Negative Impacts of Fluorescence - a yes/no proposition?

[Texas Leaguer]

There is currently some interesting discussion on the forum about fluorescence including a poll on price penalties/premiums, and another cool thread on phosphorescence. Having spent my early childhood in California I first became aware of phosphorescence by going out on a ‘grunion run’. Seeing your footprints glow on a dark beach is a really formative experience for a five year old!

With regard to diamonds, fluorescence is a cool property on one hand, and a valuable identifying characteristic, but also an important valuation characteristic. Although there have been cycles of interest in highly fluorescent diamonds through the years and temporary exceptions to the rule, the diamond market in general does not favor fluorescent diamonds from a valuation standpoint.

Clearly the big concern about strong fluorescence is based upon possible negative visual impacts. Conventional wisdom holds that “over blues” with obvious oily/hazy appearance are rare. But is the deleterious effect that causes an over blue a yes/no proposition or is it more likely a continuum like other diamond attributes? That is, a strongly fluorescent diamond might have no haziness, slight, moderate, or pronounced haziness (over blue).

What are your thoughts?

 

[yssie]

What exactly causes the "overblue" effect?

I spent several years working with all sorts of fluorescent markers and can't think of any good reason to consider fluorescence the sole, straightforward cause of haziness/oiliness in a diamond. I asked this question on here three years ago and Garry pointed to presence of other inclusions as a factor:
[URL='https://www.pricescope.com/community/threads/what-causes-haziness-in-some-stones-w-fluor.156221/']https://www.pricescope.com/community/threads/what-causes-haziness-in-some-stones-w-fluor.156221/[/URL]

This is the GIA paper quote: Tradespeople further observed that some gem diamonds with a hazy appearance also fluoresced strong blue to UV radiation. (Paper here)

The paper is careful not to assign causation - or even definitive correlation - to strong blue fluor and the haziness/oiliness often associated as a potential problem with stones w/ strong fluor.

So - if there is a causal relationship here as is commonly suggested here on PS and in conversations with jewellers, if strong blue fluor is responsible for the haziness/oiliness, can one of our tradespeople or experts help me understand why?
[...]

Or is it just a happenstance characteristic of a diamond that has certain other properties?
[...]

Thanks so much for pointing me to that thread Garry.

I'm understanding from that thread and the others linked that fluor is not thought to cause haziness/oiliness - these stones are already "milky", and some happen to also have fluor. Which answers my questions - and more questions, like insight into how the association began..

Fluoro is one of some causes, but not all fluoro stones are milky / cloudy.

e.g. One reason I caution people against low clarity eye clean stones is they are often cloudy and suffer a big hit on brilliance.

I will be watching this thread closely, as I'd love a more in-depth answer to that question!

 

[Mikla]

I think a lot depends on the individual person. I can tell a diamond that has anything over faint fluorescence without a black light. To me it appears hazy and cloudy (not oily) on the surface regardless of clarity. The effect bothers me so I personally avoid diamonds with fluorescence. However, I have seen many posts of flourescent diamonds where the poster absolutely loves the effect. So, I would say it's in the eye of the beholder, and not a hard and fast rule.

 

[Texas Leaguer]

What exactly causes the "overblue" effect?

According to the GIA study that is referenced most often, "luminescence centers" in diamonds are caused by defects in the crystal lattice. Since a diamond can have any number of different defects, the combinations possible are varied, as are the visual effects that result.
Nitrogen impurities are the most common, but things such as graining are also associated with fluorescence. Presumably the presence of these kinds of defects could potentially combine with the visual effects of fluorescence to the point where it become obvious (over blue).

I wonder if polarization has anything to do with it? Some of the strongly fluorescent stones I have seen have a vague haziness that is very subtle, almost like the light is being slightly diffused within the stone. Since the emitted light is going in all directions, it might somehow "compete" with the light that otherwise reflects and refracts directionally, thereby slightly diminishing the crispness of the light return.

That last part is both a question and speculation on my part- something for the physicists here. And I know there are some!

 

[yssie]

What exactly causes the "overblue" effect?

According to the GIA study that is referenced most often, "luminescence centers" in diamonds are caused by defects in the crystal lattice. Since a diamond can have any number of different defects, the combinations possible are varied, as are the visual effects that result.
Nitrogen impurities are the most common, but things such as graining are also associated with fluorescence. Presumably the presence of these kinds of defects could potentially combine with the visual effects of fluorescence to the point where it become obvious (over blue).

I wonder if polarization has anything to do with it? Some of the strongly fluorescent stones I have seen have a vague haziness that is very subtle, almost like the light is being slightly diffused within the stone. Since the emitted light is going in all directions, it might somehow "compete" with the light that otherwise reflects and refracts directionally, thereby slightly diminishing the crispness of the light return.

That last part is both a question and speculation on my part- something for the physicists here. And I know there are some!

I can definitely understand that clouds, wisps, and graining can create haziness that perhaps some fluorescence highlights, but I think in that case they're exacerbating factors rather than causes. That last is an interesting proposition - I do hope someone with more knowledge will elaborate!

 

[CharmyPoo]

I am very interested in the answer but don't have one to contribute. I recently purchased a 1 ct over blue.

 

[Texas Leaguer]

What exactly causes the "overblue" effect?

According to the GIA study that is referenced most often, "luminescence centers" in diamonds are caused by defects in the crystal lattice. Since a diamond can have any number of different defects, the combinations possible are varied, as are the visual effects that result.
Nitrogen impurities are the most common, but things such as graining are also associated with fluorescence. Presumably the presence of these kinds of defects could potentially combine with the visual effects of fluorescence to the point where it become obvious (over blue).

I wonder if polarization has anything to do with it? Some of the strongly fluorescent stones I have seen have a vague haziness that is very subtle, almost like the light is being slightly diffused within the stone. Since the emitted light is going in all directions, it might somehow "compete" with the light that otherwise reflects and refracts directionally, thereby slightly diminishing the crispness of the light return.

That last part is both a question and speculation on my part- something for the physicists here. And I know there are some!

I can definitely understand that clouds, wisps, and graining can create haziness that perhaps some fluorescence highlights, but I think in that case they're exacerbating factors rather than causes. That last is an interesting proposition - I do hope someone with more knowledge will elaborate!

I have been in touch with the GIA library to see if there is a ready answer to this question somewhere in the archives, and there does not appear to be one. I have been told that my theory on polarization is not a likely cause.

I find it curious that there is not some definitive understanding of this particular issue since so much is known about fluorescence in general and there has been so much discussion and concern about “over-blues” historically in the business.

It does seem logical that the cause is some sort of combination of attributes. One possible culprit is graining, particularly the white or reflective variety. It is known to cause milkiness, yet it is necessary to examine the stone at magnifications greater than 10x power in order to assess it. It may be present to an extent not apparent until it gets illuminated by fluorescence.

Here is an article from G&G Winter 2006 that deals with this type of graining.
http://www.gia.edu/Winter-2006-A1-Internal-Whitish-Reflective-Graining-King (you have to hit the pdf button to see the artilce)