Fluorescence does not occur in most diamonds. In fact, about 65 percent of all diamonds exhibit no fluorescence at all, yet it is mentioned on most diamond lab certificates. So what is it exactly?
Fluorescence is the glowing color (typically blue) that appears when some diamonds are exposed to long-wave ultraviolet light. When the ultraviolet light source is removed, they stop fluorescing. This is a naturally-occurring optical phenomenon and is completely harmless, but for years it was thought that it was a negative attribute in a diamond.
In fact, fluorescence can really be a good thing in diamonds of a lower color grade (I or lower). Since daylight is a source of ultra violet light, if you look at a diamond of this quality with strong fluorescence the blue color can cancel out the yellow body-color, making it appear more colorless (white).
The myth about fluorescence being a bad thing in diamonds of higher color grades was disproven by the Gemological Institute of America (GIA) when they conducted a very extensive study of the affect of fluorescence in diamonds. They compared over 1000 stones, and the percentage of diamonds that it affected negatively was so minuscule it was nearly non-existent! It is known that high color diamonds with very strong blue fluorescence can display a cloudiness referred to as ‘overblue’ but it occurs so rarely that most jewelers will never encounter it in their entire life. The GIA study also showed that the difference between varying levels of fluorescence was indistinguishable to nearly all non-jewelry trade customers they asked, or put otherwise, for most people buying jewelry, fluorescence had no visible effect on a diamond’s color, appearance or transparency.
The diamond necklace and earrings in the pictures above might help depict how little difference there is between stones that fluoresce and those that don’t – In normal daylight (in the picture on the left) the diamonds all appear to be perfectly matched in color; it’s impossible to guess which diamonds have no fluorescence and which diamonds have medium or even very strong fluorescence. The photo on the right shows the same necklace and earrings under ultraviolet light – just look at all the different colors!