H&A AGS000 gets an HCA score of 4.1 - confused?

[ssc5174]

H&A AGS000 gets an HCA score of 4.1 - confused?

Check this out. I recently took a look at a Hearts & Arrows AGS000 stone - stats as follows:

2.55 cts
H Color
Si1
Depth 61.5%
Table 56.7%
Crown Angle 35.6
Pavilion Angle 41
Culet - none

This stone scores a 4.1 on the HCA. I''m confused how a H&A, AGS000 can score so poorly on the HCA. Does this HCA tool even work? The stone looked very nice.

 

[Regular Guy]

Not sure if this applies or is helpful...but some basic facts should maybe be clarified.

See this post. First of all, have you seen the documentation on the diamond. Does it have a "contemporary" AGS document, showing one of the zeros as for light performance?

If not, this may explain the differential.

 

[ssc5174]

The stone has a current AGS cert (May 10th, 2006) with a light performance score of "0"

 

[JulieN]

HCA is not used to second guess the 0 grade.

How did it look under Ideal Scope?

And the diameter?

 

[ssc5174]

HCA is not used to second guess the 0 grade - can you clarify?

The dealer had a "proportion scope"....it looked nice under the scope.

 

[JulieN]

Proportion scope, like a Hearts and Arrows viewer?

If it doesn't look like the IS images you're used to seeing, then it's not an IS. The viewer only shows symmetry but will not affect leakage.

AGS grading is only done on the apparent view, and as long as bad proportions are not breached, then it does not affect the cut grade.

There are two possibilities, and only an Ideal Scope image will clear it up (or I guess a .srn,) IMO.

1. The stone you are looking at is truly gorgeous and and competes on the same level (or better!) as the hearts and arrows rounds that score under 2. Minor facet configuration, which is NOT taken into account in HCA, plays a larger than usual role.

2. Many people believe that the AGS 0 grade is a little broad. This could be a stone that, with proper minor facet configuration, just barely made the 0 grade.

 

[Regular Guy]

2. Many people believe that the AGS 0 grade is a little broad. This could be a stone that, with proper minor facet configuration, just barely made the 0 grade.

You''d think if it''s even sort of H&A, this would cover for irregularities in facet construction.

 

[JulieN]

Oh, which brings me to: "Alternatively hearts and arrows diamonds, which have excellent optical symmetry, but often HCA scores around 2, may out-perform diamonds with lesser symmetry and lower HCA scores."

 

[Regular Guy]

2 vs 4.1.

That''s a big stretch!

 

[JulieN]

Yes, but the score is affected more crown side and pavilion side. The only instances that I have personally seen where the HCA >2/AGS0 is crown-side, and not pavilion-side. I doubt you will see any 4 HCA with 41.3 PAs that make the 0 grade. Maybe that GIA rounding to .5 does have logic behind it, as Jon suggests!

You will notice that the X falls outside of the AGS outline for the 0 grade, which is the AGS guideline for the 0 grade.

"Does the HCA even work?" is, IMO, the same question as "How does a stone outside the box get a 0?"

 

[Regular Guy]

Date: 8/15/2006 10:18:19 AM
Author: JulieN
Yes, but the score is affected more crown side and pavilion side. The only instances that I have personally seen where the HCA >2/AGS0 is crown-side, and not pavilion-side. I doubt you will see any 4 HCA with 41.3 PAs that make the 0 grade. Maybe that GIA rounding to .5 does have logic behind it, as Jon suggests!

Exception noted...I think you changed your text from earlier, which I did not follow.

You will notice that the X falls outside of the AGS outline for the 0 grade, which is the AGS guideline for the 0 grade.

''Does the HCA even work?'' is, IMO, the same question as ''How does a stone outside the box get a 0?''

Well...I think generally, being outside the box is accounted for by minor facets, right? And you''d think H&A would get them back in line.

Mostly, I''m seeing icky green.

The exception motivates the question, for me:

Should AGS0 be run though HCA? Why or why not?

 

[JulieN]

I'm a mad editor; it usually takes me about 3 minutes before everything is in place.

oh, I see what you mean now about minor facets affecting hearts and arrows. I don't know the answer.

http://www.whiteflash.com/round_ideal_cut/Round-Ideal-Cut-cut-diamond-2435200.htm

HCA used as a rejection tool, then do not reject AGS 0 stones. "Please do not use it for final selection; it will not replace an analysis with an Ideal-scope and/or an independent appraisal." But I would still run the calculation; I think if I had an AGS stone that was >2, I would want to make sure it is a good 0, and not closer to 1. I have never seen an IS image of one of these 4 HCA/AGS 0 stones, so I don't know if it's one of those very rewarding but tricky combinations, or it's just on the cusp of the 1 grade.