The way a diamond reacts and glows under ultraviolet light.
A unique quality possessed by some diamonds to give off light when exposed to specific ultraviolet wavelengths. It is an unusual quality that can enhance the appearance of lower color diamonds(J-Z) in certain lighting conditions. However, when fluorescence is very strong the diamond may have an oily appearance that detracts from beauty and value. Only 50% of all gem-quality diamonds fluoresce, and only 10% strongly fluoresce. When gem-quality diamonds fluoresce, it is a bluish color.
When exposed to ultraviolet light, a diamond may exhibit a more white, yellow or blue tint, which may imply that the diamond has a property called Fluorescence. The untrained eye can rarely see the effects of fluorescence. Diamond grading reports state whether a diamond has fluorescent properties. Fluorescence is not considered a grading factor, only a characteristic of that particular diamond.