There is a book by Jerome A Gonicberg and Marshall L. Ritch titled
PRINCIPLES OF CENTRIFUGAL RUBBER MOLD CASTING published by the A. J.
that covers casting low temperature base metals in rubber molds and
mold making. My copy was printed in 1992 (4th printing) so it may be
out of print. I think the Oster Company was sold though there is an
Oster Pewter Company that is an offshoot of it.