Bob''s Flashes - Total Depth for Ideal Cut Diamonds

[dimonbob]

Bob’s Flashes – Total Depth for Ideal Cut Diamonds

When you read the depth measurement on a GIA-GTL Diamond Grading Report, it is a single number, like 60.7%. That is a good number until you realize that it needs to be broken down into three numbers before it really tells you anything.

The Total Depth measurement is broken down into three parts:
Crown Height
Girdle Thickness
Pavilion Depth
Each one is important and has much to do with the beauty of the diamond.

I am going to combine the Ideal standards of the American Gem Society (AGS) and the Accredited Gem Appraisers (AGA). The reason there is not a set number for the pavilion or crown is because there is not a set pavilion or crown angle. There is also the 53-57.5% table size to consider.
Crown Height is approximately - 15%
Girdle Thickness is approximately - 2%
Pavilion Depth is approximately - 43%
If you have these numbers or within less than 1% on either side, you probably have an ideal depth only.

When you are dealing with a vendor with a GIA “certificate” on his diamond and you want more information on measurements than is on the certificate, ask him to get you a Sarin report. If the depth percentage is like 56% or 65%, don’t bother.

 

[fire&ice]

O.K. I keep hearing this and maybe I am off base. It appears that the dealers stress depth. Are those the most important numbers? Or is the table % *equally* as important?

 

[oldminer]

A whole lot of diamond below 56% depth or above 65% depth are either not brilliant or look smaller than necessary for their weight. For this good reason the consumer is recommened to pay attention to total depth.

Table percentage is also iomportant, but not in the same way. The size of the tabler does not directly have an effect on apparent size. There are many other effects associated with table size of importance, however.

Don't neglect either one.

 

[fire&ice]

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On 5/27/2003 9:13

9 AM oldminer wrote:

A whole lot of diamond below 56% depth or above 65% depth are either not brilliant or look smaller than necessary for their weight. For this good reason the consumer is recommened to pay attention to total depth.

Table percentage is also iomportant, but not in the same way. The size of the tabler does not directly have an effect on apparent size. There are many other effects associated with table size of importance, however.

Don't neglect either one.
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Thanks Dave. Would the tolerances for table % be greater than tolerences for the depth%'s of pav./girdle/crown?

I understand both are important; but, other than size appearance, is the depth #'s more important.

 

[oldminer]

The degree for tolerance of "faults" varies from shape to shape. ROunds don't react like radiant cuts or princess cuts. Some square or recatngular diamonds allow larger tables without serious visual problems and other shapes, like rounds or ovals don't do so well.

These poercentages are not "connected" in some way that you can trade one with the other. Each stone has its own character. Some talented cutters make a very pretty diamond out of what sounds like a poorly fashioned stone.
There will be issues, but maybe the diamond will appear good for some people.

 

[pqcollectibles]

Hey Bob, et al!

If the total depth measurement is within ideal specs and the girdle is tooo thick, above 2%, is that a potential for light leakage?

In a case where the overall depth is correct, and the crown is deeper than the 15%, does that contribute to steep crown angles? Is the risk for chippage greater? Would it make mounting the diamond "harder" to do, ie less grippage for prongs, bezel, etc.?

 

[Stephan]

If find "ideal cuts" that you can find on the market a little to deep.
I saw a lot of H&A, and they all look beautiful, but the most beautiful diamond I saw is this one:
58% table
33.7° crown (14%)
43% pavillion
medium girdle
59.5% depth
It has MORE fire than an ideal cut and it is not so dark as an ideal cut.
When I go shopping, I try to look at these points:
-pav: MAXIMUM 43%!
-crown: 33.5° - 35°
-table: 55% - 59%
-depth: max 60.5% !
-VG-EX pol/sym

H&A viewer is very usefull, only to check the symmetry, not to check the shape of the hearts because that is only marketing.

Remember:
1) the biggest problem on the market is to deep pavillion.
2) only buy a stone if your eyes say "yes".

 

[Garry H (Cut Nut)]

Just a note - the %'s will not addup because GIA and AGS measure girdles at the thinnest point.
You ususally need to add another 1.7% to make the #% add to total depth.

A diamond with an overly thick girdle can be beautiful and worth buying if the price / spread ratio is OK

 

[Stephan]

I 100% agree with you.
As I live in Belgium, I often buy HRD certificates.
They measure at the thickest point of the girdle, so the pav and crown % are correct.