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Girdle Cheating Diamonds

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Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
14,919
There is a new trend that we have identified.
Some cutter or cutters are producing diamonds with girdles that are thin at the spot where labs like AGS and I believe GIA take their measurements.
The result is a two fold rippoff.

1. The stone weighs more (the cutters main motivation) so it spreads less.
2. The girdle facets are around 4 degrees steeper, so if you bought a stone with a 34 degree crown angle then around 1/4 of the crown facets are excessively steep.

The light return falls from around 1.0 (perfect symmetry model) to 0.90 for this example.

All the more reason for consumers to use the services of an up to date appraiser.
BTW HCA will not catch this because the crown input data on this stone is 33 degrees. This stone recieved a borderline Ex / Good score. The result should be more like 3-4.

Girdle cheating.jpg
 

Richard Sherwood

Ideal_Rock
Joined
Sep 25, 2002
Messages
4,924
The GIA's method of measuring girdles at their thinnest areas needs to be updated. The Sarin-Megascope method of showing measurements at both those points and at the crown/pavilion main junction is far superior. I like the graph where the varying thicknesses of the girdle is laid out in a straight line, like it was unrolled.
 
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