Questions about HCA tool

[Josh48329]

First off, I would just like to say that this is a WONDERFUL site! I have been kind of hovering around for just a couple of days now, and have already learned so much!

Anyway, with my first post, I have some questions about the HCA tool. I noticed that there is a green box (GIA excellent candidates) as well as a white box (AGS ideal candidates) on the chart once the analysis is run. I would assume that it would be best to find a diamond that fits within both boxes if at all possible, but that is not my main question...

How is it possible to take a diamond that has graded "AGS Ideal 0" in light performance, polish, and symmetry and yet it still falls outside of the white box on the plot? An example of this is AGS 01040382310075 if anyone is curious. Is this because that particular diamond has a 55.5% table, whereas the chart for the analysis is 56%? Is it a slight error with the tool? Have the grading "tolerances" (for lack of a better term) changed? Is my understanding flawed? And, most importantly, as long as the overall score is below 2 does it matter?

Along those lines, it seems that as long as the number is below 2 its actual value doesn''t matter? i.e. a 0.7 is not necessarily supposed to be better than a 1.2?

Thanks in advance!

 

[Lorelei]

Date: 12/4/2009 3:12:18 AM
Author:Josh48329
First off, I would just like to say that this is a WONDERFUL site! I have been kind of hovering around for just a couple of days now, and have already learned so much!

Anyway, with my first post, I have some questions about the HCA tool. I noticed that there is a green box (GIA excellent candidates) as well as a white box (AGS ideal candidates) on the chart once the analysis is run. I would assume that it would be best to find a diamond that fits within both boxes if at all possible, but that is not my main question...

How is it possible to take a diamond that has graded ''AGS Ideal 0'' in light performance, polish, and symmetry and yet it still falls outside of the white box on the plot? An example of this is AGS 01040382310075 if anyone is curious. Is this because that particular diamond has a 55.5% table, whereas the chart for the analysis is 56%? Is it a slight error with the tool? Have the grading ''tolerances'' (for lack of a better term) changed? Is my understanding flawed? And, most importantly, as long as the overall score is below 2 does it matter?

Along those lines, it seems that as long as the number is below 2 its actual value doesn''t matter? i.e. a 0.7 is not necessarily supposed to be better than a 1.2?

Thanks in advance!

Hi Josh

This happens sometimes on the HCA, if you could post the carat weight for the AGS stone we can look it up and tell you why this has happened in this case.

Also the HCA is a rejection tool, a lower score is not better than a higher score. Basically all scores under 2 are considered equal pending further evaluation with images such as Idealscope. Stones which score below 1 can show obstruction issues due to their shallower angle configurations ( darkening of the diamond at close scrutiny due to head shadow). A good place to aim for with ring stones is between 1 and 2 HCA.

 

[stone-cold11]

Yes, it is possible for a AGS0 performance based cut grade to fall outside the AGS0 box on the HCA. That is just a cutters guideline, a stone can get AGS0 as long as the facets works well together and scores well on the AGS system.

HCA is done with step size for the table, so the numbers are rounded to the table size.

No, as long as the score is below 2, it is worthy of further evaluation. If IS/ASET image is available, that will trump HCA score.

 

[Josh48329]

Date: 12/4/2009 4:11:46 AM
Author: Lorelei

Date: 12/4/2009 3:12:18 AM

Author:Josh48329

First off, I would just like to say that this is a WONDERFUL site! I have been kind of hovering around for just a couple of days now, and have already learned so much!


Anyway, with my first post, I have some questions about the HCA tool. I noticed that there is a green box (GIA excellent candidates) as well as a white box (AGS ideal candidates) on the chart once the analysis is run. I would assume that it would be best to find a diamond that fits within both boxes if at all possible, but that is not my main question...


How is it possible to take a diamond that has graded ''AGS Ideal 0'' in light performance, polish, and symmetry and yet it still falls outside of the white box on the plot? An example of this is AGS 01040382310075 if anyone is curious. Is this because that particular diamond has a 55.5% table, whereas the chart for the analysis is 56%? Is it a slight error with the tool? Have the grading ''tolerances'' (for lack of a better term) changed? Is my understanding flawed? And, most importantly, as long as the overall score is below 2 does it matter?


Along those lines, it seems that as long as the number is below 2 its actual value doesn''t matter? i.e. a 0.7 is not necessarily supposed to be better than a 1.2?


Thanks in advance!

Hi Josh


This happens sometimes on the HCA, if you could post the carat weight for the AGS stone we can look it up and tell you why this has happened in this case.


Also the HCA is a rejection tool, a lower score is not better than a higher score. Basically all scores under 2 are considered equal pending further evaluation with images such as Idealscope. Stones which score below 1 can show obstruction issues due to their shallower angle configurations ( darkening of the diamond at close scrutiny due to head shadow). A good place to aim for with ring stones is between 1 and 2 HCA.

The carat weight of the stone is 1.238cts.

While I am not necessarily in the market yet (still doing some more research), would one typically worry about the rather large feather that close to the edge of a stone as far as durability or anything? I''m assuming the one towards the center would generally be acceptable without issue/concern as long as it was "eye clean"?

 

[stone-cold11]

http://www.agslab.com/pdf_sync_reports/1040382310075-PLDQR.PDF

Feather depends, get WF to examine the feather and it''s effect on durability, no way to tell just from a clarity plot.

 

[Regular Guy]

You''ve gotten good advice.

The HCA score is based on looking at 8 facets versus 57 for the diamond, and so, when all the other facets are brought into consideration for the more complete picture, as it''s understood is done in particular with the AGS platinum report, the evaluation of zer...if received on the report...should be a more reliable rendering of conformity to cherry performance than the outline would lead you to believe for the HCA.

But, Stone raises an important issue that I don''t think has been addressed sufficiently here:

Date: 12/4/2009 4:14:39 AM
Author: Stone-cold11

No, as long as the score is below 2, it is worthy of further evaluation. If IS/ASET image is available, that will trump HCA score.

Like an IS/ASET image will trump the HCA, so will the zero on the certificate.

But, how clear is it whether the IS/ASET image trumps the zero...if those data do not align? And, if you had to choose between the veracity of one or the other, is it clear which you would choose?

With the image, you are looking "live" - ish at the stone, and its performance, so this is designed to be a good indicator. But, what errors can go into the presentation of the data? There may be ways in which the diamond is positioned poorly, or the image is not taken correctly with the camera, right?

Since there are enough fish in the sea, the best advice is to get two thumbs up, versus having to make a choice. Otherwise, I''d like to say your guess is as good as mine...

 

[stone-cold11]

HCA, is a 2D prediction tool, is designed using IS. IS views the stone in 3D, takes into account of how the various minor facets works together with each other, specifically for light returns only, maybe scint., not fire.

Example is HCA score below 2 can still show leakage in IS. HCA score above 2, usually between 2-3, IS can still not show leakage if the optical symm is there and lower half is large enough to compensate. Both are rejection tool.

 

[Lorelei]

Date: 12/4/2009 6:51:38 AM
Author: Stone-cold11
http://www.agslab.com/pdf_sync_reports/1040382310075-PLDQR.PDF

Feather depends, get WF to examine the feather and it''s effect on durability, no way to tell just from a clarity plot.

Yes asking WF is the only reliable way to check out that feather, I wouldn''t anticipate any problems but best to check to give you peace of mind.