Blue Fluorescent Diamonds

Final Filtration and LEDS: A Four-Prong Solutionto Overgrading Blue Fluorescent Diamonds
http://www.colored-stone.com/stories/mar09/fluorescent-diamonds.cfm

Here are the conclusions Michael Cowing reached on ending the chronic problem of overgrading blue fluorescent diamonds. His study demonstrates that the 'true body color' of a diamond can be easily and accurately graded against master diamonds at normal wearing distance from daylight fluorescent overhead illumination (3 to 4 feet distant) where neither the UV nor 'visible violet' is strong enough to influence the color grade. He offers a four-prong inexpensive combination of solutions involving present and future grading illuminations:
1. The desired grade for a blue fluorescent diamond should be reaffirmed as its 'true body color' defined historically in the diamond trade as that color seen in typical artificial lighting where fluorescence is not stimulated. This color is correctly seen at typical viewing distances from fluorescent and incandescent ceiling lighting—usually covered with some kind of plastic diffuser.
2. Since lab grading is done from about 2 to 10 inches from fluorescent tubes (rather than 3 to 4 feet away where UV has significantly decreased), Cowing recommends the use of a polycarbonate plastic like Lexan as an effective and inexpensive filter to remove UV from 400nm down—without affecting perception of the visible spectrum.
3. To solve the fluorescence whitening caused by 'visible violet' Cowing recommends use of flat-white plastic diffusers which attenuate violet and all visible wavelengths equally, so that fluorescence is not stimulated nor is the diamond’s color altered. Such white diffusers have the added bonus of reducing spectral reflections and glare.
4. In concert with the movement to the 'green' technology of LED lighting, use of white LED lighting such as the investigation’s Dazor LED desk lamp, not only provides inherently, UV-free grading light, but is dimmable without change in color temperature down to 2000-4000lux, so as not to stimulate fluorescence from the visible-violet.
- Michael D. Cowing

An interesting viewpoint on blue fluorescent diamonds. It makes sense.