AGS Ideal 0 vs. GIA Excellent vs. HCA - Chart Discrepency!

[Lurky McLurks]

Hi Experts,

I have noticed a discrepancy in the HCA chart that shows the outline of the potential AGS 0 Ideal diamonds compared to the tabular chart found in the FAQ pages alleged showing the same thing. I''ve attached both charts below. My diamond has the following characteristics.

Depth %: 60.6
Table %: 57
Crown Angle: 34.5
Pavilion Angle: 40.6

According to the HCA, the diamond scores a 0.7, and falls within the AGS 0 Ideal and the GIA Excellent. However, according to the chart on the FAQs page, the diamond does not fall within the AGS 0. Thoughts? Gary? JohnQuixote? Thanks for the advice and help!

(I''m leaning toward trusting the HCA chart over the tabular chart, as the depth % is taken into account, but I just don''t know...).

 

[whatmeworry]

Go with the HCA chart. It''s more accurate. The tab chart is based on a the what cutters should shoot for to try be assured to get the 0 grade. Sort of like aiming for the center of the target. Again being inside the box doesn''t assure you of the 0 grade. It would just be a candidate.

From the octonus website, a more accurate box with AGS grading based on the actual software.


http://www.octonus.com/oct/mss/gia&agspgs.phtml

 

[John P]

Date: 8/20/2008 12:17:30 PM
Author:Lurky McLurks
Hi Experts,

I have noticed a discrepancy in the HCA chart that shows the outline of the potential AGS 0 Ideal diamonds compared to the tabular chart found in the FAQ pages alleged showing the same thing. I've attached both charts below. My diamond has the following characteristics.

Depth %: 60.6
Table %: 57
Crown Angle: 34.5
Pavilion Angle: 40.6

According to the HCA, the diamond scores a 0.7, and falls within the AGS 0 Ideal and the GIA Excellent. However, according to the chart on the FAQs page, the diamond does not fall within the AGS 0. Thoughts? Gary? JohnQuixote? Thanks for the advice and help!

(I'm leaning toward trusting the HCA chart over the tabular chart, as the depth % is taken into account, but I just don't know...).

Hi Lurky.

It looks like you found an error on the FAQ table in the 40.6 range. Either that or Marty Haske was going from an old chart when he created these in 2006.

Current cut guides from AGS predict those broad numbers to earn 0 (exact score would be based on all 57 facets of course). In a big picture sense the AGS, HCA and GIA all agree that you're in a very nice performance "zone."

 

[John P]

Date: 8/20/2008 1:39:18 PM
Author: whatmeworry

Go with the HCA chart. It's more accurate. The tab chart is based on a the what cutters should shoot for to try be assured to get the 0 grade. Sort of like aiming for the center of the target. Again being inside the box doesn't assure you of the 0 grade. It would just be a candidate.

Good advice, especially noting the highlighted.

From the octonus website, a more accurate box with AGS grading based on the actual software.

http://www.octonus.com/oct/mss/gia&agspgs.phtml

Also useful, but a similar caveat applies: Where the official AGS cut guides are conservative the Octonus charts are liberal.

The Octonus charts presume perfect wire-frame symmetry and complimentary lower halves/stars, so some configurations predict scores too high for reality. As an example; 0 is predicted on several charts at 41/35.5 but many diamonds at that configuration will not earn 0.

Alternately the AGS cut guides are harder than lab grading. They give a 1 for any deduction, but in reality the deduction must be greater than 0.49 to result in a 1 at the lab. AGS takes this official position because they would rather give cutters information that errs on the strict side.

Since AGS bases their grade on how all 57 facets work together a set of comprehensive charts is not practical. Any of these charts are broad predictions. For a definite answer one would need to send the diamond to the lab or run its full scan through the PGS software.

 

[strmrdr]

Date: 8/20/2008 2:52:39 PM
Author: John Pollard
Since AGS bases their grade on how all 57 facets work together a set of comprehensive charts is not practical.

That ended up being the official policy per Peter at AGS when we had the long discussion on PS about updated charts a while back.
Which is why Octonus published the newer charts and not AGS.

It is a policy that makes sense and I agree with.

 

[Lurky McLurks]

Thanks everyone!

I know I have a great cut stone (toot toot!), but I really liked the fact that even though it is GIA certified Excellent, that it also had the geometric *potential* to be an AGSL certified 0. I stumbled upon PS after already purchasing my stone, but I really feel as though I lucked out with my dimensions (I''m taking it to get appraised by Patrick here in LA for quality confirmation).

Here are the full specs:
GIA cert. Excellent cut
Depth: 60.6%
Table: 57%
Crown Angle: 34.5
Pavilion Angle: 40.6
Color: G
Clarity: VS2*
Culet: None
Girdle: Thin to Medium, faceted.
HCA Score: 0.7

* After about a week of obsessivly looking, I think I spotted an inclusion that can be seen by looking up through the side/bottom of the stone at a very specefic angle. After researching on PS, I believe this is acceptable for VS2, as I cannot see anything from directly above (eye clean...check). I purposly avoided feathers in my stone for VS2, just a mind thing for me. Thoughts on this....? It doesn''t bother me that I can see the inclusion**, I know my gf will never see it, and plus it gives the stone some character in this depressing world of diamond hunting in which perfection is the goal!

** The visible inclusion from the side is what prompted my soon to be appraisal, I don''t care about the inclusions as long as the value of the stone matches what I payed (i.e. if the appraisal says its actually SI1 instead of VS2, the stone is going back).

Thoughts on this logic???

 

[strmrdr]

Date: 8/20/2008 3:52:25 PM
Author: Lurky McLurks


** The visible inclusion from the side is what prompted my soon to be appraisal, I don't care about the inclusions as long as the value of the stone matches what I payed (i.e. if the appraisal says its actually SI1 instead of VS2, the stone is going back).


Thoughts on this logic???

sounds good to me

 

[Lorelei]

What is the size of your diamond? A tiny inclusion can indeed make a diamond more unique to me, but an appraisal could be a good move just to give you some peace of mind, your diamond sounds gorgeous!

 

[Lurky McLurks]

Woops - forgot the most important part of my diamond (to some people).

Carat: 1.02
Measurements: 6.51 x 6.53 x 3.95 mm
And also ex. polish and symmetry.

 

[Lorelei]

Date: 8/20/2008 4:02:52 PM
Author: Lurky McLurks
Woops - forgot the most important part of my diamond (to some people).

Carat: 1.02
Measurements: 6.51 x 6.53 x 3.95 mm
And also ex. polish and symmetry.

The larger the diamond, sometimes it is easier to see inclusions, even in VS clarity grades, so that is why it is useful to know.