Conflicting numbers. Which is more accurate AGS or HCA?

[DanMgy]

I am currently looking at two AGS graded round stones and there is a contradiction between their report and the HCA score, specs below listed below. Looking at the ASET images on the report stone #2 appears to have much more structure and symmetry.

Stone #1
AGS Light: 0
HCA 1.9

Cut: 0
Polish: 0
Symmetry: 0
Table: 56.8%
Depth: 61.7%
Crown Angle: 35%
Pavilion Angle: 40.9%
Culet 0

Stone #2
AGS Light: 1
HCA: 0.7

Cut: 1
Polish: 0
Symmetry: 0
Table: 56.3
Depth: 60.1
Crown Angle: 33.4
Pavilion Angle: 40.8%

So this raises two questions for me;

1. Stone #1 has a 0 light rating but scores lower on the HCA report, so is the AGS or the HCA going to be more accurate?
2. Based on the numbers which will perform better, which will have more “life” in the stone?

I have tried to look for photos of different graded HCA stones but have been unsuccessful. Any insight of person experience on what you have seen or got would greatly be appreciated.

Thanks - D

 

[rhr75]

I personally would still opt for an AGS000 stone simply because the general marketplace places more of a premium on that vs. an HCA score which is really only understood by a smaller subset of buyers. I know this doesn't answer your question on light performance, but that would be my thought on it. Also, remember, the HCA is a general advisory tool, it doesn't take into account all the specific variances in the overall cut. So again, I'd trust the lab who has actually handled the diamonds vs. an online calculator that does not take into account the totality of the stone's specific dimensions.

 

[denverappraiser]

I"m not understanding your question. AGS doesn't have a score they call 'light'. Do you mean their cut grade, the whole report or the part below that?

HCA is evaluating a completely different set of data from what AGS is evauating. On the HCA scale, all scores below 2.0 are identical. It's not like school where 98% and 94% are both A's but one could be described as 'better' than the other. 1.9 and 0.7 are not different.

 

[DanMgy]

I"m not understanding your question. AGS doesn't have a score they call 'light'. Do you mean their cut grade?

I was trying to figure out how to link to a AGS report but couldn't find one right away. But on the AGS "Platinum Light Performance" report they have a catagory called "Light Performance". All the newer reports which contain the ASET image have that score in them, I believe it is the first score under/in the Cut Grade catagory.

But, you answered the question I was really looking for an did not understand. Using your analogy, grades are scored as letters, so anything under that 2 mark is an A and above it would be a B. It is just different types of A's based on prefernce. Righ?

 

[diamondseeker2006]

Since #1 has been graded with better cut and light performance, that would be the preferred stone of the two.

 

[denverappraiser]

I"m not understanding your question. AGS doesn't have a score they call 'light'. Do you mean their cut grade?

I was trying to figure out how to link to a AGS report but couldn't find one right away. But on the AGS "Platinum Light Performance" report they have a catagory called "Light Performance". All the newer reports which contain the ASET image have that score in them, I believe it is the first score under/in the Cut Grade catagory.

But, you answered the question I was really looking for an did not understand. Using your analogy, grades are scored as letters, so anything under that 2 mark is an A and above it would be a B. It is just different types of A's based on prefernce. Righ?

Correct.
On the AGS grading system, 'light performance' is one of the components of their cut grade as well as part of the title of the report.

Use AGS as shopping information in preference over the HCA.

 

[Dreamer_D]

The HCA should be used as a binary tool -- scores less than 2 mean evaluate further, scores over 2 mean reject. So in fact both of these stones are equal on the HCA.

Given that, I would trust AGS as the determining factor and select the AGS0 stone.

 

[Dreamer_D]

That said, is there a significant price differenc between the two stones? What is the lgf ratio of the two? Will you see them in person or can you get an IS image of the two stones to compare?

I ask because the second stone might be a nice find and good value if priced lower than the first, if it has a good IS image and the lgf ratio helps balance the shallow crown. It could be a good find.

 

[stone-cold11]

Just post the AGS report number and the carat weight as stated on the report.

 

[DanMgy]

I will post the link to the stones a bit later this evening.

But as a follow up question, any stone that falls under a HCA score of 2 should be considered EX/ID in narrowing the selection process. What would you do in a case where a stone scores above a 2 but is rated 000 by AGS? Would you ignore the HCA score and just go with the AGS grading?

Thanks!

 

[yssie]

I will post the link to the stones a bit later this evening.

But as a follow up question, any stone that falls under a HCA score of 2 should be considered EX/ID in narrowing the selection process. What would you do in a case where a stone scores above a 2 but is rated 000 by AGS? Would you ignore the HCA score and just go with the AGS grading?

Thanks!

I would want more info.

AGS0 w/ HCA over 2 that I would not want http://www.jamesallen.com/diamonds/D-VVS1-Ideal-Cut-Round-Diamond-1278529.asp
AGS0 w/ HCA over 2 that I would snatch up http://www.jamesallen.com/diamonds/F-VS1-Ideal-Cut-Round-Diamond-1362079.asp
AGS1 (dinged for polish) w/ HCA under 2 that I would not want http://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-2192350.htm

 

[CaprineSun]

AGS1 (dinged for polish) w/ HCA under 2 that I would not want http://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-2192350.htm

May I ask why not? I'm reading the polish as excellent. I'm still learning and would love your opinion.

 

[yssie]

AGS1 (dinged for polish) w/ HCA under 2 that I would not want http://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-2192350.htm

May I ask why not? I'm reading the polish as excellent. I'm still learning and would love your opinion.

AGS' highest grade is Ideal, Excellent is one below. To get the top cut grade AGS0 on the Diamond Quality Document the stone must have 0s in light performance, symmetry, and polish grades - otherwise the overall cut grade is no higher than the lowest of those three. GIA allows stones w/ VG pol/sym to make EX cut grade, as does AGS' Diamond Quality Report.

Nothing outright wrong with the one I linked - just seen better AGS0s (or AGS1s w/ grade lowered for finish as the case may be) wrt light escape under the table - the simulated ASET hints at it, WF's actual pics demonstrate it. AGS0 is a range, not all are created equal - and these stones do come with a premium so I want to be sure of what I'm getting. Many are comfortable just trusting the AGS0 moniker - certainly you're not going to wind up with anything flat out ugly by doing that.. really depends on how picky you want to be, and what you want to be picky about..

 

[CaprineSun]

AGS1 (dinged for polish) w/ HCA under 2 that I would not want http://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-2192350.htm

May I ask why not? I'm reading the polish as excellent. I'm still learning and would love your opinion.

AGS' highest grade is Ideal, Excellent is one below. To get the top cut grade AGS0 on the Diamond Quality Document the stone must have 0s in light performance, symmetry, and polish grades - otherwise the overall cut grade is no higher than the lowest of those three. GIA allows stones w/ VG pol/sym to make EX cut grade, as does AGS' Diamond Quality Report.

Nothing outright wrong with the one I linked - just seen better AGS0s (or AGS1s w/ grade lowered for finish as the case may be) wrt light escape under the table - the simulated ASET hints at it, WF's actual pics demonstrate it. AGS0 is a range, not all are created equal - and these stones do come with a premium so I want to be sure of what I'm getting. Many are comfortable just trusting the AGS0 moniker - certainly you're not going to wind up with anything flat out ugly by doing that.. really depends on how picky you want to be, and what you want to be picky about..

Thanks for the response--- especially the bolded.
So from this thread and the other one I posted I have gathered:

- HCA becomes useless when a stone is AGS0 as it is a tool for exclusion & practically all AGS0 would be contenders given the strict grading.

- However, AGS0 stones do not equate a "no brainer" in selecting a stone. Each still must be evaluated on their own merits and characteristics & further tools.

 

[yssie]

Thanks for the response--- especially the bolded.
So from this thread and the other one I posted I have gathered:

- HCA becomes useless when a stone is AGS0 as it is a tool for exclusion & practically all AGS0 would be contenders given the strict grading.

- However, AGS0 stones do not equate a "no brainer" in selecting a stone. Each still must be evaluated on their own merits and characteristics & further tools.

It's actually not all that hard to find AGS0s w/ HCA > 2 - but I think you are right in saying that for a stone graded AGS0 on the DQD, esp. one w/ the simulated ASET map, the HCA is no longer useful - you often will have more precise tools. Most people who know about HCA will run it through anyway I reckon

BIG ditto on the bolded. That's by far the most important thing IMO - whether a stone is top grade by GIA, AGS, HCA, EGL, HRD standards... if you know that you want a stone of a certain type/make, you've got to do the legwork to check that the stone is of that type/make - the papers aren't going to do it for you unless your requirements and theirs match exactly!

 

[diamondseeker2006]

Just wanted to say that a 1 on polish would not be a significant negative for me. That stone above looked like it might have a little leakage and I assume that was what Yssie was looking at. But there are stones that just miss getting 0 for cut because polish is excellent (while light performance and symmetry are ideal), and many of those can be a great buy.

 

[yssie]

Just wanted to say that a 1 on polish would not be a significant negative for me. That stone above looked like it might have a little leakage and I assume that was what Yssie was looking at. But there are stones that just miss getting 0 for cut because polish is excellent (while light performance and symmetry are ideal), and many of those can be a great buy.

yeah - that's why I picked it, the one would make it a great find for me too if it wasn't a bit leaky - avoid the AGS0 premium, too