GIA Insider Article on Pattern

[JohnQuixote]

GIA Insider Article (6/30/06)

"How Do GIA Students Visually Estimate the Quality of a Diamond's Pattern?"

http://www.gia.edu/newsroom/issue/2798/2565/insider_newsletter_details.cfm#3

Marty Haske pointed out this statement in the pattern-rating guidelines:

Excellent – Very strong contrast between bright and dark areas. The diamond is extremely attractive, with no distracting pattern features. Symmetrical radiating mains are permitted as long as they don’t extend beyond the table facet or darken the area around the stone’s culet.

This is curious since many premium diamonds have visible mains - many of you know them as arrows - extending all the way to the girdle as a result of precise cutting, or patterning, of the pavilion. It seems even the diamond they use as their example for EX shows this effect (below). Maybe the description is worded strangely (?) It's true that contrast/pattern effects are darker under the table, but the mains do visibly extend under the crown facets. No doubt we can get clarification from someone at the lab.

 

[Regular Guy]

John,

Didn''t you see their footnote. Their trays, which were gray in color, were arrayed in Spain. As a result...

The rays in Spain, were falling with their mains, in the (table of the) plain.

 

[JohnQuixote]

"By George. He's got it!"

Ira, if there is a better worse joke in all of PS we'll be hard pressed to find it.

 

[adamasgem]

On further thought, i believe GIA''s conceptions (or misconceptions) are highly influenced by the KittyDock(TM)''s inconsistent and variable lighting envirionment being used to "rate/grade" diamonds. Sales tool, maybe, technical use, ZERO.

Difficult problem at best, with different "envirionments" needed to accurately judge each aspect of performance.

The "problem" needs to be addressed mathematically to get any consistency in grading, much like AGS has done.

 

[RockDoc]

Did Brian read the insider?

Did he self destruct at the inaccuracy of it?

Methinks someone''s "skirt" is showing!

Rockdoc

 

[adamasgem]

"Excellent – Very strong contrast between bright and dark areas. The diamond is extremely attractive, with no distracting pattern features. Symmetrical radiating mains are permitted as long as they don’t extend beyond the table facet or darken the area around the stone’s culet."

Confusing, to say the least.. Do they mean you can''t see arrow heads

 

[RockDoc]

Yes Marty........

But what about the HEARTS???????????????

I''ve seen stones with decent arrow patterns with distorted hearts.

I do acknowledge Brian''s "bywords" of "it''s all in the hearts".

Seems like they left out at least half of what needs to be considered...... agreed?

That is why I asked if Brian was self destructing.....

Rockdoc

 

[JohnQuixote]

Date: 7/4/2006 1:42:42 AM
Author: RockDoc
Yes Marty........

But what about the HEARTS???????????????

I've seen stones with decent arrow patterns with distorted hearts.

I do acknowledge Brian's 'bywords' of 'it's all in the hearts'.

Seems like they left out at least half of what needs to be considered...... agreed?

That is why I asked if Brian was self destructing.....

Rockdoc

Hey Rock, I believe this assessment of 'pattern' in the lab relates to contrast effects, not precision 'patterning' as per cutting. Sure, the pavilion mains are integral to both, but in this case the lab is looking for balanced contrast in the crown; static and through a range of tilt.

A big pink question mark appeared in the air over Brian's head, just like mine, when Marty pointed out the 'mains not radiating beyond the table' bit. However it's the 4th, and and there are more important things afoot...

We'll be off painting steaks and digging potatoes.

 

[RockDoc]

HI john

Well happy 4th to all of the gang in Houston...

Rockdoc

 

[adamasgem]

Date: 7/4/2006 1:42:42 AM
Author: RockDoc
Yes Marty........

But what about the HEARTS???????????????

I''ve seen stones with decent arrow patterns with distorted hearts.

I do acknowledge Brian''s ''bywords'' of ''it''s all in the hearts''.

Seems like they left out at least half of what needs to be considered...... agreed?

That is why I asked if Brian was self destructing.....

Rockdoc

Certainly it is about symmetry, and I beliieve the "hearts" show symmetry and perfection in the pavilion, although I do not know whether a "perfectly formed" heart pattern, and what relative size of the "V"''s is necessary for good performance.

Perfection in optical symmetry and better yet, physical symmetry, is the goal, and of course the crown and pavilion must be cut in balance. I think that all the present cut grading systems (GIA, AGS) do not sufficiently quantify and reward symmetry aspects, probably because of the measurement problems. Bill Bray has made a valid attempt in BrayScore, but even his grading is limited by the measurement systems.

Contrast enhanching devices , like the typical hearts and arrows viewer, make valid attempts to enable this, but a high accuracy analysis is not there yet, and it is still very subjective and time consuming with the current tools.

If you take the typical hearts and arrows viewer, and take two different size stones cut EXACTLY alike, you WILL GET two different "pictures" of the hearts and arrows, because the lighting angles are different in a fixed size viewer. The larger the diameter the viewer, the smaller the effect of lighting differents verses size of the stone.

 

[Paul-Antwerp]

Like you say, Marty, it is all in the symmetry.

Nothing proves this more than our experience in princess-cuts. There, the positive effect of working with the highest possible symmetry is dramatic.

And it is much easier to observe than in rounds. I am even considering of adding pictures of princess-cuts in the H&A-viewer to our information, since it shows the extreme symmetry, and although there is no connection to arrows or hearts, you can rely upon the fact that the combination of symmetry with the correct proportion-sets is a guarantee for amazing stones.

Live long,

 

[WinkHPD]

Date: 7/4/2006 3:14:16 PM
Author: Paul-Antwerp
Like you say, Marty, it is all in the symmetry.

Nothing proves this more than our experience in princess-cuts. There, the positive effect of working with the highest possible symmetry is dramatic.

And it is much easier to observe than in rounds. I am even considering of adding pictures of princess-cuts in the H&A-viewer to our information, since it shows the extreme symmetry, and although there is no connection to arrows or hearts, you can rely upon the fact that the combination of symmetry with the correct proportion-sets is a guarantee for amazing stones.

Live long,

Paul,

I just got off the phone with Peter Yantzer at AGS and in our conversation he was telling me how the pavilion mains set the basis for light performance in the round brilliant stones. Thus the tighter the tolerances the more likely the better performance of a stone. When the cutter "cheats" the culet over "just a smidgeoen" to save weight the light performance decreases. As the public becomes more and more aware of these things the more information they are going to want, such as the variances from the average that is shown on report. It would seem from our conversation that Peter is saying that his research shows that Marty''s and your comments about symmetry is being proved in the lab

I suspect that although the average buyer just wants to know "does it look good?" that that there will be more and more who want the availability of the complete Sarin/OGI/Helium report to be assured that their "super ideal" cut diamond is indeed a superior "super ideal" in all aspects.

Wink

 

[adamasgem]

It is all about symmetry, but the relative size of the stone versus the viewer also will effect the "picture" you get. If you do a DiamondCalc H&A simulation on a 6mm and 12mm stone, both with the same proortion set, you "see" two different pictures, and while with a perfectly symmetric stone shows a small distorion, an asymmetric stone may be more distorted..

The next two posts will give the proportion sets used

 

[adamasgem]

Here is the first measuremnt set

 

[adamasgem]

Here is the second part of the measurement set.. I recommend a 3 to 4" diameter H&A viewer, the larger the better, somewhat easily built to accept a camera with colored acrylic tube..

 

[pyramid]

Excellent – Very strong contrast between bright and dark areas. The diamond is extremely attractive, with no distracting pattern features. Symmetrical radiating mains are permitted as long as they don’t extend beyond the table facet or darken the area around the stone’s culet.



Would the appearance of the radiating mains appearing as black under the crown facets or appearing white under the crown facets have something to do with crown height/angle or pavillion depth/angle?