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 | |||
|---|---|---|---|
|
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 | |||
|---|---|---|---|
| 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 | ||
|---|---|---|
| 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 | ||
|---|---|---|
| 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 |