Fluorescence

Some diamonds emit visible light when subjected to ultra-violet radiation.
The strength of the fluorescence is graded as None, Faint, Medium, Strong
and Very Strong. The higher degree of fluorescence the lower the quality
and the cheaper the diamonds become. We never recommend, and try not to
stock diamonds with any degree of fluorescence. Diamonds that have a
strong or very strong fluorescence can appear to be cloudy or milky in a
standard lighting and viewing environment.