Kevin Whitmore and Judy Anderson at Rio Grande have done extensive experiments on what gemstones can withstand the heat of being fired in PMC3 at 1110 degrees.
You can find the list of stones on line at:
http://www.pmc-conference.com/
“Stone fired in place into PMC”
Go to Tech Resources for 2002 Conference, and it’s the 2nd one on
the list.
He lists which stones survived, and which ones survived with some
color changes.
Seems like a good place to start.
Elaine
Elaine Luther
Metalsmith, Certified PMC Instructor
http://www.CreativeTextureTools.com
Hard to Find Tools for Metal Clay