Article Over Grading of Blue Fluorescent Diamonds Revisited

[Rockdiamond]

Very interesting! Would you say that your batting average for these Israeli stones was worse for fluorescent stones than for nonfluorescent (or weakly fluorescent) stones? In the cases where you were wrong, were you more frequenlty overgrading or undergrading compared to GIA?

Some very interesting paths that, to me, definitely relate to the discussion- and the reasons the theory and experiences diverge.
Last time I bought in Israel was 2006, so it's hard to recall specific stones- but I can recall missing in both directions.
Buying a yellow I was sure would get Fancy Yellow- GIA gave it Y-Z. Or thinking a stone was H, and it comes back J.
I definitely recall things going the other way as well. I expected a Y-Z and got FLY ie.
In discussing this over the years with colleagues, it's been suggested that a combination of factors contribute. Jet lag. Differences in the windows/ interior lighting. But also suggested differences in the natural light

And at the stores in the Carribean, was the demand for K-L stones limited to those with fluorescence, or also nonfluorescent stones?

In the vast majority of cases, stones back then were sold sans GIA. Especially the K-L-M goods.
It was a lot of fun back then. I worked for a large South African sight holder. We had so many stones. It was common for me to allow the buyers to pick from parcels of 2ct stones in "top silver" ( K-L-M) containing 20+ stones- none GIA graded.
The nicer blue stones always went first.
Again, anecdotal, but buyers picking the diamonds using their eyes tend to gravitate to the nicer fl stones in these colors, in my experience.
Part of the reason the discussion of why top silver MB/SB stones theoretically can't show improvement is a bit frustrating is all the real world experience I've had with them. You do not need direct sunlight to see the effect.

 

[Texas Leaguer]

Drk,
Thank you for your detailed thoughts on possible causes for the transparency issue. A lot to chew on there! My observations tend to track with those you cited in the GIA study. That is, the haziness associated with fluoro diamonds seems to be on a continuum, with some stones showing no transparency deficit at all and others to a varying extent. It is usually subtle. The really obvious ones (overblues) are not common. So, to me, transparency issues are not a simple "yes/no" determination (as is commonly suggested) but rather a matter of degree.

I have also noticed that a seemingly high percentage of strongly fluoro stones are associated with twinning and/or graining. These could suggest some of the defects that you mention that might be playing a part in light scattering, either by themselves or in conjuction with fluorescence. One of my theories is that the fluorescent emissions are illuminating these internal characteristics and aggravating their impact on transparency. Certain types of clouds might play the same way.

Another thought that occurred to me, which I am WAY out of my league to be able to analyze, is polarization of the light. If I am not mistaken, the light waves become polarized as they bounce inside the diamond. Because emission would presumably be taking place in all directions, could it be somehow creating dissonance with the rays that we would normally be returned to the eye from an inert diamond?

One last thought, the whitening that some report seeing might actually be a result of a change in transparency. Increased opacity might give the appearance of body color whitening.

 

[drk14]

Again, anecdotal, but buyers picking the diamonds using their eyes tend to gravitate to the nicer fl stones in these colors, in my experience.
Part of the reason the discussion of why top silver MB/SB stones theoretically can't show improvement is a bit frustrating is all the real world experience I've had with them. You do not need direct sunlight to see the effect.

All of this is consistent with the hypothesis that whitening is caused by some other factor that is likely to be present in MB/SB stones. Correlation does not imply causation. SB stones emit fluorescent light (by definition). SB stones may (in some cases) appear whiter (less colored) than they should -- I'll take your word for this, for the sake of argument. Consequently, there will be a correlation between strong fluorescence and whitening. This does not necessarily imply that fluorescence causes whitening.

 

[drk14]

One last thought, the whitening that some report seeing might actually be a result of a change in transparency. Increased opacity might give the appearance of body color whitening.

Absolutely true -- this is certainly a plausible explanation! However, since I have not seen the effect for myself, I have rely on the observations of others. I have the impression that those who claim a positive whitening effect from SB fluorescence will not agree that these stones have less transparency...

More experiments are needed! Who wants to send me diamonds???

 

[Rockdiamond]

. Consequently, there will be a correlation between strong fluorescence and whitening. This does not necessarily imply that fluorescence causes whitening.

This makes total sense. It could be also be that we're lumping stones together ( as is GIA) when there is likely different sorts of fluorescence that have not been distinctly identified yet. It's my experience that some fl stones have the element that causes the whitening, and others don't. So maybe there's two things acting together in the diamond.

One last thought, the whitening that some report seeing might actually be a result of a change in transparency. Increased opacity might give the appearance of body color whitening.

Really good point- the blue itself which causes the whitening ( or blue-ing in the case of D-E-F stones) may actually be a minuscule lessening of opacity.

 

[drk14]

So, to me, transparency issues are not a simple "yes/no" determination (as is commonly suggested) but rather a matter of degree.

I completely agree.

I have also noticed that a seemingly high percentage of strongly fluoro stones are associated with twinning and/or graining. These could suggest some of the defects that you mention that might be playing a part in light scattering, either by themselves or in conjuction with fluorescence. One of my theories is that the fluorescent emissions are illuminating these internal characteristics and aggravating their impact on transparency. Certain types of clouds might play the same way.

Again, I feel that the fluorescence emission would be too weak to cause any such effect. Nonetheless, it is interesting that you have noticed a correlation between SB fluorescence and other types of crystal defects. This lends support to the notion that whitening (if present) is not caused by fluorescence itself, but by some other factor (e.g., light scattering by defects) that correlates with fluorescence.

Another thought that occurred to me, which I am WAY out of my league to be able to analyze, is polarization of the light. If I am not mistaken, the light waves become polarized as they bounce inside the diamond. Because emission would presumably be taking place in all directions, could it be somehow creating dissonance with the rays that we would normally be returned to the eye from an inert diamond?

I'm not sure I understand what you mean by "dissonance" in this context. My initial gut feeling is that polarization is not a factor. But who knows? Perhaps inert diamonds appear more yellow than they should due to the effects of Haidinger's brush?

 

[drk14]

It's my experience that some fl stones have the element that causes the whitening, and others don't. So maybe there's two things acting together in the diamond.

This is in complete agreement with observations published by Moses et al. (1997):

"...certain fluorescent stones were picked [i.e., identified as having different body color] more often than others of equal fluorescence strength in the same color set."

"Because some highly fluorescent diamonds in a set were singled out and others were not, it is possible that other factors are affecting color appearance more strongly than fluorescence strength."

 

[Texas Leaguer]

I'm not sure I understand what you mean by "dissonance" in this context. My initial gut feeling is that polarization is not a factor. But who knows? Perhaps inert diamonds appear more yellow than they should due to the effects of Haidinger's brush?

Never heard of that one before, but I can actually see it on my computer screen. It's very vague but appears just like the illustration. I wonder if others here can see it too?

I was actually speculating about polarization in terms of the haze, not the color perception. By dissonance I mean a reduction in the directional quality of the light rays and if that would somehow create a 'fuzziness' to the light. (how's that for a scientific term!).

 

[drk14]

I was actually speculating about polarization in terms of the haze, not the color perception. By dissonance I mean a reduction in the directional quality of the light rays and if that would somehow create a 'fuzziness' to the light. (how's that for a scientific term!).

I cannot think of any physics that would produce such an effect.

 

[Rockdiamond]

Is it possible the phenomena of whitening is caused by physical attributes beyond current scientific understanding?
That would explain why scientific analysis can't explain a widely observed physical property.

 

[Texas Leaguer]

Is it possible the phenomena of whitening is caused by physical attributes beyond current scientific understanding?
That would explain why scientific analysis can't explain a widely observed physical property.

The issue is not that some whitening can't be scientifically attributed to blue fluorescence under the right circumstances. Cowing's study documents fluro induced whitening. The issue is that in most circumstances it will be far too weak to have any impact. Therefore, if you think you are seeing whitening in conventional lighting it is likely the result of something other than fluorescence.

Diamonds change appearance with different lighting, whether they fluoresce or not. In the realm of perception, suggestibility is a factor. If you expect a diamond to look whiter because it is fluorescent, chances are your perception will accommodate that expectation.

 

[Texas Leaguer]

I cannot think of any physics that would produce such an effect.

You are not the first to tell me that!

 

[drk14]

Is it possible the phenomena of whitening is caused by physical attributes beyond current scientific understanding?

Depends on what you mean by "understanding". Physicists (and other scientists) have been at it for a very long time, so the chances that there may be some new physics at play (i.e., phenomena not previously investigated) is slim, in my opinion.

However, real systems are complex. The sheer number of possible interactions and events can be so large that even if the nature of those interactions is understood, the system may exhibit behavior that was not predicted. For example, the physical and chemical interactions that produce weather phenomena are for the most part well understood, but that doesn't mean that the predicted weather forecasts are accurate.

The optical phenomena in a single diamond are ultimately produced by the interactions between a quadrillion photons and almost a septillion carbon atoms (as well as quintillion impurities)! Even though a lot is known about the physics of the individual interactions, making predictions requires some simplifying assumptions that may deviate from reality. Thus, there could be some phenomena that have not yet been explained, but that would be explainable within the constraints of known physics, if we just made some adjustments to the simplifying assumptions.

 

[Rockdiamond]

Bryan- you continually address this as though it's some imaginary aspect.

The issue is that in most circumstances it will be far too weak to have any impact.

Bryan, this has NOT been established. You can't see it, so hold your beliefs.
I, and pretty much every dealer I know has seen and experienced it.
Winston picking the colorless examples that did show blue, calling them "Premier" and charging more for them was not based on some pie in the sky.
Looking at large parcels of K-L-M colored good, where the MB/SB stand out, is not imaginary either.

 

[drk14]

You can't see it, so hold your beliefs.
I, and pretty much every dealer I know has seen and experienced it.

Perhaps the two of you can agree to disagree about this. In the experiment by Moses et al. (1997), 60% of trained observers from the diamond industry perceived a whitening effect in very strong fluorescent stones (without knowing that whether the diamonds were fluorescent or not), but 40% did not perceive any such effect on the apparent body color. Interestingly, those who saw a difference only did so consistently when the diamonds were observed table-up. So it seems that David is in the the 60% and Bryan may be in the 40%.

 

[Texas Leaguer]

Bryan- you continually address this as though it's some imaginary aspect.


Bryan, this has NOT been established. You can't see it, so hold your beliefs.
I, and pretty much every dealer I know has seen and experienced it.
Winston picking the colorless examples that did show blue, calling them "Premier" and charging more for them was not based on some pie in the sky.
Looking at large parcels of K-L-M colored good, where the MB/SB stand out, is not imaginary either.

Please review drk's calculations and analysis. He confirms what other journals have established, that UV in artificial light (except when diamond is within inches of the source) is too weak to cause noticeable color whitening. These are not just my 'beliefs'.
Let me also refer you back to conclusions of the GIA study also mentioned drk in this thread. For example.

• Untrained observers (average consumers) could not notice any differences in apparent body color in diamonds of equal color grade but different levels of blue fluorescence.

 

[Rockdiamond]

Re the Moses experiment:
Yes, I agree the effect is seen face up.
I'm interested in what a "trained observer" was. Color and clarity grading are two completely independent skills.
I have definitely experienced different levels of color sensitivity from one person to the next. Some people see color better than others.
DRK- maybe this falls under your area of expertise.... has it been scientifically/medically established that there are varying degrees of color blindness- which would also equate to differing degrees of color sensitivity? That could be another piece of the puzzle.

To explain my interest in this discussion- and why Bryan and I seem to get into a bit of a disagreement: I think both of us are dedicated to transparency in our field.
Regular readers know that a seller telling them an EGL report is as good as a GIA report is either uninformed, or less than honest.

So what if a dealer is claiming a K MB looks whiter than an inert K color?
There's a lot of confusion about fluorescence, and it's effect on a diamond.
That's why I think this is an important discussion.

 

[Rockdiamond]

Please review drk's calculations and analysis. He confirms what other journals have established, that UV in artificial light (except when diamond is within inches of the source) is too weak to cause noticeable color whitening. These are not just my 'beliefs'.
Let me also refer you back to conclusions of the GIA study also mentioned drk in this thread. For example.

• Untrained observers (average consumers) could not notice any differences in apparent body color in diamonds of equal color grade but different levels of blue fluorescence.

Bryan, Bryan, Bryan. NONE of this is "established science". We have no reasonable way to prove you are right or wrong.
A few posts above DRL wrote this:

Perhaps the two of you can agree to disagree about this. In the experiment by Moses et al. (1997), 60% of trained observers from the diamond industry perceived a whitening effect in very strong fluorescent stones (without knowing that whether the diamonds were fluorescent or not), but 40% did not perceive any such effect on the apparent body color. Interestingly, those who saw a difference only did so consistently when the diamonds were observed table-up. So it seems that David is in the the 60% and Bryan may be in the 40%

If you believe no whitening occurs, tell your clients that. Clearly, there are many who do see it- regardless of what a journal article says.
As I wrote, I feel that this is an important issue for consumers, and it's just not settled.
You keep pointing to journals, and I keep pointing to real life experiences.

 

[drk14]

I'm interested in what a "trained observer" was. Color and clarity grading are two completely independent skills.

From the Moses paper:

Most industry participants (25 total) were Laboratory Graders — "trained individuals employed by GIA GTL, who routinely perform diamond color grading using the D-to-Z scale and GIA's standard grading procedure."

A smaller number of participants were described as Trade Graders (5 total) or Trade Observers (5 total). Trade Graders were "trained individuals employed by diamond manufacturers, who routinely
perform diamond color grading using the D-to-Z scale and a standard grading procedure." Trade Observers were "individuals employed by diamond manufacturers or diamond brokers, who have a working knowledge of diamond color-grading practices but either do not carry out color grading on a daily basis or, if they do color grade, they use less stringent guidelines than those used by the Laboratory and Trade Graders."

 

[Karl_K]

one thing that could explain different strengths and over blues is density of emitters in the material.
Few emitters == less bright
More emitters == more bright
too many emitters == cloudy
Another variable could well be inclusions both 10x visible and micro inclusions.
We know that micro inclusions can effect the appearance of a diamond. (pinks and browns)
The density of inclusions and micro inclusions could also effect the level of brightness and over blue.
It would not surprise me to someday hear that it was a combo of the amount of emitters and micro inclusions that determine the strength of the FL and over blue(or yellow).

This would also explain the real blue white stones which were described as having very very clean crystal along with very strong fl.
The had a lot of emitters but very few or very small micro-inclusions.

 

[Karl_K]

David do you still have some pics of the alien diamond?
Since its long sold you could post them for educational reason to show how weird diamonds and FL can get.

 

[drk14]

It would not surprise me to someday hear that it was a combo of the amount of emitters and micro inclusions that determine the strength of the FL and over blue(or yellow).

Karl,
You are definitely on the right track.

Any haziness must be caused by structures on the order 0.1-10 microns in size, with localized refractive index that differs from that of the surrounding crystal lattice. Micro inclusions could be one potential source of such scattering structures.

As to fluorescence, for sure the strength of emitted fluorescence is directly proportional to the concentration of optical centers (e.g., N3) within the diamond matrix.

However, the question at hand is under what conditions (if any) is the amount of emitted fluorescence photons sufficient to produce a change in body color that is visible to (some) human eyes?

You call the fluorescent color centers "emitters". However, photons carry energy, and there is no stored energy in these defect that allows photons to be emitted without input energy. Therefore, in accordance with the first law of thermodynamics, "emitters" are also "absorbers". Specifically, the color center must absorb high-energy photons (shorter wavelength) before it can emit photons of slightly lower energy (longer wavelength). Moreover, because only a fraction of absorbed photons are re-emitted as fluorescent (longer-wavelength) photons, the color centers must absorb more photons than they emit.

Now, under visible-light excitation (400-415nm), if you are able to see the emitted fluorescence in the diamond, shouldn't you also be able to see the absorption of the VV photons (especially since the number of photons absorbed is so much larger than the the number of emitted photons)?

 

[Karl_K]

Now, under visible-light excitation (400-415nm), if you are able to see the emitted fluorescence in the diamond, shouldn't you also be able to see the absorption of the VV photons (especially since the number of photons absorbed is so much larger than the the number of emitted photons)?

We see a lot of things we do not identify/classify, even if they are not so subtle that they are unnoticeable. So my answer is an honest .. don't know/maybe/maybe not :}

 

[Rockdiamond]

David do you still have some pics of the alien diamond?
Since its long sold you could post them for educational reason to show how weird diamonds and FL can get.

I can't recall the stone you're referring to Karl- we've had quite a few....was it green?
Which also brings to mind another point.
There are Fancy Colored Diamonds that experience drastic color change due to fluorescence based on lighting.
The manner in which it changes the color in "normal" room lighting may be relevant.
I don't know the answer offhand, but I can certainly check for examples over the next few days.

DRK and Karl- I certainly think you guys may be introducing some amazing new theories as to why some MB/SB stones do whiten, and others do not

DRK- thanks for clarifying about the qualifications of the observers- it makes sense.

 

[Texas Leaguer]

drk,
On the haziness issue. Let's set aside fluoro induced haziness for a moment and focus on general transparency deficits caused by any combination of inclusions or crystal defects. Do you think it is technically feasible to develop an objective test for overall transparency? I can envision that such a test would provide very useful information to the consumer because clarity grade and transparency are not always directly proportional. For instance you can have eye-clean stones with haziness (e.g. Si1 grade based on clouds) and Si2 with one discrete crystal visible to the naked eye that is otherwise crisp and transparent. Consumers are often seduced by eye-clean stones without understanding the tradeoff they are sometimes making. Especially when they are interested in precision cutting and unaware that transparency deficits can diminish light performance in even the best cut diamonds.
Just curious if you are familiar with instrumentation that could be adapted to this specific purpose in diamond analysis.

 

[Karl_K]

David it was a fancy yellow(not sure which) asscher gia graded that in a lot of different lighting looked green. You had a lot of pics of it. I lusted after that diamond for more than 6 months before it sold.

 

[Rockdiamond]

David do you still have some pics of the alien diamond?
Since its long sold you could post them for educational reason to show how weird diamonds and FL can get.

I think I found it!!! Is this it Karl?
We loved it too- my wife practically threw me out of the house when I told her we'd sold it- she wanted it for herself.


https://www.gia.edu/report-check?reportno=16255564

Although the fluorescence was yellow as opposed to blue, this stone certainly showed how drastic a color change is possible when light and fluorescence react together. The stone went from brownish to greenish in a very obvious way, just based on the lighting.
Both the pics above were taken in natural lighting- if I could have taken a shot in the light box ( we didn't have it yet back then) the stone would have looked much more brown different than these two pics

 

[Karl_K]

Interesting color change but no its not the right one as I recall.
It was almost a neon green in lighting with uv as I recall and was a yellow.
Then again I may be remembering wrong. Its been a long time.

 

[drk14]

Experiments to Try for Yourself...

I would hazard to guess that most PS readers don't have access to a drawerful of fluorescent diamonds from which to draw their own conclusions about the possible whitening effects in such stones, so I will propose a few experiments that can be done cheaply, for anybody who is interested.

Experiment 1:

Next time you visit the supermarket, go to the soda aisle, and have a look at some bottles of club soda, seltzer water and tonic water (any brand, as long as the bottles are clear plastic):


Ask yourself: Is there any noticeable difference in "body color" of the three liquids, and if so, what? Optional questions: Would you describe any of the liquids as "blue white"? If you had three equivalent diamonds (same cut, carat, clarity) with body colors corresponding to each of the three liquids, would you be willing to pay more for any of these three diamonds? How much more?

If you want to be more thorough and scientific about this experiment, purchase one of each bottle, then have somebody else remove the labels and mark each bottle with a code (e.g., "X", "Y", and "Z" in random order), keeping track of which code letter corresponds to which product (but not telling you this information, to make it a blind study). Alternatively, you can administer the test to friends and family. For extra points, repeat the test in different lighting conditions (e.g., indirect sunlight, overhead fluorescent lights, etc.), to see if the answers change.

Spoiler alert: My next post will include some information that may bias how you answer the experimental questions. Some of you may already know some scientific facts/trivia about these types of beverages that will influence your answer, or may be tempted to Google the relevant information. If you have encountered a spoiler, then you should definitely only do the "blind" form of the test, and/or administer the experiment to other people who have not seen any spoiler information.

Happy sciencing!

 

[drk14]

Fluorescence Experiments...

Ok, so why am I having you study beverages from the supermarket? And what does this have to do with fluorescent diamonds?

It turns out that tonic water contains quinine molecules, which are fluorescent:



This should be a pretty good model for blue fluorescence in diamonds caused by N3 centers, because the concentration of N3 centers in fluorescent diamonds is similar to the concentration of quinine in tonic water, and the quantum efficiencies of N3 and quinine are also similar. Moreover, the excitation and emission spectra for quinine in tonic water bear a significant resemblance to the corresponding spectra for N3 fluorescence in diamond. Here are the 2D and 3D spectra for tonic water (measured by a Jasco FP-6500 spectrofluorometer, an instrument similar to the ABII used in the Luo & Breeding 2013 paper):



These spectra show that the quinine fluorescence in tonic water is excited by wavelengths in the range 300-410 nm (LWUV and some visible violet), and emits fluorescence in the range 380-600 nm (with a peak around 455 nm, which is blue).

Compare to the N3 excitation and emission spectra from Luo & Breeding (2013):



Based on the above, I hypothesize that the appearance of fluorescence in tonic water under LWUV and/or VV excitation will have a similar appearance (both in hue and intensity) to diamonds with blue fluorescence!

This brings us to...Experiment #2, described in the next post.