GIA grading question

[less_confused]

Hi -

I wonder if I am misunderstanding the HCA tool.
A brilliant stone with 0.6 HCA (all Excellents) was graded VERY GOOD by GIA.
It was graded excellent polish and very good symmetry.

It seems to be just outside the preferred zones to rank as an excellent cut, but GIA also includes a range that seems frankly too blue. In essence, it feels like the cut-off on the 'shallower' side is too severe and yet GIA is too loose on the other end.

I have much to learn

 

[stone-cold11]

yap, GIA grading is more towards the deeper side. Post the numbers use for the HCA input and we can tell more.

 

[Lorelei]

Date: 9/6/2009 1:56:52 AM
Author:less_confused
Hi -

I wonder if I am misunderstanding the HCA tool.
A brilliant stone with 0.6 HCA (all Excellents) was graded VERY GOOD by GIA.
It was graded excellent polish and very good symmetry.

It seems to be just outside the preferred zones to rank as an excellent cut, but GIA also includes a range that seems frankly too blue. In essence, it feels like the cut-off on the ''shallower'' side is too severe and yet GIA is too loose on the other end.

I have much to learn

Post all the info from the report then we can see why this stone was given VG, some of these can be great options so it is important to evaluate each carefully.

 

[less_confused]

Thanks for your invaluable insights. Here''s the stats:
Depth: 60.1%
Table: 56%
Crown Angle: 33.5°
Crown Height: 14.5%
Pavilion Angle: 40.6°
Pavilion Depth: 43.0%
Star length: 55%
Lower Half: 80%
Girdle: Thin to Medium, Faceted (3.0%)
Culet: None

It''s getting 0.6 but it looks to be dead center in the zone.

 

[stone-cold11]

yap, GIA is leaning to the deeper pavilion in this case. But with this pavilion angle, there might be some obstruction issue so best to check out it''s idealscope image.

 

[Lorelei]

Date: 9/6/2009 9:57:33 AM
Author: less_confused
Thanks for your invaluable insights. Here's the stats:
Depth: 60.1%
Table: 56%
Crown Angle: 33.5°
Crown Height: 14.5%
Pavilion Angle: 40.6°
Pavilion Depth: 43.0%
Star length: 55%
Lower Half: 80%
Girdle: Thin to Medium, Faceted (3.0%)
Culet: None

It's getting 0.6 but it looks to be dead center in the zone.

The pavilion angle is actually bordering on the shallow zone, < 40.6 can show obstruction where the diamond visibly darkens at close scrutiny due to the viewer's head/ body blocking the light - not in all cases but sometimes this can happen and it could be what you are seeing. Looks like the pavilion angle is the reason for the VG cut grade. If you can see the diamond again look at it closely and see if this effect intensifies.

 

[teal]

I am also confused by GIA. My diamond is only graded good but the HCA gives it all excellents and one very good. OH well, who cares...diamond is gorgeous

 

[Lorelei]

Date: 9/6/2009 7:48:36 PM
Author: teal
I am also confused by GIA. My diamond is only graded good but the HCA gives it all excellents and one very good. OH well, who cares...diamond is gorgeous

If the VG is for spread this is normal as only diamonds with depths of 60.3% and below get Ex in this category but even if not no need to worry, the HCA cannot see the diamond and is used for elimination only, not selection. I am sure your diamond is gorgeous!