AGA v. AGS grading of this princess

[jones47]

Here are the specs:

Shape: Princess
Dimensions: 6.11 x 6.04 x 4.65
Carat Weight: 1.448ct
Color: H
Clarity: VS1
AGS Cut Grade: Ideal
Polish: Ideal
Symmetry: Ideal
Fluorescence: Negligible
Girdle: 2.89%
Total Depth: 77.06%
Crown Depth: 15.31%
Pavilion Depth: 58.13%

Looks like a great diamond to me (anything jump out at anyone?)
Anyway, it''s an AGS 0, but the AGA DIY cut grader on gemadvisors has it as a 2A. Anyone have any insight as to what is going on here? I looks like the total depth is the big problem. I would love to hear opinions. Thanks!

 

[valeria101]

Simple enough.. the two grading systems take into account different parameters and do not always agree.

In this case, it doesn''t sound like much of a disagreement after all - the use guide for the AGA system recommend the first 2-3 grades as ''top quality'' and your diamond is in there (see ''Fancy Shapes'' under ''Knowledge'' on top of this page). And as far as I know, the AGA tables do not account for brilliance, while AGS does, so I''d rather go with AGS. AGA has been (or is about to be) supplemented by a different set of grades measuring brilliance - something that AGS has already incorporated in their grades.

... as far as I understand, at least.


Anyway, looking at what happens with the cut grades for rounds, labs do not agree completely about what and how to grade. I would not expect any different about princess cuts - actually, it is likely that this more intricate cut would cause even more dissent about cut grades.

Either choosing among diamonds or among grading authorities, there''s still some choice left to make for you

My 2c

 

[Paul-Antwerp]

AGA cut-charts are based upon observation of stones throughout the years.

When AGS launched their cut-grade for princesses last year, this was based upon intensive research of numerous virtual stones with all possible combinations. As such, AGS has taken us outside of the old box, and given us a completely new princess-cut.

Because of this, the AGA-charts could not foresee something this new and so drastically different.

Looking at this specific stone, I can see the efforts of the cutter to avoid going too far away from the ''outdated'' AGA-wisdom. He is looking for the lower end of the AGS-0-area (still extremely high, I should say), so that he can still get a relatively high AGA-grade. In this way, he avoids the difficulty of having to explain why the stone would have an even lower AGA-grade.

Personally, I would go for a deeper pavilion, thus avoiding the central white cross of light leakage, that this stone probably has. In the crown-side, I would go for a lower crown height, with probably a much shallower crown angle than in this stone. Personally, I think that you then end up in the high area of AGS-0. The disadvantage then is that the AGA-score of that stone would be lower.

All in all, with AGS-0, you have a great stone there, and if a princess has an AGS-grade, one should plainly disregard AGA. I have the impression that this cutter did not have the guts to take that last step. But that is a matter of how far you want to take the madness.

Live long,

 

[jones47]

Thanks for the opinions, that''s helpful. I hear everyone talk about the importance of a high crown with princess cuts, but >15 does seem maybe too high. Here is an idealscope image. I see the light leakage in the middle that you were talking about Paul, but it doesn''t seem quite as bad as I thought. Any thoughts on this?

 

[oldminer]

We no longer use the AGA Cut Class grades in the AGA lab whenever a firm or individual allows us to use the ImaGem system that measures perfomance. Of course, we find AGS 0 princess cuts to perform very well with light, but not score so well due to the different way they are cut from what we ever observed over the years leading to the new AGS 0 princess cut grade. The new cut stones are simply different that any traditionally cut princess. Depth percentage, as Paulk has explained to me, is not key to the perfromance grade and is now misleading in the AGA Cut Class grading that some folks still use.

If you have a traditional cut princess, the AGA grades have meaning. If you have a new AGS 0 princess, then you need either AGS software or a device like the ImaGem technology we use to appreciate the cut.

 

[valeria101]

Date: 4/2/2006 1:05:55 PM
Author: jones47

I hear everyone talk about the importance of a high crown with princess cuts, but >15 does seem maybe too high.

... as long as brilliance works out, I wouldn''t say that... because high crowns look neat when the diamonds are set (without much of a crown, most of the stone is sunk between the prongs - never to be seen). Personal opinion though.



Here is an Ideal Scope image. I see the light leakage in the middle that you were talking about Paul, but it doesn''t seem quite as bad as I thought. Any thoughts on this?

That is not the ''white cross'' flat spot (as far as I understand Paul''s post)... it would look different. And yes, this IS looks great to me too.

My 2c.

Btw. re ''white cross of leakage'' - here''s what one looks like on the IS image (the white patch in the middle of the stone in the picture below). IMO, this stone has it very minor an would not hold it at fault for that much. But it can get quite ''spectacular''

... see next post.

 

[valeria101]

I do not have an Ideal Scope picture of this one, but ... is it even needed? With plenty of light from behind in the photo, the leakage area in the middle looks like a large bald spot. Maybe this doesn''t make this diamond ''bad'' - just not particularly awesome because of its cut. It isn''t mine or anything - the picture was a great example of the said detail of princess cuts that has been discussed here on the forum before that I kept it as example.

(Sorry for the ramble... hope at least some helps

)

 

[squarediamondlove]

Date: 4/2/2006 1:05:55 PM
Author: jones47
Thanks for the opinions, that's helpful. I hear everyone talk about the importance of a high crown with princess cuts, but >15 does seem maybe too high. Here is an idealscope image. I see the light leakage in the middle that you were talking about Paul, but it doesn't seem quite as bad as I thought. Any thoughts on this?

I actually think the Light Scope image of this stone looks great for a princess. The 15% crown hight works for this stone. I think I remember seeing this stone in person in GOG and though it looks really well. I was however able to detect a small amount of light leakage on the right side of the table just with my eyes but that's about it. The light leakage is very very minimal. The only down side is that the leakage is not even, but appears more on one side of the stone; this gives the impression that the stone is not symmetrical when it actually is.

However the price is right b/c its just under 1.5 and the stone is actually really nice!

 

[jones47]

Thanks for all the feedback, everyone.

It does seems like a nice stone to me. I guess my only concern is how deep it is. 77% seems very high, especially since I''ve been hearing that these deep stones are becoming a trend with the AGS 0 princesses (and not necessarily a desireable trend).

I guess the bottom line is how it performs though, and this one seems to do alright.

 

[Paul-Antwerp]

Date: 4/3/2006 11:04:55 AM
Author: jones47
Thanks for all the feedback, everyone.

It does seems like a nice stone to me. I guess my only concern is how deep it is. 77% seems very high, especially since I''ve been hearing that these deep stones are becoming a trend with the AGS 0 princesses (and not necessarily a desireable trend).

I guess the bottom line is how it performs though, and this one seems to do alright.

The higher depth is not a trend, it is a necessity to obtain light performance in a princess-cut. A lot of people, professionals even, still do not understand that there is no connection between depth and spread in a princess-cut.

Therefore, there is nothing undesirable if an AGS-graded princess-cut has a higher depth. It means that the other angles (not directly related to depth) are not unnecessarily steep, and that there is no hidden weight there. Also, all angles are working together to get great light performance.

In this particular stone, while it still is a top-stone, I would prefer a deeper pavilion, and a less high crown. That would make it a super-top stone.

Live long,

 

[jones47]

Thanks for all the opinions on this stone. It''s really interesting to hear everyone''s thoughts.

 

[jones47]

How is it that there is no correlation b/w depth and spread in princess stones? Intuitively, it seems like there would be a strong correlation. If you''re locked into a certain carat weight (say one carat) lengthening the diamond is going to shorten the width. I guess adjustments to the crown and pavillion angels (as well as table size?) could compensate for the greater depth, but it still seem like in practice there would be a strong correlation.

Given the rest of the data on this stone, do any of the pros have concerns about the depth?

 

[Small]

Date: 4/5/2006 12:41:50 AM
Author: jones47
How is it that there is no correlation b/w depth and spread in princess stones? Intuitively, it seems like there would be a strong correlation. If you''re locked into a certain carat weight (say one carat) lengthening the diamond is going to shorten the width. I guess adjustments to the crown and pavillion angels (as well as table size?) could compensate for the greater depth, but it still seem like in practice there would be a strong correlation.

Given the rest of the data on this stone, do any of the pros have concerns about the depth?

While I have no info to add about the princess stone itself I did want to mention that Paul cuts AGS 0 princess (crafted by infinity) so I''d pretty much take his words to heart. I have one of his RBs and it''s stunning

...I hear as much about his princess cuts too.

 

[Paul-Antwerp]

Date: 4/5/2006 12:41:50 AM
Author: jones47
How is it that there is no correlation b/w depth and spread in princess stones? Intuitively, it seems like there would be a strong correlation. If you''re locked into a certain carat weight (say one carat) lengthening the diamond is going to shorten the width. I guess adjustments to the crown and pavillion angels (as well as table size?) could compensate for the greater depth, but it still seem like in practice there would be a strong correlation.

Given the rest of the data on this stone, do any of the pros have concerns about the depth?

Last year, I have written a few articles on this subject, which can be found in the Journal: article 1 and article 2

Let me also try to summarize this briefly in another way. If this sounds clearer, it might become the core of a new article.

For the rules of light performance, the same physical rules apply to rounds as to princess-cuts. After all, light will not use other rules, just because of another shape.

However, in the notation of depth, there is a clear difference between rounds and princess-cuts. Depth in a round is a percentage of the average diameter of the stone, whereas in princess-cuts, depth is a percentage of the smallest diameter of the stone. It is comparable to temperature being the same physical phenomenon, but some people are using Fahrenheit, while others are using Celsius. The result is that 30° in one system is not at all 30° in the other system.

Because of depth being a different way of measurement in princess-cuts, there already is a psychological barrier to understanding it.

Now, let us delve deeper into detail, and understand how totally different looking depths can be similar.

First, let us look at the pavilion with high interest. In all diamonds, the pavilion-side is the foundation of light return. If that foundation is not good, it is useless to have a fantastic crown. After all, what can the crown do, if the pavilion does not return light towards the crown.

In a round, a pavilion angle should be around 41° (without going into too much detail), resulting in a pavilion depth of around 43%. In a princess-cut, the P2-angle (going from the points directly towards the culet) should also be around that same 41°. It is this angle which defines the pavilion depth. If we would calculate the pavilion depth as a percentage of the diameter from point-to-point (since that is how the facet goes), the pavilion depth would also be around 43%. However, in a princess-cut, depth is measured in relation to the smallest diameter (so from side-to-side). Calculated in this way, we end up with a pavilion depth of around 62%.

As you see, your depth of 43% is noted as 62%.

In the pavilion of a princess-cut, one can hide a lot of weight without changing the depth. The P1-angle goes from the side of the princess down, without reaching the culet. Traditionally, this P1-angle is cut very steep, and without changing the depth or the diameter, one can increase the weight of the stone with 15%. This is very bad for the light performance of the stone, and you will see that most AGS-princess-cuts have a much shallower P1-angle.

In traditional princess-cuts, you will see the combination of a steep P1-angle (thus gaining excess-weight) and a shallower pavilion angle. The result is that the pavilion is not well-built (hidden weight and too shallow for light performance) and what is lost in the pavilion, cannot be recovered in the crown.

In the crown, weight is often won in traditional princess-cuts, by a high crown-height in combination with steep crown-angles. It is not uncommon to see crown angles of 45°.

In a round, the best crown angles are around 34° (give or take), and the same rule should apply to princess-cuts. Of course, with the same crown height, and a much higher crown angle, one has much more weight for the same depth (thus less spread).

Still, within the new AGS-system, we often see the same errors. By choosing a lower P2-angle, these cutters can use more of the natural crystal, and use a higher diameter for the same rough crystal. The lower angle often results in a clearly visible white central cross of light leakage in the idealscope. One can offset this with a higher crown with higher crown angles. In this way, one avoids the dramatically high pavilion depths, while not adding to spread.

In light performance, I would consider these the lower side of the AGS-0''s or AGS-1''s.

Sorry for giving too much info in one reply. I hope that it is somewhat clear however.

Live long,

 

[jones47]

That was helpful, Paul. Thank you.

If I''m interpreting the helium report correctly, the angles seem to fall within a reasonable range of your suggestions, Paul. Would you agree? (see below). If anyone else wants to weigh in on these angles or the stone in general, please do so. The more opinions, the better.

Avg Min Max
Crown Main 1: 39.37 38.30 40.35
Crown Main 2: 36.19 35.74 36.99

Pav. Main: 60.81 60.45 61.31
Pav. Corner: 39.67 39.66 39.68


Thoughts anyone?

This diamond has one of the best brilliant scopes I''ve seen. The more I think about it, the more I think I should go for it. Can anyone give me a good reason to pass?

 

[jones47]

bump

 

[jones47]

last bump, I promise. Anyone have any thoughts on the crown/pavillion angles?