Is most color grading the grading of "TONE"?

[pricescope]

Marc,

I''d like to thank you very much on behalf of the Pricescope community for taking time to share your insight on this matter and hope to see your participating more on this forums

 

[Richard Sherwood]

Yes, I appreciate Marc''s candor as well.

It''s not often you can get a major gem lab to speak so clearly and candidly regarding such a sensitive subject.

 

[Garry H (Cut Nut)]

Date: 4/4/2006 11:13:20 PM
Author: Richard Sherwood
Yes, I appreciate Marc''s candor as well.

It''s not often you can get a major gem lab to speak so clearly and candidly regarding such a sensitive subject.

So true Rich - I learned a lot in that conversation.
Perhaps Marty you might disagree with the "pure science" of IGI''s approach?
But it seems to me to be a system chock a block full of common sense.

Now - Peter Yantzer has replied - but in fairness he is flat out like a lizard drinking - preparing for the AGS Conclave - so the response is brief:

Hi Garry:
Our masters go down to S/T color. Yellows and browns are graded with the same masters.
Heartily,
Peter

 

[adamasgem]

Date: 4/3/2006 2:37:58 PM
Author: oldminer
Of course, the idea of automated color grading is the goal. Efficiency of grading is another major goal.
The best way is to make a machine that can reliably color grade most diamonds and automatically reject any that cannot be graded by machine. In that way, the time for grading most diamonds will be minimized and human grading will only be required for the exceptional cases.

Dave.. That''w what I try to do with the SAs2000, basically flag stones that don''t dfit the cape series. Spectra tells it all..

 

[adamasgem]

Date: 4/5/2006 1:51:44 AM
Author: Garry H (Cut Nut)

Date: 4/4/2006 11:13:20 PM
Author: Richard Sherwood
Yes, I appreciate Marc''s candor as well.

It''s not often you can get a major gem lab to speak so clearly and candidly regarding such a sensitive subject.

So true Rich - I learned a lot in that conversation.
Perhaps Marty you might disagree with the ''pure science'' of IGI''s approach?
But it seems to me to be a system chock a block full of common sense.

Now - Peter Yantzer has replied - but in fairness he is flat out like a lizard drinking - preparing for the AGS Conclave - so the response is brief:

Hi Garry:
Our masters go down to S/T color. Yellows and browns are graded with the same masters.
Heartily,
Peter

Garry
To paraphrase GIA historically.. from my website
"diamonds should be graded at their poorer color in artificial light devoid of ultraviolet"..PERIOD! END OF STORY
A sheet of Lexan (polycorbonate) effectively blocks out the UV component, and when placed over the fluorescent lights, is a very effective tool for color grading visually. Tom Tashey, along time ago, demonstrated this with another UV blocker..

Labs, including GIA have pandered to the trade to upgrade the color in strong or very strong fluor..
Using a source with ultra violet and allowing the grader to hold the stone closer to the light pumps more UV into the stone, and the stone appears whiter (for blue fluor stones)..

WHAT GRADE DO YOU WANT, IS THE PROBLEM, NO CONSISTENCY UNLESS YOU BLOCK OUT THE UV COMPONENT OF THE LIGHT SOURCE

The face up view issue, when applied to fancy cuts (which should be grades along the long axis of the stone in the face down position) is highly cut dependent, just as the face up appearance is with varyining light sources in RBC''s....

It is nice that Marc from IGI can reply,

 

[adamasgem]

Date: 4/4/2006 11:13:20 PM
Author: Richard Sherwood
Yes, I appreciate Marc''s candor as well.

It''s not often you can get a major gem lab to speak so clearly and candidly regarding such a sensitive subject.

Rich I just had Rockdoc boil his masters...

Rockdoc and you should get together and rerun the color grades on the SAS2000..
Yuo remember my comment regarding the masters we ran..

I''ll get him to make some comments here regarding what he "saw" after boiling.. He played before oan after on the Gran he has..

TO ALL READING: IF YOU HAVE BRUTED GIRDLE MASTERS, BOIL THEM IN ACID!!!!!!

 

[Modified Brilliant]

Borderline grades undergo strict procedures in our labs: usually these stones are put asside and are looked at later, sometomes the day after and by different people. The most vital part of this procedure is correct calibration: when someone is grading color, after a few stones the eyes calibrate and fine-tune to very high sensitivity: if at any moment the grader''s eyes experience doubt, the procedure is to move on and keep the doubt-stone asside.
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Marc, your procedure also works for an appraiser working independently. My initial impression of color might be borderline. At that point, I move on with my analysis and return shortly thereafter with my final conclusion. Thanks for sharing.

www.metrojewelryappraisers.com

 

[RockDoc]

RE: Grading face up.

I don''t know how many of you have seen Gabrielle''s or Richard at Eightstar''s ring.

Gabi consistently gets K-L''s to face up like G-H stones. Richard''s 8 star that he wears also looks several color grades higher.

For assigning a specific color grade, grading face down, in several lighting envoronments and using lexan or an equivalent UV blocker is certainly a far more accurate way of determiining the color grade of a "colorless diamond".


RE: Boiling..... After boiling of the diamonds in my master set, most improved slightly as compared how they looked before.


AS for color grading stones with dark inclusions, I also use the term BRACKISH with the color grade, and explain the details of it to the client.

Rockdoc

 

[oldminer]

We know trhe face-up, apparent, color of diamonds can be greatly affected by the cutting style. This is why fancy color diamonds are always graded face-up. There used to be a lab in NYC owned by Steven Hoefer that graded the body color of fany shapes throught the side and assigned that color 3. Then each diamond was graded face up and the zones of lighter (1 or 2) or darker (4 or 5) were drawn into the view of the stone. Zones that faced up body color we assigned the number 3. His system, while not commonly appreciated was a very good one for describing how effective the cut had been in altering the perception of color.

By convention, the D-Z cape stones are supposed to be graded by body color and not face-up. It is only a convention, not some natural law or principal of major importance. It is just the tradition of diamond grading and how we have done it for 70 plus years. It could be in for some changes.

It seems to me that for the D-R range of most common hues, that we really are grading perception of the tone, especially when comparing different color stones in order to assign GIA type color grades.

The boiling out of diamond masters with strong acid has much to recommend it to professional appraisers. See your local diamond cutter for a good cleaning.

 

[Sunshines]

Hi Garry,

just want to thank you for helping to throw my query to AGS.......... You know what guys, I am so addicted to this web that this is the first I will check whenever I logged into my PC. Thanks for all the great tutorial you experts share with us.... ....

. And hope there will be more coming of course!