Fluorescence in diamond is the reaction to an ultra violet light source. GIA includes this information as an identifying characteristic, however it can sometimes affect the look of the diamond in daylight. Most diamonds that have fluorescence have blue fluorescence. This means that in a “black light” commonly found in night clubs and haunted houses, the diamond will glow blue to varying degrees. The grading scale that GIA uses is as follows;
A diamond’s fluorescence can affect the apparent color grade of the diamond. Sunlight has a small concentration of UV light and will cause the diamond to fluoresce to a small degree in daylight. A medium to strong blue fluorescence can counteract the yellow color in a near colorless diamond and make the diamond look colorless.
Conversely a colorless diamond with a blue fluorescence can make a diamond appear waxy or milky in sunlight. It is best to judge how a diamond looks in daylight before you make a final decision on whether to purchase the stone.
Example of blue fluorescence in diamond
Example of yellow fluorescence in diamond