Article Over Grading of Blue Fluorescent Diamonds Revisited

[psadmin]

Michael Cowing from Accredited Gemologist Association (AGA) Certified Gem Laboratory has put together an article about blue fluorescent diamond over grading.

https://www.pricescope.com/journal/blue-fluorescent-diamonds-color-grading-issues

Thank you Michael.

 

[MarionC]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Excellent article. thanks.

 

[Tekate]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

That is very interesting. It would appear to me that these diamonds are higher rated than they should be.. but their color in outside light would make them appear whiter. Thanks for posting this, and if I'm wrong, please correct me.

 

[Modified Brilliant]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Thank you for a very interesting article, Michael. Well documented. On a less scientific note-- As an appraiser, I always find it interesting when I show a client that their diamond has strong fluorescence, the reaction is most always positive. If the diamond never had a lab report, the person never knew about the fluorescence, in most cases. It's too bad that the trade has attached the "fluorescence" stigma and not the consumer. In the real world, the consumer does not seem to be very concerned. At least that has been my observation during my three plus decades in the jewelry trade. Jeff Ira, G.G.

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

one technical detail:
Some white LED (rarer now) use UV light + a phosphor to output white light thus, some UV will get out just like a florescent bulb.
If the phosphor is damaged or improperly applied the levels have been found to be very high.
Most newer white LEDs now use a royal blue LED combined with a phosphor so produce very little to no UV.
Careful selection is required to insure little to no UV.

 

[michaelgem]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Karl,

Thanks for this information. I had not heard of this problem with early white LED's:

"Some white LED (rarer now) use UV light + a phosphor to output white light thus, some UV will get out just like a florescent bulb.
If the phosphor is damaged or improperly applied the levels have been found to be very high.
Most newer white LEDs now use a royal blue LED combined with a phosphor so produce very little to no UV." Karl

Experience with LED illumination for the Over Grading of Blue Fluorescent Diamonds study showed a roll off in the visible violet (VV) with the result that grading of even strong and very strong blue diamonds yielded the "true body color" within the typical one grade margin of error.
This is documented on page 48 , Figure 12. in the pdf:
http://acagemlab.com/the-overgrading-of-blue-fluorescence-the-problem-the-proof-and-the-solution/#more-112

Michael

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Thank you for a very interesting article, Michael. Well documented. On a less scientific note-- As an appraiser, I always find it interesting when I show a client that their diamond has strong fluorescence, the reaction is most always positive. If the diamond never had a lab report, the person never knew about the fluorescence, in most cases. It's too bad that the trade has attached the "fluorescence" stigma and not the consumer. In the real world, the consumer does not seem to be very concerned. At least that has been my observation during my three plus decades in the jewelry trade. Jeff Ira, G.G.

I agree Jeff, clients who are prepared to buy a Strong Blue that has been screened for milkyness are the happiest clients in my 40 years of selling diamonds.

The stigma came and major price reductions came out of Korea in the early 1990's when there was a TV expose along the scare promoted by Michael. Many thousands of blue fluoro stones were returned to retailers who replaced them with None stones over the space of a year or so. The stigma stuck after that and rapaport introduced the "price guidance" that established it 'forever'.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Experience with LED illumination for the Over Grading of Blue Fluorescent Diamonds study showed a roll off in the visible violet (VV) with the result that grading of even strong and very strong blue diamonds yielded the "true body color" within the typical one grade margin of error.
This is documented on page 48 , Figure 12. in the pdf:
http://acagemlab.com/the-overgrading-of-blue-fluorescence-the-problem-the-proof-and-the-solution/#more-112

Michael

Hi Michael, as we have discussed over a beer several times before, in my experience when people are out of daylight there is almost never enough light to see even 3 or 4 grades (say a 1ct RBC D to H) color difference in a face up set clean diamond.

A couple of other points:

Martin Rapaport commented in the April 1998 issue of the “Rapaport Diamond Report”: “Unfortunately, the probability of a lab overgrading a fluorescent stone is much greater than a non-fluorescent stone and a large percentage of high color mistakes turn out to be fluorescent.” “Obviously from the market perspective there appears to be a reasonable basis for price discrimination against fluorescence. The labs are going to have to be very serious about not overgrading the color of fluorescent stones even though these stones tend to appear whiter than they are”.
The point above is that these diamonds do face up whiter when seen in enough light.

Re Tom Tashey:
He spoke of a 0.89ct marquise brilliant with Very Strong Blue fluorescence: “In the DiamondLite [Verilux lamps, without UV filter] this stone was graded table down as a high “D”. ... When viewed table down, with the UV filter between the lamps and the diamond, the color grade of the diamond shifted to that of a low “H”.” Tashey also found that diamonds with “medium” to “strong” blue fluorescence generally shifted one to two grades when the filter was used.
A marquise cut from the very same piece of rough will show more color face down than a round brilliant cut (and a lot more face up).

Finally Michael, please compare the photo you have used of the GIA I colored example from G&G 1997. I do not have my mag copy at hand, but in the PDF download, and my recollection of the article the differences in body color are a fair bit less. If you adjusted the color in the scan process or for explanation purposes should you say so?

 

[Diamond_Hawk]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Great information. Thank you!

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Karl,

Thanks for this information. I had not heard of this problem with early white LED's:

"Some white LED (rarer now) use UV light + a phosphor to output white light thus, some UV will get out just like a florescent bulb.
If the phosphor is damaged or improperly applied the levels have been found to be very high.
Most newer white LEDs now use a royal blue LED combined with a phosphor so produce very little to no UV." Karl

Experience with LED illumination for the Over Grading of Blue Fluorescent Diamonds study showed a roll off in the visible violet (VV) with the result that grading of even strong and very strong blue diamonds yielded the "true body color" within the typical one grade margin of error.
This is documented on page 48 , Figure 12. in the pdf:
http://acagemlab.com/the-overgrading-of-blue-fluorescence-the-problem-the-proof-and-the-solution/#more-112

Michael

neat.
Another problem with led lights is the color temperature can vary a lot depending on how they are driven and this can effect perceived color and could produce more VV light.
They are are also a very direct light source that could lead to issues with reflections.
I have found that some led illuminated loops actually make it harder to see into a diamond because of surface reflections and could affect color grading also.
While I think we can agree that carefully selected and driven led lighting would be a step in the right direction it is not perfect. Someone could think hey I will buy a $3 led lamp from china, save several hundred bucks and think they are good to go. That might not be the case.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Impressive work Michael. I have cited your original study many times over the years and have been surprised at how little awareness there is about this particular issue and the science behind the whitening effect in general.

One of the key takeaways from me, in addition to concern about color grading accuracy of fluoro diamonds, is the fact that your readings and measurements rather conclusively demonstrate that the color whitening effect is not present in the vast majority of real world lighting conditions.

While many people in the trade believe that they see this effect and so tout it as a benefit, I have not seen anyone dispute your scientific findings. This raises the question - if UV is too weak in virtually all indoor settings to activate fluorescence and thereby cause a whitening effect, then what do you think is behind the notion that this trait is somehow beneficial to a diamond's appearance in the real world?

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

then what do you think is behind the notion that this trait is somehow beneficial to a diamond's appearance in the real world?

It strong or higher looks really neat when it is seen under sunlight and other uv sources.
I like it a lot for that reason.
I dropped the "it makes it look whiter" a while back because it is so lighting dependent.

 

[ADN]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

While many people in the trade believe that they see this effect and so tout it as a benefit, I have not seen anyone dispute your scientific findings. This raises the question - if UV is too weak in virtually all indoor settings to activate fluorescence and thereby cause a whitening effect, then what do you think is behind the notion that this trait is somehow beneficial to a diamond's appearance in the real world?

Great question...I've been wondering this myself. Perhaps it's got as much to do with all the 'information' that can be found online from all the 'experts' (qualified or not) that put whatever they believe to be true out there without anything to substantiate it -- if it's said/read/repeated enough times it has to be true...right?...
At the end of the day, it's like Abraham Lincoln once said..."You can't believe everything you read on the internet"

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

A friends of mine wife has a diamond that is rated gia none but in sunlight shows signs of having strong florescence yet under a gia approved light source it indeed has none.
Her husband took it to work where they have a bunch of UV leak detectors to use with dye in cooling systems and indeed under a couple of them it glowed bright blue.
The gia test does not catch all cases of florescence.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

While many people in the trade believe that they see this effect and so tout it as a benefit, I have not seen anyone dispute your scientific findings. This raises the question - if UV is too weak in virtually all indoor settings to activate fluorescence and thereby cause a whitening effect, then what do you think is behind the notion that this trait is somehow beneficial to a diamond's appearance in the real world?

Great question...I've been wondering this myself. Perhaps it's got as much to do with all the 'information' that can be found online from all the 'experts' (qualified or not) that put whatever they believe to be true out there without anything to substantiate it -- if it's said/read/repeated enough times it has to be true...right?...
At the end of the day, it's like Abraham Lincoln once said..."You can't believe everything you read on the internet"

ADN,
Actually I think it was Al Gore who said that.

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Michael,
Do you know of any study that actually measured the UV light levels and wave lengths in common indoor lighting conditions both office and home?

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

A friends of mine wife has a diamond that is rated gia none but in sunlight shows signs of having strong florescence yet under a gia approved light source it indeed has none.
Her husband took it to work where they have a bunch of UV leak detectors to use with dye in cooling systems and indeed under a couple of them it glowed bright blue.
The gia test does not catch all cases of florescence.

I have mentioned this in several threads on the topic Karl - the problem is that we (in gemology) use ancient technology based on the only 2 easily available UV frequency's. This is wrong - I have cited an excellent more recent G&G article that shows that fluorescence is very invisible UV spectrum variable that makes this very obvious.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

then what do you think is behind the notion that this trait is somehow beneficial to a diamond's appearance in the real world?

It strong or higher looks really neat when it is seen under sunlight and other uv sources.
I like it a lot for that reason.
I dropped the "it makes it look whiter" a while back because it is so lighting dependent.

An example - after showing a lady a fluoro demo she said check this 3 stone ring. It was an heirloom and had different shaped old cuts in it that were identifiable. One side stone was about strong blue, the others inert to the UV light source; she said aha! That is the one that I love. Turns out she was attracted to it without knowing why. The 3 stones were all high color.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Michael,
Do you know of any study that actually measured the UV light levels and wave lengths in common indoor lighting conditions both office and home?

Complex because you would need to measure at average diamond viewing heights and across a whole range of invisible and VV spectrums.
Edited to add the G&G article
Search for "Fluorescence Produced by Common Optical Defects in Diamond" and it is in the Summer 2013 edition of G&G.
The PDF is not sharp enough to show the peaks and troughs in the 3D chart on page 85 fig. 3. But you will get the 'picture'.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

A friends of mine wife has a diamond that is rated gia none but in sunlight shows signs of having strong florescence yet under a gia approved light source it indeed has none.
Her husband took it to work where they have a bunch of UV leak detectors to use with dye in cooling systems and indeed under a couple of them it glowed bright blue.
The gia test does not catch all cases of florescence.

I have mentioned this in several threads on the topic Karl - the problem is that we (in gemology) use ancient technology based on the only 2 easily available UV frequency's. This is wrong - I have cited an excellent more recent G&G article that shows that fluorescence is very invisible UV spectrum variable that makes this very obvious.

Garry,
I can't make out what you are saying in that last sentence. Can you link the G&G article?

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

A friends of mine wife has a diamond that is rated gia none but in sunlight shows signs of having strong florescence yet under a gia approved light source it indeed has none.
Her husband took it to work where they have a bunch of UV leak detectors to use with dye in cooling systems and indeed under a couple of them it glowed bright blue.
The gia test does not catch all cases of florescence.

I have mentioned this in several threads on the topic Karl - the problem is that we (in gemology) use ancient technology based on the only 2 easily available UV frequency's. This is wrong - I have cited an excellent more recent G&G article that shows that fluorescence is very invisible UV spectrum variable that makes this very obvious.

Garry,
I can't make out what you are saying in that last sentence. Can you link the G&G article?

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.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Michael,
Do you know of any study that actually measured the UV light levels and wave lengths in common indoor lighting conditions both office and home?

Complex because you would need to measure at average diamond viewing heights and across a whole range of invisible and VV spectrums.

The 2010 study does provide measurements from different light sources at varying distances. One of the main insights is how grading can be made more accurate simply by increasing the distance between the diamond and the light source during observation, even with a UV component present in the source.

But a more complete solution involves filtering out the UV and using a diffuser.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Google image search
Fluorescence Produced by Common Optical Defects in Diamond figure 3 gem & Gemology
and you will find slightly higher resolution graphics.
focus on the one with N3 mentioned - thats what causes fluoro in 99% of the diamonds we are discussing.

Visible light is from just below 400nm to just above 700nm, UV to Infra red respectively.
From those charts one can see that there is excitation occurring from the exact same blue frequency of the blue emission (as well as some other in the visible spectrum).

That means that blue light with a frequency of 415nm cause blue excitation and makes a diamond look whiter whenever there is blue in the light spectrum.
There are many different light types - some like halogens and tungsten dont make much blue light, but lots of others do.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Google image search
Fluorescence Produced by Common Optical Defects in Diamond figure 3 gem & Gemology
and you will find slightly higher resolution graphics.
focus on the one with N3 mentioned - thats what causes fluoro in 99% of the diamonds we are discussing.

Visible light is from just below 400nm to just above 700nm, UV to Infra red respectively.
From those charts one can see that there is excitation occurring from the exact same blue frequency of the blue emission (as well as some other in the visible spectrum).

That means that blue light with a frequency of 415nm cause blue excitation and makes a diamond look whiter whenever there is blue in the light spectrum.
There are many different light types - some like halogens and tungsten dont make much blue light, but lots of others do.

I will look it up. I'm sure I have read that article before.

One key issue as I understand it is that the mere presence of the wavelengths capable of exciting fluorescence is not adequate. They must be present in sufficient intensity. And intensity drops off very quickly with distance from indoor light sources, as demonstrated in detail in the 2010 study.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Google image search
Fluorescence Produced by Common Optical Defects in Diamond figure 3 gem & Gemology
and you will find slightly higher resolution graphics.
focus on the one with N3 mentioned - thats what causes fluoro in 99% of the diamonds we are discussing.

Visible light is from just below 400nm to just above 700nm, UV to Infra red respectively.
From those charts one can see that there is excitation occurring from the exact same blue frequency of the blue emission (as well as some other in the visible spectrum).

That means that blue light with a frequency of 415nm cause blue excitation and makes a diamond look whiter whenever there is blue in the light spectrum.
There are many different light types - some like halogens and tungsten dont make much blue light, but lots of others do.

I will look it up. I'm sure I have read that article before.

One key issue as I understand it is that the mere presence of the wavelengths capable of exciting fluorescence is not adequate. They must be present in sufficient intensity. And intensity drops off very quickly with distance from indoor light sources, as demonstrated in detail in the 2010 study.

Thanks Bryan - please see the connection - inorder to see color differences or yellowishness, you need good light. You cannot tell the difference between a D and a L in a dimmly lit restaurant.
If you have enough light to pick a 1ct H from a D face up in a ring etc then your going to have some radiation that will excite at least a small blue fluoro effect.
The better and more light, the better your color acuity AND the better the blue fluoro assistance to washing away the yellow tint.

I have been telling Michael this for years. In person he has never disagreed with me.
I am open to proof that I am wrong, but everything I have read and heard so far has not come close.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Look at this chart - I chopped off an experimental error - You can see there is excitation taking effect right down to very slightly greenish blue.

 

[Garry H (Cut Nut)]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Take a room with artificial light and a window with venetian blinds half closed and you can see that the light from window is way way brighter than the artificial light. The tool I used is a shiny icecream scoop.

 

[Karl_K]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Garry,
Modern low-e windows block up to 75% of UV and film coatings can block up to 99.9%.
Min code in many areas of the US require low-e glass as the min. in new construction or replacement windows.
Newer windows use a film between the 2 panes in the window to achieve 95%+ they are thinner than the films that go on the outside so not as effective.
The future is films between the glass as they are now cheaper than older low-e coatings so UV blocking will be higher in the future.
There may not be as much uv in that light as you think unless they are older windows.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Look at this chart - I chopped off an experimental error - You can see there is excitation taking effect right down to very slightly greenish blue.

The 3D graph by Thomas Hainschwang on page 42 of the Cowing study illustrates the same concept, BUT with the added element of "intensity". Those results support the conclusion (same page) "At normal viewing distances from artificial illumination the violet light intensity, just like the UV, is too weak to excite noticeable fluorescence".

I could not manage to copy the chart seperately. Perhaps Michael can post it here.

 

[Texas Leaguer]

Re: Article: Over Grading of Blue Fluorescent Diamonds Revis

Google image search
Fluorescence Produced by Common Optical Defects in Diamond figure 3 gem & Gemology
and you will find slightly higher resolution graphics.
focus on the one with N3 mentioned - thats what causes fluoro in 99% of the diamonds we are discussing.

Visible light is from just below 400nm to just above 700nm, UV to Infra red respectively.
From those charts one can see that there is excitation occurring from the exact same blue frequency of the blue emission (as well as some other in the visible spectrum).

That means that blue light with a frequency of 415nm cause blue excitation and makes a diamond look whiter whenever there is blue in the light spectrum.
There are many different light types - some like halogens and tungsten dont make much blue light, but lots of others do.

I will look it up. I'm sure I have read that article before.

One key issue as I understand it is that the mere presence of the wavelengths capable of exciting fluorescence is not adequate. They must be present in sufficient intensity. And intensity drops off very quickly with distance from indoor light sources, as demonstrated in detail in the 2010 study.

Thanks Bryan - please see the connection - inorder to see color differences or yellowishness, you need good light. You cannot tell the difference between a D and a L in a dimmly lit restaurant.
If you have enough light to pick a 1ct H from a D face up in a ring etc then your going to have some radiation that will excite at least a small blue fluoro effect.
The better and more light, the better your color acuity AND the better the blue fluoro assistance to washing away the yellow tint.

I have been telling Michael this for years. In person he has never disagreed with me.
I am open to proof that I am wrong, but everything I have read and heard so far has not come close.

While the bolded part seems intuitive, it does not seem to be born out by the science. It appears there is a level of intensity of the UV and VV wavelengths that must be achieved before significant excitation takes place. Therefore, you can have plenty of light to see by yet have no fluoresecence-driven whitening taking place.