Link to excellent AGS article on CUT

[Garry H (Cut Nut)]

http://www.gemology.ru/cut/english/optical/index.htm

This is a well written article with thought provoking substance.

Well done AGS and MSU gem center for making it possible for all to read it.

 

[trichrome]

Gary,

You know what? Numbers are interesting.... but the more
I'm thinking about it and the more I'm starting to get involved
in the industry, the more I believe that at the end, I will
always trust my eyes... If I find a certain stone filled with life,
I'll buy it.... Now of course you need those certs, to please
those so compulsive internet customers who were trained by
Cut Geeks like you !!

Trichrome.

 

[DiamondExpert]

Nice link, Garry.

Good on ya, mate!

 

[Garry H (Cut Nut)]

Thanks guys (and Bump).

Anyone care to comment on the idea that darkness in a diamond caused by leakage contributes to contrast?

This article has some sting in its tail!

 

[Garry H (Cut Nut)]

This is an example of a DiamCalc model using no leakage (black tray) for a steep deep AGS O that leaks inside the table.
Note the darker blue is the effect of blackness and blue from low angle lighting. This area would appear failry dark - what Peter Yantzer would call "murky" or "muddy".

 

[Garry H (Cut Nut)]

Here is the same stone with light leakage from under the stone shown.

 

[Garry H (Cut Nut)]

Rhino this shows some interesting stuff about the tray you use and your love of "dark reds".

 

[Mara]

I know that sometime the little darkness to the left of my table area tends to look somewhat like contrast or even that hard-to-define scintillation. Somewhat interesting. Light leakage along the round edges of the stone tend to show contrast as well.

 

[Garry H (Cut Nut)]

Wrong Mara, leakage at the edge makes a diamond look much much smaller - 1ct can look like .80ct!
That is my # 1 concern with this approach.

 

[trichrome]

Garry,

When you're looking at any diamond face up, and when you're seeing those
black (darker) triangles alternating with white ones...yes...this contributes to give some life to
the stone....it's like looking at a zebra who's running : you're seeing this pattern in
movment and it gives "something" to the body of the animal...if all zebras were white,
you'll not be as much attracted by them.

This is my artistic point of view.

Trichrome.

 

[Garry H (Cut Nut)]

Thricrome that is exactly what the idea of contrast is all about.
The question I am asking is how should dark areas from leakage be handled?
In a nice stone with minimal leakage the star you see through an ideal-scope provides a well dispersed amount of darkness.
In the image I posted above I do not like the dark ring inside the table, and the fact that the out side areas of the stone are returning very little light.

I will show a nice stone that looks very good through an ideal-scope in the 2 AGS type formats - first with no back light:

 

[Garry H (Cut Nut)]

This is the same stone with back lighting - note thaere is no where near as much difference and still plenty of contrast with this one - and not soo much leakage

 

[Mara]

Garry I meant MY stone!!! I have some leakage along the edges, and I see the contrast as dark to the brilliance of the diamond's 'white'. There is not so much leakage on the edges that there is NO light return, so the light return that is there, contrasts against the darkness of the leakages...looks somewhat like a scint at times.

 

[Garry H (Cut Nut)]

The nice stone just posted shows that effect too Mara,
But the Steep Deep AGS zero posted above has mainly very low angle blue illumination returning and leakage at the girdle.

An 8* or ACA new line stone has even more light return reight at the edge - so should appear bigger for a given diameter.

 

[Rhino]

Greetings Mate!!!

Just caught this thread and bookmarked the article. I'll give ya my .02c after reading. You know I love this stuff.

Peace,
Rhino

 

[dimonbob]

Thanks Garry,
That was very interesting. I might have to read in several more times to get it through my thick skull.
We keep learning, and learning, and learning. It never stops.

 

[Garry H (Cut Nut)]

Please do that Bob.
I have only read it 3 times.
I read the GIA first article 10 or more.

Everyone print it and read it on paper.
Write on it etc.

Then come back and discuss it

 

[Boulder]

Just bookmarked it and will have to read it soon. Thanks for pointing out this article!

 

[Garry H (Cut Nut)]

I am back on line - for all those who missed my acid tongue

diluted with Dutch beer

 

[niceice]

Thanks for posting that Gary! An excellent read!