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AGS 000, but HCA above 2.0

B

brimley

Rough_Rock
Joined
Feb 28, 2014
Messages
21
Hi -

It has been said on this board (poster Gypsy's advice) to use HCA as a rejection tool and then use ideal scope as a selection tool. Or, alternatively, skip all of that and find an AGS 0 stone.

I have been following this advice in my shopping process, and only recently started encountering AGS graded stones - and some of them end up with AGS 000 gradings, but have specs that result in the HCA giving a rating above 2.0, even as high as 3.9. If AGS rates light performance at 0, but the HCA tool gives a 3.9 rating – does AGS win? I’m not sure how to treat these stones, so for the time being, I have to reject them.

Thanks!
 
I wondered about that also. I found two diamonds the same size that were both AGS 000. One had an HCA of 1.0 and the other 2.0.
I know it shouldn't matter, but I went with the HCA 1.0 which was further down into the red zone.
 
You don't run the HCA on AGS 0 cut stones, it's already been evaluated for light performance by AGS. Their evaluation is far more in depth than the limited number of angles used by the HCA. The HCA's value is rejecting poor performing GIA Excellent cut grade stones, since GIA's highest cut grade has relatively broad standards. AGS trumps both, hands down.
 
If I found a diamond with an hca 3.9 that got ags0 I would want to see a real aset to confirm the grade.
That said it does happen.
 
hawk25|1393887714|3626805 said:
You don't run the HCA on AGS 0 cut stones, it's already been evaluated for light performance by AGS. Their evaluation is far more in depth than the limited number of angles used by the HCA. The HCA's value is rejecting poor performing GIA Excellent cut grade stones, since GIA's highest cut grade has relatively broad standards. AGS trumps both, hands down.
Click to expand...
I don't agree with that in all cases, the AGS grading is not perfect and the hca can tell you to look further and verify.
There are combos that get AGS0 that I would not buy.
 
Check the IS/ASET.

PSers have simplified the advice, as in "HCA is a rejection-only tool" and "do not run HCA on AGS 0 stones" but the reality is it is more complicated than that.
 
I would seek more information on such a diamond, if it was otherwise really what I wanted in terms of budget and other specs. Pictures, scopes, sarin.
 
JulieN|1393905187|3627014 said:
Check the IS/ASET.

PSers have simplified the advice, as in "HCA is a rejection-only tool" and "do not run HCA on AGS 0 stones" but the reality is it is more complicated than that.
Click to expand...
Experienced PSers can look at a set of numbers on an AGS report and say that's weird and I need to investigate further or its normal for an ags0 and good to go to the next step.
Someone not as familiar with diamonds specs can not do that and need to do more work to draw the same conclusions.
 
Personally I don't get the advice to ignore HCA and just assume it's a great stone because it's AGS000. I would thoroughly check out the stone. It's obviously scoring badly on the HCA for a reason; whether it's an overly steep pavilion angle or something else, I would not ignore that.
 
Thank you all. I think I have a pretty clear picture of how to proceed from here.
 
The purpose of the HCA is to narrow down stones particularly within the very wide GIA Excellent range. This isn't even an issue with vendors such as Good Old Gold and WhiteFlash who provide ASET and Idealscope images. I'd never plan to buy a diamond blind just by the numbers. I would always want to have the images showing light performance, so I'd see those on an AGS0 stone as well as any other. That is my advice, as others have pointed out. I never run the HCA on an AGS Ideal cut stone because it has already been "screened" technically. So then you still look at the magnified photos and at least an idealscope image to verify the light return. I have seen an AGS0 or two that I wouldn't buy. I never understand people who come here and buy diamonds blindly from a drop shipper with no images.
 
Whatever happened to that alleged bias that the HCA had against deep diamonds? Is it still there? Or bias against a steep crown with a large table or a certain pavilion angle range? Or against ones that face up marginally smaller for their weight? I ran the numbers on one earlier today, it has a 35.3 crown angle and 58% table (or something) but was graded AGS 0 and scored 2.3 or so. It's on JA's site. Looked okay in the video.

I was gone from PS for a couple of years and haven't kept up with the changes in the HCA.
 
Thank you all - this has been most informative for me with respect to putting HCA in perspective.
 
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