I need some opinions from the diamond experts here. One of
our students in our diamond class is insisting that all
diamonds are currently graded under 20X. He does not take our
word that is not so. So, I would appreciate some comments
here. Especially, from Mr. Roskin whose book is one of the
best on clairy grading.
There are idiots in any class that won’t believe their
instructors. Maybe he’s confused though. While the standard for
diamond grading states a 10x corrected magnifier, most graders
use a binocular microscope. So each eye is seeing 10x. Maybe he
wants to add the two together? Or perhaps he’s referring to the
practice of many gemologits with zoom scopes to at least look at
the stone under higher magnification, even though grading calls
must be made on the basis of what’s visible at 10x. Checking
with higher magnification with a zoom scope is an easy way to
make sure one has not missed something silly. But this should
be explained as “cheating”, not as the standard. The standard
doesn’t even require a binocular scope or darkfield illumination.
A lot of old timers in the industry are quite happy to do most
of their day to day grading just with their loupe. The 10x one.
You can’t see as much with a 20x loupe. Too short a depth of
field, and even with a hastings triplet, at 20x, you’re starting
to get significant distortion.
You know all that already of course. This is just something to
print out to back you up. the GIA standards, similar to other
standards around the world in this respect, specifies only 10x.
So do FTC standards for diamond grading. Whether certain graders
choose, on their own, to also use higher magnification for their
own peace of mind is their own business. Some do, many do not.
All must use the visibility of inclusions at 10x as the actual
basis for their grading decisions.
Peter Rowe G.G.