone mold (silicone will adhere
permanently to other silicon otherwise) and pour on another layer
of silicone, completely covering everything except the ends of the
pencils. Allow that to cure.