Best way to measure the quality of a Princess cut?

[ChunkyCushionLover]

Date: 5/26/2010 4:28:49 PM
Author: John Pollard

Date: 5/26/2010 3:27:22 PM
Author: Rockdiamond

...would you ( John or Neil) say it's accurate that AGS favors stones with a tables smaller than 70%?

Yes - and GIA and AGSL both favor round brilliants with tables smaller than 63%.

'Hey! I know people who like RBs with 65 or 70% tables...' Are they wrong to like them? No way. But it's fair to say that modern grading metrics note that some visual components may be reduced in such diamonds. Fine. Viva le difference.

GIA doesn't have a metric for princess cuts. When it comes out I'll be surprised if the upper threshold for table size differs much from AGSL, the old AGA charts and current ray-tracing studies; at or near 70%. Remember that AGSL and GIA are within 1% on the upper end for round brilliant table size allowed (Ideal/Ex): In fact candidates for AGS0 range from 47-61% while candidates for GIA EX are limited to 52-62%. AGSL allows more table sizes but has fewer configurations possible since their metric follows the inverse c/p cutter's line more closely.

Back on point: AGSL will award 0 in light performance if the diamond meets minimum requirements for brightness, dispersion & contrast without too much light loss through the pavilion, regardless of table size. Logically at some point increasing the table size can prevent top dispersion/contrast. In RBs the top number (AGSL and others) is around 63%. In Princess cuts (AGSL and others) that threshold is around 71%.

I've seen AGS 0 graded princess cuts with 72%+ tables (even some WF ACA), on the AGS website (which may be a bit dated 2005) they even include some suggested guidelines where 80% table was theoretically possible to still achieve AGS 0. Could you please clarify how you came up with that 71% number. It is intuitive that as the table size increases the crown height and angle decreases, at some point some of the cumulative deductions (brightness, contrast, dispersion, leakage) will add together so that the stone falls out of the AGS ideal standard, but it is my understanding that this point is not defined by any numerical threshold such as table% unless a deduction for durability will be made for crown angles less than 30 degrees or too thin a girdle.

'Hey! I know people who like PCs with 75% or 80% tables...' Are they wrong to like them? No way. But it's fair to say that modern grading metrics note that some visual components may be reduced in such diamonds. Fine. Viva le difference.

 

[John P]

Date: 5/27/2010 12:19:14 AM
Author: ChunkyCushionLover

Date: 5/26/2010 4:28:49 PM
Author: John Pollard

Back on point: AGSL will award 0 in light performance if the diamond meets minimum requirements for brightness, dispersion & contrast without too much light loss through the pavilion, regardless of table size. Logically at some point increasing the table size can prevent top dispersion/contrast. In RBs the top number (AGSL and others) is around 63%. In Princess cuts (AGSL and others) that threshold is around 71%.

I've seen AGS 0 graded princess cuts with 72%+ tables (even some WF ACA), on the AGS website (which may be a bit dated 2005) they even include some suggested guidelines where 80% table was theoretically possible to still achieve AGS 0. Could you please clarify how you came up with that 71% number. It is intuitive that as the table size increases the crown height and angle decreases, at some point some of the cumulative deductions (brightness, contrast, dispersion, leakage) will add together so that the stone falls out of the AGS ideal standard, but it is my understanding that this point is not defined by any numerical threshold such as table% unless a deduction for durability will be made for crown angles less than 30 degrees or too thin a girdle.

My opinion regarding the 71% threshold is not limited to AGSL. The AGSL cut guidelines do pose candidates @ T75 and T80% (the guides are published in 5% increments) but I have not seen a live example. Similarly, the RB guides indicate T47-49% possible for AGS0 in RBs but, again, I have yet to see such a configuration.

Please link your examples of T75-80% AGS0 PCs; I'd be interested to check them out.

 

[Dancing Fire]

Date: 5/26/2010 5:23:40 PM
Author: Rockdiamond
I LOVE great cut on stones.
Hopefully, it''s a positive aspect to this forum having different professional viewpoints contributed.

RD...had you ever seen or sold any AGS 0 cut stones?

 

[kenny]

Date: 5/27/2010 1:03:10 AM
Author: Dancing Fire
RD...had you ever seen or sold any AGS 0 cut stones?

He always goes by the numbers, so he knows they must look great.

 

[ChunkyCushionLover]

Date: 5/27/2010 12:54:22 AM
Author: John Pollard

Date: 5/27/2010 12:19:14 AM
Author: ChunkyCushionLover

Date: 5/26/2010 4:28:49 PM
Author: John Pollard

Back on point: AGSL will award 0 in light performance if the diamond meets minimum requirements for brightness, dispersion & contrast without too much light loss through the pavilion, regardless of table size. Logically at some point increasing the table size can prevent top dispersion/contrast. In RBs the top number (AGSL and others) is around 63%. In Princess cuts (AGSL and others) that threshold is around 71%.

I've seen AGS 0 graded princess cuts with 72%+ tables (even some WF ACA), on the AGS website (which may be a bit dated 2005) they even include some suggested guidelines where 80% table was theoretically possible to still achieve AGS 0. Could you please clarify how you came up with that 71% number. It is intuitive that as the table size increases the crown height and angle decreases, at some point some of the cumulative deductions (brightness, contrast, dispersion, leakage) will add together so that the stone falls out of the AGS ideal standard, but it is my understanding that this point is not defined by any numerical threshold such as table% unless a deduction for durability will be made for crown angles less than 30 degrees or too thin a girdle.

My opinion regarding the 71% threshold is not limited to AGSL. The AGSL cut guidelines do pose candidates @ T75 and T80% (the guides are published in 5% increments) but I have not seen a live example. Similarly, the RB guides indicate T47-49% possible for AGS0 in RBs but, again, I have yet to see such a configuration.

Please link your examples of T75-80% AGS0 PCs; I'd be interested to check them out.

I don't see any real world 75 - 80% table examples that have achieved AGS 0 light performance, to copy a Karl K term it seems "twitchy" to deliberately try to cut to achieve such proportions.
If you look at the suggested guidelines for 80% table in a 2 chevron, Pavillion 2 angles have to be 42 degrees if they are 43 the grade becomes 2 or 3, the tolerance for cutting error (and scan error) is too small.

I also believe that the Ideal cut grade is also broad and there are some combinations that have much more brightness than others within AGS 0 ideal so just achieving the minnimum standard to reach the 0 grade does not produce the brightest diamonds.

I just don't feel its right to equate AGS performance based grading to a range of proportions as RD is trying to do. You have illustrated a well supported practical limit (although maybe 72 - 73% is close enough as well) but this is different from the theoretical limit based on the grading algorithms.

Which labs give a cut grade or suggest proportions for Princess Cuts based on proportions?

 

[Rockdiamond]

I've seen ( and sold) quite a few AGSL graded rounds- but few princess cuts.
The ones I have seen had tables smaller than those commonly seen on princess cuts.
But really, we should defer to the real experts here, like Kenny, CCL and Dancing fire- after all, these are people who have really studied Pricescope, and learned far more useful info as compared to what us tradespeople have to offer.

Hey John, you want to go get a beer?

 

[Dancing Fire]

Date: 5/27/2010 12:44:41 PM
Author: Rockdiamond
I''ve seen ( and sold) quite a few AGSL graded rounds- but few princess cuts.
The ones I have seen had tables smaller than those commonly seen on princess cuts.
But really, we should defer to the real experts here, like Kenny, CCL and Dancing fire- after all, these are people who have really studied Pricescope, and learned far more useful info as compared to what us tradespeople have to offer.

Hey John, you want to go get a beer?

were they all 60/60 cuts?

 

[netcbc]

Hello, just an update, the appraiser hwgem rated the cut as "Excellent", it falls in the category of cut between 0-2, in person to me it sparkles just like the youtube video above so I''m super happy. I feel like a got steal on this stone as I''m showing similiar stones at least $4K more online prices.

I will post the ASET later but it shows a good amount of red.

 

[Rockdiamond]

Date: 5/27/2010 3:03:37 PM
Author: Dancing Fire

Date: 5/27/2010 12:44:41 PM

Author: Rockdiamond

I''ve seen ( and sold) quite a few AGSL graded rounds- but few princess cuts.

The ones I have seen had tables smaller than those commonly seen on princess cuts.

But really, we should defer to the real experts here, like Kenny, CCL and Dancing fire- after all, these are people who have really studied Pricescope, and learned far more useful info as compared to what us tradespeople have to offer.


Hey John, you want to go get a beer?

were they all 60/60 cuts?

NO DF- the AGSL 0 Cut grade stones we''ve had were generally 58% or smaller on the table.
netcbc- CONGRATS!!!! Sounds like you did real good!!!

 

[John P]

Date: 5/27/2010 3:51:57 PM
Author: netcbc
Hello, just an update, the appraiser hwgem rated the cut as ''Excellent'', it falls in the category of cut between 0-2, in person to me it sparkles just like the youtube video above so I''m super happy. I feel like a got steal on this stone as I''m showing similiar stones at least $4K more online prices.

I will post the ASET later but it shows a good amount of red.

Congratulations. Sounds like a positive appraisal experience. The most important thing is that you''re happy.

 

[John P]

Date: 5/27/2010 11:27:31 AM
Author: ChunkyCushionLover

Date: 5/27/2010 12:54:22 AM
Author: John Pollard

My opinion regarding the 71% threshold is not limited to AGSL. The AGSL cut guidelines do pose candidates @ T75 and T80% (the guides are published in 5% increments) but I have not seen a live example. Similarly, the RB guides indicate T47-49% possible for AGS0 in RBs but, again, I have yet to see such a configuration.

Please link your examples of T75-80% AGS0 PCs; I'd be interested to check them out.

I don't see any real world 75 - 80% table examples that have achieved AGS 0 light performance, to copy a Karl K term it seems 'twitchy' to deliberately try to cut to achieve such proportions.
If you look at the suggested guidelines for 80% table in a 2 chevron, Pavillion 2 angles have to be 42 degrees if they are 43 the grade becomes 2 or 3, the tolerance for cutting error (and scan error) is too small.

I also believe that the Ideal cut grade is also broad and there are some combinations that have much more brightness than others within AGS 0 ideal so just achieving the minnimum standard to reach the 0 grade does not produce the brightest diamonds.

I just don't feel its right to equate AGS performance based grading to a range of proportions as RD is trying to do. You have illustrated a well supported practical limit (although maybe 72 - 73% is close enough as well) but this is different from the theoretical limit based on the grading algorithms.

Appreciate the comments - it differs for good reason in practice. I agree that a bit higher can be reasonable, keeping 2-3 chevron configurations and/or big carat weights in mind. Lots of fish in the sea.

Which labs give a cut grade or suggest proportions for Princess Cuts based on proportions?

None that I know of. Some highly considered boutique labs / appraisers consult charted guidelines. Some of those I'm asked to keep confidential, others are published. I don't use such a system - for reasons I've long stated about fancy shapes & variability. Also since minimum thresholds don't really suit my purposes.

I consider the AGS Cut Guides as helpful Cliff's Notes-from-afar, especially since they take into account differences in configuration and overall mm spread. But the guides also make assumptions which are aren't realistic for most real-world PCs. At best, as the name implies, they are guides.

Straying somewhat (now that the OP is happy): One of the confounding things when discussing "princess cuts" is the ham-fisted way different configurations continue to be lumped together. A 3.00ct 2chev pavilion PC and a 0.50ct 5chev pavilion PC are completely different animals. And this does not even touch-on the implications of varying cut precision, which ranges farther afield in this shape than RBs. I've often said the trade (as a whole) is 100 years behind the round when it comes to assessing and even discussing other shapes. Imagine trying to sell OECs, Trad57s and Leos as if they were all a single classification. Can you imagine the confusion and variability from diamond to diamond? Yet casually ask the average jewelry salesperson what chevron configuration the Princess he's showing you has. Often he/she has no idea.

 

[John P]

Date: 5/27/2010 12:44:41 PM
Author: Rockdiamond
Hey John, you want to go get a beer?

Reliably.

Actually (exposing my geek-self here) my idea of a good time would be a keg and enough frosty mugs for everyone in this thread who wants to play + a large room w/ northern daylight, grading lamps, halogen spots, fiber-optics, Nikon loupes, tweezers, cloths, Zeiss microscope, helium scanner, DiamCalc on widescreen monitor, PGS, desktop ASET and access to a few hundred diamonds.

Put on the rock & roll, toast & discuss.

 

[netcbc]

I think I''m happy since I feel I got a great deal but I''m no expert. Would you guys say I got a good price for quality?

 

[Dreamer_D]

Date: 5/27/2010 5:41:41 PM
Author: John Pollard

Date: 5/27/2010 12:44:41 PM
Author: Rockdiamond
Hey John, you want to go get a beer?

Reliably.

Actually (exposing my geek-self here) my idea of a good time would be a keg and enough frosty mugs for everyone in this thread who wants to play + a large room w/ northern daylight, grading lamps, halogen spots, fiber-optics, Nikon loupes, tweezers, cloths, Zeiss microscope, helium scanner, DiamCalc on widescreen monitor, PGS, desktop ASET and access to a few hundred diamonds.

Put on the rock & roll, toast & discuss.

Will you provide the diamonds and can we keep them afterwards?

 

[John P]

Date: 5/27/2010 6:24:37 PM
Author: netcbc

I think I'm happy since I feel I got a great deal but I'm no expert. Would you guys say I got a good price for quality?

I suggest you not use the appraisal's "replacement value" to establish your insurance premium. That price tag might exist somewhere on earth - like a ski lodge in Aspen with it's own Tiffany & Company serving caviar - but for that amount it should come with top finish marks, a salesperson who will dance-on-command and a free helicopter ride.

Date: 5/27/2010 7:04:39 PM
Author: dreamer_d

Will you provide the diamonds and can we keep them afterwards?

We're still working on that free-sample initiative. It's a very popular request!

 

[netcbc]

Thanks for all the info everyone, I'm just noticing I forgot to mention the price of purchase, it was $11.6K USD. Here is the ASET, took it quickly with Iphone as I stored the stone and everything at a safety box with the bank.

Rundown once again
Shape Princess
Carat Weight 1.85 ct
Color F
Clarity is vs2
Depth % 74.2 %
Table % 68.0 %
Symmetry % Very Good
Polish Very Good
Dimensions 6.77x6.52x4.84 mm
L/W Ratio 1.04

Appraiser Excellent Cut

Good buy?

 

[netcbc]

Bad pic, but what do you think of the ASET?

 

[stone-cold11]

get a better pic?

 

[netcbc]

Better pic, what do you guys think of the ASET, any descriptive insight would be great aside from "looks good, ok, etc"

 

[oldminer]

If you have the ability to shop for a diamond in person, you might consider using the guidlelines from the AGA Cut Class parametric charts which were written long before AGSL did their princess cut design and analysis work. http://gemappraisers.com/oldcutgraderules.asp From Cut grade 2B and better you can broadly shop all the various princess cut faceting patterns and discover which diamond looks just right and best for you. So long as the basic parameters are within the 2B and better range, you are not getting an inherently poorly cut diamond with durability faults or with so much depth that the diamond looks way smaller for its weight than a better cut would look. Well within the 2B and better guidelines are nearly all AGS0 princess cuts. I suppose there may be some that are close, but not quite there. I really can''t be certain and possibly John Pollard will help us here.

To properly get a final AGA Cut Class grade use the automated grader which follows the RULES of USAGE. Without using these rules, you will grade a bit too strictly. http://gemappraisers.com/oldcutgrade.asp


I have not seen an AGS0 princess which did not meet my own beauty standards, but this is personal to each viewer. There are many, many other valid choices for beautiful and nicely cut princess cut diamonds which don''t meet the AGS0 pattern and design, yet are just fine for consumers to love and purchase. They offer a fine look, a bit different than the AGS0, but come with zero premium on their cost because they are "unbranded". However, you must be a good shopper to pick a good off-brand since there are so many miserably cut princess cuts in the mix. That''s why I suggest using the AGA CUt Class tools as a screening method. Use your eyes for the final choice.

Of course, you could buy an AGS0 princess cut in the dark and have no worry in the world about it looking superb.

 

[WinkHPD]

Date: 5/27/2010 5:41:41 PM
Author: John Pollard

Date: 5/27/2010 12:44:41 PM
Author: Rockdiamond
Hey John, you want to go get a beer?

Reliably.

Actually (exposing my geek-self here) my idea of a good time would be a keg and enough frosty mugs for everyone in this thread who wants to play + a large room w/ northern daylight, grading lamps, halogen spots, fiber-optics, Nikon loupes, tweezers, cloths, Zeiss microscope, helium scanner, DiamCalc on widescreen monitor, PGS, desktop ASET and access to a few hundred diamonds.

Put on the rock & roll, toast & discuss.

Ah, I can see it now, everyone holding their various beers up to the north light and going, "Well, this has an AGS 0 head, but the foam was scraped at 30 degrees rather than 45 degrees, so the head is in the lower 10% of the AGS 0 grade. This lager is a nice L color, but Kenny''s pale Ale is more like an H-I and that Porter Wink is drinking is more like a C7.

"0h look! At 10x this one has a cloud of bubbles that is affecting the transparency, it will need to be at least an SI2, maybe an I1.

Oh, the equipment is for the diamonds, well, never mind.

 

[John P]

Date: 6/10/2010 10:42:13 AM
Author: luckystik3
Better pic, what do you guys think of the ASET, any descriptive insight would be great aside from 'looks good, ok, etc'

On 5/25 I said that including an impartial expert eye will give you more than we can offer here. My opinion has not changed.

The insight we can draw from a static ASET image in an unknown setup is limited. Based on experience analyzing diamonds in standardized setups this image is not representative of an AGSL 0-2 light performance grade. But you have a qualified AGS member appraiser who has seen it in-person and feels it falls there. That person was able to see, feel and analyze the diamond beyond our ability via cybercafe.

Opinions aside, an in-person evaluation by a qualified independent trumps our armchair comments.

 

[netcbc]

Thanks John, that makes a lot of sense.... I guess I was thinking the ASET was the end all to verifying the quality.

 

[John P]

Date: 6/10/2010 1:10:48 PM
Author: luckystik3
Thanks John, that makes a lot of sense.... I guess I was thinking the ASET was the end all to verifying the quality.

You're welcome. The ASET is a fantastic tool, but any assessment-from-afar is limited. Compare it to meeting a lovely lady - measurements are like knowing height and weight. A photo can show how she looks in 2D. An ASET image reports on her likely personality but there is no substitute for meeting her in person and going on that first date.