Couldn''t tell - What difference should I have seen between an AGS Ideal cut and GIA Very Good cut s

[Jillian]

So, I''ve been researching a lot and playing with the HCA quite a bit to help in finding my dream upgrade ring. I went to a local store that had brought in a new center stone for me to see in a three stone diamond ring that I had looked at previously. The 2 side stones were AGS Ideal cut (although the certs are from 2003) and the center stone was GIA Very Good cut (cert 1102846578 1.69 ct. for those interested). For some reason I cannot pull up the AGS certs online but what I have on my copy for one of the side stones is:

Carat Weight: .812
Table: 55%
Crown Angle: 34.8
Pavilion Angle: 40.7
Total Depth: 61.5%
Crown Height: 15.7%
Pavilion Depth: 42.7%

I looked at this ring in every possible light condition available - bright store lights, outside daylight, dark room, fluorescent lit room, everywhere I could think of except in candlelight. I am perplexed because these stones did not look any different to me. I tried and tried to find a difference but just couldn''t. I have very good eyesight. What would you expect to see different between these 2 cuts? I was very surprised because the HCA scores were very different between the side stones and the center stone. Please provide any input you can.

Thanks!

 

[Lorelei]

Date: 8/11/2009 12:54:35 AM
Author:Jillian
So, I've been researching a lot and playing with the HCA quite a bit to help in finding my dream upgrade ring. I went to a local store that had brought in a new center stone for me to see in a three stone diamond ring that I had looked at previously. The 2 side stones were AGS Ideal cut (although the certs are from 2003) and the center stone was GIA Very Good cut (cert 1102846578 1.69 ct. for those interested). For some reason I cannot pull up the AGS certs online but what I have on my copy for one of the side stones is:

Carat Weight: .812
Table: 55%
Crown Angle: 34.8
Pavilion Angle: 40.7
Total Depth: 61.5%
Crown Height: 15.7%
Pavilion Depth: 42.7%

I looked at this ring in every possible light condition available - bright store lights, outside daylight, dark room, fluorescent lit room, everywhere I could think of except in candlelight. I am perplexed because these stones did not look any different to me. I tried and tried to find a difference but just couldn't. I have very good eyesight. What would you expect to see different between these 2 cuts? I was very surprised because the HCA scores were very different between the side stones and the center stone. Please provide any input you can.

Thanks!

GIA Ex and VG cut grades are not created equal, some VG can have greater visual beauty than Excellent so take each one as an individual. In order to guess at any differences between the two in question we would need the info on both. Also GIA cut grades can be downgraded because of what GIA see as excessive brillianteering, or undesirable ( to them) girdle thickness etc, the trick is to evaluate each diamond carefully regardless of the cut grade given. Some GIA VG's have super proportions and finish and can be very beautiful diamonds.

What was the girdle thickness on the VG diamond, the star and lower girdle facet percentages, and were there any comments in on the grading report?

 

[stone-cold11]

Lorelei, the center stone is like the stone posted previously. The stone has a 90% LF which bump down the cut grade.

59.5D, 60.0T, 33.5CA, 41.4PA. Girdle thin-med.

Probably slight leakage but could be compensated by the large lower facet.

 

[Lorelei]

Date: 8/11/2009 6:40:32 AM
Author: Stone-cold11
Lorelei, the center stone is like the stone posted previously. The stone has a 90% LF which bump down the cut grade.

59.5D, 60.0T, 33.5CA, 41.4PA. Girdle thin-med.

Probably slight leakage but could be compensated by the large lower facet.

Oh yes thats right, https://www.pricescope.com/community/threads/confused-follow-up-with-more-info-to-gia-very-good-cut-ags-ideal-cut-question.122363/ I saw immediately the LGF measurement on that thread but wasn't sure if it was the same diamond in question. Pav angle much too steep also which is not good. Jillian the diamond you posted on this thread in the first post is much better cut.

 

[strmrdr]

Date: 8/11/2009 6:40:32 AM
Author: Stone-cold11
Lorelei, the center stone is like the stone posted previously. The stone has a 90% LF which bump down the cut grade.


59.5D, 60.0T, 33.5CA, 41.4PA. Girdle thin-med.


Probably slight leakage but could be compensated by the large lower facet.

Very good, someone has been paying attention.
There is a very good chance there is no significant leakage.
It is around AGS1 potential.
It takes a bit of a hit in contrast and fire.
In theory it might edge into ags0 light performance depending on optical symmetry and the exact numbers.

 

[strmrdr]

Where this diamond would take a hit in the real world is lower lighting.
CFL in the home would not be best for it.

 

[oldminer]

"GIA Ex and VG cut grades are not created equal, some VG can have greater visual beauty than Excellent so take each one as an individual."



The above is interesting to me and probably quite confusing to others. We have often discussed how the GIA cut grading system has missed the mark in some respects or is overly broad in the upper categories. I think cut grading of diamonds should relate to two elements: Light and Craftsmanship. The amount of light return, contrast and scintillation is crucial. The non-light part of this grade, "craftsmanship" relates to durability, details of polish/symmetry, and to visual size to weight relationships.

By the time a diamond scores at "Ideal", "Superior" or "Excellent" it shouild combine successfully ALL the required attributes to the extent that 99% of people who view it agree it has no visual fault and that the diamond is unquestionably beautiful. Once you go down through Very Good to Good most observers having seen the best stones will recognize the faults in cut and in beauty with the lesser cuts. Since diamonds are graded beyond the level of just what the eyes can detect, it makes sense the "Very Good" graded stones look quite nice, virtually as good as Excellent, etc, but would have some sort of minor light or craftsmanship fault which is material and can be repeatedly found.

Such a system is arbitrary, not based on truths of the universe, but a man-made artifact. What we have right now is a system in use that people can''t readily comprehend. I suppose it is full of faults which the diamond gods should work to correct, because it makes for confusion where a system like this should make for better understanding.

 

[Lorelei]

Date: 8/11/2009 7:55:24 AM
Author: oldminer
'GIA Ex and VG cut grades are not created equal, some VG can have greater visual beauty than Excellent so take each one as an individual.'



The above is interesting to me and probably quite confusing to others. We have often discussed how the GIA cut grading system has missed the mark in some respects or is overly broad in the upper categories. I think cut grading of diamonds should relate to two elements: Light and Craftsmanship. The amount of light return, contrast and scintillation is crucial. The non-light part of this grade, 'craftsmanship' relates to durability, details of polish/symmetry, and to visual size to weight relationships.

By the time a diamond scores at 'Ideal', 'Superior' or 'Excellent' it shouild combine successfully ALL the required attributes to the extent that 99% of people who view it agree it has no visual fault and that the diamond is unquestionably beautiful. Once you go down through Very Good to Good most observers having seen the best stones will recognize the faults in cut and in beauty with the lesser cuts. Since diamonds are graded beyond the level of just what the eyes can detect, it makes sense the 'Very Good' graded stones look quite nice, virtually as good as Excellent, etc, but would have some sort of minor light or craftsmanship fault which is material and can be repeatedly found.

Such a system is arbitrary, not based on truths of the universe, but a man-made artifact. What we have right now is a system in use that people can't readily comprehend. I suppose it is full of faults which the diamond gods should work to correct, because it makes for confusion where a system like this should make for better understanding.

As a consumer I have seen some GIA Excellents ( steep deeps) which show definite detrimental leakage in images and some VG cut grade which look very good indeed, albeit confusing to some however it would appear there are great diamonds to be found in both cut grades. For example I would much rather have a GIA VG which has been downgraded for a very thin girdle which is said not to be an issue by a trusted pro which also has proven proportions, rather than a leaky steep deep Excellent.

 

[oldminer]

Your own selection criteria may be good for you, but it may not work for everyone equally. This is due to the faults in the existing system which I am pointing out and you apparently also agree with. If the proper deductions were shown for Steep-Deep versus a Thin Girdle, then more people could readily understand what makes you decide the way you do. Selecting diamonds on a visual basis should mean that every "Very Good" looks just about equal to "Excellent" ones, but that there are minor faults or minor yet repeatable grading reasons why they differ in overall grade. This would be in the tradition of existing diamond grading, but be far more fact based grading. For now, we live with what we have and you are doing a good job of explaining how you''d choose to people who know little about the way grading is presently done.

 

[Jillian]

So CFLs in the home is the only place I would/should notice a difference between these 2 stones?

 

[John P]

Date: 8/12/2009 12:44:43 PM
Author: Jillian
So CFLs in the home is the only place I would/should notice a difference between these 2 stones?

There and low light conditions in general. 90% is pretty extreme. GIA & AGS have 77-79% as central numbers in top grade ranges for a reason.

Here is a thread with more discussion about lower halves and the impact on performance.

https://www.pricescope.com/community/threads/how-does-lower-girdle-length-affect-face-up-performance.87181/