HCA vs GIA

[climbman]

I''ve been wondering how one should value HCA versus GIA. I will give an explicit example around which we can discuss. The following scores very well on HCA (0.8, Ex Ex Ex Vg, predicting it would be an AGS0), but gets a Vg cut grade from GIA. Of course, Vg is still nice, but it would seem surprising that HCA could give such a high rank and the two do not accord. I can read the HCA picture and see that it accurately predicts that it falls outside of the GIA Ex cut grade. So again, the question is, why is there a discrepancy such as this?

http://www.jamesallen.com/diamonds/G-VS2-Ideal-Cut-Round-Diamond-1186752.asp

 

[Lorelei]

Pavilion angle, 40.4 will not get GIA Excellent cut grade. Ask for an Idealscope image if you are seriously interested in this one, it looks like it is facing up a little small for 1.5 cts but it might be a nice diamond. Check also that the diamond doesn't darken when viewed closely, this can sometimes happen with a shallow pavilion angle - an effect called obstruction. The gemologist at JA will tell you if this is an issue or not ( most likely not).

 

[climbman]

ok, but in your estimation, is this a diamond that should be considered an ideal type of performer (as hca might suggest), or just a notch below, as gia might suggest?

 

[Lorelei]

Date: 7/27/2009 5:21:26 PM
Author: climbman
ok, but in your estimation, is this a diamond that should be considered an ideal type of performer (as hca might suggest), or just a notch below, as gia might suggest?

The HCA is used for elimination not selection, I edited my post above to add more info - I would say it could be worth further investigation as above. It could be a great looking diamond but more info is needed to know for sure.

 

[Regular Guy]

This article may be helpful.

Generally, many of us, myself include, would trust hca over GIA, but as Lorelie says, that''s still maybe round one, after which it''s helpful to look further.

 

[climbman]

Thanks to you both for the thoughts! The case study makes for an interesting read. I was really more trying to learn than focus on this particular diamond.