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Inclusion or Crack? A Fine Line

Posted by Yvonne Raley on

We’re getting sucked into the lore together, my customers and I.  Once you own a couple of pretty pieces, you want more: bigger, better, more perfect looking.  And so the stakes increase.  Most of you now own a loupe, and the new customers already come equipped.  That’s the reputation I built, for better or worse.

And with May, the birthstone month of emerald, just having ended, I can breathe a little easier, because as perfection goes, emerald is one of the greatest challenges.  A naturally included and somewhat brittle stone, emerald easily gets chipped and scraped during storage.  In the little plastic bags, diamond papers, and even in the gem trays, they bump into each other and nick the surface of their neighbor.  Given the ever decreasing stash of my gem dealer friend D, I now have to triple loupe everything.  Catching a flaw in a 4mm stone is not easy even with a loupe, and when you add to that the time it takes to match two stones, your afternoon can quickly get sucked out from under you.
Meanwhile, the numbers of those who want one of these pieces is increasing – perhaps because supplies are shrinking elsewhere as well, and prices correspondingly rise.
Add to that another problem with gemstones in general, and emeralds in particular: inclusions.  These are tiny little openings inside the gem where stuff gets trapped that makes the gem look ugly.  That’s what makes oiling, polymer, and other coatings so attractive for the seller.  They seep into the crevices and open spaces, smoothing out the ugly spots.
Emeralds are among the most highly included gems I work with.  And consequently the most problematic.  The line between an inclusion is as narrow as a tightrope.  Here’s why: when gems are faceted, it is the cutter’s challenge to make sure none of the inclusions reach the surface.  When they do, then that gets judged to be a crack or a nick, and the stone becomes a reject.  When you try to repolish the table of such a gem, the crack opens up more and more, until the stone is so flat you can’t use it at all.  That’s why with extremely rare gems, like larger alexandrites, the stone is left as is and sometimes still sold at a high price.  I’ve also seen this with a green diamond once. It had a “hole” as it was described to me, and there was no polishing it out.  Still it was worth over $40,000, because of its rarity.
When you slice the more included material, as is now done with emeralds, you face an even bigger problem.  For one, the rough is more included to begin with.  Secondly, when it is sliced, and the inclusions are too long, the stone can just break in two.  Or it can look like it has a crack that goes across the entire surface, as if you had dropped it or hit it with a hammer.  If you have rough sliced and are paying for it, you can end up with nothing but slices like that, and it’s your cost.  Or you sell them anyway – sometimes I do.  If you think they won’t break, then they are emeralds with inclusions on the outside, not cracks.
Emerald Rough, Included, not Faceting Grade
A smaller piece of rough.
So is it ever a crack?  Well, yes.  If it wasn’t there before the setter touched it.  If it wasn’t there before it went into ultrasonic for cleaning (generally not advised for emeralds) or when it was steamed at close range and there was no crack before.  Then it’s a crack.  But it’s still a fine line.  A stone had a fine inclusion that got bigger from the pressure of hammer setting.  The inclusion opened up into a crack, we say.  Or just “it cracked,” Or “it opened up.”  Take your pick. 
Same Rough After Slicing.  The top two are from the rough in the second picture, which looked cleaner initially.  But the inclusions came to the surface.  The second two slices (from the first picture) fared much better, though a piece broke off on the slice on the right and the stone had to be shaved down.
So in a way, there’s not always an intrinsic difference between the two.  You can tell, sometimes, more easily with less included stones for sure, that the stone did crack from some sort of pressure: in a sapphire, for instance, a crack will reflect light like a little rainbow, as opposed to the “silk”, the white lines, that are naturally part of the stone. 
The upshot: it depends on the stone, on what exactly you see, and on the before and after of cutting, setting, cleaning and polishing.  It’s just not a straightforward matter.  A very philosophical answer, I know.

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