Fluorescence might be the most misunderstood of the diamond characteristics.
Fluorescence is the white light or glow that a diamond emits when it is exposed to long wave UV rays. Most diamonds exhibit a blue fluorescence. Many people mistakenly think that a diamond’s fluorescence is a negative, when in reality it very, very rarely affects the appearance of the stone.The fluorescence scale has 5 grades: None, Faint, Medium, Strong, and Very Strong. There are those who believe that all diamonds with fluorescence look milky or oily, but that is just not the case. Between 25-35% of all diamonds have some sort of fluorescence, but very few of those have any affect of the stone.