What is Fluorescence?
Fluorescence is the colored glow that only a small percentage of diamonds in the world emit when exposed to ultraviolet light. The Gemological Institute of America (GIA) grades diamonds on a scale of "None" to "Very Strong." This grading has to do with how intense the glow is under a UV light, so a diamond with no fluorescence will not glow at all whereas a diamond with very strong fluorescence will glow a lot. Unlike the Four Cs, the main criteria on which diamonds are graded, fluorescence is a supplemental characteristic of diamonds.