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Question for Serg

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Rhino

Ideal_Rock
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Mar 28, 2001
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6,271
Hi Serg,

I was attempting duplication of a stone and got it down to the exact numbers. The stone is graded by AGS as an "ideal", and measurement on the OGI further confirms that as well.

It accurately portrays it''s LightScope image counterpart and I believe the measurements are all right on excpet in the DiamCalc software it lists the stone as an AGS "3" due to girdle thickness.

OGI reports girdle thickness at the valley is 2.2 and at the bezel 3.9% AGS and OGI report the girdle as being ideal (slightly thick) yet the Diamcalc says the stone is a 3 due to girdle thickness.

Is there a reason for this I don''t understand? Here is the pic (below). The stone is in our "For Sale" section if you''d like to compare.

Kind regards,
Rhino

br916evs2.gif
 

Serg

Ideal_Rock
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Mar 21, 2002
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2,472
Dear Rhino,


During cut quality estimation AGS as well as GIA use not numerical,
but verbal description of the girdle thickness.
If you specify a "slightly thick" girdle in DC, it will report AGS0.


To convert numerical values into verbal we use data that GIA provides
on its courses and Marty Haske's observations.
Unfortunately, these data are not precise, inconsistent and even
sometimes not correct (for large diamonds).
For more details, you may read the https://www.pricescope.com/community/threads/reasonable-price-for-a-2-31-carat.2917/

"Topic subject REASONABLE PRICE FOR A 2.31 CARAT

Scotch,

We are agree that the girdle thickness should be entered preferable as numbers (% or mm when the numbers form the Sarin report are available). The problem is that GIA does not include the numbers in the certificates, just only verbal description. A couple of years ago we faced the problem of correspondence between verbal description and the numbers and we tried to find somewhere the table or description of this correspondence. We applied to GIA but our request was unfortunately ignored. The most serious information on this subject we could find was the Martin Haske's site.
http://www.gis.net/~adamas/cut.html#girdle
We have been using this information up to the present. The general conclusion of this research is that the description is constant when the girdle thickness is measured in mm. As being measured as % it depends on the diamond size and cannot be used.
These data adjusted with GIA's textbooks. Diamond Grading Assignment 8 p. 22, 23,25( The GIA girdle thickness is measured at Bezel); Diamond Grading Assignment 18 Girdle Thickness Percentage Chart
If you know more noteworthy information about this subject we will appreciate for it. I don't know how the things taught by the GIA corresponds to how they estimate diamonds.

And speaking about the Sarin report: they use different measurements in different parts of report: they print bezel measurements in the "report" and they print valley measurements at the chart.”


Unfortunately, even if there exists a more correct system for
converting of girdle thickness values into their verbal representation, it
is inaccessible for us. Though, it is not accessible to most of the market
participants as well. However, I personally doubt that GIA and AGS
would be able to create a completely precise convertion system for all
types of girdle distortion.


By the way, if you decrease the girdle thickness in your example by
0.1, you would get AGS0. This shows a few more problems of the AGS
grading system. For example, a small real physical change of the
girdle thickness leads to drastic deterioration of the final AGS
grading.

PS: The problem that you pointed out existed when DC was not
implemented. Simply it was not so noticeable before. :)
 

Rhino

Ideal_Rock
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Joined
Mar 28, 2001
Messages
6,271
Hi Serg,

Thanks for that.

I hear ya about the girdle thickness at the bezel being shown in report yet the valley's when the girdle thickness is defined.

When I get back up to the store next week I'll post a chart I've found in the OGI software that relates all girdle measurements in terms of % as opposed to millimeters (although you get both).

The statement above that measurements in millimeters for girdle thickness would not be an accurate assessment for girdle thickness on a report is something I would agree with since that can change for the size of the diamond in question. %'s of the diameter is better as it would be relative to the size of the diamond in question. AGS on their reports (as I'm sure you already know) list girdle % at the valley.

What you might want to implement into the software is any girdle valley thickness between .51 - 2.95% be listed as "AGS Ideal" since this is what they do. Just my .02c

Rhino
 

Serg

Ideal_Rock
Trade
Joined
Mar 21, 2002
Messages
2,472
----------------
On 12/27/2002 3:52:05 PM

Hi Serg,


What you might want to implement into the software is any girdle valley thickness between .51 - 2.95% be listed as "AGS Ideal" since this is what they do. Just my .02c

Rhino


----------------

Rhino,
If someone gives a link to an official AGS document which contains the
grading system based on the girdle thickness in percents we would
immediately implement it in DC. It is very simple.
 
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