GIA Very Good = HCA 0.8 ?

[thaihunt]

Ran across this diamond, GIA Very Good, and plugged the numbers into HCA. Came out with Excellents across the board with h a 0.8 score. Thoughts on the diamond and how to explain the grading of VG with an Excellent HCA score?

1.50
Table: 58%
Depth: 60.1%
Crown: 33%
Pavilion: 40.8%
7.41*7.43*4.46
Girdle: Med to Slightly Thick

 

[Stephan]

GIA, like most of the diamond cutters, prefers deep diamonds.

However, is there something written under ''Comments'' in your certificate?
What are star and lower girdle length?

 

[jet2ks]

Do you have the rest of the info on this diamond? Polish and symmetry would be the first place I would look.

 

[thaihunt]

Comments say there is some surface graining and additional pinpoints.

Not sure what you mean by star and lower girdle length, but I see the following measurements:

From cullet to girdle: 43%.
From girdle to table: 13.5%

Are those what you''re referring to?

 

[thaihunt]

Polish and Sym are both excellent.

 

[Stephan]

Date: 4/29/2009 3:43:15 PM
Author: thaihunt
Not sure what you mean by star and lower girdle length, but I see the following measurements:
From cullet to girdle: 43%.
From girdle to table: 13.5%
Are those what you''re referring to?

No...

 

[thaihunt]

Let me try again then

I see two more measurements - can''t tell exactly what they''re referring to, but one is on the top of the diamond, and the other is on the bottom. They are 55% (top) and 75% (bottom). Hopefully those are what you need.

 

[Stephan]

You''ve got it.
It sounds OK, even if I''m not a surface graining fan.
Could you have an IdealScope picture?

 

[phoenixgirl]

I trust the HCA more than the GIA when it comes to cut grading.

The GIA probably doesn''t like the crown angle or table. But all the angles on your stone are working together in the right ways. It''s the way the angles interact, not their numbers alone, that determine cut quality.

Better to find a GIA VG that scores high on the HCA than a GIA excellent that doesn''t. If you search you can find some shockingly poor GIA excellents!

 

[thaihunt]

Thanks for the responses. I requested a ideal-scope image and will certainly post it here when it arrives. Cut and light performance are my main priorities, so I just wanted to make sure that I shouldn''t be turned off because of the VG rating.

 

[Stephan]

Date: 4/29/2009 4:27:24 PM
Author: phoenixgirl
Better to find a GIA VG that scores high on the HCA than a GIA excellent that doesn''t. If you search you can find some shockingly poor GIA excellents!

That''s so true!

 

[Ellen]

Date: 4/29/2009 3:39:38 PM
Author: QueenMum
GIA, like most of the diamond cutters, prefers deep diamonds.

However, is there something written under 'Comments' in your certificate?
What are star and lower girdle length?

Are you thinking this diamond is deep? At 60.1, that's not deep, nor is the PA.


To the OP, I'd rather see the crown angle at 34 plus. This stone, overall, is leaning just slightly towards the shallow-er side. It "may" lack a bit of scintillation/possibly appear slightly glassy/possibly lack a bit of fire. Numbers are rounded, so in actuality, might be a bit better, or might not.

Plus, look where the x is (on HCA), it's outside the boxes. You'd prefer it in the overlap area, or closer to. Don't just look at the numerical score.

 

[Stephan]

No, this diamond is not deep, that''s why it only scores VG for the GIA.

 

[stone-cold11]

Date: 4/29/2009 4:37:40 PM
Author: Ellen

Date: 4/29/2009 3:39:38 PM

Author: QueenMum

GIA, like most of the diamond cutters, prefers deep diamonds.

However, is there something written under ''Comments'' in your certificate?

What are star and lower girdle length?

Are you thinking this diamond is deep? At 60.1, that''s not deep, nor is the PA.

I don''t think QM meant it that way. Just that GIA''s Ex is in the higher PA range, not the lower PA range for the respective CA. A lower PA will less likely to get a Ex in cut but still be 2>

 

[Stephan]

Date: 4/29/2009 4:37:40 PM
Author: Ellen
It ''may'' lack a bit of scintillation/possibly appear slightly glassy/possibly lack a bit of fire.

I don''t think so.
Perhaps a little more obstruction than in a steep/deep.
A longer lower girdle (around 80%) would be better than +/-75%.
If I''m wrong, Karl will correct me.
So let us take a look at the IdealScope!

 

[Ellen]

Ok, I understand what you were saying now!

However, I wouldn''t necessarily say that GIA likes them deep, although many EX are deep. More that they have to balance each other out. If you leave the PA alone, and make the CA 33.5, you''re back in EX territory (with the x). Make it 34, and you''re in the overlap. You can look at it either way, bring the CA up higher, or make the PA deeper.

 

[Stephan]

Date: 4/29/2009 4:37:40 PM
Author: Ellen
It ''may'' lack a bit of scintillation/possibly appear slightly glassy/possibly lack a bit of fire.

Fire is difficult to discuss as there are differences between diffuse or spot lighting.
To my eyes, slightly shallow diamonds have better and more intense fire under spot lighting than deep ones.
Deep diamonds have better fire under diffuse lighting than shallow ones.
But that is just what my only eye can see, the other one is blind.

But what is even more constant to my eye is the lack of scintillation of steep/deep diamonds.

 

[Ellen]

Date: 4/29/2009 5:03:31 PM
Author: QueenMum

Date: 4/29/2009 4:37:40 PM
Author: Ellen
It ''may'' lack a bit of scintillation/possibly appear slightly glassy/possibly lack a bit of fire.

I don''t think so.
Perhaps a little more obstruction than in a steep/deep.
A longer lower girdle (around 80%) would be better than +/-75%.
If I''m wrong, Karl will correct me.
So let us take a look at the IdealScope!

An IS won''t necessarily show what I''ve noted.

 

[Stephan]

Date: 4/29/2009 5:09:16 PM
Author: Ellen
An IS won''t necessarily show what I''ve noted.

I didn''t mean that.

I only think that with such angles, there won''t be any fire scintillation issue.
Look at Brian''s recent recuts.
So the only thing I want to see with IS/ASET is if the facets are nicely aligned, and if there is not too much obstruction that could be caused by slightly painting the girdle (if a diamond is slightly painted, it is possible that the GIA doesn''t mention it).
I also ask for IS/ASET because we all know GIA numbers are rounded, so the picture will tell us if there is any light return issue with this diamond.

 

[strmrdr]

I am going to assume that this is actually degrees...
Crown: 33%
Pavilion: 40.8%

ie 33 degrees and 40.8 degrees.

The combo is pretty good.
I would like the lowers to be in the 76.5-77% range which gia would round down to 75...
If it was over 77.5 it would round up to 80.
So likely it is ok there.

With the 58 table and 33 crown it will tend towards the bright side rather than fiery.

It is much better than a lot of gia EX cuts so im not worried about the cut grade.

An IS would help.

 

[strmrdr]

Date: 4/29/2009 5:08:00 PM
Author: QueenMum

Date: 4/29/2009 4:37:40 PM

Author: Ellen

It ''may'' lack a bit of scintillation/possibly appear slightly glassy/possibly lack a bit of fire.

Fire is difficult to discuss as there are differences between diffuse or spot lighting.

To my eyes, slightly shallow diamonds have better and more intense fire under spot lighting than deep ones.

Deep diamonds have better fire under diffuse lighting than shallow ones.

But that is just what my only eye can see, the other one is blind.


But what is even more constant to my eye is the lack of scintillation of steep/deep diamonds.

Ellen is right but it is a matter of how much.
In this case with decent optical symmetry and the correct lowers it is a small amount.
It doesn''t mean it wont be fiery, it will just lean towards the bright side.