Jump to content



Recommended Posts

I have been debating on purchasing a diamond on the internet versus a brick and mortar.  The last jeweler I spoke with told me that he chooses all of his rocks by their ASET.  He also said that GIA tripple X cuts can vary greatly in an ASET and that it lets him pick the best of the best.  Is there substance to that?  Hard for me to believe that there is a large variance between stones that have the same GIA cut grade.  

Link to comment
Share on other sites

Thanks for the info, I wasn't sure if he was selling me on the ASET just to steer me away from buying a GIA XXX online.  He showed me his stones (in the ASET), which he says all pass his ASET standards before he buys - they all looked very nice.  He also showed me photos of ASETs for GIA XXXs that didn't look as good as his rocks.  


Without a jewelers eye, I'm not sure if I would be able to tell the difference between a "good" GIA XXX and an "outstanding" GIA XXX in natural lighting. I am just going to have to decide if the price trade-off is worth it.  


Thanks again!

Link to comment
Share on other sites

The issue can be separated in three parts:


1) Are there differences in appearance in GIA-X(XX) stones?

2) Can the differences be detected through an ASET image?

3) Can the ASET image be used (by a consumer) as the only input for picking a stone?


To 1), the answer is undoubtedly yes. GIA deliberately included in its "excellent" grade diamonds that look quite different from each other, whereas AGS took almost the opposite stance, and defined a relatively specific "best" look, then grading stones on how far from that "best" they are.


GIA's reasoning is that different people have different preferences as to the balance between fire, brightness, sparkle and contrast, and this should be reflected in the grading system; here is a (fairly technical but still readable) article to explain how GIA built its cut grading system: http://diamondcut.gia.edu/pdf/cut_fall2004.pdf.


Whatever the merits of both points of view (and technical strengths of the respective grading methodologies), the fact is that I have never seen a GIA-excellent (or an AGS-0 or 1) look bad from a cut-derived point of view. Certainly GIA EX can look different from each other, and I prefer some to others.


To 2), again the answer is yes, different proportions (all graded GIA EX) result in different-looking ASET images. The big caveat there is that for any comparison of ASET images to be meaningful, the conditions in which the images to compare are taken have to be very similar (or the viewer has to be good at understanding and compensating for those differences). Putting the same stone at a 1° different angle to the lens means getting different results - and 1° on a typical 1 carat diamond means 0.1 mm.


To 3), I think the answer here is "not really", for three reasons:


i. Not all the differences in ASET images are "meaningful" in terms of appearance. An image that has (say) 10% blue and one that has 15% blue may well look different in a magnified ASET image, but the two diamonds may well look indistinguishable without magnification in normal light.


Vice versa, some differences due e.g. to transparency (not clarity) are not easily revealed by reflector images.


ii. Personal preferences play a significant role in choice; there are some GIA VG that I prefer to some EX (and frankly there are some AGS-0 that I like more/less than others), but they aren't necessarily those someone else would find more attractive. Nor do they necessarily have "better" ASET images based on conventional criteria (lots of red, a little green, some blue, no black/white).


iii. Typically a consumer views only a limited number of diamonds, and usually not all of these have ASET images, particularly images that are taken in a consistent manner across vendors. Developing the "eye" to understand how to interpret an ASET image in terms of what the diamond looks like in normal conditions takes more practice than that; learning to correct for the inconsistencies in image taking takes a lot more (if it can be done at all).


Seen from the other point of view (i.e. is the jeweler "telling the truth"?), a dealer may well rely on the ASET to form a judgement, but his preferences aren't necessarily those of the consumer, and some of the preferences are likely not to be related "objectively" to the ASET image.

Edited by davidelevi
Link to comment
Share on other sites

GIA xxx encompasses a rather deliberately broad range.  That’s both their biggest criticism and one of their strengths.  Something like 60% of the round stones coming out of the lab have an ‘excellent’ cut grade and 60% of what’s left are ‘very good’.  That’s a seriously skewed scale if the objective is to identify the best of the best based on the lab report alone.

At the same time, not everyone agrees on what’s the best.  There’s a tradeoff between light return at 90 degrees and light returning, say, a 15 degree angle off of center for example, and it’s not correct to say that 90 degrees is best.  You can’t have both.  Stones that do well in a Pepsi challenge type of environment with direct overhead light do poorly with soft low angle lights and visa versa. 

You’ve actually got an advantage in having a local store who has an ASET that they presumably know how to use, and stones to show you.   The first step is to look at some real stones, both under the ASET and in ‘real life’.  The guy seems willing to talk to you about it so hear what he has to say.  Can you see the difference that the ASET is showing you? 

While you’re doing this, by the way, it’s good to do the same test with color.  The steps are quite tiny and people are often surprised how difficult it is to tell the difference between a G and an I for example.  At the end you are going to have to draw a line somewhere and it’s helpful to do that based on actual stones you’ve seen rather than just what you’ve read about online.

Edited by denverappraiser
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...