Why Princess Table and Depth % data is useless

[Garry H (Cut Nut)]

These stones all have 70 % table and 70% depth %.

The crown angles on princess can vary enormously. They are not tied together either the way the minor facets on a round diamond are. For example one of these images has a 60 degree lower crown angle and a 25 dergree upper crown angle. Sarin and Ogi scanners are also incapable of measuring these angles - and there are only 2 Helium scanners (that can do it) in USA.

The same rules apply as the 60 60 page on the tutorial - the table and depth % do not tell you if you have a 5% crown height and 65% pavilion, or a 15% crown and 55% pavilion depth.

But wost of all - the critiacal pavilion - it can have 5,7 or 9 chevrons on the pavilion (5 in this example) and they can be all 2 degrees different or much more.

And then we have the Big triangluar pavilion facets - if the corner central chevron was say 39 degrees - then in the case shown - the big triangular facets can vary between 40 degrees and 60 degrees.

If you want to check out a princess sight unseen - then demand an ideal-scope photo.

A sarin generated gem adviesr is better than nothing - some overseas manufacturers have Helium scanners, and they will be providing their stones with Gem adviser files and this is the best method.
We wil soon see the first AGS graded princess cuts on the market - they will be good because they are using good technology, including the ASET scope - which is a multi colored ideal-scope. This helps to tell if the light return is from better light supply directions etc.

 

[researcher]

Gary~
This is where I always get confused. I can understand table and depth information being useless when used "out of context" so to speak, but when used in conjunction with the crown and pavilion info it seems to be pretty useful in determining the better stones. When I had done my initial diamond investigation after learning of Dave Atlas''s grading charts, I would pick stones based on their beauty, and then ask to see the numbers. Time and again I picked the stones that followed the basic guidelines. There are always exceptions to every rule, but for the majority of stones there must be basic table and depth parameters for the best stones--right? I find this stuff fascinating and really appreciate your taking the time to post these examples!

 

[icemyster]

Gary,

I would echo the last reply...I love reading your insight...thankyou. I am curious, because when I seek princess cuts to call into the store, I follow the traditional priciples and have good success getting consistant performers on the brilliance scope, of course there are stone with the "perfect" measurements that still come out poorly. I suppose my question to you would be, when sorting through a list of stones looking at each for no more than a second...what better indicator is there to at least narrow down the field?

Thanks

 

[Garry H (Cut Nut)]

Date: 5/7/2005 11:42:27 AM
Author: icemyster
Gary,

I would echo the last reply...I love reading your insight...thankyou. I am curious, because when I seek princess cuts to call into the store, I follow the traditional priciples and have good success getting consistant performers on the brilliance scope, of course there are stone with the ''perfect'' measurements that still come out poorly. I suppose my question to you would be, when sorting through a list of stones looking at each for no more than a second...what better indicator is there to at least narrow down the field?

Thanks

Of course you can use the AGA list to cull out stones with thin girdles and too big a table, too off square, too deep, too small a spread etc etc.

But it may be just as relevant to sort with an ideal-scope - it takes 15 seconds to reject or consider for further examination IceMyce

 

[oldminer]

Gosh, I was hoping someone would defend me...Thanks. Of course, that''s why I use both my own AGA system AND offer Ideal-Scopes. They work well together. Ideal Scopes also work well with ImaGem. They ought to work well with the GIA and AGS systems, too. I''d be quite surprised if all these things don''t mutually work together fairly well.

 

[icemyster]

Right on Gary.

As I''ve stated in other threads on the subject, I stand better chances of finding winners among those princess cuts whose tables are less than their total depths but this is not a hard fast rule. Interestingly AGS''s latest research on the subject concurs with my findings on this as well. If you take note in the most current princess cut quideline charts they published your chances of getting superior performance decrease as table size increases.

Peace,

 

[researcher]

I think you''re right, Dave. Honestly, your charts (and advice) is what led to me getting a triple VH stone!

I agree that the Ideal Scope is also necessary, but when buying online I think customers need to have something to narrow their search criteria with, and your charts help the "unsophisticated" make sophisticated choices

 

[Rhino]

Date: 5/7/2005 6

2

5 PM
Author: icemyster
Right on Gary.

As I''ve stated in other threads on the subject, I stand better chances of finding winners among those princess cuts whose tables are less than their total depths but this is not a hard fast rule. Interestingly AGS''s latest research on the subject concurs with my findings on this as well. If you take note in the most current princess cut quideline charts they published your chances of getting superior performance decrease as table size increases.

Peace,

Oy ... didn''t realize my assistant had logged onto my laptop and posted. The previous post was from me, Rhino. Not my assistant Tim. Tim is Icemyster and sits along side me at our store.

 

[researcher]

Date: 5/7/2005 6

2

5 PM
Author: icemyster
Right on Gary.


As I''ve stated in other threads on the subject, I stand better chances of finding winners among those princess cuts whose tables are less than their total depths but this is not a hard fast rule. Interestingly AGS''s latest research on the subject concurs with my findings on this as well. If you take note in the most current princess cut quideline charts they published your chances of getting superior performance decrease as table size increases.


Peace,

Icemyster,
I''m curious--at what point does the chance of getting superior performance decrease? It seems there are "magic numbers" that no one wants to share

I mean, what is the AGA making their decisions based on? Is it in part numbers?

 

[mdx]

Dave
We have found the Ideal Scope an extremely efficient tool for Princess cut stock selection. After selection we grade then according to your charts and find the two results very compatible.

Gary

Nice post, we see hundreds of examples of that you are demonstrating in your images
when looking at goods to purchase.

I reckon there is more variation in Princess cuts than any other commercial cut

Johan

 

[Garry H (Cut Nut)]

Exactly Johan, and that''s why I have been saying for years that the monir facets on rounds only play a minor effect - it is to do with the way they are "tied" together.

Also round dimamond minor facets have very very little impact on weights and yeilds. But the Princess variations are huge - I did not save the weights on those - probably should have - but there would be about 15% variation without changing girdle thickness.

 

[Garry H (Cut Nut)]

Date: 5/7/2005 10:43:14 AM
Author: researcher
Gary~
This is where I always get confused. I can understand table and depth information being useless when used ''out of context'' so to speak, but when used in conjunction with the crown and pavilion info it seems to be pretty useful in determining the better stones. trouble is Researcher you can not get any let alone accurate crown and pavilion data from any scanners. When I had done my initial diamond investigation after learning of Dave Atlas''s grading charts, I would pick stones based on their beauty, and then ask to see the numbers. Time and again I picked the stones that followed the basic guidelines. There are always exceptions to every rule, but for the majority of stones there must be basic table and depth parameters for the best stones--right? Wrong I am afraid Researcher

- AGS charts show that there is a huge range of proportions - and they have even decided to accept Princess for AGS 0 that have a 25% lessor spread than a round diamond! I find this stuff fascinating and really appreciate your taking the time to post these examples!

Can anyone suggest other things that need explaining about this issue - I am considering adding this to the Tutorial - opinions?

 

[researcher]

Can you share the AGS info? How does the AGS grade stones?

 

[researcher]

Oh, and wouldn''t the "huge range of proportions" still not have extremes? I mean, there aren''t any AGS 0 stones with depths of 95%, right?

 

[Rank Amateur]

Understanding why the %s don't work as well is easy to understand. What I don't understand is why you leave the % input option in the HCA.

Maybe it's doing more harm than good?

 

[researcher]

I understand the %''s not working as well, but where do you start when looking at stones as a consumer if NOT with the numbers?!?!

 

[Garry H (Cut Nut)]

RankAm I ;eft the total depth % because I changed the angles but always bought the stiones back to 70% depth because that was the whole point to the exercise.

Researcher I have not been given permission to share the AGS charts with anyone other than manufacturers who are interested in cutting for AGS certifiecation.

But I have messed this one up - the whole thing is meaningless - so do not try to use it - but the format remains the same - there is one of these for 55, 60, 65, 70, 75 and 80% table sizes. And this is only for 5 chevron stones - 7 and 9 chevrons get different results again.

There are more sweet spots at 55 and 60 and very few at 80%

 

[valeria101]

Perhaps add a page about what the numbers on those certs say and what they do not. That is the first thing that is available... while the rest of your tutorial will make it clear why that information is not enough and what can be added, giving a reasonable interpretation to GIA numbers is really useful. Starting with the "necesary" and building up towards "sufficient" info would make the tutorial more helpful, IMO.

Same as Researcher says

Date: 5/8/2005 10:28 AM
Author: researcher
I understand the %''s not working as well, but where do you start when looking at stones as a consumer if NOT with the numbers?!?!

Some example of Princess cuts make me wonder if these guys even have a crown at all ! Is it hard to model one without via GemAdviser

- as a peek into no go teritorry... Explaining how this cut makes use of the rough material would be fun. Especially with a chart about prices, size and weight. These seem to make a nice argument in favor of those better cut princesses with larger spread or better brilliance.

 

[Paul-Antwerp]

Date: 5/7/2005 9:42:14 PM
Author: Garry H (Cut Nut)

Can anyone suggest other things that need explaining about this issue - I am considering adding this to the Tutorial - opinions?

Hi Garry,

I think the title of this thread could just as well be ''Why Australian speak can be clear sometimes, it can just as well be confusing''.

I fully agree with your assessment that table and depth do not say anything about light performance, but you should have made your point clearer.

If you look at table size, the most important point is that a lower table size increases the probability of higher light performance. Many replies have been stressing on this. However, a probability is definitely not a certainty. Would you agree with this estimate? With a table size of 60%, you have a chance of 1 in 4, while with a table size of 75%, you have a chance of 1 in 15.

If you look at depth, I think that you are missing the most important point. Today, too many people are thinking that they should get a lower depth, while they should try to get a higher depth. In my journal-article, I have shown that 75% depth in princesses actually is around 63%, if one would calculate in the same way as in rounds. A depth of 65% is in this way actually 53%. Would anyone consider a round stone with a depth of 53%? Also, from our experience in cutting AGS-0''s, we see that most of these stones have a depth of around 78%.

I would like to tell more right now, but I have to run. I will be back later today.

Live long,

 

[strmrdr]

Garry,
"Wrong I am afraid Researcher - AGS charts show that there is a huge range of proportions - and they have even decided to accept Princess for AGS 0 that have a 25% lessor spread than a round diamond!"

Thats a downside of performance based grading if I gave you an ideal scope and a pile of princess diamonds the same thing would happen.
Right?
A smallish for its weight high performance stone will pass the test and be accepted.

 

[oldminer]

If finer performing princess cuts are possible to cut with reasonable depth, then ones with a 78% depth are going to look quite small for their weight. I don't think it is fair to call such a stone "Ideal" without qualifying that its Light Performance is Ideal and its Cut Quality is less than optimal. Any consumer or retailer with common sense would prefer a larger lookiong, equally high performance diamond.......at least, I think they would. Does anyone disagree or agree with this argument?

I'd love to hear other people comment.

xxxxxxxxxxxxxxxxxxxx

Also, the title of this thread indicates that depth and table percentage readings are useless. I believe it would have been preferable to say they are going to be of less importance, but a definite part of the new process for AGS. Outside certain ranges stones won't get the AGS 0 grade. These measures are still therefore active as screening tools for cutters, graders and the consumer. Admittedly, the range is far wider, but "useless", is too harsh.

Dealers will continue to favor stones cut to economic realities that grade well. Consumers will continue to seek the biggest bang for their buck with diamonds that perform well and look as large as practically possible, within certain performance restraints. In other words, a wider range of diamonds will now be offered as "Ideal" and it still will be up to experts as to what combinations are the best range of overall stones...... It isn't as if all AGS 0 princess cuts will be alike. In fact, they will be very diverse and still subject to many opinions of overall quality when comparing stones. Light Performance ALONE does not make a diamond totally Ideal or Not Ideal without qualification.

 

[Paul-Antwerp]

Date: 5/8/2005 1:29:59 PM
Author: oldminer
If finer performing princess cuts are possible to cut with reasonable depth, then ones with a 78% depth are going to look quite small for their weight. I don''t think it is fair to call such a stone ''Ideal'' without qualifying that its Light Performance is Ideal and its Cut Quality is less than optimal. Any consumer or retailer with common sense would prefer a larger lookiong, equally high performance diamond.......at least, I think they would. Does anyone disagree or agree with this argument?

I''d love to hear other people comment.

I am sorry, David, but it seems to be only me who comes back to this subject.

The fact is that, in a princess, there is no inverse connection between depth and spread. It is fairly easy to cut two stones with the same diameter and the same weight, while one has a depth of 65% and the other one a depth of 75%. This is directly opposite to your point that a stone with 78% depth will look quite small.

To once again put it in the words of R.E.M.: ''It is the end of the world as we know it''. Please wake up, and look with other eyes. I know that I had to do it, and it is definitely enlightening.

The main point is that all currently available princess-cuts are bad light performers. In essence, their pavilions are all cut to retain weight, and we all know that the pavilion is the main contributor to light performance. With most pavilions cut badly, the crown cannot repair much, and the only observation that one can make, is that a higher crown with a smaller table is better than a lower crown. At that point in time, you are forgetting that, before the light came back into the crown area, most of the light performance has already been ruined by the pavilion.

Now, because of AGS, we will see new princess-cuts with well-cut pavilions. The old observations and the old rules (based upon these observations) do not apply anymore. Please realise that they are becoming obsolete.

Live long,

 

[oldminer]

Thanks for your insight Paul. I now get your point, We will see how things turn out. Obviously, there are some major changes on the way.

 

[Rhino]

Date: 5/7/2005 6

5:26 PM
Author: researcher

Date: 5/7/2005 6

2

5 PM
Author: icemyster
Right on Gary.


As I''ve stated in other threads on the subject, I stand better chances of finding winners among those princess cuts whose tables are less than their total depths but this is not a hard fast rule. Interestingly AGS''s latest research on the subject concurs with my findings on this as well. If you take note in the most current princess cut quideline charts they published your chances of getting superior performance decrease as table size increases.


Peace,

Icemyster,
I''m curious--at what point does the chance of getting superior performance decrease? It seems there are ''magic numbers'' that no one wants to share

I mean, what is the AGA making their decisions based on? Is it in part numbers?

Hi Researcher,

That was me who had posted that (Rhino). In answer to your question we begin to see declination in getting top performing stones as the table increases over total depth. Ie. We stand our best chances for tables smaller (as stated), there are still a number of good performers when table is = (or almost) to total depth but when the table gets larger, the chances are slim to none for getting top performers. Since time = money I will generally not waste time calling in stones where table is greater. In the future I will now *only* do this when I know it has received an AGS "0" grade. When the system is made more public and more stones (and their optical results) have been studied and noted you''ll see this confirmed over and over again and we''ll be posting examples on our website as well. In the prerelease charts AGS has given to us in the trade this lil truth has become evident as well and correllates with the research we''ve done on the subject.

I recall coaching you when you were in the market and am glad to see your results.

Peace,

 

[Rhino]

Hey Dave!!!

Never had the chance to contact you once I returned from vacation. Hope all is well with you and your staff. How''d the princess cuts and sq H&A I sent over do on the Imagem?

 

[Rhino]

Date: 5/7/2005 8:15:56 PM
Author: Garry H (Cut Nut)
Exactly Johan, and that's why I have been saying for years that the monir facets on rounds only play a minor effect - it is to do with the way they are 'tied' together.

Hi Gary!

Just curious. If 2 rounds have the same general proportions (lets say 34.5/40.8/56) and one diamond has lower girdles that are 70% length and another has 80% length, in your opinion you consider this to be a minor visual difference between the 2?


I agree with your assessment in the case of princess cuts regarding minor facet proportions especially considering pavilion angle 1 (on the triangle, if memory serves me right). Screwing up pavilion facets on princess cuts one way or the other can contribute to a sloppy looking stone as well as extraneous leakage.

 

[Rhino]

Date: 5/8/2005 2:38:58 AM
Author: Paul-Antwerp

If you look at table size, the most important point is that a lower table size increases the probability of higher light performance. Many replies have been stressing on this. However, a probability is definitely not a certainty. Would you agree with this estimate?

Can''t speak for Gary but I agree 110%.

With a table size of 60%, you have a chance of 1 in 4, while with a table size of 75%, you have a chance of 1 in 15.

Extremely interesting. Did you pull this info from the prerelease charts Paul?

If you look at depth, I think that you are missing the most important point. Today, too many people are thinking that they should get a lower depth, while they should try to get a higher depth. In my journal-article, I have shown that 75% depth in princesses actually is around 63%, if one would calculate in the same way as in rounds. A depth of 65% is in this way actually 53%. Would anyone consider a round stone with a depth of 53%? Also, from our experience in cutting AGS-0''s, we see that most of these stones have a depth of around 78%.

I would like to tell more right now, but I have to run. I will be back later today.

Paul, drop me an email as I have some interesting findings to share with you as well on this matter. Just to expound upon what you''re writing here with regards to princess cuts with 75% depths being comparable to rounds of 63% ... do you draw this conclusion by taking the corner to corner measurements into account? One thing I''ve never been too fond of with regards to princess cut measurements is the strict "side to side" measurements. The reason for this is because it is really not taking into account the full circumference of the stone especially when you consider that the *spreadiest* parts of a princess cut are in the corners.

Also of note (relating to depth) is that high performing princess cuts are easier to find when princess cuts have depths in the mid 70''s than in the mid 60''s. Your explanation shows a very good reason why (on top of the fact that it also increases chances of getting that smaller table).

Good post.

Peace,

 

[Paul-Antwerp]

Just out of curiosity, I quickly calculated the lowest possible total depth for different table sizes, which can still get an AGS-0 cut-grade. These figures are absolute minima, and with this, you are working really at the edge of the chart.

For a table size of 55%, you need at least 69.66% depth
For a table size of 60%, you need at least 69.50% depth
For a table size of 65%, you need at least 69.50% depth
For a table size of 70%, you need at least 70.00% depth
For a table size of 75%, you need at least 73.33% depth
For a table size of 80%, you need at least 72.16% depth

For each table size with this depth, you have to cut with one specific set of 2 pavilion angles and 2 crown angles. If not, no go. In order to have some more leeway to realistically cut for AGS-0, you need at least 4% more depth than indicated above.

Live long,

 

[Garry H (Cut Nut)]

Date: 5/8/2005 3:28:37 PM
Author: Rhino

Date: 5/7/2005 8:15:56 PM
Author: Garry H (Cut Nut)
Exactly Johan, and that''s why I have been saying for years that the monir facets on rounds only play a minor effect - it is to do with the way they are ''tied'' together.

Hi Gary!

Just curious. If 2 rounds have the same general proportions (lets say 34.5/40.8/56) and one diamond has lower girdles that are 70% length and another has 80% length, in your opinion you consider this to be a minor visual difference between the 2?

Hi Rhino,
There is no weight gain advantage to the cutter to make a stone with a 70% or a 90% lower girdle facet, so therefore the argument is mute - how many such stones do we see with really bad minor facet structures - answer - very very few - reason - cutters are not that silly.

Do we see many minor facet screwed up princess? Boy do we ever? Does the cutter do it for yeild and monetary gain? - you betcha!

 

[Rhino]

Date: 5/8/2005 1:29:59 PM
Author: oldminer
If finer performing princess cuts are possible to cut with reasonable depth, then ones with a 78% depth are going to look quite small for their weight. I don't think it is fair to call such a stone 'Ideal' without qualifying that its Light Performance is Ideal and its Cut Quality is less than optimal. Any consumer or retailer with common sense would prefer a larger lookiong, equally high performance diamond.......at least, I think they would. Does anyone disagree or agree with this argument?

I'd love to hear other people comment.

Herein lies the balance between *performance* and *size for the weight*. My current thinking is this Dave. If a princess cut has been cut on the deeper side (like >76%) but does display superior optics it should be valued somewhat less than a comparable performing princess cut of shallower depth. IMHO the cutter who can cut a princess cut with depths in the low 70's/high 60's and maintain superior optics (with regards to both light return and optical symmetry) should be rewarded with the more valuable stones. I would always value them more.


Peace,