around 1970 we had 'Plasticraft'
to make keyrings etc with embedded acorns etc

gogling it gives things likle:
http://www.craftsforum.co.uk/showthread.php?p=32537

blackbat wrote:
On Thu, 15 Oct 2009 04:23:03 -0700 (PDT), Lino expert
wrote:

"Plastic Embedding" perchance?
Smelt like the biggest, most toxic acid drop in the whole of
christendom?

Can't remember what it was called.
Had a small ceramic mould that had 5 smaller indents to make keyrings
of differing shapes.
It *did* stink though.