Newsletter - March 25, 2009

The Jewelry Crafter

A newsletter for the home jeweler

This newsletter will be published every 2 weeks, and will include hints and tips for your jewelry business. Any feedback or comments about the topics presented here are always appreciated. Click here to e-mail us.

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Gemstones and Metal Clay

By

Mary Harvey

With the growing popularity of Metal Clay (Artclay Silver or PMC), many jewelry makers are trying this interesting medium. You can do so much with it – roll it, texture it, sculpt it, make settings for glass or ceramic shards, or even set gemstones in it. Recently, I’ve had several people ask me which gemstones are safe to use with metal clay, so this week, I will try to answer that question.

Metal clay is fired in a kiln at a high temperature, so any gemstones that are incorporated into a metal clay design must be able to withstand high heat. Nothing is more disheartening than creating a metal clay piece with a gemstone, firing it, opening the kiln door and finding the stone cracked, shattered, or melted. So which stones are safe for metal clay? Most lab created stones, and some natural stones can be used, but you have to know the limitations for each type of stone.

The most popular stones to use with metal clay are synthetics. According to a gemstone manufacturer, most colors of cubic zirconia, lab created corundum (ruby, garnet, alexandrite), lab created spinel (aquamarine, zircon, sapphire) and YAG (a diamond simulant available in various colors) can be used safely. Certain colors have a tendency to shift, or change color slightly, when fired, so test firing a stone may be required. Most synthetic stones are safe to 1600 degrees. Some colors of CZ (green, blue, tanzanite and black) should only be fired to 1110 degrees, or they will be damaged or shift color.

You must be careful when using lab created stones. Some “simulated” stones are actually hardmass glass, and will melt when heated. Be sure you know that the stones you are buying is safe for firing in metal clay.

Using natural stones in PMC can be more challenging. Normally, most stones that measure over a 7.5 on the Moh’s scale of hardness can be used. These include garnets, peridot, sapphire and natural ruby. However, natural stones will sometimes have inclusions, and these may cause the stone to shatter when heated. As with some of the synthetics, a few of the natural stones may also shift color when heated.

Some natural stones that should never be fired include diamonds, amethyst, emerald, citrine, iolite, blue topaz, opal or pearls. These stones will either be damaged or destroyed by the high heat of a firing cycle. However, these stones can still be used in metal clay settings if they are set after firing.

Again, the key is to know what kinds of stones you have and what the limitations are for each type of stone. If you ever have questions, call your supplier and they can usually help you determine if a stone is safe to use with metal clay.