Clarity and light performance

[Tmb2087]

I posted a while back about a diamond I put on layaway. It’s triple excellent and scored a 1.8 on HCA but it is an SI2 and I was concerned about the clarity affecting light performance. (Crystal, cloud listed on report in that order) I haven’t had the chance to go in person to look at it again. But I got the above email from their GIA gemologist, and it seems to contradict what I’ve learned here. A triple excellent diamond can have big clouds that subdue light performance, correct? This shop has a very good reputation in my area and has been around for a long time. But this has me concerned, should I be?

 

[Karl_K]

The cut grade at GIA is given by a scanner.
They put the diamond in a scanner it measures the angles and %(some are calculated from other measurements) and it spits out the cut grade after grossly rounding the numbers.
It outputs:
cut grade
symmetry grade
numbers to put on the report..

For some diamonds color is also machine graded.

 

[Rockdiamond]

I would strongly disagree that GIA's cut grade has anything to do with what we discuss here as "light performance"

 

[Texas Leaguer]

It's best to think of overall lab cut grade as completely independent of clarity grade. It's better to think of it as a measure of craftsmanship as opposed to absolute light performance, as other factors are involved.

GIA cut grade is a table-based mathematical calculation of various measurements of the diamond and comparing that set of measures to pre-defined tables; Excellent, Very Good, Good, Poor

AGS light performance cut grading is much more sophisticated and exacting, involving computerized ray tracing and evaluating the impacts of the 3D geometry of all the facets on various aspects of light perfomance; brightness, leakage, contrast and fire. Yet, these calculations are STILL independent of clarity and other factors that can impact observable light performance.

The lab report can give some clues as to factors which can limit the actual light performance of an otherwise top cut. The clarity grade is the big one, but other factors such as polish grade, comments as to characteristics not plotted, and the potential for transparency issues related to fluorescence.

In neither case (GIA or AGS) is the overall cut grade judged by a human grader. It is an objective assessment rendered automatically by inputs from the non-contact measuring device according to the particular system designed by the lab. And it must be seen in the context of the other factors evaluated at the lab for a more complete picture of the diamond's performance.

An independent evaluation by a qualified professional is always recommended, especially for any diamond with lower clarity grade and/or items in the report that suggest caution.

 

[headlight]

I feel like we are talking about more than 1 thing here. First off, to @Tmb2087 you need to know (if you haven't picked up on it already), this forum does not give much credence to the GIA Cut Grading System. The point being that the majority of the participants here do not agree with the statement made by the gemologist at your jeweler: "Since this diamond is graded triple excellent, you can be assured it has excellent light return". However... and to the trade who have already commented, please correct me if I am wrong... there is a light return issue and a clarity issue. I believe OP's concern was if the clarity characteristics on a particular stone would be an IMPEDIMENT to the beauty of the stone (how I am interpreting the concern). I think that is a separate issue from what we here on PS are talking about when we evaluate a diamond as to its light performance (or lack thereof). So, really, as I see it, the gemologist at the jeweler has convoluted the matter. I don't know if that store's "gemologist" is a GIA G.G., but, if so, that is unfortunate because even I, a gemology student, who just only recently earned GIA Diamonds Graduate but still has a ways to go toward reaching G.G., knows that these are 2 separate things. Yes, I understand that ultimately, at the end of the day as the saying goes, regardless of what we call it and how we want to "package" it, the retail customer-end user just wants to know if all the elements of what is on the lab report will yield an attractive stone... the culmination of its proportions and any adverse impact from clarity characteristics. Case in point: My diamond (in avatar), is GIA E color, YET it is cut deep (of course, not by GIA standards LOL, but by PS standards). So, in this instance, if the stone was not cut as deep as it is, it could have possibly received a color grade of D... but because of its depth which can adversely impact its perceived color, it is graded an E (yes, it still may have been an E). To our trade contributors, if this doesn't sound right to you I can assure you I had this exact conversation with one of my GIA instructors so I'm not making this up! By the same token, REGARDLESS of a stone's proportions and how that translates into light performance, if a stone's clarity characteristics have an adverse affect on a stone, that in and of itself will be an impediment. And, from my interpretation, I believe that is what the OP's concern is... and the "gemologist" at the jeweler did not answer this question appropriately nor accurately. She gave a blanket "triple X" response. She did not address the clarity issue.

 

[sledge]

You've gotten some excellent advice from trusted trade members here. They've put it much more delicate than I would have.

I personally feel that email you got was borderline ethical, considering the person should have known the nuances of the subject matter. It's tempting to kick the dead horse, but I will resist.

In regards to the stone you have on layaway, can you post a video, picture and/or lab report? Perhaps we can further advise you. Even if the stone has perfect proportions, a black crystal right smack dab in the middle of the table is going to impede light performance. Of course, I'm not saying or implying you have a black crystal, just using as reference.

Just my 2 cents, but I think anytime you are looking to purchase a SI2 stone, you have to accept the fact you may find a few duds before your stud. Not saying good eye clean SI2's don't exist, but they are hard to find. Especially ones with inclusions that don't impede light performance.

You have right to be concerned. I'm just uncertain how to help you without more data to analyze. You indicated crystals and clouds (in that order) were the inclusions. By chance is there a "clouds not shown" or "clarity based on clouds not shown" note on the side? Both have different meanings but could both indicate transparency issues, especially with SI2 clarity.

 

[lovedogs]

No offense, but that email is just nonsense. Triple X cut has nothing to do with clarity. Of course giant clouds or inclusions negatively affect brilliance/diamond quality bc they affect how the stone looks to your eyes and how light is reflected

 

[Tmb2087]

This is the report. The first time I looked at the stone, I really did like it especially when compared side by side with a couple of other stones but I’m not experienced enough to tell if it truly has great light return. I think what I’ll do is take it to an independent appraiser once I pay it off. If it’s not the stone I’m hoping it is, they have a 30 day guarantee so I’ll just exchange or return it.

 

[mission1]

It's slightly deep due to the crown angle/table combo, and faces up very slightly smaller than an ideal cut (though not enough to be visible). However, from other posts on here I understand that 36/40.6 can be nice (try doing a search on it), and the HCA score is good.

However, as it's an SI2 you're right to be concerned about the cloud even though it's the second grade marker - at the very least can you look at it in person through a loupe and compare side by side to another stone that doesn't have clouds listed? To be honest I'd be sufficiently put off by the gemologist though...!