Girdle, inclusions, and treated diamond

[wwwang]

If the crown height is 14.5, pavillion depth is 43, and the total depth is 61.4, does that mean the girdle is 61.4 - 14.5 - 43 = 3.9%? That sounds very thick to me, but the cert states "slightly thick".
The inclusions are crystals and pinpoints. Is there any preference on what kind of inclusions should be avoided?
Is there a way to find out if the diamond was treated besides relying on the reputation of the vendor?

 

[denverappraiser]

3.9% is huge for a big stone and it’s about what’s to be expected on a tiny one. The grading by the lab will depend on how the lab does it and they aren’t all the same. There are 16 points to be considered. Some labs will use the minimum, some will use the maximum, some will use an average, some will only use the ‘peaks’ while others will only use the ‘valleys’. It’s decidedly a pain to deconstruct. Find an appraiser with a Sarin or ask your jeweler to show you one and you can look at all 16 although what to do with the data is a whole ‘nuther problem.

Most treated diamonds, meaning clarity enhanced stones are pretty easy to detect under microscopic examination although it does take a little bit of practice to get good at it. Some treatements, like HPHT annealing take special equipment that’s pretty unusual both at jewelers and the independent appraisers. This will be notated on the report from any of the major labs.

Neil Beaty
GG(GIA) ICGA(AGS) NAJA
Professional Jewelry Appraisals in Denver

 

[solange]

What does the "huge" 3.9 mean?
Will that influence the value of the stone, the spread or the general appearance of the stone?

 

[stebbo]

Date: 11/3/2007 11:00:39 AM
Author:wwwang
If the crown height is 14.5, pavillion depth is 43, and the total depth is 61.4, does that mean the girdle is 61.4 - 14.5 - 43 = 3.9%? That sounds very thick to me, but the cert states 'slightly thick'.

It's not as bad as it sounds. 3.9% will be the distance between the facets where the pavilion and crown %'s are measured off, but that'll thin down by about 1.7% in a diamond with no funny business going on.

 

[MrNyceGuy]

Date: 11/4/2007 8:55:02 PM
Author: stebbo

Date: 11/3/2007 11:00:39 AM

Author:wwwang

If the crown height is 14.5, pavillion depth is 43, and the total depth is 61.4, does that mean the girdle is 61.4 - 14.5 - 43 = 3.9%? That sounds very thick to me, but the cert states ''slightly thick''.

It''s not as bad as it sounds. 3.9% will be the distance between the facets where the pavilion and crown %''s are measured off, but that''ll thin down by about 1.7% in a diamond with no funny business going on.

Great illustration stebbo! When I first started learning about diamonds (about 2 months ago on Pricescope) it took me a while to wrap my head around what the girdle spread meant (i.e. thin to thick on one diamond). I think that illustration helps to visualize it and clear up any confusion. Thanks for the post

 

[jazzgal4ever]

Yes, Thank you Stebbo for the illustration. I am relatively new to this and that helped me as well!

wwwang, good luck on your search!

~nicole

 

[wwwang]

Thanks for the help, however, this is still confusing:
1. Stebbo''s illustration is correct only when the girdle is round. When it is "faceted", would the line be drawn streight as the orange dotted line, rather than the curve as Stebbo''s original green drawing?
2. When people talk about the girdle, do they talk about the thinkest part or the thinnest part? Or average? Some told me girdle should not be more than 2.7%, and how do we calculate this 2.7%? Is it the total depth - crown depth - pavillian depth - 1.7%?
3. If the girdle is not all the same around, should the GIA cert give a range rather just one number?

Oh my, now we are in math class. Somebody must be smarter than me. Thanks a lot.

 

[wwwang]

I checked on a few GOG''s posted diamonds above 2 ct, found the girdles posted are always smaller than the calculation of "total - crown - pavillian depth", by the range of 1.5 - 1.9%. My formula of girdle calculation must be wrong.

For the diamond I am interested in, my "calculated" girdle is 3.9%. Fred''s maximum tolerated girdle, as it is also GIA''s ideal cut criteria, is 2.7%. The difference 3.9% - 2.7% = 1.2%, this is lower than GOG''s pattern of 1.5 - 1.9%. Therefore, I estimated my real meassured girdle should be around 2.0 - 2.4%.

Am I wrong or not?
It would be nice to know what is GIA''s criteria for a "slightly thick" girdle. Is there a way to find out?

 

[JohnQuixote]

Date: 11/5/2007 10:52:35 AM
Author: wwwang
I checked on a few GOG''s posted diamonds above 2 ct, found the girdles posted are always smaller than the calculation of ''total - crown - pavillian depth'', by the range of 1.5 - 1.9%. My formula of girdle calculation must be wrong.

For the diamond I am interested in, my ''calculated'' girdle is 3.9%. Fred''s maximum tolerated girdle, as it is also GIA''s ideal cut criteria, is 2.7%. The difference 3.9% - 2.7% = 1.2%, this is lower than GOG''s pattern of 1.5 - 1.9%. Therefore, I estimated my real meassured girdle should be around 2.0 - 2.4%.

Am I wrong or not?
It would be nice to know what is GIA''s criteria for a ''slightly thick'' girdle. Is there a way to find out?

The labs set their own standards and, as Neil pointed out, approaches vary. Check this thread for an overview with graphics. It outlines the AGS method which is pretty transparent.

You want the girdle to be thick enough to be durable and thin enough that it''s not hiding weight. GIA or AGS tn-med-stk are all perfectly acceptable. Both labs will also disclose treatments (and neither accepts fracture-filled diamonds for grading).

I''d also suggest a forum search on Fred before using that advice to guide your decisions.

 

[wwwang]

Wow, great stuff. Thank you very much John.

 

[:)]

Get Fred out of your head - wavy girdles are a scare tactic