Fluorescence is the reaction of a diamond to ultra violet rays (which are found in white light). The effect can minimize transparency and possibly create an oily appearance in the diamond.

The existence of fluorescence can affect the value of higher color and higher clarity diamonds. The impact of the degree of fluorescence may be summarized in the following way:

• Absence of Fluorescence: Ideal
• Faint Fluorescence: Acceptable
• Medium Fluorescence: Tolerable
• Strong Blue Fluorescence: Undesirable

As negative the impact of fluorescence may be on some diamonds, its presence may be a positive feature in diamonds of "H" and lower color. There the whitish haze add luster to these darker stones.