GIA cut grade vs. AGS cut grade system. Which's better??

[tenbinko]

I've read on various websites that GIA uses a 2-D system to produce their cut grade while the AGS a 3-D system... and people at the AGS said that "Our Light Performance cut Grade is complex and is a three dimensional, computerized Ray Tracing of the light entering the stone. It measures the angle of each facet, not just the averages, as well as the size and symmetry of each facet."

But on GIA's website, I read that ray-tracing software was used, too... they just validated, evaluated, and refined their results and produced their cut grading system in 2006. Are those jewelers who claim that GIA uses a 2-D model wrong? Or is it that now, GIA uses the data in its huge electronic bank and assigns a cut grade after measuring all proportions and then manually checking the girdle, without actually seeing the performance of a 3-D model of the diamond on the computer?

People say that a GIA 3-Ex is surely beautiful, though an AGS ideal could look a bit worse in some cases due to painting at the girdle.

If you're buying a diamond blind, is it safer to go with GIA 3-Ex, then, given that the grader's taken a look at the diamond overall light performance manually?

Thanks so much in advance for any clarification.

 

[Regular Guy]

Others should check me, but you can't use a sifting system backwards.

Although 3 D calculations may have been used to come up with GIA's system, once the proportions were then computed and "frozen," you can't get back to 3D from the fixed picture and proportions created. With GIA, the given diamond, whichever one it is, is compared to the fixed picture and proportions.

With AGS, each diamond is mapped, 3D, and then analyzed that way...afterwards.

Both are limited for output of "actual" light performance, regardless of the proportions. But...diamond smart guys over many years suggest proportions provide high correlation with performance.

Although you might like what GIA does with painting, I think this aspect is more trivial.

The main point, regardless of the original foundation & formula, is that GIA applies a 5 level model and big center target, and AGS applies a 10 level grade, with a smaller target for zero.

Though you can game any system, it'll be harder to game an AGS 0.


Ira Z.

 

[Paul-Antwerp]

Hi Tenbinko,

I admit that all these systems and the way they are marketed can be confusing. I fear that while I will try to clarify, the entire thing will become even more confusing. Sorry for that.

In summary, what you have learned from various websites is correct in its basis. A bit more in detail, you could phrase it as such:

- AGS uses a 3D-system. The scientific basis is a study of 3D, and it is translated into a system that uses the full 3D-scan of the diamond.
- GIA uses a 2D-system. The 'scientific' basis (apostrophes have meaning here) is a mixture of 3D-'study' and human observations. This was translated into a system that uses rounded 2D-averages.

In this description, the GIA-system comes out very badly, but that it is not really the impression I want to leave. Even though I cannot support the methodology, it works for most stones.

As for the graders manually adjusting the grade, I think that neither system allows that.

Live long,

 

[tenbinko]

Thanks, Ira and Paul.

I thought painting/digging features were checked manually, so I made the assumption that at GIA, gemologists would assign a grade after looking at the girdle while at AGS, a cut grade would be assigned without people carefully checking the girdle.

So, it's possible for a GIA 3-Ex to not look so good... but experts in the industry have said that if they find a stone that's either a GIA 3-Ex or AGS 0, and it has a HCA score of less than 2, they can call it a day because the stone is sure to be beautiful?

Or, buying blind, if a stone had, say, a 40.8-deg pavilion, 34.5-deg crown, 56% table, 61% depth, 80% lower halves and 55% stars and excellent symmetry and an Excellent cut grade from GIA, it should be fine, right, as those are fairly ideal parameters?

But Ira, if neither GIA nor AGS can assess light performance adequately or as well as you think diamonds should be evaluated, who else can, for us consumers buying diamonds online and not able to view them in person?

 

[Paul-Antwerp]

Tenbinko,

You are coming close to explaining an important catch-22-situation in our industry.

As a professional buying diamonds all the time, I will never, never ever, under no circumstances whatsoever, buy a diamond blind, even if it comes with all paperwork one could imagine.

On the other hand, as a cutter catering indirectly to consumers, I am hoping to offer them sufficient information so that some consumers buy blind.

Live long,

 

[diagem]

Or, buying blind, if a stone had, say, a 40.8-deg pavilion, 34.5-deg crown, 56% table, 61% depth, 80% lower halves and 55% stars and excellent symmetry and an Excellent cut grade from GIA, it should be fine, right, as those are fairly ideal parameters?

"Should be fine" is extremely subjectivity, I would say chances for a 3-X GIA RB with the numbers you mention above to be situated in the upper echelon of most generic RB cuts is a posibility.
If this is enough for "buying blind"? For the majority obviously yes. It's certainly in my opinion a safe zone only.

But for consumers who prefer purchasing higher accuracy level of craftsmanships (which obviously translates into specific and consistant play-of-light) these numbers & proportions are simply not enough. Today we know for a fact that the minor facets (e.g. Upper girdle facets, lower girdle facets & star facets) are as crucial (maybe even more than the main facets) to the play-of-light of a Diamond performed by its movements.

Accurate placing & cutting of these minor facets is a major part of the play-of-light formula, I believe most cutters presently do not put much weight on these factors.

 

[tenbinko]

Thanks for everybody's response... it seems that every option comes with its own advantages and disadvantages and there's simply no perfect solution. A consumer would of course like to view the diamonds in person, and do so under a variety of lighting conditions, including normal, office-type lighting, and get all technical reports too, to make a final selection, all at the local jewelry store too too see the diamonds action, but of course, getting that whole package wouldn't be possible... the lighting's misleading, the technical analyses are absent (and not even a microscope is available for you to use in some cases... just well-dressed and/or good-looking salespeople trying to coax you into buying the most expensive item possible), and the prices abominable, etc. I guess buying online, we have to accept the simple fact that we can't see the diamonds... but what do you think of GCAL's certificate? I know very little about it... but it seems that it provides two things that neither GIA nor AGS provides, a picture of the diamond's actual light performance and an image of its optical symmetry as well. I've attached two pictures here.

Along with a GIA 3-Ex or AGS-000, would these pictures indicate that for sure, the diamonds are very beautiful? My guess is no, though I wish it's yes... I've seen images on the web of AGS ideals which looked darker than GIA Ex's due to girdle painting, and those diamonds that performed worse had amazing Idealscope images, which I guess would be similar to GCAL's optical brilliance images?

 

[Karl_K]

which I guess would be similar to GCAL's optical brilliance images?

Gcal will not submit their diamond lighting and criteria for peer review.
We can take a pretty good guess at what they are doing based on the images but it is not an open standard.
My problem is how do I interpret it accurately if I don't know what and how they are doing it?

 

[Regular Guy]

Thanks, Ira and Paul.

But Ira, if neither GIA nor AGS can assess light performance adequately or as well as you think diamonds should be evaluated, who else can, for us consumers buying diamonds online and not able to view them in person?

Hi, Tenbinko,

I'll share 3 thoughts with you:

1) I do tend to think the science of diamonds works pretty good, and that the light performance metrics are relatively adequate, and can be used for your basis of evaluation. Also...I'm although I'm with Paul about really wanting to hold yourself as the ultimate witness...see point #3 below...for a layperson like myself...since it really is hard to tell the "wheat from the chaff...," by relying on significant measure on things like angle measures and on-line resources to sift among the best...you effectively narrow to what you can pretty reliably regard as among the very best options available to you.

2) When shopping for fair trade options from Botswana, I was hopeful about those gemscan optical measures. But, consistent with Karl's comments, I think Stone Cold provide me sufficient quick evidence that they are not very trustworthy, though better than nothing...if nothing is your only option. Probably, a target of like AGS zero is much better than nothing, and if you have that option available, without a huge premium...it's a good option.

3) Finally, since everything in a vacuum is either nice, or only relatively good...try to remove your relatives. That is...

a) First, of course, whatever you buy, you should know in advance of your buying it that you can return it within a comfortable measure of time, and
b) set up in advance that you can bring your diamond to a place with nice options you can select among instead. Be honest with the vendor (you know.. a Tiffany's, or a place that has Hearts of Fire, or some place with a reputable or vetted set of goods), and let him know that you're likely to be happy with what you'd already purchased...but invite him to have a shot...and compare with abandon. It's a win win for both you and the vendor. Hopefully...you will like what you got!


Ira Z.

 

[tenbinko]

Thanks, Ira.

What I know now is that sound science, or the research done by AGS and GIA, can be used to narrow down choices and the level of correlation to actual performance is very high. (And I wish I had the luxury to compare diamonds, haha, but I don't know if any vendor will allow that, but I'll see what happens...)

Even though the research done by AGS and GIA is not foolproof or does not guarantee superb performance 100% of the time, to the best of your knowledge, a GIA-3EX or AGS-0 can't look that bad compared to most diamonds, can it? I'm asking this on behalf of my friends who don't or won't have the time to do too much research: if people buy a diamond that has achieved a GIA 3-EX or AGS-0, can it be said that it is with 100% certainty they will not get a dull or lifeless stone, however subjective terms like "dullness" or "life" can be?

 

[denverappraiser]

Thanks, Ira.

What I know now is that sound science, or the research done by AGS and GIA, can be used to narrow down choices and the level of correlation to actual performance is very high. (And I wish I had the luxury to compare diamonds, haha, but I don't know if any vendor will allow that, but I'll see what happens...)

Even though the research done by AGS and GIA is not foolproof or does not guarantee superb performance 100% of the time, to the best of your knowledge, a GIA-3EX or AGS-0 can't look that bad compared to most diamonds, can it? I'm asking this on behalf of my friends who don't or won't have the time to do too much research: if people buy a diamond that has achieved a GIA 3-EX or AGS-0, can it be said that it is with 100% certainty they will not get a dull or lifeless stone, however subjective terms like "dullness" or "life" can be?

A GIAxxx or an AGS0 above a clarity of, say, I2 will not be lifeless or dull. It will be in the top several percent of the diamonds out there in terms of light return and brilliance.

 

[Paul-Antwerp]

Your question in other words is: if a stone is graded GIA-3EX or AGS-0, can this suffice as information to buy?

There is no right answer to this question, as it depends on the requirements of the consumer. For me personally, but I am not a consumer, it does not suffice, and let me explain you why:

- Since I would buy to re-cut to another cut-quality, I need to study further measurements in order to judge the loss in weight.
- I need to study stress in the stone, to assess the risk of putting the diamond on the cutting-wheel again.
- I need to personally check color, to be sure that the lab-grade is correct, and will be confirmed when graded a second time.
- In the same way, I need to personally check clarity.

That is why a diamond is never a commodity in my eyes.

Back to your question: For some consumers, simply having the lab-grade is sufficient. For many other consumers, it will just be a starting-point. It depends on the consumer, his or her desires and sophistication.

Live long,

 

[tenbinko]

Thanks, guys, I was just wondering whether it's technically possible for the 3-Ex stones to be dull in real life, and it seems that this is not really possible, because a 3-Ex or 0 grade guarantees performance to some degree. I know that some 3-Ex stones will be better than others, or better or worse compared to 0 stones, but if it's safe to assume that a diamond bought online with a 3-Ex or 0 grade will perform reasonably well, despite those grades being essentially predictive, then I'll promote online buying among my friends, who wish to save money and buy something beautiful as well.

 

[denverappraiser]

Thanks, guys, I was just wondering whether it's technically possible for the 3-Ex stones to be dull in real life, and it seems that this is not really possible, because a 3-Ex or 0 grade guarantees performance to some degree. I know that some 3-Ex stones will be better than others, or better or worse compared to 0 stones, but if it's safe to assume that a diamond bought online with a 3-Ex or 0 grade will perform reasonably well, despite those grades being essentially predictive, then I'll promote online buying among my friends, who wish to save money and buy something beautiful as well.

'Dull' is not a well defined term and there are a few things other than cutting that can cause it (clarity and cleaning) but yes, a 3x or 0 of decent clarity can be expected to perform at least reasonably well regardless of where it's purchased.

Diamonds being sold online are NOT different from diamonds being sold in stores. In fact mostly the dealers aren't even very different. The majority of the online dealers are no more or less than a jeweler who happens to be in someone elses' neighborhood. They may sell crap and they may not but the difference isn't with their address. Regardless of where you buy your diamond, the dealer is going to be getting it from an outside supplier and those suppliers sell to both venues more-or-less equally. The online lists are nicely public and highly price competitive which makes them extremely useful for shopping purposes even if you end up buying locally. I absolutely encourage you to shop with your local merchants and to make whatever deal with them you can. By all means show them what you've found elsewhere as an alternative and see if they want to compete. Heck, I would even be willing to pay MORE to get it locally. The tricky question, of course, is how much more. There is a limit.