Girdle Help

[pretty_carbon]

Could someone help out with girdles? I''ve been searching this forum and haven''t specifically found an answer to my question, though I have learned an awful lot in doing the reading.

I know that in 2005 AGS re-ramped their grading by introducing a performance-based rating system rather than the old proportion one.

The Accredited Gem Appraisers website has a "cut tool" which seems entirely proportion based (which I assume is pre-2005). The diamond I have has a thin-slightly thick girdle (Faceted, 1.6% to 4.1% - I assume valleys to peaks) which makes the proportion Ib proportion. This pulls the overall diamond "down" to Ib.

Is this similarly penalized in the new AGS system? Is this something to worry about as I can happily report that I''m getting diamond ocd. Does the Ia and Ib class system endure in the new ratings?

The stone itself is an AGS0 in the new rating and has an HCA of 1.6, with only spread earning "very good" in place of excellent, and that''s the parameter I am least fussy about.

Thanks in advance.

 

[jet2ks]

The girdle is fine. Thin to slightly thick is a desireable range and will earn the highest grade from AGS or GIA. If oldminer (Dave Atlas) sees this thread, he can better address the AGA cut tool.

As far as the VG on spread with the HCA, that is totallly normal for well cut diamonds. Only stones with total depth under 60.4% earn an EX and they many times get a VG in some other category.

 

[oldminer]

The girdle percentages you list are "thin to slightly thick" and would not cause a diamond to drop to AGA 1B if all else was 1A. You are right, the AGA Cut Class grades were created by me during the 1990''s when the rest of the diamond world was thinking of many other things. Now that cut grading has caught on a lot more science and attention is being paid to this very important aspect of what makes diamonds so special and beautiful. The AGS Cut Class grades are totally proportion based and somewhat limit choices because they are related to Tolkowsky angles and percentage even in the fancy shapes, to varying extents. We now know that there are some fine performing stones somewhat outside the AGA predictive grades, but for pre-purchase screening BEFORE choosing a diamond, they remain very useful charts and rules.

 

[pretty_carbon]

thanks jet2ks and oldminer - very helpful

I see that one "1b" rating alone wont cause a diamond to drop into the class ib of doom. My crown angle is 35deg but it is combined with a pavillion angle of 40.8 and a total depth of 61.9%. So the crown angle is a little big for class Ia but the girdle range I have (thin to slightly thick) won''t cause any penalties under new AGS.

The diamond is AGS0 and falls nicely in the "ideal" box on HCA. It''s a wonderfully performing stone. But it would be nice if an ideal is an ideal is an ideal whichever way you slice it!