Natural Gemstone Firing Guide

Use these charts to guide your selection of which gemstones to consider and which to avoid when firing stones in PMC®.

Last edited: 10/24/2019

Stone Firing Guide

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.

Kiln-Firing Results

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.
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.
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.
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.
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

 

Torch-Firing (Butane) Results

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