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Pros . . . what is "even" color distribution?

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Re: Pros . . . what is "even" color distribution?

Post by Tom Gelb » February 19th, 2011, 10:13 am
Written by Yssie » February 18th, 2011, 1:16 pm:
Written by Tom Gelb » February 18th, 2011, 12:42 pm:what dkodner wrote is for the most part very much correct. However the following is not quite right "But what they are looking at is if the color is even throughout the parts of the stone that show color. With a "bow tie" effect in most fancy cuts, if they did not do it this way, every one of them would be graded as uneven." The evenness of a color as defined by GIA is not about how similar the color is where it is visible (if that is what Mr. Kodner is meaning), rather it is a function of how much of the diamond shows color versus absence of color (i.e. extinction, brilliance, etc.) when viewed face up. If a diamond shows color over 50% or more of the crown then it would be graded as even, if less than 50% it would be graded as uneven. To continue with the pear shape example, if the bow tie (which would be defined as absent of color) were quite large and more than 50% of the crown when viewed face up, then it would have been graded as uneven. Similarly for the baguette, since the color is only at the heads and the majority of the diamond shows no color it was graded as uneven.
If anyone needs more clarity I would be happy to respond.
I hope this helps.


Huh.

So it sounds like it's not actually a measure of distribution at all (as in, it doesn't consider the location of the colour throughout the stone), just a binary > or < 50% visible colour *somewhere* as seen face-up.

Which explains why a pear that looks clearly more coloured at the tip may get an "even" grade, because more than 50% of what we see face-up is showing colour - doesn't matter where it's showing that colour (that it's all on one side of the stone and not on the other).

Am I understanding properly?


Yes that sounds like you understand.
Thomas Gelb G.G. , MBA
Gelb Gemological Consulting
Re: Pros . . . what is "even" color distribution?

Post by Leibish & Co. » February 19th, 2011, 10:46 am
Written by tyty333 » February 17th, 2011, 11:36 am:
Written by kenny » February 16th, 2011, 8:04 pm:This one was graded Not Applicable.
What the heck does that mean?

Picture 25.png


Picture 26.png



Just means its so darn cute the distribution doesnt matter :bigsmile:

hi Yssie,
Sorry for the late reply regarding your question,

First, I saw Tom answered most of the grey areas on this matter, and as the former head of Colored diamonds of GIA, he defiantly knows how the distribution issue is graded at GIA, i definitely enjoyed reading and learning from his answer, thank you Tom

I mentioned in my post those shapes, since according to our experience, this shapes tend to be more problematic when it comes to color distribution(not saying every stone of this shape has that problem, not at all, i'm just saying that in comparison to other shapes they need to be cut more "carefully" in order to get an even color distribution due to their cut).

Regarding MQ, PS, OV etc. the shapes that have bow tie, As Tom mentions, if GIA would consider bow tie as uneven than 99% of diamonds from those shapes would be uneven. off course stones those shapes that can be uneven, but the color distribution needs to be not equal on different parts of the stone( in over 50% of the stone, thank you Tom for his piece of info, i didn't know that) not only the regular bow tie.

Best

Itzik


Leibish & Co.
Re: Pros . . . what is "even" color distribution?

Post by Rockdiamond » February 19th, 2011, 5:14 pm
Great discussion! Thanks for hosting it Kenny.
I'll admit it's always been a grey area for me.
This stone made me scratch my head. For the life of me I could not see why GIA graded it "uneven", but this conversation has been very illuminating. Probably if I had looked at it from the side, it might have been clear.
Hopefully dkodner is correct about us "old dogs"!
Image
Image
David
President-Diamonds by Lauren/ Rock Diamond Corp
Partnering with Yoram F to produce the only Modern Antique Diamonds on the market cut specifically to show off their yellow color
Re: Pros . . . what is "even" color distribution?

Post by Yssie » February 19th, 2011, 6:00 pm
Another thanks Itzik, David, Thomas, David ::)

This has been an enlightening discussion!
Some circumstantial evidence is very strong, as when you find a trout in the milk.
~H.D.Thoreau

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