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Should we discourage or recommend FL stones?

Rockdiamond

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Awesome Bryan- progress!!! We agree on so much and the differences are subtle. My comments in red below
Fair enough David. Apology accepted.

I never demand that anyone agrees with me, so we can certainly agree to disagree.

I should not have to clarify this for you since we have had this discussion many times before, but here is my basic position on the topic at this point in time:
  • Blue fluorescence is capable of masking yellow color in response to UV and (to a lesser extent) VV of sufficient intensity. Agree- and this point is crucial.(but only if we're discussing colorless and near-colorless. In fancy yellow colors the effect can be opposite- increasing yellow)
  • I have seen color masking (whitening) Agree
  • In the majority of indoor lighting environments whitening does not take place, because blue emissions are not sufficiently stimulated due to insufficient intensity of wavelengths capable of causing them. Not true in my experience
  • The oft touted benefit of color grade improvement of fluorescent stones is WAY over-sold. Can't agree here based on changes in the market- I don't see a lot of sellers "touting" this. Maybe this was the case years ago, but today, other factors drive purchases in my experience. Maybe it's taking place in jewelry stores, but I don't hear of it. Kind of important personally to me- I have had stones that showed color improvement, and described them to clients thusly. No one ever claimed I was wrong- and we get a tiny percentage of returns.
  • The concern about transparency deficits (milkiness) due specifically to fluorescence is similarly overblown for the fact that in most indoor lighting the milky effect is not produced because fluorescence is not stimulated. Here, we also see things differently. I've seen more dull fluorescent diamonds than I could possibly count. Arguing over the reason they are dull is pointless.
  • Consumers need to evaluate strong fluorescent stones for any negative factors by viewing them in sunlight. Agree
  • Lab overgrading of color of strong blue fluorescent diamonds is a potential concern and consumers should have diamonds reviewed by qualified professionals specifically for this issue. Agree ( again, only for colorless and near colorless- in Fancy Yellows fluorescence causes UNDERGRADING)
  • Discounts of fluorescent diamonds can provide shoppers with potential savings due to irrational market perceptions. Agree
  • Stuff that fluoresces is really cool. Especially diamonds. WHAT- ARE YOU NUTS????....kidding of course we agree
My position is not in opposition to conclusions reached by the GIA in their studies and surveys.
 

sledge

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@sledge Attached is a pdf copy of the full Cowing study. Get a cup of coffee!

Whether one thinks that overgrading of blue fluorescent stones is a thing of the past, or may still be happening to some degree in the labs, the background information laid out in the article provides important insights and references on blue fluorescence and it's visual impacts.
Thanks for the share @Texas Leaguer, I will take a read.

Before I dive in, I saw some of your other comments in this thread. With WF having a GIA UV box and with the additional fluor analysis that WF performs on your stones, do you also evaluate color in that process to determine if the (minimal) amounts of fluor in "negligible" AGS certed stones have any effect on color grading?

I find this interesting because as you noted earlier, negligible includes "none" to just below medium. If you ever do discover such stones, I'd anticipate they would be in the higher intensity level of that range.

Also, I think this brings up another good point, even if indirectly. Much like color, fluor levels are RANGES so it seems logical someone could buy a SBF stone and be very close to VSBF. Does fluor ranges also work like color ranges, in the fact that as your intensity levels grow, the range also grows? So there is little range in faint, but more range in strong?

Or am I drawing a false connection because AGS negligible is maybe more varying than other categories of fluor?
 

Rockdiamond

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Does fluor ranges also work like color ranges, in the fact that as your intensity levels grow, the range also grows? So there is little range in faint, but more range in strong?
Your main point- that variance fluorescence grades work like color grades is pretty much the way I see it as well. Actually, if we're speaking of GIA- there's even a fairly wide range in faint. As we go up the scale predicting what GIA will call fluorescence is a total crap shoot.
 

Texas Leaguer

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Thanks for the share @Texas Leaguer, I will take a read.

Before I dive in, I saw some of your other comments in this thread. With WF having a GIA UV box and with the additional fluor analysis that WF performs on your stones, do you also evaluate color in that process to determine if the (minimal) amounts of fluor in "negligible" AGS certed stones have any effect on color grading?

I find this interesting because as you noted earlier, negligible includes "none" to just below medium. If you ever do discover such stones, I'd anticipate they would be in the higher intensity level of that range.

Also, I think this brings up another good point, even if indirectly. Much like color, fluor levels are RANGES so it seems logical someone could buy a SBF stone and be very close to VSBF. Does fluor ranges also work like color ranges, in the fact that as your intensity levels grow, the range also grows? So there is little range in faint, but more range in strong?

Or am I drawing a false connection because AGS negligible is maybe more varying than other categories of fluor?
Our first step when a lot of diamonds come from the lab is to do a full gemological verification before the diamonds are put in stock and posted to the website. From time to time we find a diamond that we feel needs to go back for re-check for one reason or another, including situations where we think color has been over graded. But I cannot recall an instance where we suspected that might have been caused by fluorescence.

Having said that, in our case most of the stones that have any detectable fluorescence are in the faint or faint+ category. As the Cowing study reveals, and as Martin Rapaport mentioned in his Op-Ed on overgrading of blue fluorescent diamonds, most of the errors occur in strong or very strong categories.

This might be an appropriate time to mention that, despite what @Rockdiamond has stated in various threads, the Cowing study has never been 'debunked'. And a good reading of the long thread on the topic will show that while aspects of the article were attacked in an effort to undermine the findings, it was defended quite well by the author and others who have read it carefully.

Here is a link to that thread for reference:
 
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Rockdiamond

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This might be an appropriate time to mention that, despite what @Rockdiamond has stated in various threads, the Cowing study has never been 'debunked'

Hi Bryan, instead of broad-based statments- let's focus.
The "Cowing Study" has quite a bit of info within it. Some of which I agree with- but not all.
To clarify my position regarding this study: There was never any consensus reached about the whitening of MB/SB stones and where it takes place. Garry's experience matches mine.
The discussion starts with Garry Holloway disputing something Michael had written- then turns specifically to whitening. Here's Garry's post on page one. Prior to the post I have quoted below, Garry mentions the reasons why Michael's suppositions in whitening are incorrect. In this post, he's actually addressing you Bryan.
Re: Article: Over Grading of Blue Fluorescent Diamonds Revis


High Bryan, in other discussions with you I posted references to this article - I just found it and posted a searchable note in an edit one post above yours.
You will note that there is quite a lot of N3 blue excitation possible from visible frequency light - not just VV and invisible UV wavelength radiation. So, may I rest my case? That blue fluoro can and does improve face up color of many if not all strong blue fluoro diamonds in almost all lighting that is adequate to determine slight (1-2 grade) color differences.
And as we read through you will notice Michael refusing, or avoiding discussion of points that contradict his study. That is one reason it went on for so long, and that you can't see a resolution.
 
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Ibrakeforpossums

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What an exciting thread! I love it when experts disagree politely.
What sort of light does GIA use to determine fluorescence? My intense yellow emerald has strong green fluor and turns into a peridot in daylight. But under my pet-stain UV flashlight it's extremely yellow with a slight greenish tone.
I would loan them my flashlight.
 

Rockdiamond

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My intense yellow emerald has strong green fluor and turns into a peridot in daylight. But under my pet-stain UV flashlight it's extremely yellow with a slight greenish tone.
Right???
We see all sorts of weird colored fluorescence on Fancy Colored Diamonds- and the deeper the color, the weirder the color!! It's so hard to classify exactly what color the fluorescence is. That might actually be important to the general discussion- maybe the specific spectrum of light we see is something the human eye can not correctly process.....


What an exciting thread! I love it when experts disagree politely.
Thank you.
I have to say, I've made every effort to recognize Bryan's opinion, and experience.
Unfortunately, the same effort does not seem to come from the other side. Agreeing to disagree need not- should not- include character assassination.
Bryan feels Michaels's study found agreement, on the aspect of whitening, I do not. Nor did Garry- I was certainly not alone on that thread. Readers can make their own decisions.

Peace Bryan.
 

Texas Leaguer

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Hi Bryan, instead of broad-based statments- let's focus.
The "Cowing Study" has quite a bit of info within it. Some of which I agree with- but not all.
To clarify my position regarding this study: There was never any consensus reached about the whitening of MB/SB stones and where it takes place. Garry's experience matches mine.
The discussion starts with Garry Holloway disputing something Michael had written- then turns specifically to whitening. Here's Garry's post on page one. Prior to the post I have quoted below, Garry mentions the reasons why Michael's suppositions in whitening are incorrect. In this post, he's actually addressing you Bryan.


And as we read through you will notice Michael refusing, or avoiding discussion of points that contradict his study. That is one reason it went on for so long, and that you can't see a resolution.
I think anyone wanting to get a sense of the discussion, the points of contention, and the quality of the contributions made by the various participants, can get a pretty good understanding by scanning the first 6 or 7 pages of the thread.
 

Rockdiamond

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Wow. I will say this- I'll always be a "New Yawka", but I've mellowed a bit since 2016......

Essentially, though, it seems such a simple argument to settle peacefully.
All agree fl causes whitening under certain lighting scenarios.
Some feel science proves whitening can only take place in direct sunlight.
Others do not feel the science is conclusive.
Does this correctly frame the debate?

I am specifically not saying you take one position, and I take another- because neither of us is alone in our beliefs.
 

Texas Leaguer

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Wow. I will say this- I'll always be a "New Yawka", but I've mellowed a bit since 2016......

Essentially, though, it seems such a simple argument to settle peacefully.
All agree fl causes whitening under certain lighting scenarios.
Some feel science proves whitening can only take place in direct sunlight.
Others do not feel the science is conclusive.
Does this correctly frame the debate?

I am specifically not saying you take one position, and I take another- because neither of us is alone in our beliefs.
That whitening takes place only in direct sunlight is being claimed by exactly NOBODY. The ENTIRE Cowing study was related to whitening taking place in the labs during grading.

Anyone wanting to get an orientation to the science around color masking of blue fluorescence can read this and other studies, and/or read the referenced thread.
 

Garry H (Cut Nut)

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The vast majority of people spend the vast majority of their time under lighting with zero UV component. UV has no affect. Incandescent, LED, halogen, argon, and most commercial fluorescent lighting all come in at barely detectable. Sunlight filtered through most glass has rather little. Shaded sunlight has close to none. Direct, unclouded sunlight is the issue, and even with that, most diamonds below Very Strong have no visible effect. This may not matter, it's a 'mind clean' topic, and if it bugs you that's a reason to avoid them, but it can have a very real effect on the price. Everyone is interested in that.
Neil our industry uses 365nm to grade Fluoescence. That is a mistake. And because of that mistake the experts have come to believe that there is little or no excitation causing a color improvement form every day light.
365nm is used because it is the largest frequency resulting from mercury vapour tube lamps. And it is primarily used, as you know, as a gemstone diagnostic tool.
The correct frequency to detect fluorescence is between 380nm and 400nm.
Violet and near visible light, which is evreywhere in most environments,

That is where the strongest excitation is created. And those frequencies pass through windows and in any lighting that you can see violet you will see a improvement in color for medium to very strong fluorescent diamonds.
1574289224121.png
From https://www.gia.edu/gems-gemology/summer-2013-luo-fluorescence-optical-defects

I have seen so many people with say 3 or 5 stone diamond rings and I ask them which is your favorite diamond - almost always they point to one - I shine a UV light on it and wallah! It is the flouro diamond.
 

Texas Leaguer

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Garry,
I have seen you make this statement before, but don't recall seeing any real evidence to support it.

"in any lighting that you can see violet you will see a improvement in color for medium to very strong fluorescent diamonds."

Care to give it a go?

We know there is UV and VV in indoor lighting, but the mere presence of these wavelengths will not stimulate fluorescence if the intensity is not sufficient. In the same way that UV from fluorescent tubes is incapable of giving us a tan, even though we spend all day every day exposed to it in our offices.
 

AV_

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'Improvement in colour' judged in terms of absorption or through the same grading procedure (there was bias, so it worked - in the box) may not qualify this blue spice.

[words shouldn't be this important]
 

Garry H (Cut Nut)

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Garry,
I have seen you make this statement before, but don't recall seeing any real evidence to support it.

"in any lighting that you can see violet you will see a improvement in color for medium to very strong fluorescent diamonds."

Care to give it a go?

We know there is UV and VV in indoor lighting, but the mere presence of these wavelengths will not stimulate fluorescence if the intensity is not sufficient. In the same way that UV from fluorescent tubes is incapable of giving us a tan, even though we spend all day every day exposed to it in our offices.
I do not know of any measurement device that covers the UV in that near visible adequately, but I do know Michael Cowing used the wrong device. I bought the closer one, but still centered around 365nm and not 390nm. You can check for yourself that Michael's is missing the peak that we learned about in 2013.
Here is my 4.2 device data:
1574297351746.png
The ideal device would measure the frequencies from 380 to 430nm.

And here it is with me sitting at my desk at 11.30am on a cloudy day just now.
1574297532359.png

Now I am not qualified to say this will raise a H Strong Blue to G or F. But there is going to be some effect positive, and only negative if the diamond concerned has certain types of inclusions. Blue Fluorescence, by itself, does not cause milky or haziness.
 
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Garry H (Cut Nut)

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Hi Bryan,
Can you tell me if GIA has changed the new device to somewhere in 3
Fair enough David. Apology accepted.

I never demand that anyone agrees with me, so we can certainly agree to disagree.

I should not have to clarify this for you since we have had this discussion many times before, but here is my basic position on the topic at this point in time:
  • Blue fluorescence is capable of masking yellow color in response to UV and (to a lesser extent) VV of sufficient intensity.
  • I have seen color masking (whitening)
  • In the majority of indoor lighting environments whitening does not take place, because blue emissions are not sufficiently stimulated due to insufficient intensity of wavelengths capable of causing them.
  • The oft touted benefit of color grade improvement of fluorescent stones is WAY over-sold.
  • The concern about transparency deficits (milkiness) due specifically to fluorescence is similarly overblown for the fact that in most indoor lighting the milky effect is not produced because fluorescence is not stimulated.
  • Consumers need to evaluate strong fluorescent stones for any negative factors by viewing them in sunlight.
  • Lab overgrading of color of strong blue fluorescent diamonds is a potential concern and consumers should have diamonds reviewed by qualified professionals specifically for this issue.
  • Discounts of fluorescent diamonds can provide shoppers with potential savings due to irrational market perceptions.
  • Stuff that fluoresces is really cool. Especially diamonds.
My position is not in opposition to conclusions reached by the GIA in their studies and surveys.
The thresholds are officially defined by their fluorescent master stones. They also have a new UV box with a specially designed test strip that allows you to compare the stone in question to samples of faint, medium, strong and very strong.

GIA-UV-Lamp-and-Viewing-Cabinet-with-Test-Strip.jpg
Hi Bryan,
Can you tell me if GIA has changed the new device to somewhere in 380nm to 400nm?
Perhaps there is a brand name on the tube.
From GIA 2013 article: "The 3D fluorescence spectra indicated that this N3-related emission reaches its maximum at 395 nm excitation energy and is not excited above 430 nm (figure 6) "


GIA patents have been adding in longer wavelengths - e.g. http://www.freshpatents.com/-dt20161006ptan20160290925.php?id=fpkwm
"In some embodiments, the light source is configured as a ring light surrounding the platform surface. In some embodiments, the light source comprises a plurality of light emitting LEDs. In some embodiments, the LEDs emits fluorescence at 365 nm or 385 nm.

In some embodiments, the LEDs are coupled with a bandpass filter. In some embodiments, the bandpass filter is set at 365 nm or 385 nm."
 

Garry H (Cut Nut)

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I have made some comments inside your post Bryan.
I hope you can appreciate the factual parts.
here is my basic position on the topic at this point in time:
  • Blue fluorescence is capable of masking yellow color in response to UV and (to a lesser extent) VV of sufficient intensity. Incorrect. Near visible violet creates a much stronger effect and passes through almost all window types. Fact.
  • I have seen color masking (whitening) That is the point, of course. But since what GIA learned in the 90's they changed the grading lamps to a CIE approved standard and set the distance to the lamps. This changed in the early 2000s (GIA never really made a statement to say when) reduced the amount of UV drastically. Fact.
  • In the majority of indoor lighting environments whitening does not take place, because blue emissions are not sufficiently stimulated due to insufficient intensity of wavelengths capable of causing them. My opinion: if there is not much light then you can never really see or discern color nuances.
  • The oft touted benefit of color grade improvement of fluorescent stones is WAY over-sold. I disagree from the experiance of having delt personally with hundreds of discerning clients, many of whom would never not now buy a fluorescent diamond.
  • The concern about transparency deficits (milkiness) due specifically to fluorescence is similarly overblown for the fact that in most indoor lighting the milky effect is not produced because fluorescence is not stimulated. Some types of inclusions cause haziness in fluorescent diamonds. Not fluorescence with most types of inclusions. Fact but research is as yet unpublished so you need to trust me.
  • Consumers need to evaluate strong fluorescent stones for any negative factors by viewing them in sunlight. In shaded sunlight. No one should examine diamonds in direct sunlight. Ever. Because the better the cut performance the darker and uglier the diamond will appear. Fact, go check for yourself.
  • Lab overgrading of color of strong blue fluorescent diamonds is a potential concern and consumers should have diamonds reviewed by qualified professionals specifically for this issue. In my opinion this is a myth for diamonds graded in the past 15 years by GIA and I expect AGS and IGI (IGI are often a little soft on color).
  • Discounts of fluorescent diamonds can provide shoppers with potential savings due to irrational market perceptions. I see no reason why in years to come Strong Blue will be sought out and attach a premium.
  • Stuff that fluoresces is really cool. Especially diamonds. Finally, Bryan, we agree! And please all make a point of alerting museums and mineral collectors to throw away their old mercury vapour lamps and use cheap LED's!
My position is not in opposition to conclusions reached by the GIA in their studies and surveys.
GIA has conflicting and changing articles. In 1997 you can see that they over graded some of the strong and very strong samples because there was clearly little or no UV in the realistic photos light source.
 

Rockdiamond

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Howdy Garry.
Thanks Mate.

@Texas Leaguer - I’m bringing a unique perspective to this forum. I’m an old ‘diamond man”. My 45 years of experience starting at Harry Winston have been built on old fashioned values. My word is my bond.
I believe I’m also one of the longest standing internet diamond dealers. We started selling online in 1998.
Again- if a seller does not keep his word, he’s not going to last.

I very much appreciate your scientific outlook- and of course Garry can teach us all a lot.
Although I am more of a “hands on” person, I ask that you please consider how rejecting my real life experience disadvantages the entire forum because it won’t allow open discussion.
I have been respectful of you and your experience.
I’d very much appreciate reciprocal behavior.
 

Texas Leaguer

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@Garry H (Cut Nut) ,
Thank you for your posts. I am trying to understand if your position has changed since the last discussion on the topic, or if you have additional info to support your position. I can't quite follow your logic.

Here is the crux of the matter to me and maybe you can just address this separately. We know that 365 is not the only UV wavelength capable of stimulating blue fluorescence, and we know that some wavelengths in the visible violet are also capable. And all these wavelengths have intensities in bright sunlight capable of causing fluorescence. However, the intensities of these wavelengths in artificial lighting are orders of magnitude weaker. Only within inches of a fluorescent tube is the intensity strong enough to cause visible whitening.

I know you are focussed on the Visible Violet in your argument. Is there something magical about these particular wavelengths that you think make them behave differently from the UV wavelengths such that intensity levels are sufficient to cause apparent whitening even at great distance from indoor light sources?
 

Rockdiamond

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Continued efforts at a reasonable respectful dialog go unanswered..ok.

Only within inches of a fluorescent tube is the intensity strong enough to cause visible whitening.

Bryan, you have no idea what you're talking about. Either you have not seen enough diamonds to have seen the sort of stones we are talking about- or you don't have vision ample to see it- or ...I can't figure out what.


You can ignore what I'm saying all day long, that does not make the fact that certain fl stones whiten outside direct sunlight- and not only within a few inches of a lamp. These are phenomena I've observed on many occasions. Garry is explaining the science behind it.
The facts won't go away regardless of your blind belief of what you're falsely calling "science".
To quote you- it's tiresome.
 

Texas Leaguer

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Dropoff of UV intensity with distance from the source:

fluoro instensity with distance graph.PNG

Relevant quotes:

From 1997 GIA Survey
"It is apparent that the Average Observers were not able to consistently discriminate any fluorescence-related effects in the viewing environments most similar to those in which jewelry is purchased and worn."

From 2010 Cowing Study
"The key point is that most diamonds are seen in most forms of artificial illumination at night or indoors out of daylight, and in these viewing environments the UV and visible violet are too weak to stimulate grade-whitening fluorescence. In contrast, the relatively strong UV and visible violet at typical distances of 1 to 7 in. from the fluorescent tubes of grading instruments can stimulate a good deal of fluorescence which whitens the appearance of a diamond.

In all other areas illuminated by artificial fluorescent and incandescent ceiling illumination the readings at typical 3–4 ft viewing distances from ceiling lights were an essentially UV-free, 0–1 μW/cm2. These readings are consistent with results from extensive surveys conducted by the author and others and provide support for the observation that at distances of more than 3 ft from artificial illumination, including ceiling mounted fluorescent lighting, indoor light is essentially UV free. In addition, because the light intensity is below 400 fc, usually under 100 fc and often less than 50 fc, there is no noticeable stimulation of fluorescence from the visible violet."
 

Texas Leaguer

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Hi Bryan,
Can you tell me if GIA has changed the new device to somewhere in 3


Hi Bryan,
Can you tell me if GIA has changed the new device to somewhere in 380nm to 400nm?
Perhaps there is a brand name on the tube.
From GIA 2013 article: "The 3D fluorescence spectra indicated that this N3-related emission reaches its maximum at 395 nm excitation energy and is not excited above 430 nm (figure 6) "


GIA patents have been adding in longer wavelengths - e.g. http://www.freshpatents.com/-dt20161006ptan20160290925.php?id=fpkwm
"In some embodiments, the light source is configured as a ring light surrounding the platform surface. In some embodiments, the light source comprises a plurality of light emitting LEDs. In some embodiments, the LEDs emits fluorescence at 365 nm or 385 nm.

In some embodiments, the LEDs are coupled with a bandpass filter. In some embodiments, the bandpass filter is set at 365 nm or 385 nm."
Garry, I cannot see any info on the device, but it appears to be an LED, not a tube. When I inquired with GIA about the patent back in our earlier discussion, they indicated they did not have a timeline to deploying an instrument.
 

Garry H (Cut Nut)

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@Garry H (Cut Nut) ,

I know you are focussed on the Visible Violet in your argument. Is there something magical about these particular wavelengths that you think make them behave differently from the UV wavelengths such that intensity levels are sufficient to cause apparent whitening even at great distance from indoor light sources?
Yes Bryan,
The vivible and near visible are the key issues here.
Please re read all my answers to your issues in the post above.
Then read the 2013 GIA article - it will help if you Control F and enter N3 - there will be 27 uses of the word. Start at about the 10th.
This article is written to examine various UV gem instruments and is well researched - but it shows why we see much stronger blue fluorescence in even none and faint diamonds when viewed under a cheap (405nm) UV LED. that light is visible violet and even passes through Lexan filters, let alone glass.
Quotes like this one are the game changers:
For example, the intensity of N3 luminescence (measured at 439 nm) when excited by 400 nm excitation is approximately double that of the same emission measured at 360 nm excitation (figure 6).
https://www.gia.edu/gems-gemology/summer-2013-luo-fluorescence-optical-defects
So yes, I have learned a lot since the MC debates. I have bought tools and done a lot of testing.

Unfortunately I can not swear that there is this or that face up measurable color change, but I will try to think of a way to tell.
 

Garry H (Cut Nut)

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Dropoff of UV intensity with distance from the source:

fluoro instensity with distance graph.PNG

Relevant quotes:

From 1997 GIA Survey
"It is apparent that the Average Observers were not able to consistently discriminate any fluorescence-related effects in the viewing environments most similar to those in which jewelry is purchased and worn."

From 2010 Cowing Study
"The key point is that most diamonds are seen in most forms of artificial illumination at night or indoors out of daylight, and in these viewing environments the UV and visible violet are too weak to stimulate grade-whitening fluorescence. In contrast, the relatively strong UV and visible violet at typical distances of 1 to 7 in. from the fluorescent tubes of grading instruments can stimulate a good deal of fluorescence which whitens the appearance of a diamond.

In all other areas illuminated by artificial fluorescent and incandescent ceiling illumination the readings at typical 3–4 ft viewing distances from ceiling lights were an essentially UV-free, 0–1 μW/cm2. These readings are consistent with results from extensive surveys conducted by the author and others and provide support for the observation that at distances of more than 3 ft from artificial illumination, including ceiling mounted fluorescent lighting, indoor light is essentially UV free. In addition, because the light intensity is below 400 fc, usually under 100 fc and often less than 50 fc, there is no noticeable stimulation of fluorescence from the visible violet."
Michael Cowing used the wrong UV meter that measures the shorter wave UV that has way less impact that visible and near visible UV - I showed the manufacturers graph yesterday.

The best whitening effect is from natural light.
Using an ordinary photographic light meter, which I just tested with an almost flat $2 UV LED, does detect that light, so I know that would work better than even my UVA 4.2 (improvement on Michael Cowings).
So comparing the light output from my window at my desk there is way more illumination than from the strongest LED or Fluorescent tube lights in my store.
Point is, even though the light has passed through a thick old small window pane, there is a lot of energy to excite the N3 centers in a blue flourescent diamond.

To compare the intensity of light from a window to artificial lamps use the back of a shiny spoon. You will be surprised.
 

Garry H (Cut Nut)

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Texas Leaguer

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Garry,
I have seen the reaction you are referring to by the cheap LED devices. It's one of the big causes of customer confusion around fluoro reporting on lab reports these days.

But to our issue, whether N3 centers are stimulated more by 365 or higher wavelengths, you still have the problem of intensity of the excitation source.

Speaking strictly of artificial lighting, distance from the light source is critical to any stimulation that may occur from any wavelength.

Here are two statements in the same 2013 GIA article you've referred to that underscore this point:

Observation of fluorescence can be affected by three main factors: (1) the nature of the emission from the UV light source; (2) the nature of the defect(s) responsible for the fluorescence; and (3) methodology, including the viewing geometry and the distance from the radiation source.

Finally, the distance between the radiation source and the diamond as well as the stone’s orientation (table-down versus face-up) may produce noticeably different fluorescence by changing the amount of excitation energy that interacts with the diamond.
 
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Rockdiamond

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Thank you for the data Garry- you've been at the forefront of true research in diamonds for so many years.

Before the discussion gets overly technical, for the non-scientists among us- can we agree that it's possible to observe whitening ( in certain, but not all, MB/SB diamonds) in many lighting situations bright enough to perceive small differences in body color?
 

Texas Leaguer

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Before the discussion gets overly technical, for the non-scientists among us- can we agree that it's possible to observe whitening ( in certain, but not all, MB/SB diamonds) in many lighting situations bright enough to perceive small differences in body color?
Nope.

Not in lighting conditions with insufficient intensities of the necessary wavelengths required to generate fluorescence. Which is most artificial lighting, unless the diamond is extremely close to the light source.
 
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