Max desired depth percentage on a princess cut diamond

[chewyTBG]

Hello, I have recently bought a diamond, this one in fact:

http://www.whiteflash.com/loose-diamonds/princess-cut-loose-diamond-2940058.htm

but am now being told by a diamond professional that the depth percentage on this diamond is way too high.

What are some other perspectives/ preferences on princess cut max depth percentage?

 

[John P]

...being told by a diamond professional that the depth percentage on this diamond is way too high.

With due respect, that professional is misinformed.

I'd wager the misunderstanding comes from the fact that depth in round brilliants is directly-tied to spread. As a result, many jewelers just assume it applies to all shapes... But simple geometry releases the princess-cut from such direct-ties. Princess pavilions have several chevrons or "tiers" - which can be used to create "bulge" - where even a shallow princess can weigh too much - or to slenderize, so a princess of depth several % above another can still maintain similar spread.

Here is an article by Paul Slegers with good information.
https://www.pricescope.com/journal/matter_depth_princesscut

 

[John P]

Quick examples. These are not actual diamond wireframes, they're just used to illustrate the point:

Weight 1.16 Cts. Spread 6x6mm. Total depth = 65%.



Weight 1.16 Cts. Spread 6x6mm. Total depth = 75%.



Summary: In princess-cuts there is no (absolutely no) relationship between depth and spread. Better to simply correlate diameter measurements in mm to carat weight.

Just as importantly, a princess with cut-quality which promotes edge-to-edge light return will tend to appear larger than others of same spread, simply because average/commercial princess cuts go dark along the edges when taken away from jewelry spotlighting. As with rounds cut is king...there are just far less well-cut specimens in the princess kingdom.

 

[chewyTBG]

Are there a combination of statistics on a stone that would indicate it would look "smaller" in person?

The professional I spoke to own her own small (2 store) chain of jewelry retail stores. My girlfriend actually works for her, and thus I would not think she would lie to me. The owners step father actually used to be the president of AGS, and she herself and her husband have been in the business for over 30 years. Is it possible that something as "basic" as this could be the belief of someone who should know such things?

 

[denverappraiser]

To be sure it’s good to pick an expert you count as reliable and then rely on her, although I would expect her to stand on her own credentials, not her step fathers.

That said, I’m with John. The biggest problem for me with depth percentage as a metric is inherent with the number itself.

The depth percentage is the width divided by the depth.

Width on a princess can be almost anything. The stone can be all sorts of square, rectangular, trapezoidal and rhomboidal shapes. The width is the smallest side to side dimension.

Depth is the sum of the crown, girdle and pavilion. The breakdown between these can be anything and it won’t change the result.

That means you’re taking the ratio of two numbers, both of which have giant margins, and making a cut conclusion on a stone that usually has over 70 facets. That’s like evaluating a car when all you know is the wheel size and color. It’s not that there’s any problem with red cars, or even the observation that a lot of fast cars are red, but knowing the color hasn’t answered the question.

By the way, there’s nothing basic about this. People have been fighting about cut grading on princess cuts since the cut was developed and it’s STILL not done. AGS is the only credible lab that even tries to do it, and although I think their parameters are quite good, they are not industry accepted standards. GIA gives no guidance at all.

 

[denverappraiser]

Are there a combination of statistics on a stone that would indicate it would look "smaller" in person?

Length and width are the most visible dimensions on a mounted princess cut. That's what gives it the 'face up' size.

 

[John P]

Are there a combination of statistics on a stone that would indicate it would look "smaller" in person?

A diamond will look small for its carat weight in two circumstances:

1. Too much weight is grouped in the body somewhere, causing reduced spread in diameter.
2. Poor angles which lose light through the bottom of the diamond, rather than returning it to the viewer's eye.

Diameter is simple to assess: The diamond you're considering weighs 0.73cts and has a diameter of 4.92mm. Common trade notions are for a princess of 0.75-0.80ct to spread about 5.00mm. So spread for weight is fine. Light performance is far more difficult to assess in a princess. You've completely covered that here, with an AGSL grading report. Nice work. In fact, I'd add that an AGSL report will also penalize a diamond for a weight-to-spread ratio which is too small. No worries.

The professional I spoke to own her own small (2 store) chain of jewelry retail stores. My girlfriend actually works for her, and thus I would not think she would lie to me.

I don't think anyone is lying. This is one of many "passed down" notions that doesn't hold water when tested. As a cut-specialist I must regularly debunk it in classes and workshops. Just as frequently I find myself explaining that several "princess cuts" can differ in make by 24 facets (or more) but have NO comment about that on the grading report. That's relevant here because you're considering a make with a 2-chevron pavilion, which can be beneficial in this size-class.

The owners step father actually used to be the president of AGS, and she herself and her husband have been in the business for over 30 years.

That's terrific! Coincidentally, I just finished a session in Cathy Calhoun's lovely store last Wednesday ("The Queen" of AGS). I know other past-presidents as well. They're solid folks. In fact, they can confirm that AGSL will penalize a princess cut which faces-up small for its weight. The one you're considering has the highest marks in all aspects of cut, thus no depth or spread issues.

Is it possible that something as "basic" as this could be the belief of someone who should know such things?

"Basic" is relative. Some of these old "guidelines" come from a time when even less cut-knowledge was available in the mainstream. With rounds there's an old "60-60" belief (any diamond with 60 table and 60 depth will be a winner) which still comes up in my travels. Like judging a princess on depth-alone, it's an outdated notion. As with any profession some pros are extremely educated. Others might have been selling ladies' shoes last week That leaves room for a lot of well-meaning people in-between.

 

[tyty333]

You've already heard from the experts but I'll mention something I saw...I looked at the ACA's that were a similar size
to your stone and with the one exception of a 70.1 depth all the rest were 74-78.5%. These are AGS0 stones. So, your's
actually falls at the lower end of table size for AGS000 stones that I looked at.

Edit - wait...so your GF works at a Jewelry store and you didnt get your stone from them? Ask the jeweler if she can do better for
you (make sure its an AGS000 stone).

 

[denverappraiser]

AGS000 princesses don’t get a lot of respect, and I think the trade is missing the boat here. I’ve seen on the order of 100 of them over the span of several years and they are consistently superb. That’s not to say that they’re the ONLY superb princesses out there but there’s no other grading standard that I’ve found that comes even close as a way of describing them. No grading report other than AGS contains anything like enough data to shop princesses based on cutting. This is an area where AGSL is head and shoulders above the ‘competition’.

 

[Rockdiamond]

Interesting discussion!

Chewy, I can not comment an any particular diamond, rather general comments.
There's many reasons the trade has not embraced the style of cut required to earn AGSL0 cut grade.
It's really a matter of preference.
I agree- many - maybe most diamond sellers are not nearly as well versed on these subjects as regular readers here.
Having said that, there's quite a few knowledgeable dealers out there as well. I think it's perfectly reasonable for a diamond vendor to comment on a princess cut diamond to say that 75% is at the deep end of what they might want to buy, or recommend. It does not necessarily mean they are out of touch with AGSL- but maybe they disagree with the conclusions.

When it comes to light performance, there's a far greater variety of results in well cut Princess Cuts, as compared to the level of variance from one round to another. A princess with a shallower crown than AGSL prefers, that shows a nice amount of dispersed green in aset can be extremely pretty to many observers- and IMO do a better job of spreading life edge to edge for maximum perceived size.

Advising princess cut consumers that sticking with AGSL will assure the right stone may not be the best advice for all shoppers, IMO.
They need to look at a variety of cut styles if possible. If they prefer the AGSL look, it does make the job of buyer far more simple

 

[kenny]

If I were shopping for a princess cut I'd just get an AGS 0.

I'd not bother paying attention to any specs.

Similarly with rounds ... HCA <2.0 and a good Idealscope pic compared to Garry's famous IS Reference Chart.
I wouldn't worry my pretty little head with all those bothersome specs.

These tools are way smarter than I am.
I trust these tools.