A Faceter’s Guide to Rough Gem Stress
by Jeff R. Graham
A spectacular slice from a large tourmaline shows a cranberry red rind, bright pink just inside, and a yellowish-green center. Although this beautiful specimen most likely isn’t destined for faceting, it helps illustrate areas of a gem that could be subject to stress. “Tourmaline,” Ambositra District, Amoron’i Mania Region, Fianarantsoa Province, Madagascar. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
"Are rough gemstones under stress? Yes, in some cases, stress or strain does exist in crystals.
Table of Contents
What Causes Gem Stress?
Into Each Faceter’s Life Some Broken Gems Must Fall
Can Any Cutting Techniques Help Mitigate Gem Stress?
Use a Fine Lap
Skin the Crystal
Improving the Odds
Tourmalines and Gem Stress
Types of Stress in Tourmaline
Rind Stress
Internal Stress
Double Whammy
What to Watch for When Buying Bi-Colored Tourmaline Rough
Color Zones
Mines
Colors
Do Research at Gem Shows
What to Watch for When Buying Indicolite Rough
Why Does Heating Cause Gem Stress?
Why Does Heating Occur at the Mines?
Signs of Heat-Treated Indicolite
Do Synthetics Have Less Gem Stress?
What Causes Gem Stress?
Many things can contribute to stress in rough gemstones. Heat treatments can cause inclusions in gemstones to explode, creating internal stress fractures. For example, commonplace corundum heat treatments can sometimes create halo-like stress fractures around inclusions in rubies and sapphires. Explosives used in mining can also stress crystals.
The natural growth of crystals can also introduce stress. For example, traces of chromium or vanadium in emerald not only give it its amazing green color but also weaken its crystal structure. Some gems, like tourmalines, show beautiful color zones. However, these zones formed when the conditions of crystal growth changed, sometimes violently.
Into Each Faceter’s Life Some Broken Gems Must Fall
Everybody loses a stone once in a while. I once had this beautiful and quite valuable 20-ct Nigerian rubellite. Unfortunately, it just split after cutting with no warning. That’s just life.
Some faceters believe you can somehow relieve gem stress and keep the stone from cracking during cutting. Some may disagree with me, but I think this is a myth. In my personal experience, if stress exists in a crystal and you try to alleviate it by cutting into it, through it, or near it, you’re only going to let the stress loose, so to speak. In some cases, this will actually create the flaw you wanted to avoid.
Of course, some people have all kinds of theories to stop gem stress from causing problems. For example, some recommend letting the stone sit in water on the lap. Personally, I think this will only accomplish two things – the stone and the water/lap will have the same temperature, and you’ll get wet.
Now, thermal shock is very bad for a stone, so this isn’t a bad idea. However, it’s only worthwhile if a significant temperature difference exists between the stone and the water. Otherwise, you’re wasting your time. I don’t think letting a rough crystal sit in water will affect gem stress one way or another.
If you want to try this out, go ahead. It probably won’t make anything worse.
Can Any Cutting Techniques Help Mitigate Gem Stress?
Based on my own experiences, I think the following recommendations may help in some cases. ... "
https://www.gemsociety.org/article/stre ... ty-roughs/
