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Light Performance vs Color

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AshNZ

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Date: 10/14/2009 12:36:45 PM
Author: Todd Gray



Date: 10/14/2009 12:15:05 PM
Author: AshNZ
Are you annoyed at learning something new?
Ash

Actually, I'm excited. However I tend to learn better visually, can you post some examples which demonstrate the principles which you are attempting to get us to understand? The forum is not only about open discussion, but learning and teaching. Perhaps this is an opportunity for you to teach - but with a class full of people who think out loud and have lots of questions...
Todd - I agree, always good to get more reference material in a thread. I'll see what I can dig up.

Edit: For starters (a good primer on Absorbtion - more to come on ray path length)

http://www.gemology.ru/3dbook/eng/crypted/1_03.htm#4



Color is generally of primary importance for gemstones, but most of diamonds are colorless or near colorless. Hence, diamonds are primarily valued for their scintillation, brilliance, and fire, which are determined by the three properties described above: reflection, refraction, and dispersion. To describe these properties in combination, the term brilliance is often used, which denotes the overall optical image of a diamond. One can say that a stone is characterized by brilliance and color.

Color of stone is a property determined by selective light absorption. The ideal diamond is absolutely colorless; however, an actual specimen always contains microimpurities and structural defects, which absorb a part of the light passing through the stone. For example, the yellow color, which is typical of most diamonds, appears in the specimens that mostly absorb the blue and green constituents of the light spectrum (Fig. 8). Rare colored diamonds has a different absorption character. Diamonds containing few color centers have a tint rather than a color. On the other hand, intense absorption affects the transparency of a stone, and dark stones are perceived as translucent.


The ultimate impression of a diamond is formed by reflection, refraction, dispersion, and absorption, which determine its : scintillation, brilliance, fire, and color.


Ash
 

kenny

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How's this?

Light loss from body color absorption is like a pinch on the arm from a baby.
Light loss from poor cut that makes light leak out the bottom of the diamond is like a kick in the head from a heavy weight boxer wearing metal boots.
 

glitterata

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Date: 10/14/2009 12:08:09 PM
Author: AshNZ
Kark_K, to quote


''For example longer light paths == less performance is not correct.''


Sorry Karl, on it''s own (which is how you made the statement), this is incorrect. Longer ray length DOES equal less performance.

I don''t know how to make it clearer than that. Unless you want to prove to me that there is no such things absorbtion...

Perhaps jump on Wikipedia...


Now, I agree with you when you combine it with other elements, but in every case longer ray paths is bad (due to absorbtion), it is just completely outweighted by other factors.






Date: 10/14/2009 11:56:44 AM

Author: glitterata

Ash, what is your definition of ''light performance''?


Unless you have a solid definition that corresponds to some meaningful and desirable visual property of diamonds, optimizing it won''t do you a lick of good.

Good question. Firstly, is there an ''Industry Standard''?

My definition (simplistically) was the ''inverse of leakage'' Truth be told, I don''t have the knowledge to have a strong grasp on this just yet.


Ash

Ash, when Karl says "For example longer light paths == less performance is not correct," he is RIGHT by your definition of light performance, "the inverse of leakage." In the cases he''s referring to, the longer light paths cause LESS leakage because of the way the light is directed. It leaves those paths in the direction of your eye instead of going out the bottom of the stone.

I am happy to learn something new. Are you?
 

Todd Gray

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Date: 10/14/2009 12:44:10 PM
Author: AshNZ
Date: 10/14/2009 12:36:45 PM
Author: Todd Gray
Date: 10/14/2009 12:15:05 PM
Author: AshNZ
Are you annoyed at learning something new?
Ash

Actually, I''m excited. However I tend to learn better visually, can you post some examples which demonstrate the principles which you are attempting to get us to understand? The forum is not only about open discussion, but learning and teaching. Perhaps this is an opportunity for you to teach - but with a class full of people who think out loud and have lots of questions...

Todd - I agree, always good to get more reference material in a thread. I''ll see what I can dig up.

Ash

Cool Beans
2.gif


Hopefully we''ll get Marty Haske to take an active interest in this thread too! He''s got a lot of experience with ray tracing and has answered a lot of the questions I''ve had over the years... In fact, Ash you might like to read his article GIA Raytrace Brilliance Study Materially Flawed
 

AshNZ

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Date: 10/14/2009 12:51:07 PM
Author: kenny
How''s this?

Light loss from body color absorption is like a pinch on the arm from a baby.
Light loss from poor cut that makes light leak out the bottom of the diamond is like a kick in the head from a heavy weight boxer wearing metal boots.
I like it kenny :)
It ensures readers don''t start asking their suppliers for absoption parameters when they make no discernable difference.



Todd - I don''t pretend to know a lot about the industry but in a short space of time I haven''t seen a lot of faith in GIA from seasoned experts, this artical adds to that... Everyone makes mistakes, but I guarantee you the scathing write-up would be due to the lack of retraction and correction - Science demands self-regulation from peer reivew, GIA can''t be taken too seriously if they think they are above this process.

I can see how 3D modeling of LP would be difficult given in the infinite number of potential lighting sources/positions.

Ash
 

oldminer

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Marty, "Adamasgem", and I have had a long conversation off-line on the Light Performance versus Color Grading issue as pertains to my adviser, Dr. Aggarwal. I think Marty is eminently qualified to offer his advice on how much light becomes lost due to increasing body color. He claims it is more substantial than I thought myself whereas Dr. Aggarwal claims that "Light Performance" would not be measurably degraded by a D to G color change. Marty definitely does not agree with this statement, but wants to mix color grading in with what we would separately call Light Performance. I prefer not to mix these two terms, but my belief Marty sees them as basically one thing named two different ways. He may well be correct and I sure can''t disagree based on having more knowledge about this than Marty has. While I have a good scientific mind, Marty has far more scientifiic formal training and I defer to him in such matters where it is obvious I might be over my head in rather deep waters.

It is a certainty that a superbly cut round diamond of K color looks of higher performance to most observers than an average cut round diamond of D color. If one would ask the same observer to name the least tinted diamond, I would think that they could also do that task upon reasonably close examination of these two stones. It might not initially be highly apparent. This is why I think Light Performance is something detached directly from Color Perception grading. Even though the K color diamond looks brighter and more full of life, the better color stone might be discerned as giving back more white light versus a more tinted light return.

I hope this makes my reasoning more clear and does not hijack the import of the thread overall.
 

Todd Gray

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Date: 10/14/2009 1:10:31 PM
Author: AshNZ
Todd - I don''t pretend to know a lot about the industry but in a short space of time I haven''t seen a lot of faith in GIA from seasoned experts, this artical adds to that... Everyone makes mistakes, but I guarantee you the scathing write-up would be due to the lack of retraction and correction - Science demands self-regulation from peer reivew, GIA can''t be taken too seriously if they think they are above this process.

I can see how 3D modeling of LP would be difficult given in the infinite number of potential lighting sources/positions.

Ash

Yea, I thought you might enjoy that article. Peer review is an important part of the science process... Speaking of which, Ash you might enjoy this article based on research conducted by the AGS Laboratory...

Excerpt from their site:

The American Gem Society Laboratories research team recently completed a study covering the illumination effects associated with a diamond''s beauty. The report, Evaluation of brilliance, fire and scintillation in round brilliant gemstones appeared in the September issue of Optical Engineering, the flagship journal of The International Society of Optical Engineering. The journal publishes peer-reviewed papers reporting on research and development in optical science and engineering and the practical applications of known optical science, engineering, and technology.
Link to article in PDF format
 

oldminer

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There may be an infinite number of ways to light a diamond, but there are finite ways to properly light it in order to create a reasonable standard lighting model for grading light return. The most important element is to create a lighting envirnment which does not blast so much light onto the diamond that accurately measuring the amount of light returned at the very top end of performance is not defeated. The model should use just enough light at the maximum level which can be fully measured with high accuracy. Then, as performance only slightly degrades, the degradation is directly measurable and not just still at the maximum of the measuring sensors in the system. We have systems now which rate the finest at the top and also rate the next couple of levels of fineness at the top as well, giving us little guidance on what is actually highest, nearly highest and third from highest. It well could be that the third from highest level of performance would simply look the best to someone, or even to a majority. We simply don''t know. Dealers tend to prefer wide grades at the top end. Labs tend to do what the trade likes best, since it is a business decision. Consumers really want more data sometimes and creating a proper lighting model is crucial to being able to give such answers in a meaningful way.

I think that if a gemologist could offer grading which made AGS0 into AGS 0.0, 0.1, 0.2, 0.3, 0.4 etc it might be what a few customers would want to know, but you can bet the diamond trade would prefer the status quo. Besides, few, if any, could visually discern the difference between a 0.0 and a 0.5. We could go too far, I suppose. It all depends on what the market, both buyers and sellers, demand.
 

Rockdiamond

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Date: 10/14/2009 11:56:44 AM
Author: glitterata
Ash, what is your definition of ''light performance''?

Unless you have a solid definition that corresponds to some meaningful and desirable visual property of diamonds, optimizing it won''t do you a lick of good.
BINGO!!!

Using one person''s preference ( or even a vocal group or people) to define how a diamond performs is one sided- and does not offer a balanced view of diamonds as a whole. What if what some define as leakage, others find attractive?
Arguing that Karl''s Octavia is better or worse due to the length of it''s light paths completely misses the entire point of beauty in a diamond.

Ash- It seems you are very well versed in physics- no doubt you have a basis for your comments- although the may not be relevant in a gemological sense.
.
If we''re talking about gemologists and diamond traders as a whole, GIA is held in very high regard. Maybe there''s dispute about grades ( "I think it''s a D GIA gave it an E") but in the industry as a whole, GIA enjoys almost universal acceptance.
Reading PS can sometimes give a one sided view of things.
I agree with you that many people- probably the most vocal ones here- are extremely resistant to ideas different from their own. Maybe it''s human nature.....
 

Regular Guy

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Date: 10/14/2009 2:28:34 PM
Author: oldminer
It well could be that the third from highest level of performance would simply look the best to someone, or even to a majority. We simply don''t know.
We think Tolkowski took pains to figure this sort of thing out...
 

Rockdiamond

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True Ira- but even Tolkowski had personal preferences- and they may have differed from yours mine, or someone else''s.

Maybe part of what we prefer ( love) comes from what we "grew up with".
I was trained at a time when the prevailing view was that Tolkowski proportions were too small in the table.
Today, the trend is definitely toward smaller tables.
That does not make slightly larger tables any less attractive to my eye.
 

adamasgem

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Date: 10/14/2009 1:10:31 PM
Author: AshNZ


Todd - I don''t pretend to know a lot about the industry but in a short space of time I haven''t seen a lot of faith in GIA from seasoned experts, this artical adds to that... Everyone makes mistakes, but I guarantee you the scathing write-up would be due to the lack of retraction and correction - Science demands self-regulation from peer reivew, GIA can''t be taken too seriously if they think they are above this process.

I can see how 3D modeling of LP would be difficult given in the infinite number of potential lighting sources/positions.

Ash
Ash.. that has been a long time problem with the self appointed world''s foremost authority, they don''t like corrections or peer review that is critical... The one good thing is that the editors of G&G don''t always let their piled high and deeps get away with it, and will publish letters to the editor, although the sanitization process to tone them down can be frustrating sometimes..

They are really good at covering up bribery and also at slinging mud for their own oligarcical $$$$ gain, a violation of the Lanham Act, especially when in a US Patent, but lawyers are expensive, I should have sued a long time ago...

Back to the subject at hand, you would be surprized at the amount of internal absorption in even a "colorless diamond". I''d have to dig out the results of forward 3D MonteCarlo studies I did (and published years ago on PS) to try to get comparison with GIA''s brilliance and fire studies of the late 90''s.
One can conviniently tweet the conditions of a metric, and add a bad taste test, such that most stones get an A, sort of like what has happened in our schools today, social promotion... we call it grade creep and BS. The only one that has been trying to keep the cut and color grading somewhat honest, appears to be AGS.
In the PS archives their are some interesting results as to the percentage of time GIA and AGS give a D color... On sample sizes exceeding 200,000 available graded stones, one is about three times as likely to get a D from GIA versus AGS. Now when it comes to secondary labs, we don''t have enough published data, but it appears you can guess how it will turn out....

I had talked with Dave and pointed out that GIA has a color grading patent which uses reflected light , which buries the signal characterization you are looking for on top of the 17% or more surface relection. There is some pointed comment about the GIA patent on my web site. http://www.adamasgem.org
 

Serg

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Date: 10/14/2009 12:08:09 PM
Author: AshNZ
Kark_K, to quote


'For example longer light paths == less performance is not correct.'


Sorry Karl, on it's own (which is how you made the statement), this is incorrect. Longer ray length DOES equal less performance.

I don't know how to make it clearer than that. Unless you want to prove to me that there is no such things absorbtion...

Perhaps jump on Wikipedia...


Now, I agree with you when you combine it with other elements, but in every case longer ray paths is bad (due to absorbtion), it is just completely outweighted by other factors.






Date: 10/14/2009 11:56:44 AM

Author: glitterata

Ash, what is your definition of 'light performance'?


Unless you have a solid definition that corresponds to some meaningful and desirable visual property of diamonds, optimizing it won't do you a lick of good.

Good question. Firstly, is there an 'Industry Standard'?

My definition (simplistically) was the 'inverse of leakage' Truth be told, I don't have the knowledge to have a strong grasp on this just yet.


Ash


Hi Ash,
for your definition " performance = "inverse of leakage"", statement as "longer light paths == less performance " could be correct( if diamond has valuable absorption ). But your definition and several others what consider cut performance as Light return are not adequate to Diamond Beauty .

Diamonds with leakage even less than Round ASG0 H&A could be Ugly .Just it.

BTW. there are even several definitions what Light Return is.
Please think firstly about better definitions for colorless diamond performance
 

Rockdiamond

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Marty- speaking of slinging mud- what bribery coverup?
There was a problem with an extremely limited number of stones- and it was made public. People were fired. Steps were taken to correct the situaion that allowed it to happen in the first place.

Are you saying GIA is currently accepting bribes for grades? Please be clear.

Can you show us a link to this 200,000 stone study?
How many stones does AGS grade a year?
How long would it take to compile 200,000 D color grades from GIA- or AGS- including studying each stone.
Plus, who''s grade supercedes the other. Who''s to say which lab was "right"?
How about the stones GIA gave E that AGS gave D- surely they exist as well.

If you''re going to sling mud, please make it accurate.
 

adamasgem

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Date: 10/14/2009 4:16:00 PM
Author: Rockdiamond
Marty- speaking of slinging mud- what bribery coverup?
There was a problem with an extremely limited number of stones- and it was made public. People were fired. Steps were taken to correct the situaion that allowed it to happen in the first place.

Are you saying GIA is currently accepting bribes for grades? Please be clear.

Can you show us a link to this 200,000 stone study?
How many stones does AGS grade a year?
How long would it take to compile 200,000 D color grades from GIA- or AGS- including studying each stone.
Plus, who''s grade supercedes the other. Who''s to say which lab was ''right''?
How about the stones GIA gave E that AGS gave D- surely they exist as well.

If you''re going to sling mud, please make it accurate.
RE: Bribery coverup... NO ONE WAS CHARGED WITH A CRIMINAL COMPLAINT, and GIA REFUSED TO RELEASE the names of the firms involved in the bribery...

AGS grades far less stones that GIA every years , maybe 3 to 5%, ... you misunderstood what I said, that being on sample sets of about 200,000 stones graded by each lab, the statistics on percentage of stones graded D''s showed you were three times as likely to get a D from GIA. Of course , the GIA minions, would say they better stones go to GIA, hence the statistically significant difference. For GIA I used snapshots of Polygon Database on stones available for sale and for the AGS sample it was a historical looksee from their database that Pete did...
I did NOT SAY 200,000 D''s and I DID NOT SAY THEY WERE THE SAME STONES, so RockDiamond, IF YOU DON''T know what you are talking about and/or can''t read, keep your trap shut.
 

oldminer

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I said:

It well could be that the third from highest level of performance would simply look the best to someone, or even to a majority. We simply don''t know.

Your said:
We think Tolkowski took pains to figure this sort of thing out...

My response to you:

Tolkowsky would have had no digital means to make the delicate range of measurements I have been referring to. He only had his eyes and the opinions of his peers, but he was not in the digital age where we can much more closely measure results. We can measure performance well beyond the ability of the human eye to discern any differences, but "beauty" remains subjective. We can agree that Tolkowsky''s personal taste in diamond appearance is not in question. He did an excellent job for his time. It remains his personal taste and someone may well disagree. Beauty is not a measurable commodity and will not always correlate to digital measures of light return. There may be some valid relationships, but I would not try to equate beauty with something so simple as digitally measured light return. It is way more complex.
 

Rockdiamond

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Date: 10/14/2009 4:45:21 PM
Author: oldminer
I said:

It well could be that the third from highest level of performance would simply look the best to someone, or even to a majority. We simply don''t know.

Your said:
We think Tolkowski took pains to figure this sort of thing out...

My response to you:

Tolkowsky would have had no digital means to make the delicate range of measurements I have been referring to. He only had his eyes and the opinions of his peers, but he was not in the digital age where we can much more closely measure results. We can measure performance well beyond the ability of the human eye to discern any differences, but ''beauty'' remains subjective. We can agree that Tolkowsky''s personal taste in diamond appearance is not in question. He did an excellent job for his time. It remains his personal taste and someone may well disagree. Beauty is not a measurable commodity and will not always correlate to digital measures of light return. There may be some valid relationships, but I would not try to equate beauty with something so simple as digitally measured light return. It is way more complex.
Extremely well put Dave!

I could not agree more.

Marty- interesting method of having a civilized conversation.
I do not believe GIA is capable of filing criminal charges.
I also believe that the companies involved were known publicly ( I remember hearing from a source about who was involved)- although I will check with sources about that one.

Marty, I apologize if I misread your meaning- which seemed to me to be critical of GIA.
I also believe your statement was ambiguous- and easy to interpret in different ways.
Are you saying there''s a study showing 200,000 stones graded by AGS, as well as 200,000 graded by GIA?
If so, over what period of time?
I''d imagine it would be years as I agree- AGS grades a tiny percentage the volume of GIA.
Wouldn''t it be possible that an extended study provide skewed results? Maybe more D colored rough hit the market over that period of time

In the context of this conversation- Ash mentioned "I haven''t seen a lot of faith in GIA from seasoned experts" .
Marty, do you feel that''s accurate describing the trade as a whole?

In my end of the business people might not love GIA''s grades ( mainly because cutters may grade their own stones more liberally) but there is a lot of respect for, and faith in GIA here in the NY wholesale trade.
 

Allison D.

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Date: 10/14/2009 4:45:21 PM
Author: oldminer

We can measure performance well beyond the ability of the human eye to discern any differences, ......
Which gets us right back to the heart of the matter.

May there be a measureable difference in the OP''s suggested scenario (two diamonds of identical make and properties with the only difference between one is a D and one is a G)? Yes, there may.

Do I believe that measureable difference is discernable to the eye? I don''t.

Given that I believe discernable is much more important that measurable in a practical application (what it looks like when I wear the stone), this wouldn''t steam the mirror for me. I wouldn''t restrict a search to D/E diamonds in the name of possibly better light performance (all other things being equal); I''d only do so if I was especially color sensitive.
 

oldminer

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Alj; You have put it in a very nice short form for the questioner. A very good reply.

I would like to make mention that diamonds are traditionally graded in categories finer than what the ey can distinguish in their upper ranges of quality. You cannot see the difference from IF to VVS2 with the naked eye or tell a VS1 from a VVS2 with the naked eye. In color grading one must look from the side to see the nuance of D to E to F color where it remains relatively invisible face-up in stones below 1 carat.

I don''t think it is a stretch of our imagination to want to categorize "Light Performance" in the same manner for those diamonds in the upper range of light return quality. We can do this today with machines which clearly see more than our eyes do. This is how diamonds get priced, branded, and marketed. I see no harm in creating naked eye invisible, yet quantitatively different, categories at the top end of light return quality to distinguish the fine increments of perceived added value such attributes may offer a small set of discerning customers. This is where we are headed although we have not yet latched on to a universally acceptable system. No doubt, we will eventually find such a system and it will work for the market just like color and clarity grading have worked.
 

Garry H (Cut Nut)

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Date: 10/14/2009 4:45:21 PM
Author: oldminer
I said:

It well could be that the third from highest level of performance would simply look the best to someone, or even to a majority. We simply don''t know.

Your said:
We think Tolkowski took pains to figure this sort of thing out...

My response to you:

Tolkowsky would have had no digital means to make the delicate range of measurements I have been referring to. He only had his eyes and the opinions of his peers, but he was not in the digital age where we can much more closely measure results. We can measure performance well beyond the ability of the human eye to discern any differences, but ''beauty'' remains subjective. We can agree that Tolkowsky''s personal taste in diamond appearance is not in question. He did an excellent job for his time. It remains his personal taste and someone may well disagree. Beauty is not a measurable commodity and will not always correlate to digital measures of light return. There may be some valid relationships, but I would not try to equate beauty with something so simple as digitally measured light return. It is way more complex.
Hi Dave,
I think it is fair to say that tolkowsky did do a ray tracing study using math and physics laws. The proportions he came up with are remarkably accurate given he did not include the girdle thickness.
Jasper Paulsen and Bruce (Beryl) Harding both showed that with a medium girdle Tolkowsky''s 53% table becomes about 56% and that you can use his math and substitute a steeper crown and derive a very good shallower pavilion.
That was not much based on personal taste.
http://www.folds.net/diamond/software_help.html here is Jaspers calculator where you can play with Tolkowsky''s formulae and fiddle the #''s. You can also read his book online
 

adamasgem

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Date: 10/14/2009 5:25:54 PM
Author: Rockdiamond
Marty- interesting method of having a civilized conversation.
I do not believe GIA is capable of filing criminal charges.
I also believe that the companies involved were known publicly ( I remember hearing from a source about who was involved)- although I will check with sources about that one.
GIA refused to even answer depositions in the Stafford/JKD case as to whether or not JKD had its submission privileges withdrawn because of the bribery. COVERUP..

Name the companies and individuals involved in the bribery if you know them... Retailers who bought from them passed the overgraded stones along to their clients, and the scumbags who were part of it will be long gone when it comes back and bites the retailers in the butt.
 

oldminer

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The topic of this thread is: Light Performance vs Color

As far as the Tolkowsky got with formulas and ray tracing, it remains to be seen what technology will do to advance this knowledge. There are many combinations beyond Tolkowsky now recognized for their combination of performance and beauty. The coming trick or two will measure the light performance in ways which are far more accurate than ray tracing based on theoretical models or less than exact measurements from scanners. Directly measuring light performance will take all nuances of individual cut into consideration without the current errors of scanning, however slight. The whole business of grading top quality diamonds is one of splitting hairs. This is the way it is done and with a lot of success.

I think that light performance does go down as more tint comes into a diamond. Marty agrees with this, but he estimates a very high rate of degradation based on his research and knowledge. I find it intuitively difficult to agree on the amount, but not on the concept. Dr. Aggarwal stares that a D to G change in color would be extremely negligible and not measurable. I am not in a position to question this, but don''t ask everyone else to blindly quote it as fact. Investigate further, seems to be the right thing to tell folks to do.
 

Rockdiamond

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Date: 10/15/2009 7:34:26 AM
Author: oldminer
Alj; You have put it in a very nice short form for the questioner. A very good reply.

I would like to make mention that diamonds are traditionally graded in categories finer than what the ey can distinguish in their upper ranges of quality. You cannot see the difference from IF to VVS2 with the naked eye or tell a VS1 from a VVS2 with the naked eye. In color grading one must look from the side to see the nuance of D to E to F color where it remains relatively invisible face-up in stones below 1 carat.

I don't think it is a stretch of our imagination to want to categorize 'Light Performance' in the same manner for those diamonds in the upper range of light return quality. We can do this today with machines which clearly see more than our eyes do. This is how diamonds get priced, branded, and marketed. I see no harm in creating naked eye invisible, yet quantitatively different, categories at the top end of light return quality to distinguish the fine increments of perceived added value such attributes may offer a small set of discerning customers. This is where we are headed although we have not yet latched on to a universally acceptable system. No doubt, we will eventually find such a system and it will work for the market just like color and clarity grading have worked.
This is an interesting analogy Dave- although it seems to me there are differences between color clarity distinctions and light performance distinctions
To grade color clarity we're going to use a loupe.
The differences between a VVS2, and a VS1 are certainly subtle, but visible with a loupe.
When you hold the diamond in a tweezers to examine it you will likely have to look at it from different angles to find the imperfection.
The bottom line is that human observation is used to quantify color and clarity. Of course this means that some borderline stones might go one way, or the other.

If we're talking about tracing the paths of light- or quantifying light performance there are no standardized or agreed upon methods of measuring.
Plus, we are we are removing the human eye as arbiter- even if that eye is using a loupe- the human eye judges the subtle differences.

For these reasons I do not believe light performance will ever be used as color and clarity are today to evaluate diamonds on the broad market.


I also agree that this thread is NOT about trashing GIA, which Marty seems intent on doing.

I will start another thread to discuss GIA's reputation among the trade.
 

adamasgem

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Date: 10/15/2009 11:47:10 AM
Author: oldminer


I think that light performance does go down as more tint comes into a diamond. Marty agrees with this, but he estimates a very high rate of degradation based on his research and knowledge. I find it intuitively difficult to agree on the amount, but not on the concept. Dr. Aggarwal stares that a D to G change in color would be extremely negligible and not measurable. I am not in a position to question this, but don''t ask everyone else to blindly quote it as fact. Investigate further, seems to be the right thing to tell folks to do.
If The highlighted is the case then the GIA patent http://www.adamasgem.org/giapat.html , which is based on using the combination of reflected and refracted light, as the human does with grading pavilion up, is no good.

A CCD camera can pick up subtle differences in color, just as a CCD based spectrophotometer can..

If you are blasting the diamond with too much light, as you might be to get performance, the reflected component might drown out your ability to make the differentiation.
 

adamasgem

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Date: 10/15/2009 11:47:10 AM
Author: oldminer
The topic of this thread is: Light Performance vs Color
Point noted Dave...
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adamasgem

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Date: 10/15/2009 12:17:44 PM
Author: Rockdiamond

If we''re talking about tracing the paths of light- or quantifying light performance there are no standardized or agreed upon methods of measuring.
RockDiamond It is NOT a matter of the ability to measure or calculate, it is in defining a non aliasing, universally agreed upon lighting envirionment, we wish to use for the performance metric.

AGS seems to have made the most rational first step compromise in this, grading on a balance of where light usually emenates from when a diamond is viewed. As computing develops, we can accurately analyze performance in many more envirionments than we could possibly measure in a single device.

Diamonds can be sometimes be easily tailored to produce the best metric results in a limited envirionment (lighting conditions) physical device. The more conditions tested, the better chance the metric isn''t being spoofed.
 

Rockdiamond

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Date: 10/15/2009 12:32:19 PM
Author: adamasgem

Date: 10/15/2009 11:47:10 AM
Author: oldminer
The topic of this thread is: Light Performance vs Color
Point noted Dave...
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If you''d like to discuss this without threadjacking Marty, here''s a thread devorted to it.
If you could leave out the parts calling people "scumbags" that might be nice.
 

HVVS

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I think that light performance does go down as more tint comes into a diamond. Marty agrees with this, but he estimates a very high rate of degradation based on his research and knowledge. I find it intuitively difficult to agree on the amount, but not on the concept. Dr. Aggarwal stares that a D to G change in color would be extremely negligible and not measurable.

I wonder if "very high rate of degradation" isn't also affected somewhat by aging of eyes, and what some people don't even notice can be a major difference to some others. As in needing more light reflected back through older eyes to get the brain to say "it's white enough." I never used to be color sensitive. G or even I was great. Now, I've started getting farsighted and definitely the I color tints are bothering me. I/J/K, I just see as dingy white. Even my H diamonds, if I look them at face down, look yuk brown. L and M are usually okay since they are candlelight ivory and not supposed to be white :) N/O/P -- forget it. Just too dark. On a gray overcast day, or down under the desk, I'll gladly take a D/E/F over most G or below now. Kind of the same way a 60 watt white bulb is brighter than a 60 watt yellow one. I'm frustrated by this. Not many bargains in in D/E/F diamonds, lol.
 

John P

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Date: 10/15/2009 12:59:22 PM
Author: HVVS

I think that light performance does go down as more tint comes into a diamond. Marty agrees with this, but he estimates a very high rate of degradation based on his research and knowledge. I find it intuitively difficult to agree on the amount, but not on the concept. Dr. Aggarwal stares that a D to G change in color would be extremely negligible and not measurable.

I wonder if ''very high rate of degradation'' isn''t also affected somewhat by aging of eyes, and what some people don''t even notice can be a major difference to some others. As in needing more light reflected back through older eyes to get the brain to say ''it''s white enough.'' I never used to be color sensitive. G or even I was great. Now, I''ve started getting farsighted and definitely the I color tints are bothering me. I/J/K, I just see as dingy white. Even my H diamonds, if I look them at face down, look yuk brown. L and M are usually okay since they are candlelight ivory and not supposed to be white :) N/O/P -- forget it. Just too dark. On a gray overcast day, or down under the desk, I''ll gladly take a D/E/F over most G or below now. Kind of the same way a 60 watt white bulb is brighter than a 60 watt yellow one. I''m frustrated by this. Not many bargains in in D/E/F diamonds, lol.
Yes and yes.

I think the basic answer was arrived at by page 2 - but the OP''s question is a good one and I enjoyed the ensuing discussion. There is definitely much to be considered; scientific, subjective and physiological.

Recipe: Throw light performance and its myriad components into a bowl, mix in color on a sliding scale with a dash of subjective grading, add two tablespoons of cut quality, fluorescence (to taste), widely variable size and shape, then cook under an infinite panorama of lighting conditions and serve to people of different ages, lens hardness and sensitivity.

Yum.
 

Allison D.

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Date: 10/15/2009 2:35:38 PM
Author: John Pollard

Recipe: Throw light performance and its myriad components into a bowl, mix in color on a sliding scale with a dash of subjective grading, add two tablespoons of cut quality, fluorescence (to taste), widely variable size and shape, then cook under an infinite panorama of lighting conditions and serve to people of different ages, lens hardness and sensitivity.

Yum.
Where's the Tabasco? I didn't think Texans could cook without Tabasco?
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(This coming from me, an Italian who can't cook without garlic.
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