Metal Clay Connections
Issue No. 9, Fall 2008

Fakes, Fractures, Fallacies, and Fire: Words of Advice by Deric Metzger, GJG, AJA, AJ

As metal clay artists, we can all agree on two things: We love what we do, and we all want our work to stand out from the herd. In an effort to enhance of our craft we turn to Gemstones. Gemstones enhance and highlight the design. They also enhance the perceived and actual value of the finished piece. Some things we do not all agree on is whether to use natural gems from the earth, or lab created stones from machines and man.

Each side of the argument has its points. Synthetics are less expensive, but natural gemstones provide more value to the work. Lab created gems are usually easier to fire in place, but natural gemstones are considered more prestigious and worth the extra effort. No matter which side of the fence you fall on, all participants in this design-philosophical argument can agree that destroyed stones or failed firings are undesirable, annoying, and costly. So after deciding on natural or synthetic stones, how should you proceed? First you will need one thing no matter your preferred gem type: A really good loupe. Here is your shopping list. 10X power (no more no less), it must be corrected for chromatic and spherical aberration, and must not have any crazy "extras" (like lights or gem clips). Expect to pay about $60 for a decent loupe.

To use a loupe properly, you need to hold both eyes open and bring the loupe close to your dominant eye within the distance of your eyelashes grazing the lens. Hold the object for viewing within an inch of so of the loupe so that it comes into focus. Usually the space between the ring finger and pinkie finger is the correct distance from the device as a depth of field. Please note that the loupe distance from the eye is critical for the clearest viewing, holding the loupe too far away can strain your eyes. Keeping both eyes open is also critical (even though you may be tempted to close one) because only having one eye open can strain it too much and give you astigmatism.

If you are using your loupe correctly to view the gem, you will be able to tell if it can be used in your metal clay work (assuming it is a gem approved for use in the kiln). A gem that does not contain any noticeable inclusion under 10x power it is considered "Loupe Clean". As a side note: the term "Eye Clean" is used to designate a gemstone that shows no inclusions when examined with the unaided eye. "Eye Clean" is not good enough for us when it comes to metal clay so please use a loupe.

Nearly any gemstone you come across (synthetics also have inclusions) can have inclusions. Some inclusions will cause problems, some will not. How does an artist without a gemological degree tell what will work and what will fail? The three most commonly encountered inclusions are as follows:

Shiny: Shiny is bad. If you find a shiny flash inside your gemstone it may be flux if it is synthetic or liquid if the gem is natural. Anything inside a gemstone made of trapped gas, or liquid can be shiny and is likely to expand at a much faster rate when heated then its surrounding gem host. It can create cracking or, in extreme cases, shattering.

Saturn: If you see a "snowball" surrounded by what looks like the rings of Saturn, you are looking at a "melt relic." This is commonly found in Corundum (Sapphires and Rubies). It is proof that the stone has been heat treated and is a decent guarantee that you can fire it in place. The rings around your snowball are diskoid fractures from where the included crystals had expanded and fractured the surrounding gem material. This does not mean it is completely safe to use however, you should still be cautious in your ramp up and cool down cycles to prevent further fractures.

Spider webs: Wisps and spider web looking inclusions aren't necessarily bad. If your gem is synthetic it can be un-melted borax or flux--these can potentially cause problems. However, if the gem is natural you may be seeing a common inclusion called "silk" which may be composed of one or more natural elements such as Bohemite or Asbestos.

Those are the 'big three' inclusions, but if you would like to know more about different types of inclusions for your own entertainment (and advancement) The "Photoatlas"series by E.J. Gübelin and J.I. Koivula (www.microworldofgems.com) is an excellent, if expensive, source.

When firing any gemstone, temperature control is critical. When professionals heat treat their gems, or produce them in the lab they follow a proven formula to ensure the best results. That means we should follow a formula as well. When you heat up your kiln, you must place then green ware (unfired) metal clay piece in at room temperature. You should not fast ramp your kiln either, as some gems are very sensitive to expansion and if they heat too fast they may fracture. I recommend the slowest ramp you can set your kiln to if you can manage the extra time; it is safer for the gem, the jewelry, and your sanity. You should also control the cooling process for the same reasons.

Heating or cooling a gemstone too quickly can result in what is known as "Thermal Shock" which is what it sounds like. Rapid changes in temperature can cause a gemstone to fracture just like putting a drinking glass filled with boiling water in the freezer. Once the firing cycle is complete, for most stones it is wise to not even open the door until the temperature reaches 800F or below. Even then you need only crack the door open to allow the rest of the cooling to complete without high risk of damage. Never ever quench a piece with gemstones in it.

There are many other things to be wary of when buying gems for your creations. Avoid buying or using anything that is diffused, bulk diffused, or any other kind of "fused". Many gems that are diffused are not stable and the treatment will destabilize, causing the stone change color when heated. Never ever use anything that has been irradiated because reheating the gem may cause the gem to take on the luster of corduroy. Do not heat assembled stones (e.g., doublets or triplets), because they are assembled using glue. Remember that "imitation" stones are an unknown material most of the time. An imitation sapphire can be anything from a synthetic blue Spinel, to an Iolite. Imitations can be of synthetic or natural origin. When buying synthetic gems always ask for information on the material and process used to create them. Flame Fusion synthetics are by and far the most internally clean lab created gemstones you can find in the average market.

After about a decade of working with metal clay and gemstones the best piece of advice I have is: If you are not 110% certain of the origin of, and treatments applied to a gemstone do not use it. No matter what type of glittering gem you choose to use in your metal clay creation, the last thing you want to do is ruin the whole thing. You want success and nothing less. Now isn't that is something we can all agree on?

For comprehensive information on natural stones that can be fired, see Deric Metzger's book "Natural Gemstones in Metal Clay" from www.demerjewelry.com.


Deric Metzger is a graduate of the Applied Jewelry Arts (GIA) is a Graduate Jeweler Gemologist (GIA) and an Accredited Jewelry Professional (GIA). Member of the Jewelers Vigilance Committee. You can contact him directly at DeMer@demerjewelry.com.

Deric Metzger