Over the years, Rio Grande has tested lots of natural gemstones for use in PMC®. You can benefit from our experience! The following charts can guide you toward stones to consider and stones to avoid when co-firing in PMC. We recommend firing gemstones in PMC3™ at the minimum firing temperature of 1110°F for 45 minutes. We also recommend ramping the temperature up at a rate of 500°F per hour. Always allow slow cooling.
Good Bet | |||
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We've had consistent success with the gemstones below. But be aware that natural gemstones can vary. Never risk an invaluable stone to the kiln. |
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Gemstone Type | Stone Only 1110°F/45 min. |
In PMC3 1110°F/45 min. |
Guide |
Chrome Diopside | not tried | survived | good bet |
Almandine Garnet | survived | survived | good bet |
Pyrope Garnet | survived | survived | good bet |
Rhodolite Garnet | survived | survived | good bet |
Tsavorite Garnet | not tried | survived | good bet |
Hematite | not tried | survived | good bet |
Moonstone | survived | survived | good bet |
White Topaz | survived | survived | good bet |
Peridot | survived | survived | good bet |
Green Topaz | survived | survived | good bet |
Black Star Sapphire | survived | survived | good bet |
Tanzanite | survived | survived | good bet |
Green Tourmaline | survived | survived | good bet |
Oregon Sunstone | survived | not tried | good bet |
Mali Garnet | not tried | survived | good bet |
Damaged/Unsafe | |||
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Unfortunately, these gemstones experienced extensive damage in the kiln. |
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Gemstone Type | Stone Only 1110°F/45 min. |
In PMC3 1110°F/45 min. |
Guide |
Blue Goldstone | damaged | not tried | unsafe |
Brown Goldstone | damaged | not tried | unsafe |
Smoky Quartz | damaged | not tried | unsafe |
Agate (Cameo) | damaged | not tried | unsafe |
Amethyst | damaged | not tried | unsafe |
Aquamarine | not tried | damaged | unsafe |
Aventurine | damaged | not tried | unsafe |
Carnelian | damaged | not tried | unsafe |
Blue Mist Chalcedony | damaged | not tried | unsafe |
Citrine | damaged | not tried | unsafe |
Iolite | destroyed | not tried | unsafe |
Jadeite | damaged | not tried | unsafe |
Malachite | destroyed | not tried | unsafe |
Mexican Fire Opal | not tried | damaged | unsafe |
Black Onyx | damaged | damaged | unsafe |
Rhodochrosite | damaged | not tried | unsafe |
Rose Quartz | destroyed | not tried | unsafe |
Tiger's Eye | darkened | not tried | unsafe |
Blue Topaz | destroyed | not tried | unsafe |
Turquoise | destroyed | not tried | unsafe |
Rainbow Topaz | damaged | damaged | unsafe |
Iffy. | |||
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In our experience, the following gemstones have suffered some slight degradation in the kiln and in some cases, we've seen inconsistent results. Try the stones below at your own risk. |
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Gemstone Type |
Stone Only 1110°F/45 min. |
In PMC3 1110°F/45 min. |
Guide |
Pink Tourmaline | damaged | not tried | unsafe |
Denim Lapis | survived | survived | iffy |
Lapis Lazuli—Dark | damaged | not tried | iffy |
Labradorite | survived | survived | iffy |
Rainbow Moonstone | damaged | damaged | iffy |
Aquamarine | survived | damaged | iffy |
Silver Moonstone | slight damage | slight damage | iffy |
Peach Moonstone | slight damage | slight damage | iffy |
Natural Gemstones | ||
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These natural gemstones were set into PMC3 and torch-fired with a butane torch for about 10 minutes, long enough to set the clay. | ||
Gemstone Type | Result | Guide |
Rhodolite | good | good bet |
Peridot | good | good bet |
Blue Sapphire, A-grade |
good | good bet |
Blue Sapphire, AAA-grade |
good | good bet |
White Sapphire | good | good bet |
Ruby, A-grade |
good | good bet |
Ruby, AAA-grade |
good | good bet |
Tanzanite | good | good bet |
Peach Moonstone | damaged | damaged/unsafe |
Silver Moonstone | damaged | damaged/unsafe |
Labradorite | damaged | unsafe |
Lab-Grown Gemstones | ||
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These lab-grown gemstones were set into PMC3 and torch-fired with a butane torch for about 10 minutes, long enough to set the clay. | ||
Gemstone Type | Result | Guide |
Blue Spinel | good | good bet |
White Sapphire | good | good bet |
White CZ | good | good bet |
Green Garnet | good | good bet |
Green CZ | damaged | damaged/unsafe |
Moissanite | damaged | damaged/unsafe |