I know what doesn't work.
This is a small piece of Andamooka opal given to me by a customer who was told that they could take high temps. I told her it probably wouldn't work but I'd try it anyway. The outgassing was pretty impressive.
ABR sells some stuff that they have in the boro section, moldavite, tekite and cyanite. Never tried any of it.
http://www.abrimagery.com/store/inde...glass-c-424_42