Blue Fluorescence: Good or Bad?
GIA researches challenge conventional wisdom
Conventional wisdom says fluorescence can be detrimental to diamonds
in two fundamental ways: perception of color and perception of clarity.
In fact, prices for diamonds with fluorescence may dip 15% below those without.
contrast this with the belief of decades ago that blue fluorescence could
be beneficial by making slightly yellowish diamonds appear more colorless.
Now researchers at the Gemological Institute of America think this old theory
may not be so far off the mark. A new study supports the belief that "strong
or even very strong fluorescence can improve the appearance, rather than
detract form it, especially in diamonds with faint yellow body color,"
says the Winter 1997 issue of GIA's Gems & Gemology.
Jewelers who obtain a grading report identifying moderate blue fluorescence
need no longer feel the diamond is inferior.
Blue fluorescence can improve some diamonds, says GIA.
Fluorescence: A Primer
Fluorescence is an emission of light that occurs when a diamond is stimulated
by ultraviolet, long-wave radiation. Most diamonds don't exhibit fluorescence.
Of those that do, it's usually blue, though it can be yellow, orange or
pink, depending on trace elements in the gem.
The GIA study focused on 1,000 diamonds, about a third of which have
varying degrees of blue fluorescence. They were examined under varying lighting
conditions and in different viewing positions. "We saw no relationship
between strength of fluorescence and color appearance with diamonds viewed
table-down," says GIA. "But again wee saw a trend towards better
color appearance with stronger fluorescence when the diamonds were viewed
table-up, regardless of light source."
Few observers reported seeing any change in the transparency or clarity
of the diamonds with fluorescence. Extremely strong blue fluorescence (know
as "overblues") have been linked to hazy transparency. While the
GIA study doesn't focus on overblues, it does suggest that fluorescence
is not a factor in diamonds' clarity when its intensity is "none"
to "very strong".
Gems & Gemology,Carlsbad, CA; (800) 421-7250.
by Robert Weldon, G.G. Copyright © 1998 by Bond Communications.