Fluorescence

[Diermint]

Fluorescence is the property in many diamonds that makes them glow in an environment rich in ultraviolet light. Diamonds can fluoresce in a number of colors, but generally all but blue are to be avoided. Faint to medium fluorescence is rarely detected under ordinary lighting conditions. Strong or very strong fluorescence may make a diamond appear “milky” or “oily”, especially in sunlight however this is reportedly rare. Blue fluorescence may enhance the color of diamonds rated “H” in color or below (I,J, etc.) by hiding their yellow tint. Diamonds rated D-F with medium+ fluorescence may sell at a discount.
Picture originally posted by mdx.

 

[Diermint]

Another Fluorescence picture (originally posted by mdx):

 

[Diermint]

Another picture of fluorescence showing some diamonds fluorescing and some not:
Picture originally posted by Richard Sherwood.

 

[kevinraja]

Blue fluorescence may enhance the color of diamonds rated “H” in color or below (I,J, etc.) by hiding their yellow tint. Diamonds rated D-F with medium+ fluorescence may sell at a discount.

Why is it that diamonds with D-F with medium Flourescence+ may sell at discount. I have read that strong or very strong flour makes the stone cloudy, but what are your comments on a F color stone with med blue flourescence?

 

[jenwill]

Here is a post from another thread. I have sopied it here with permission of Joyver, who was the original poster of this information:

the question was:

Why does fluorescence make a stone face up whiter?

and the answer:

I can give you an answer, but I'm afraid it's a bit technical. The short version is that in light rays Yellow and Blue are inverse colors and when they are combined your eye sees them as white. For those of you that want the long answer, here goes.


(In case you're wondering where I'm getting this form, I have an IT background with some high level work in multimedia)
Your eye sees 3 main colors, Red Green and Blue (not red, yellow and blue), all others are some combination of them. Rays of light (like those that pass through a diamond) are direct light. Colours which you see in paints and dyes are reflected light, not direct light. So when you combine colors you'll get different results with reflected light and direct light. This is why everyone thinks that blue and yellow makes green. That is true for paints (reflected), but not for rays (direct). For rays, the absence of color is black, and the combination of all colors is white. So if you want to turn yellow rays (like the ones passing through a diamond) white, you have to add the missing colours. On the image of the color wheel attached, a color in direct light is formed by combining adjacent ray colors. For example Cyan is equal parts green and blue, magenta is equal parts blue and red, and if you find yellow, you'll see that it's equal parts red and green. So a yellow diamond produces rays of equal parts red and green. The only color in the combination your eyes see that is missing is blue. So if we add equal part blue to the yellow (red and green combined) we get red, green and blue which forms every color combination for your eye, producing white rays! See color wheel below.....


Hope that helps!

 

[jenwill]

in reference to above