The matter of depth in a princess-cut by Paul Slegers

[pricescope]

Kudos to Paul for his new article: The matter of depth in a princess-cut

 

[oldminer]

Paul is making good points. Well worth reading. One must allow greater latitiude in depth percentage for all fancy shapes, and especially where length is greater than width. I think cutters know more about these percentages than anyone tells us. One can have high performing deep diamonds and equally high performance regular depth diamonds. No one would choose overly deep unless the price was adjusted lower to make the smaller looking stone a less costly diamond.

The best diamonds have normal depth ranges. I can''t get past the idea that overly deep stones have a value per carat disadvantage that indicates less ultimate "quality".....Quality of Cut.

 

[Garry H (Cut Nut)]

Excellent article Paul.
The crown facets on most princess cuts are also tied together the same as the crown facets on round brilliant.
The main and huge variance is as you note - in the unconnected pavilion facets. and it is even more complex when we get into non square stones which AGS have not yet attempted to quantify with a list of recomended paramaters for candidates (although their system will be able to grade them).

 

[valeria101]

I was waiting for this after the problem surfaced on an older thread

It makes a useful read. Thanks !

 

[valeria101]

Date: 4/20/2005 12:54:50 PM
Author: oldminer

No one would choose overly deep unless the price was adjusted lower to make the smaller looking stone a less costly diamond.

Well... this is one important point that the article is missing - that the extra depth (and mass) does not necessarily cost more.

As far as I know, there are two "commercial arguments" against that extra depth: #1 that it makes diamonds look smaller for the money, and #2 that it makes them less brilliant.

#1 sounds interesting, but it's just half truth, because the statement fails to mention that prices are adjusted for spread, so "smaller for the weight" does not equal "smaller for the money". Perhaps some stats showing that might be of use to be added to the article.

#2 is one bit of folklore never explained. It may come as a silly interpretation of that ubiquitous scheme (link to one example) used by shows to explain "best cut" as a happy middle between "too shallow" and "too deep" without explaining why or what "too much" is.

Silly as is, the scheme must be the widest spread and best known explanation of "cut quality" out there. The article says this is not the case for all diamond cuts, and that's one useful beginning of an explanation. It might help to add a line about why total depth does not doom brilliance in fancies

Just a rookies' review about what a hypothetical random reader with little if any knowledge of gem cut intricacies (like me now, and definitely like me some very short time ago) might find puzzling.

 

[oldminer]

Overly thin diamonds will prove not to be at the highest level of light return. They simply leak too much light.

Overly deep diamonds may have many cases where they are top or nearly top performers. SOMETIMES proper price adjustments are made per carat, lowering the price of deep stones because they do not look as large as more moderate depth ones. That alone, the appearance of apparent size, is what makes for less value. There is nothing wrong at all with this. The market is intelligent and generally makes good adjustments.

What we have seen for years are consumers not understanding that apparent size does play a part in value. People have bought overly deep stones in place of well cut stones because they thought they were finding a bargain....so much weight and so much less money where, in fact, they were buying lumpy, too deep, stones that looked very nice, but did not have the apparent size, the spread, of a well cut example. The education of what makes for "BEST" separates a few smart buyers from the herd.

There are cuts, such as princess, that inherently work best at depths deeper than rounds. This is to be expected and defining the best of these special cuts is an ongoing challenge. However, don't just take this at face value. There still will be a difference in VALUE, in a smart market and among EDUCATED DEALERS and CONSUMERS, between a properly deep diamond and an overly deep diamond, even when both have identical or highly similar light behavior properties.

We are learning more all the time, but the above issue may confuse people into thinking any diamond that performs well is a "super fine" stone. The "best" is comprised of fine light return and fine make, not light alone. No doubt more guidance will be forthcoming, but performance ought to be balanced with proper spread for a given weight and cutting style.

I am agreeing with Paul's article, in case anyone thinks I am making an argument otherwise. This is sort of an addendum that closes the loop for people who might not be able to make a final conclusion that works.

 

[WinkHPD]

I am going to guess that a lot of people will read that article and perhaps not understand it completely, like me.

I could not begin to tell you why one angle is better than another, only that there are those who do understand it.

For those of us who appreciate beauty however, it is good that someone does understand what makes one stone sparkle and shine more than another as the innovations in cutting over the last twenty years have brought us stones that could only be accidentally found, if at all in the "good old days".

The truly best thing about the new grading parameters and the guidance they provide to the cutters in my opinion, is the increased beauty that is VISUALLY detectable by the eye of the consumer. So, for those of you, who like me, get headaches trying to wrap your brain around all of the technical information, take comfort in knowing your eye will always be the final arbiter of what is best for you, and your eye will see a LOT more beatiful stones now that AGS has brought a comparative scale to us for not just rounds but princess cut diamonds. Soon the mountains of drek princess cuts will no longer be acceptable and the newer brighter stones will take their rightful place in the market. For those of you who like the princess, your time is coming!

Wink

 

[Paul-Antwerp]

I think that you have missed the basic point of the article. I know that everyone expects me to talk about a diamond''s light performance, but in this case, I was not.

I basically wanted to address the following issue: Does a higher depth in a princess mean that it has a lower spread?

Spread, in this case, is best described by the stone weighing more for the same diameter, or having less diameter for the same weight.

In the meantime, I have made some calculations with Diamcalc, and in these calculations, I was just looking at the connection between spread and depth, not at the light performance of any of these stones.

To start, I took a stone with a diameter of 6x6mm., and a table of 75%. I fixed the C1 at 36.50° and the C2 at 31°. This remains identical in all the following examples, and thus the crown height does not change.

For stone 1, I set the total depth at 75%, thus using a P2 of 43°. With a P1 of 63°, this stone weighs 1.31 Cts.

For stone 2, I keep the same total depth of 75%, and with a P1 of 55°, the stone weighs 1.16 Cts.

For stone 3, I keep the same weight of 1.16 Cts, with a P1 of 59.1° and a P2 of 38.4°, thus ending up with a total depth of only 65%.

Now please compare stone 2 and 3, both having the same diameter, the same crown and the same weight. This means that they have the same spread (weight by surface area). The only difference is that one has a depth of 75% and the other one only 65%.

I hope that my point is somewhat more clear now.

Live long,

 

[RADIANTMAN]

Thanks Paul for explaining a point so often misunderstood. Depth percentage in shapes like radiants and princesses mean almost nothing without additional information to help interpret the data. As an indicator of spread it is so imperfect as to be almost useless. The only way to measure spread is to actually measure it directly - length x width for a princess, length x width minus the area lost due to the cut corners for a radiant.

A princess measuring 6 x 6 will be "bigger" than one measuring 5.8 x 5.8, no matter what the depth percentages are.

 

[oldminer]

Paul;

Thank you for your very concise further explanation. It is very clear now. I appreciate you taking the time to make it perfectly clear.

Now, I would pose the question. How would these three diamonds with different weights and/or angles, yet with identical spread work with light?

Is one predictably superior to the others in light performance?

Would they all grade the same AGS grade?

 

[Paul-Antwerp]

When putting together these examples, I did not pay attention to how their light performance would be. I was just trying to show that depth does not equal less spread.

If I check their performance according to AGS-charts now, they all score in the AGS5 to 6-range. But that is no surprise either, since there are far less high performing combinations with a table of 75% than there are with smaller tables.

Starting from stone 1, with all other parameters remaining equal, I could maximize up to AGS-0 by using a P1 of 61%. This shows that by keeping everything equal, diameter, depth, complete crown and P2, we can go from AGS cut-grade 6 up to 0 just by adjusting the P1 correctly.

Unfortunately, on almost all Sarin-measurements, P1 is not mentioned.

Live long,

 

[RADIANTMAN]

Paul:

Do you know what the range of depth percentages AGS 0''s are likely to have? The sense I get looking at the cutting parameters they have provided is that the depth %''s are likely to be fairly high.

Also, the spread criteria they are using seems to be quite lenient. Am I correct that the new AGS 0''s are likely to be very lively but somewhat small looking diamonds?

 

[Garry H (Cut Nut)]

Stan they are quite lenient on spread, but because the light return is better, these stones can look quite big.

PAUL LET ME TROT THIS IMAGE OUT AGAIN _ SAME DEPTH AND TABLE SIZES _ IT IS

 

[Paul-Antwerp]

Date: 4/21/2005 2:44:19 PM
Author: RADIANTMAN
Paul:

Do you know what the range of depth percentages AGS 0''s are likely to have? The sense I get looking at the cutting parameters they have provided is that the depth %''s are likely to be fairly high.

Also, the spread criteria they are using seems to be quite lenient. Am I correct that the new AGS 0''s are likely to be very lively but somewhat small looking diamonds?

Hi Radiantman,

When first looking at the charts and using them, I also had the first impression that we were ending up with very high depth-percentages. At the same time however, I realised that the higher depth in these stones did not mean less spread, since the necessary P1 (which is the major contributor to extra weight) is lower than the industry generally uses now.

I have also made calculations, looking for the minimum side-to-side diameter needed in order to get an AGS-0. If I then take that minimum side-to-side diameter, and from there calculate the average diameter of a square stone (thus including the point-to-point diameter), that average diameter of the AGS-0 is 6.51 mm.

The spread-criteria that you are mentioning are part of the whole calculation, and after the light performance of a stone is fully calculated, and the stone is outside of the spread-criteria, it will get an extra penalty by being further downgraded. In AGS-0 however, the other criteria automatically take you far away from that spread-borderline, and there is no risk of ending up under that spread-minimum.

I hope that this is clear.

Live long,

 

[cjfilm]

what is considered normal depth range?

.

 

[Paul-Antwerp]

Date: 4/21/2005 3:32:34 PM
Author: Paul-Antwerp
I have also made calculations, looking for the minimum side-to-side diameter needed in order to get an AGS-0. If I then take that minimum side-to-side diameter, and from there calculate the average diameter of a square stone (thus including the point-to-point diameter), that average diameter of the AGS-0 is 6.51 mm.

Sorry, I was re-reading this, and my sentence is not complete. Unfortunately, I was too late to edit the post.

I wanted to say that I made calculations for the minimum side-to-side diameter for an AGS-0 of 1 Ct. From there on, calculating the average diameter of that stone, this is 6.51 mm.

Pretty amazing, if we think that this is almost exactly the average diameter of a super-ideal round.

Live long,

 

[researcher]

I''m also wondering what an "overly deep" stone means. My stone has a depth of 74.1%. Although some people here on PS thought it was too deep, my stone scored a triple VH on the BrillianceScope and has a beutiful Ideal Scope image. I guess I''m just curious about how the points made in the article relate to the spread of my stone (which I''ve never thought was good), and how my stone will rate with the new standards. Any insight is greatly appreciated!!!

3.22 carats
8.14x7.95x5.89
74.1% depth
71% crown
M-TK
VG
VG
11.2% crown
43.6 crown angle
60.5% pavilion
40.0 pavilion angle

 

[RADIANTMAN]

Paul - thanks for your response. I''m not really clear, though about what you mean by the average diameter of a square, or why that corresponds to spread.

The circle representing the spread of a 6.5 mm round diamond has an area of
33.18 square mm - that is its geometric spread. A square princess cut with precisely the same geometric spread would measure 5.76 x 5.76.

A 1 ct princess measuring 5.5 x 5.5, which today would be considered a good princess spread, has an area equivalent to a 6.2 mm round.

Do you have a way of calculating what the actual range of measurements of a 1 ct AGS 0 princess cut will be?

 

[Paul-Antwerp]

Hi Stan,

You are right in talking about the surface of a stone, and not about the diameter.

When calculating the smallest possible side-to-side diameter of an AGS-0 princess of 1 Ct, this is 5.44 mm. Now remember, this is the smallest possible diameter, and many diameters will be even higher.

This should ease your fear for stones with high depth and low spread.

Live long,

 

[RADIANTMAN]

Thanks Paul. That sounds like the AGS 0 princesses will be similar in spread to what the market now considers a correct princess spread. I was nervous because it was my understanding that the AGS considered 6 mm to be a satisfactory spread for a stone 1.38 - 1.45 cts. That seemed to me to be somewhat small by current standards (1.50 ct 6.4-6.5mm), though I didn''t do the math to normalize it to a more recognizable size like 1 ct. Thanks for doing the work for us.

 

[researcher]

Does my previous question not make sense? I''m just wondering why it was skipped....

 

[Garry H (Cut Nut)]

It is out of context here.
Post it on the regular board please.

 

[valeria101]

Date: 4/22/2005 12:57:52 AM
Author: Garry H (Cut Nut)
It is out of context here.
Post it on the regular board please.

You must have replied to "Researcher", but this might just apply to my rambling as well...

How do the numbers below (=the chart) fit with the article ?

 

[valeria101]

... this should have been attached to the previous post.
I just used Pricescope's database to check if depth has anything to do with the size of princess cuts. Apparently it does.

 

[RADIANTMAN]

I don''t think Paul meant to say that there is no correlation between depth % and spread. Of course there is. My understanding of his point is that while a princess with a higher depth % is more likely to have a smaller spread, this is not necessarily true for any individual stone. The complexity of the cutting makes it possible to cut a princess with a lower depth % that actually spreads smaller than one with a higher depth %. Because of this, you really have to look at the actual measurements of the stone to get a reliable read on how it spreads.

For some reason, last night I became obsessed with the question of how the new AGS 0 princesses will spread, so I sat down and calculated the AGS''s ideal measurements for various carat weights. Assuming my math is right, here are the spreads (subject to some rounding error):

1.00 5.4mm
1.25 5.8mm
1.50 6.2mm
2.00 6.8mm
3.00 7.8mm
4.00 8.5mm
5.00 9.2mm

The AGS allows a 5% fudge factor from these numbers - that is a 1.05 ct need not spread more than a 1.00. Princesses hitting these spread numbers will weigh about 15% less than a round of the same spread. A 1.00 ct AGS 0 princess will spread about the same as a 0.85 ct AGS 0 round.

 

[diamondsbylauren]

Hi researcher- I would think that it should be just fine to ask a question here.

The "standards" for diamond cutting ore too often used to justify a price- and at the same time, make other diamonds look bad.

I use my eyes to judge stones- and in many cases, the "ideal" cut diamond is in fact smaller in appearance than a "non ideal" stone.

At 74.1% your diamond is at the deeper edge of acceptability- yet I''ve seem many princess cuts with 75% depth that were'' To Die For"
Yes, if you compare the 75 depth with a 68%''er the deeper stone will look smaller.

Hopefully, this was compensated for in the price you paid.
But please don''t let anyone use numbers to tell you there''s something wrong with your diamond if you love it.

 

[researcher]

Thanks for addressing my question, David. I''m a numbers person, and was just curious as to whether calculating the depth and spread of princess cut stones in this manner would better predict the levels of light return in high-performing stones. Knowing that my stone is a high performer, I thought it would make for a good example. I realized a little too late that I don''t have enough information (the second pavilion and crown %''s), but being told to go somewhere else to post (after being ignored) when I was just trying to understand the article better was, in my opinion, a little rude. Sorry for not being a diamond expert!

I therefore very much appreciate your response, David. As always you are high class

 

[Garry H (Cut Nut)]

Apologies Researcher.
I skimmed and thought you were posting a "should I buy this" request.

Does your stone look a bit like this thru an ideal-scope?
I have modelled this with DiamCalc using the scant info (the crown info is badly flawed- not possibly i think to get that combination of height and angles with 71% table).

The second pavilion angle might be around 58 or 59 degrees.

There are some very small ''candidate'' targets on the AGS charts around those parameters, so it is possible your stone could recieve AGS for performance (but would be marked down a bit for the VG VG).

 

[valeria101]

Date: 4/22/2005 11:34:44 AM
Author: RADIANTMAN

My understanding of his point is that while a princess with a higher depth % is more likely to have a smaller spread, this is not necessarily true for any individual stone. The complexity of the cutting makes it possible to cut a princess with a lower depth % that actually spreads smaller than one with a higher depth %.

This rings crystal clear. Thanks

 

[DON HULIO]

This is my first time posting, so here it goes...hopefully, not too long winded...I am going to propose to my girlfriend in July 05.
I have just purchased a princess cut diamond from a personal jewler friend of mine. It was kind of a leap of faith, and here is the reason why: I have not personally viewed the diamond, however, my friend has been in the business for over ten years, and he personally viewed the stone. He informed me that it is a great looking stone, with good action and scintilation(sp?)and good fire. He said that he is highly critical when evaluating diamonds, and his only complaint is that the diamond is cut slightly deeper than an ideal cut. I will receive the diamond within the next week via next day air. The deal is done, but I''m still interested in knowing more. So, here is my question: based on the following specifications, is this princess cut a good stone, and is it a good value for the price that I''ve payed?

It is GIA certified:

Shape and Cutting Style: RECTANGULAR MODIFIED BRILLIANT
MEASUREMENTS: 5.53 X 5.23 X 3.93 mm (1.057)
WEIGHT: 1.01 carat

PROPORTIONS:
Depth: 75.1 %
TABLE: 77%
GIRDLE: Medium to Extremely Thick (Hopefully good for not chipping)
Cutlet: NONE

Finish:VERY GOOD
Symmetry: GOOD

Clarity Grade: VS2
Color Grade: D
Fluorescence: Faint

My personal jeweler friend assured me that his price of $4000.00 for the stone was unbeatable,$4100 mounted in a four point tiffany setting, white gold with platinum tips. I have read almost everything on this website in an effort to educate myself, and from what I have gathered, this is a good diamond, for a great price. Any input is appreciated. Thank You. Don Hulio