HI Guys!
I'd love to incorporate your questions into a tutorial on this subject.

Anyone who has questions about flouresence, please post them.
I'll  answer and add the exchange to my initial post- I will remove the questions after you post them so we can garner them all together in one "super-post" All the questions and answers together, as opposed to a multi page thread.

how does that sound?

Can a diamond have more than one flour....can they react differently in different light sources? Do colored diamonds occur more often with or without flour? Do setters ever take flour into account when creating new pieces?

I think I got a good start on numbers one and two.....
If anybody has a good fluorescence photo, I'd love to see it and possibly incorporate it into the tutorial.

WOW! That  is so cool!

I was wondering if there are any rules with fluor and treated colored diamonds.  Do they fluoresce in a particular color with a certain treatment?

Cool picture Rhonda!

Hi All! IN considering this question, it occurred to me that a discussion of the effects of Fluorescence  Fancy Colored diamonds was complicated and different enough to separate the two discussions.
Seems like most of the questions were about Fancy Colors anyway, so let's go!
Here's what I've got so far, I'll start to answer more of the questions in the next few days!

THANK YOU to all who are posting questions-I really appreciate the input!

What are the implications of Fluorescence on gem quality Fancy Colored Diamonds?
This discussion will include light yellows from S-T through Vivid Yellow, Browns, Pinks, and any other Natural Colored Diamond


Is fluorescence bad?
Here's why: Grading is more complex than a simple Yes or No answer.  Grading involves assessing desirability, or judging diamonds.
Fluorescence is an aspect which works in concert with other physical characteristics with some unusual results.

An important note: IN a small percentage of fluorescent diamonds, the characteristic is so very strong as to make the diamond dull and lifeless. There's no mistaking this problem- anyone looking at the diamond would notice. This is extremely rare. Stones that suffer this effect trade for pennies on the dollar compared to a nice looking diamond that has Strong Fluorescence. We will exclude any diamond in this category from the following comments regarding Visual and Value

In Natural Fancy Colored Diamonds there are different shades of fluorescence. As in colorless diamonds.
GIA's Fluorescence Grades:
Faint: This has never proven to be an issue in any way- either from a visual, or a price standpoint.
Medium Blue ( or Yellow, Green or White)
Strong Blue, Yellow, Green or White

How does Medium, or Strong  florescence affect a diamond visually?
Any conversation considering all the different Natural Fancy Colors- as well as shades of those colors- will need to focus on many shades separately. For example, the effects of Fluorescence in Brown, as compared to Yellow diamonds are completely different.that occur in diamonds there's just so many answers to this one.

Let's start with Yellow Diamonds:

How does florescence affect a Light Yellow diamond shades S-T up through Y-Z?
I don;t recall seeing a light yellow with anything but Blue Fluorescence which is what we'll focus on.
Visual:
IN general- florescence will make a diamond look more yellow than it's actual body color indoors, but lighter outdoors- or in other bright lighting situations.
In lighter Yellows Strong florescence will cause the greatest Chameleon like affect. The diamond may look pretty darn yellow sometimes and almost "Blue White" at other times.
Is this desirable? Why not? A lot of folks actually look for this type of stone. Only in rare cases will this mean the diamond looks "dull".
Value:
Light yellow diamonds in these shades  are among the least costly of all the colors- so there's virtually no effect on the price for Medium or Strong Fluorescence


How does florescence affect a Yellow diamond shades Fancy Light Yellow up through Fancy Vivid Yellow?
Visual:
Here again, the medium and strong blue stones may actually look darker than the body color. GIA seems to take this into account- many "Fancy Yellow" graded diamonds, with strong florescence look quite like a "Fancy Intense Yellow" in normal room lighting. High content UV light- such as sunlight may lighten such stones a little- but generally these shades have enough yellow "oomph" to still have a Yellow appearance. In limited cases, the effect of  Strong Blue may be noticeable on sunlight.

Value: Here we start to have to consider the effect of GIA's issuance of Medium or Strong Blue on the price of the higher priced grades. In the shades of Fancy Light Yellow, Fancy Yellow, and Fancy Intense Yellow, the presence of Medium Blue may cause a 10-20% decrease in price, while strong blue may chop 25%-33% off the price.
Vivid Yellows are so rare- it's virtually impossible to chart a price curve.
I've also bought diamonds in these yellow shades where the Fluorescence was very hard to notice- even Medium or Strong- and other factors made the diamond worth as much or more than an "inert" diamond.

Brown and Pink Diamonds:
Coming soon.....



Click here for the Thread on florescence in white diamonds.

LOVE this kind of stuff!!

I got a little stone from a pawn shop and it turned grey blue in the sunlight...was that flourecense???  By the way Ms. Fancy Pants has Medium Blue Flouresence...she looks pretty darn yellow. 

I've just had fun playing with my black light key chain, which arrived today. (Thank you David!)

My ering has quite strong fluorescence and so does my oval. The strongest I've seen is one of the stones in my eternity band - looks amazing! I'll try to get some pics at the weekend.

Quick question - do sapphires ever fluoresce? My earrings don't do anything under the blacklight, but the sapphire in my ring looks quite different. Am I imagining this, or can gemstones have fluorescence?

Jen

Thanks David, it was really interesting to see what it did under the black light. I'll try to get a photo at the weekend, because it was quite unexpected.

Plus, I have an exam on Monday, so more than happy to engage in that level of study avoidance.

Jen