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GIA Symmetry

Karl_K

Super_Ideal_Rock
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Aug 4, 2008
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Yea the prosumers see those a lot.
If not daily, close to it.
Do you have a scan of it, the mains and lower angles would be interesting?
 

flyingpig

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Nov 7, 2015
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Yea the prosumers see those a lot.
If not daily, close to it.
Do you have a scan of it, the mains and lower angles would be interesting?
What are we looking at? The mains look alright. Are some lower girdle angles too steep?
 

Texas Leaguer

Ideal_Rock
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Jul 27, 2009
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From the chart it looks like the star and upper girdle facet precision is a bit off.
 

Karl_K

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Interesting the mains have deviation with one high one to pull up the average, and the lowers have significant deviation in both angle and length and the uppers have a ton of deviation as does the star%.
Weird how messed up the uppers are.
But most of the bad stuff in the ASET comes from the pavilion deviations.
But the biggest take away is that the numbers do not really reflect the 3d deviation of the stone.
 

flyingpig

Ideal_Rock
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I think it is well cut in a sense.
The cutter somehow manage to achieve Ex Cut (despite working with steep and shallow angles), Ex Symmetry (despite high deviations), HCA below 2.0, and 0.75 carat mark.
 

Texas Leaguer

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I guess the real question here is at what point does deviation at the 3D scan level translate to sufficient variance in meet point symmetry to warrant a penalty in the GIA system?

GIA graders are not looking at hearts and arrows views or concerning themselves with optical precision. As long as the facets appear to be meeting up at the proper points around the stone at 10X the diamond can get a grade of excellent in symmetry.

Unless things have changed at GIA (which is always possible), the symmetry grade as well as polish, are assessed manually by visual inspection of the grader. The 3D scan is used in some ways in the process, to determine a baseline overall cut grade and to flag things like painting and digging. But if those pass, I think the final symmetry grade is basically a human grader call.

Anyone have an opinion as to whether that is a fair assessment?
 
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