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- May 1, 2008
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Looser than you might think Garry? Human eye symmetry judgments at 10X don't pick up 1-2 degree variations in facet angles, much less 3/4 or half degrees.Garry H (Cut Nut)|1387319535|3576375 said:...To achieve GIA Excellent symmetry the stone must have reasonably tight variations in angular differences...
A couple of years ago in a class I was teaching, I passed the attendees three diamonds: All had EX lab symmetry; great meet-point and twist, but one had huge swings in CA/PA, up to a degree on the PA. With 10X magnification no one spotted the angular issues. I did that exercise to illustrate this very point, btw.
That diamond woua .SRN file, and it's likely to be teased out in a H&A viewer. But typical human 10X symmetry inspection will still miss it. That may be conquered as we rely more and more on mechanical scans for the 2D sym grade.