Gemstone suitability for use in PMC

      Now that I have begun to offer melee diamonds and semi-precious colored gemstones on my website, Heart of Stone Studio, people have written to ask which gemstones can be used in firing precious metal clay. Genuine diamonds can, of course, and CZs (cubic zirconias) as well as synthetic stones, but real colored gemstones are another matter. For one thing, if the stone contains any major inclusions that heat and cool at a different rate than the surrounding stone, they can cause the stone to crack or explode. Or, a small fracture, when heated, can expand to become a big, damaging fracture. The other possibility is that the crystalline structure of the gem does not lend itself to firing. Regardless the reason, the result is a double mess--a damaged stone that's also locked in place in your piece.

     So, I called the folks at Rio Grande, a large and reputable jewelry supplier out of Albuquerque, NM. Their research department experimented with firing a variety of different stones in two types of PMC.  I've made up a chart of their findings that I hope the PMC enthusiasts will find useful:

Gem Suitability for Use in PMC	Information provided by Rio Grande
Gemstone	Dry Fire	PMC 3
Chrome Diopside	not available	Survived
Garnet: Almadine	Survived	Survived
Garnet: Pyrope	Survived	Survived
Garnet: Rhodalite	Survived	Survived
Garnet: Tsavorite	not available	Survived
Hematite	not available	Survived
Moonstone	Survived	Survived
Peridot	Survived	Survived
Black Star Sapphire	Survived	Survived
Tourmaline	Survived = iffy	Damaged = iffy
Denim Lapis	Survived = iffy	Damaged = iffy
Lapis Lazuli	Damaged	Damaged
DO NOT TRY THESE STONES
Amethyst
Aquamarine
Black Onyx
Blue Topaz
Blue Misty Chaldecony
Cameo
Carnelian
Citrine
Iolite
Jadeite
Malachite
Mexican Fire Opal
Rhodochrosite
Rose Quartz
Tiger Eye
Turquoise ------------------------------- Any information that PMC experts might like to add would be welcomed.