Clarity is used for lower Light Performance by GIA and AGS

[oldminer]

If there is poor clarity, cloudiness or fluorescence these folks are going to "predict" light performance will not be different, but intend to put this lack of performance under clarity grading. Incredible! Here the consumer finds an "excellent" cut and thinks, "Sell, it isn''t a fabulous clarity, but it has a wonderful light performance.". Boy, they may well be surprised!

If a diamond has poor light behavior, then how can that component grade Excellent when it is obvious to any grader that this isn''t the case. How is good communication of the diamond''s appearance to be transmitted to end users or other dealers?

The jury is certainly not done deliberation on this hot topic. The GIA Symposium ws full of differing opinions and vbery thougtful people. Most of these people are dedicated to bringing honesty to the diamond trade. There is a very powerful, traditional minority that prefers the old smoke and mirrors stuff. This will change over time, but it won''t totally go away any time soon.

Using an expert is still going to be the right path for consumers who want assurance a particular diamond is right for them. I will say that the creation of cut grading systems by the major players is coming along, but there are plenty of knowledgeable people who are less than thrilled with what is now being offered. You take the good with the bad as things change.

 

[Regular Guy]

Dave,

I don't understand. I can't quote what I don't understand, because the context is not anywhere that I can see in the text of your post...only in the title. I thought that contemporary AGS grading was more like your own approach of doing direct assessment of light performance...using whatever methods they do.

 

[adamasgem]

Date: 8/29/2006 1:08:05 PM
Author:oldminer
If there is poor clarity, cloudiness or fluorescence these folks are going to ''predict'' light performance will not be different, but intend to put this lack of performance under clarity grading. Incredible! Here the consumer finds an ''excellent'' cut and thinks, ''Sell, it isn''t a fabulous clarity, but it has a wonderful light performance.''. Boy, they may well be surprised!

Well, it depends on what one expects from a predictive system. At least it can separate cut and its potential for light return from color, clarity, and other factors you mention which may effect some total "measured" light return for a "particular" envirionment.

I notice you didn''t mention color.

A D color stone is going to return much more light than a K color of the same size and cut. The "optimal cut" for a K color stone WILL NOT BE the same for a D color. It is a matter of optical physics. It is a non linear optimization problem. It is a function of the lighting envirionment and the lighting color temperature.

Are we double pork chopping when we inherently ding a stone twice. Seems that those who "measure" light performance should discuss the effect of color grade and self absorption on "light performance".

I KNOW that predictive systems suce as ray-tracing can factor that in.

How does a measured light performance system factor color grade in??

If a diamond has poor light behavior, then how can that component grade Excellent when it is obvious to any grader that this isn''t the case. How is good communication of the diamond''s appearance to be transmitted to end users or other dealers?
Since we are talking about "good communication" of a diamond''s appearance, and light performance depends on the envirionment the stoneis subjected to, shouldn''t a little disclosure of the measures used be in order from everyone involved in "measuring" light performance.

The jury is certainly not done deliberation on this hot topic.

Yup, the grand jury can even ask questions, just like in the real world..

The GIA Symposium ws full of differing opinions and vbery thougtful people. Most of these people are dedicated to bringing honesty to the diamond trade. There is a very powerful, traditional minority that prefers the old smoke and mirrors stuff. This will change over time, but it won''t totally go away any time soon. Too bad.. Did GIA have their smokescreen up and running and the walls covered in mirrors???

Using an expert is still going to be the right path for consumers who want assurance a particular diamond is right for them. The consumer is getting a lot of sometimes conflicting opinions right now.

I will say that the creation of cut grading systems by the major players is coming along, but there are plenty of knowledgeable people who are less than thrilled with what is now being offered. There is certainly room for improvement, and that will happen, even if some (like GIA) are dragged kicking and screaming away from their G-D like positions ..

You take the good with the bad as things change. And they change, and they change, etc, etc, etc. You reject the force fed bad things, spit them out so they don''t leave a lasting taste in your mouth... Too bad that a lot of retail "merchants" grew up on sour balls as a steady diet.

 

[diagem]

Date: 8/29/2006 1:08:05 PM
Author:oldminer
If there is poor clarity, cloudiness or fluorescence these folks are going to ''predict'' light performance will not be different, but intend to put this lack of performance under clarity grading. Incredible! Here the consumer finds an ''excellent'' cut and thinks, ''Sell, it isn''t a fabulous clarity, but it has a wonderful light performance.''. Boy, they may well be surprised!
Personally speaking, i simply think that this and other things will confuse the consumer more..., even more than they allready are.

If a diamond has poor light behavior, then how can that component grade Excellent when it is obvious to any grader that this isn''t the case. How is good communication of the diamond''s appearance to be transmitted to end users or other dealers?

The jury is certainly not done deliberation on this hot topic. The GIA Symposium ws full of differing opinions and vbery thougtful people. Most of these people are dedicated to bringing honesty to the diamond trade. There is a very powerful, traditional minority that prefers the old smoke and mirrors stuff. This will change over time, but it won''t totally go away any time soon.

Using an expert is still going to be the right path for consumers who want assurance a particular diamond is right for them. I will say that the creation of cut grading systems by the major players is coming along, but there are plenty of knowledgeable people who are less than thrilled with what is now being offered. You take the good with the bad as things change.
The problem with that is that "most experts" i know, dont possess these type of technicall knowledge!!! In my opinion, this will confuse experts as well as consumers.

Adamasgem is right, what about COLOUR!?!?
Cutters will have to adapt different types of cutting formulas for different color shades and especially different hue''s to reach maximum light behaviour...??

Take for example Fancy colored diamonds..., I never checked, but am willing to bet none are cut to maximize light performance.

I guess that the GIA and AGS are competing on who is more innovative in diamond design...

 

[oldminer]

While no system is perfect, it seems incredible that regardless of how poorly a diamond transmits light, it will receive the predicted light performance grade based on cut paramters. The hundreds of postings here and elsewhere that convinced me years ago that the flaw of the AGA Cut Class system was because it was parameter driven, now have been "improved" and copied to the new programs of the top dogs....

I always said we could do better. We can. The many arguments will have to be made all over again to convince far larger institutions that they are not doing the best job for the industry or end user.

 

[gladstone]

Date: 8/29/2006 1:08:05 PM
Author:oldminer
If there is poor clarity, cloudiness or fluorescence these folks are going to ''predict'' light performance will not be different, but intend to put this lack of performance under clarity grading. Incredible! Here the consumer finds an ''excellent'' cut and thinks, ''Sell, it isn''t a fabulous clarity, but it has a wonderful light performance.''. Boy, they may well be surprised!

If a diamond has poor light behavior, then how can that component grade Excellent when it is obvious to any grader that this isn''t the case. How is good communication of the diamond''s appearance to be transmitted to end users or other dealers?

The jury is certainly not done deliberation on this hot topic. The GIA Symposium ws full of differing opinions and vbery thougtful people. Most of these people are dedicated to bringing honesty to the diamond trade. There is a very powerful, traditional minority that prefers the old smoke and mirrors stuff. This will change over time, but it won''t totally go away any time soon.

Using an expert is still going to be the right path for consumers who want assurance a particular diamond is right for them. I will say that the creation of cut grading systems by the major players is coming along, but there are plenty of knowledgeable people who are less than thrilled with what is now being offered. You take the good with the bad as things change.

May I modify the above sentence to say:

Using an up to date expert is still going to be the right path for consumers who want assurance a particular diamond is right for them

 

[strmrdr]

2 questions:
Is there any evidence that clarity over gia si-2 has any visible affect on light return? if not then its a non-issue.
Does any level of fluorescence actually effect light return? - how would you prove it?

fluorescence is a material property like color and clarity it don''t belong in the cut grade.

 

[adamasgem]

Date: 8/29/2006 3:16:17 PM
Author: DiaGem
Adamasgem is right, what about COLOUR!?!?
Cutters will have to adapt different types of cutting formulas for different color shades and especially different hue''s to reach maximum light behaviour...??

Take for example Fancy colored diamonds..., I never checked, but am willing to bet none are cut to maximize light performance.

I guess that the GIA and AGS are competing on who is more innovative in diamond design...

If GIA and AGS are competing, then that''s no challange for AGS. AGS wins hands down. AGS can handle it, GIA''s Farceware(TM) wouldn''t stand a chance.

 

[adamasgem]

Date: 8/29/2006 11:03:58 PM
Author: strmrdr
2 questions:
Is there any evidence that clarity over gia si-2 has any visible affect on light return? if not then its a non-issue.
Inclusions absorb light and effect the ray path, so theoretically they have an effect

Does any level of fluorescence actually effect light return? - how would you prove it?

I and others have shown it, it has been "proven", period. There is even a GIA authored article on the Tavenier diamond that shows the same thing I have been showing for years. On a fluorescent stone, you put in energy below the visible and get visible light out. It effects the color grade and the perceived "light return" on a measurement based system, if there is any UV excitation.

fluorescence is a material property like color and clarity it don''t belong in the cut grade. I agree.. so a "measurement" based system should be UV free..

 

[Regular Guy]

Date: 8/29/2006 11:03:58 PM
Author: strmrdr

Is there any evidence that clarity over gia si-2 has any visible affect on light return? if not then its a non-issue.

Dave, unless you have some specific comment on this, if not on my comment that you''re inappropriately implying bad things about one of the two major grading agencies you''ve started this post about, you might consider backtracking on this whole deal.

Theory is one thing, practice is another. Ordinarily, this is your point, but turn about is fair game.

 

[strmrdr]

Marty I can agree that in theary:
color
inclusions
and from what you say fluorescence can affect light return. (id like more info do you have any links?)

But real world and talking gia/ags graded: si2 and up ,j and up and strong to none ,how much effect is there?
From what has been said only a very small percentage of even strong fluorescence stones will get milky in daylight. correct?
In all 3 cases is it enough to even worry about?

My thinking is that small changes in cut would have a much larger effect. agree? or disagree?

Dave, the same questions for you if you would please.

 

[adamasgem]

Date: 8/30/2006 12:00:14 AM
Author: strmrdr
Marty I can agree that in theary:
color
inclusions
and from what you say fluorescence can affect light return. (id like more info do you have any links?)
I can dig out the Tavenier jornal article and extract under fair use. otherwise read my article http://www.adamasgem.org/giafluor.html "Diamonds should be graded at their poorer color in artificial light devoid of ultraviolet" quoting GIA, "poorer color" implies that UV excited stones with fluor are going to be whiter due to apparent increased transmittance in the 450-480nm band

But real world and talking gia/ags graded: si2 and up ,j and up and strong to none ,how much effect is there? Probably not much from what .. Color has more effect, as a guess since I have done some analyses on that
From what has been said only a very small percentage of even strong fluorescence stones will get milky in daylight. correct? Very small percentage are milky, or suffer loss of transparency
In all 3 cases is it enough to even worry about?

My thinking is that small changes in cut would have a much larger effect. agree? or disagree? Again it depends on the lighting envirionment (angles) used and color temperature of the light whaat type of discrimination one will get. You NOTE that I say "discrimination'' and not necessarily a measure of "goodness".

Dave, the same questions for you if you would please.

 

[adamasgem]

Date: 8/30/2006 12:00:14 AM
Author: strmrdr
Marty I can agree that in theary:
color
inclusions
and from what you say fluorescence can affect light return. (id like more info do you have any links?)

Except from referenced journal article showing the increased apparent transmittance of the same diamond under UV excitation. Increased transmittance = less absorption=more light returned.. get the picture ? Type Ia diamonds have similar characteristics with and without UV when they fluoresce blue, which most fluorescent diamond do.

This is what I can see with and without UV excitation with the SAS2000, but who am I.
Now G-D published this so it must be right

At the same time in their G&G fluorescence article, they said that fluorescence doesn''t effect color grading.. They can''t have it both ways..

 

[diagem]

Date: 8/30/2006 12:00:14 AM
Author: strmrdr
Marty I can agree that in theary:
color
inclusions
and from what you say fluorescence can affect light return. (id like more info do you have any links?)

But real world and talking gia/ags graded: si2 and up ,j and up and strong to none ,how much effect is there?
From what has been said only a very small percentage of even strong fluorescence stones will get milky in daylight. correct?
In all 3 cases is it enough to even worry about?

Imagine the SI2 clarity is based on a "Cloud", then you would have really something to worry about!!!

My thinking is that small changes in cut would have a much larger effect. agree? or disagree?

Dave, the same questions for you if you would please.

 

[adamasgem]

Date: 8/30/2006 6:48:44 AM
Author: DiaGem

Date: 8/30/2006 12:00:14 AM
Author: strmrdr
Marty I can agree that in theary:
color
inclusions
and from what you say fluorescence can affect light return. (id like more info do you have any links?)

But real world and talking gia/ags graded: si2 and up ,j and up and strong to none ,how much effect is there?
From what has been said only a very small percentage of even strong fluorescence stones will get milky in daylight. correct?
In all 3 cases is it enough to even worry about?

Imagine the SI2 clarity is based on a ''Cloud'', then you would have really something to worry about!!!

My thinking is that small changes in cut would have a much larger effect. agree? or disagree?

Dave, the same questions for you if you would please.

The cloud may be platelets, sometimes giving yellow fluorescence, or it could be a milky overblue.. like some "whites".

Look, a poorly cut D IF may give only as much light return (in some undefined environmnet) as a well cut J would. Problem with measurements is the light source definition.

You can try the theory out in DiamondCalc by changing the absorbance characteristics..

 

[diagem]

Date: 8/30/2006 7:10:21 AM
Author: adamasgem

Date: 8/30/2006 6:48:44 AM
Author: DiaGem

Date: 8/30/2006 12:00:14 AM
Author: strmrdr
Marty I can agree that in theary:
color
inclusions
and from what you say fluorescence can affect light return. (id like more info do you have any links?)

But real world and talking gia/ags graded: si2 and up ,j and up and strong to none ,how much effect is there?
From what has been said only a very small percentage of even strong fluorescence stones will get milky in daylight. correct?
In all 3 cases is it enough to even worry about?

Imagine the SI2 clarity is based on a ''Cloud'', then you would have really something to worry about!!!

My thinking is that small changes in cut would have a much larger effect. agree? or disagree?

Dave, the same questions for you if you would please.

The cloud may be platelets, sometimes giving yellow fluorescence, or it could be a milky overblue.. like some ''whites''.

Look, a poorly cut D IF may give only as much light return (in some undefined environmnet) as a well cut J would. Problem with measurements is the light source definition.

You can try the theory out in DiamondCalc by changing the absorbance characteristics..

I think usually clouds are based on "platelets", in this case the light paths and the light return will be blocked.
I did notice though, that when you look at a diamond with a cloudy appearance in room with no direct artificial lightning, the effect of the cloud becomes minimal, sometimes to a point of nonexistence.

 

[oldminer]

When diamonds are graded, it is, by tradition, that we split hairs. Diamonds with SI2, SI1 and even VS inclusions may, from time to time, have sufficient light return changes that it can be "measured". We may not see any difference, but people buy IF and VVS1 diamonds where there is a large price difference and no visible difference.

If an inclusion blocks a bit of light, it has an effect on light return. Whether you can see it, makes little difference in grading diamonds. Diamonds are graded well beyond what one can see with the naked eye.

Is grading of SI2 and better stones going to generally okay with predictive tools, Probably yes in most cases. Is it the right way or the best method? Probably not.

Some people won''t care at all and oithers are the kind of people who care a great deal about perfection and accuracy. So in the end, it all depends on your personality and needs.

 

[adamasgem]

Date: 8/30/2006 8:40:18 AM
Author: oldminer
When diamonds are graded, it is, by tradition, that we split hairs. Diamonds with SI2, SI1 and even VS inclusions may, from time to time, have sufficient light return changes that it can be ''measured''. We may not see any difference, but people buy IF and VVS1 diamonds where there is a large price difference and no visible difference. Dave, you are hammering on changes in measured light return due to clarity yet you don''t know whether the "change" in your measured light return (with your unknown envirionment) is due to color, clarity OR cutting. Smoke screens and mirrors..You measure some "value", that it, period.

If an inclusion blocks a bit of light, it has an effect on light return. Yes, that is true. Whether you can see it, makes little difference in grading diamonds. Diamonds are graded well beyond what one can see with the naked eye.

Is grading of SI2 and better stones going to generally okay with predictive tools, Probably yes in most cases. Is it the right way or the best method? Probably not. See above

Some people won''t care at all and oithers are the kind of people who care a great deal about perfection and accuracy. So buy a D flawless, no fluor, best optimal cut for some UNKNOWN envirionment!!!! tSo in the end, it all depends on your personality and needs. And whetehr or not you believe the hyperbole.

 

[oldminer]

Marty: The grading of diamonds into ultra-fine discreet levels is not my system, but the one everybody has used for a long time. The system iteslf is hyperbole to an extent.

Put yuorself in the postion of a consumer who gets a grading report with a predicted cut grade of excellent when the diamond has mediocre performance due to fluorescence and /or inclusions. Do you think they are being well served by such a flawed method?

Admittedly you don''t know the lighting inside an ImaGem box, but it provides discreet and repeatable light grades. These light grades are not presently a universal standrard, but there is no other standard that is universal yet, either. What is being offered is information to stimulate thought, create a dialogue and to attempt to formulate meaningulf future standards.

You are very good at criticism, but where''s the beef in your position? Do you make a positive offering or simply criticism? What system would you prefer and why? People want to know if you have good ideas or just prefer to pick bones. You probably have some good advice for the trade, so why not offer some of it?

 

[adamasgem]

Date: 8/30/2006 9:39:25 AM
Author: oldminer
Marty: The grading of diamonds into ultra-fine discreet levels is not my system, but the one everybody has used for a long time. The system iteslf is hyperbole to an extent. I might tend to agree with you on that.

Put yuorself in the postion of a consumer who gets a grading report with a predicted cut grade of excellent when the diamond has mediocre performance due to fluorescence and /or inclusions. Do you think they are being well served by such a flawed method? If you are talking about GIA "flawed product", I'll tend to agree with you on that.

Admittedly you don't know the lighting inside an ImaGem box,(Do you?) but it provides discreet and repeatable light grades. So, they are discreet and "repeatable" These light grades are not presently a universal standrard, but there is no other standard that is universal yet, either. A standard has to be DEFINABLE ...


What is being offered is information to stimulate thought, create a dialogue and to attempt to formulate meaningulf future standards. Sorry Dave, it sounds to me (as well as others I have talked to and some who have commented) like a continuing sales pitch with next to ZERO usefull information being offered.

You are very good at criticism, but where's the beef in your position? Where is My beef? That makes me laugh out loud, the pot calling the kettle black.

Do you make a positive offering or simply criticism? I do both... And I offer pointed technical criticism where warrented. And I believe I am in a better position to do that than some others (Names withheld to protect the guilty).

What system would you prefer and why? First, an open one. You want people to embrace blindly..

People want to know if you have good ideas or just prefer to pick bones. That is for the readers to decide, I tell it as I see it, politics be damned...

You probably have some good advice for the trade, so why not offer some of it? I'll offer some advice. Show some hard facts, because all I have seen is a lot of marketing and unsubstantiated claims. We did show some progress in the thread regarding linear measurements, but again, we haven't seen any substantiation. Real comparison data on differing "calibrated" systems both for repeatability and accuracy.

What about the Imagem paradigm for light performance top grrades in terms of cutting parameters so we can have a sanity check. What does an Imagem EX(or top grade) really mean??? I would hope it is not like a GIA FarceWare(TM) EX..

Without disclosure, it is just more Voodoo For Jewelers, as far as I am concerned.

 

[oldminer]

I have seen the lighting inside the box. Nothing terrifically exotic, but good minds with lots of experience think it is an appropriate lighting model for the task. The measures taken are simple and well defined already.

I believe you are right in much of your criticism about more facts are needed. I will encourage more disclosure and more hard evidence in the coming weeks.

 

[Regular Guy]

My older son is going into 6th grade, and will probably be taught shortly about compare and contrast. He might be asked to compare two or three documents. For example, see three sets of notes here:

1) From above, in this thread, from Dave:


"Is grading of SI2 and better stones going to generally okay with predictive tools, Probably yes in most cases."

2) More immediately, lower in this thread, from Dave:

Date: 8/30/2006 9:39:25 AM
Author: oldminer

Put yuorself in the postion of a consumer who gets a grading report with a predicted cut grade of excellent when the diamond has mediocre performance due to fluorescence and /or inclusions. Do you think they are being well served by such a flawed method?

3) This, taken today, written earlier, from the Forum Policies:

"11. This forum is, above all, a place for consumer assistance and education, not advertisement. If you are a member of the trade, please follow the following post content rules:
Post helpful advice.
Do not make blatant commercial posts or requests to visit your website.
Do not use a promotional slogan in your signature. You may sign your posts with your name, credentials and company name.
d) Do not create fear-based doubts in consumers'' minds in order to scare them into using your services.
Do not mention your products or services unless requested in the thread by a consumer."

Also, beyond compare & contrast, my son will be asked to provide analysis. I''ll suggest some...because, where you say:

Date: 8/30/2006 9:39:25 AM
Author: oldminer
Marty: The grading of diamonds into ultra-fine discreet levels is not my system, but the one everybody has used for a long time. The system iteslf is hyperbole to an extent.

Though I am not Marty, neither am I trying to reinforce a system that I don''t believe in. People who will use your appraising service, though they may have their own agenda, which you seem to base this whole approach on, will also be asking you for your advice. It is hoped that the benefits of that will continue to be available, so that a shopper will figure out a way to navigate between the hypberbole you have bolstered, and the differentiation that you think a consumer might be wise to actually attend to. A consumer does actually have an interest in an expert''s advice. We hope that can continue to be available from you. In particular, we hope you take care in engaging in cognitive dissonance creating activities, which may cloud what is real vs unreal for yourself.

 

[Paul-Antwerp]

Date: 8/30/2006 9:39:25 AM
Author: oldminer
Put yuorself in the postion of a consumer who gets a grading report with a predicted cut grade of excellent when the diamond has mediocre performance due to fluorescence and /or inclusions. Do you think they are being well served by such a flawed method?

If you are talking about ''Excellent'', this is GIA-system. Are you positively sure that visible mediocre light performance is due to fluorescence or inclusions or just to the predicted cut-grade being flawed, regardless of fluorescence or clarity?

And in the possibility that you are taking the same position with regards to AGS-grading of light performance, do you have examples of stones with graded Ideal light performance, which exhibit visible mediocre light performance, caused by fluorescence and/or inclusions?

 

[oldminer]

Paul, when I directly asked Peter Yantzer the question on this, he said the AGS does not want to double fault a stopne with lower light performance AND clarity even if such is the case. The light performance is calculated based on nothing interfering with it, even if it does to some varaible extent.

I''m not trying to use scare tactics. this is information for the trade and the public. Check it out and see if you agree or don''t.

 

[Paul-Antwerp]

Date: 8/30/2006 11:42:30 AM
Author: oldminer
Paul, when I directly asked Peter Yantzer the question on this, he said the AGS does not want to double fault a stopne with lower light performance AND clarity even if such is the case. The light performance is calculated based on nothing interfering with it, even if it does to some varaible extent.

I''m not trying to use scare tactics. this is information for the trade and the public. Check it out and see if you agree or don''t.

You are not answering my question, Dave.

I asked the following, with regards to AGS: Do you have EXAMPLES of stones with GRADED Ideal light performance, which exhibit VISIBLE mediocre light performance, CAUSED BY fluorescence and/or inclusions?

 

[oldminer]

Of course not. Stones with excellent ratings will most likely have generally very fine light performance. Unless a diamond is a junk stone or cloudy, what else could be the case? However, the statement that there will be some degree of light degradation dependent on clarity, fluorescence and cloudiness is a totally logical one. Do you have any knowledge that incremental changes don''t occur?

 

[Lynn B]

OK, I'm just a layperson here -- so I'll (gladly!) leave the techie-talk to the experts. But I do have a question...

Date: 8/29/2006 2:48:58 PM
Author: adamasgem

I notice you didn't mention color.

A D color stone is going to return much more light than a K color of the same size and cut. The 'optimal cut' for a K color stone WILL NOT BE the same for a D color. It is a matter of optical physics. It is a non linear optimization problem. It is a function of the lighting envirionment and the lighting color temperature.

So, assume we have two virtually identical diamonds, cut to super-ideal proportions... one is a "D" and one... isn't.

Are you saying that the D will be a better performer, solely because of its color grade?

 

[strmrdr]

Date: 8/30/2006 1:15:10 PM
Author: oldminer
Of course not. Stones with excellent ratings will most likely have generally very fine light performance. Unless a diamond is a junk stone or cloudy, what else could be the case? However, the statement that there will be some degree of light degradation dependent on clarity, fluorescence and cloudiness is a totally logical one. Do you have any knowledge that incremental changes don''t occur?

Dave you made the claim and now are being called to back it up shifting the question to someone else is not right.
There have been several questions asked here that you havent answered yet.
This topic stinks of FUD its up to you to prove otherwise.

 

[strmrdr]

Date: 8/30/2006 1:20:56 PM
Author: Lynn B
OK, I'm just a layperson here -- so I'll (gladly!) leave the techie-talk to the experts. But I do have a question...

Date: 8/29/2006 2:48:58 PM
Author: adamasgem

I notice you didn't mention color.

A D color stone is going to return much more light than a K color of the same size and cut. The 'optimal cut' for a K color stone WILL NOT BE the same for a D color. It is a matter of optical physics. It is a non linear optimization problem. It is a function of the lighting envirionment and the lighting color temperature.

So, assume we have two virtually identical diamonds, cut to super-ideal proportions... one is a 'D' and one... isn't.

Are you saying that the D will be a better performer, solely because of its color grade?

In theory in some light conditions yes.
In virtual models yes.
In the real world not that you or anyone would notice until you hit the tinted range.

 

[Cehrabehra]

Date: 8/30/2006 9:39:25 AM
Author: oldminer
Marty: The grading of diamonds into ultra-fine discreet levels is not my system, but the one everybody has used for a long time. The system iteslf is hyperbole to an extent.

Put yuorself in the postion of a consumer who gets a grading report with a predicted cut grade of excellent when the diamond has mediocre performance due to fluorescence and /or inclusions. Do you think they are being well served by such a flawed method?

Do you really believe that an excellent cut diamond that is flawless/D/No flour that produces excellent light return... really makes it seem that an equally excellent cut diamond that is SI1/H/med flour is simply "mediocre performance"? I mean what sort of other characteristics are you talking about to create what you consider "mediocre performance"? I3/P/strong blue? Where''s the line between excellent and mediocre?