Confused about different AGS certificates. Can experts chime in??

[rockabee]

So I think there are 3 different types of AGS reports:
1) Diamond Quality Document - Has numerical grade for cut (e.g., AGS O), light performance, propotion, symmetry, and polish
2) Diamond Quality Report - Has ideal/exc/etc grade for cut, symmetry, and polish
3) Diamond Quality Analysis - Basically like #1 for small stones, except no plot

My questions are on cut. My understanding is that in the DQD the best rating is AGS000, the stone is put through a sarin and then light performance is simulated and then graded, along with cut, etc. In the DQR, the best cut/finish rating is AGS triple Ideal and the grade is determined simply by measuring the proportions of the stone (i.e., no actual light performance test). At first I thought that it must be that the DQD is more strict than the DQR since it is based on simulated performance and quite frankly, since HCA plots the AGS0 area on every cut chart.

But the data is conflicting. If we have a 56% table, crown ang 37.4%, pav ang 40.2%. The DQD cut chart says that this would be AGS0 proportions.

http://www.agslab.com/members/content/docs/cuttinground/6mm-56Guidelines.pdf

However, according to DQR, those proportions would lead to a VG cut rating, two notches below ideal!

http://www.agslab.com/pbcg/AGSL_Proportion_Charts.pdf

However, for a 56% table, CA 34.6%, PA 41% stone, now the DQR rates it Ideal while the DQD puts that combination in the AGS2 range.

What gives? How can there be such a flip flopping discrepancy between these two cuts under the two AGS systems? Should I give more credence to one over the other?

 

[yssie]

The first link you posted is from 2004. I believe AGS revised their RB cut determinations early '05.

The second plot is from 2008.

 

[stone-cold11]

Yap, old guidelines. Also when they change the guideline, they then started using the performance based grading system instead of proportion based system for the DQD while DQR initially has no cut grade until 2008.

DQD is done by ray tracing simulation on the actual 3D model, while DQR is based on 2D average proportion of the stone. The guidelines for the DQD are just guidelines as it is a 2D average numbers, if in 3D, the facets do not work well with one another, it will not get an AGS0. DQR do not take such things into consideration.

 

[John P]

Date: 11/17/2009 10:48:02 PM
Author:rockabee

So I think there are 3 different types of AGS reports:
1) Diamond Quality Document - Has numerical grade for cut (e.g., AGS O), light performance, propotion, symmetry, and polish
2) Diamond Quality Report - Has ideal/exc/etc grade for cut, symmetry, and polish
3) Diamond Quality Analysis - Basically like #1 for small stones, except no plot

Update: The DQD is now called the "Platinum Report" and the DQR is now called the "Gold Report."

As SC mentioned, the DQD - now Platinum - incorporates AGSL's 3D ray-tracing metric to arrive at performance values for brightness, dispersion, leakage and contrast. It is diamond-specific and "Ideal" polish & symmetry are required for the overall AGS0 grade. It is their strictest report.

The DQR - now Gold - has always mimicked GIA's approach. Prior to 2006 it did not include a cut grade. Now it mimics their current approach; using averaged 2D proportions to assign a predictive grade (though their top grade differs in center and width from GIA's). It is not diamond-specific and, like GIA, their top cut grade ("Ideal") allows the top two grades in polish & symmetry.

Here are examples of DQD changes over the years. More discussion (on the 000 topic) in this thread.

 

[stone-cold11]

John, so will AGSL continue to issue DQD format report by request until the end of this year before completely changing over to the Platinum report format?

 

[rockabee]

thanks everyone for your responses.

sc, i got the link for the DQD cut chart off of AGS''s website so does that mean that the cut charts have not been updated since then for DQD? I understand that the DQD charts are just a guideline and that the real performance needs to be tested before a grade will be given. So in a sense, the cut chart isn''t even really that important. I guess you could have proportions that fall in AGS 1 that actually get graded AGS0 or AGS3.

 

[stone-cold11]

http://www.octonus.ru/oct/mss/gia-agspgs.phtml

Apparently there is an update in 2007.

 

[rockabee]

john,
since DQR is a proportion based system, as long as the stone falls within the cut parameters given on the chart, will it get that AGS grade?

i can see the commercial benefit of that to sellers. because if i cut my stone a certain way, i can be more assured that it will get a certain grade than submitting it to get a DQD (where there is risk I shoot for an AGS 0 and wind up getting something lower). not to mention i read on other threads that it''s a less expensive report.

but as a consumer who is looking at stones and doesn''t have an AGS cert, if i wanted to get a true sense of whether or not a stone would qualify for AGS Ideal, then it seems to me that I should focus on the AGS DQR cut table. If my understanding of what you are saying is correct, even if it falls within the AGS 0 cut proportions, it doesn''t really mean as much. so if its true that AGS0 (DQD) proportions are only a guideline while AGS Ideal (DQR) are the actual grading system, then wouldn''t it be helpful if HCA added the AGS Ideal (DQR) outline as well on its cut charts?

 

[John P]

Date: 11/18/2009 8:30:37 AM
Author: rockabee
thanks everyone for your responses.

sc, i got the link for the DQD cut chart off of AGS''s website so does that mean that the cut charts have not been updated since then for DQD? I understand that the DQD charts are just a guideline and that the real performance needs to be tested before a grade will be given. So in a sense, the cut chart isn''t even really that important. I guess you could have proportions that fall in AGS 1 that actually get graded AGS0 or AGS3.

That is correct. The official AGSL cut guides were generated with 0 deducation (when up to 0.49 are allowed) so they tend to err on the conservative side.

SC, the link you posted was generated outside of AGSL using PGS models with perfect wire-frame symmetry. They err on the liberal side.

the real performance needs to be tested before a grade will be given.

Yes. Which drives the old-school trade absolutely batty and - in large part - is why fixed charts were employed for the Gold Report. A step backwards IMO.

 

[John P]

You're a quick study rockabee.

Date: 11/18/2009 8:48:17 AM
Author: rockabee
john,
since DQR is a proportion based system, as long as the stone falls within the cut parameters given on the chart, will it get that AGS grade?

i can see the commercial benefit of that to sellers. because if i cut my stone a certain way, i can be more assured that it will get a certain grade than submitting it to get a DQD (where there is risk I shoot for an AGS 0 and wind up getting something lower). not to mention i read on other threads that it's a less expensive report.

A+

but as a consumer who is looking at stones and doesn't have an AGS cert, if i wanted to get a true sense of whether or not a stone would qualify for AGS Ideal, then it seems to me that I should focus on the AGS DQR cut table. If my understanding of what you are saying is correct, even if it falls within the AGS 0 cut proportions, it doesn't really mean as much. so if its true that AGS0 (DQD) proportions are only a guideline while AGS Ideal (DQR) are the actual grading system, then wouldn't it be helpful if HCA added the AGS Ideal (DQR) outline as well on its cut charts?

Personally, as a consumer, I'd only be concerned with MY diamond. Therefore, to me, the Platinum report, which evaluates all 57-58 facets in 3D, would be the optimum choice. Charts schmarts...Platinum is diamond-specific.

As for the HCA, it's not in the same evaluative league (and not meant to be) as even the 2D GIA report or AGSL Gold report, much less the Platinum. It's also another judgment; you may have noticed that the center of Garry's HCA system is not the same as the center of GIA or AGSL's systems.

It's most important to remember the HCA is just creating a "chalk outline" for a broad prediction. The lab reports evaluate the actual diamond - some in greater degrees than others.

Where the HCA takes a few basic measurements even 2D lab reports take more averages into account, and the AGS Platinum models the entire diamond in 3D to assess how the facets work together visually. Trying to apply AGS0 parameters to that HCA metric is highly predictive at best because, again, HCA is designed for rejection. Lab reports are designed for selection. Garry does a nice job of clarifying this on the results page.

 

[John P]

Date: 11/18/2009 7:49:00 AM
Author: Stone-cold11
John, so will AGSL continue to issue DQD format report by request until the end of this year before completely changing over to the Platinum report format?

I believe so SC. I think I recall that end of 2009 = end of old format (?)

 

[rockabee]

john, many thanks for the insights, very helpful.

 

[John P]

My pleasure.