A diamond will glow under a black light because it is reacting to the UV lighting, proving the presence of
fluorescence in the stone. Depending on the strength of the fluorescence, a diamond will glow with a faint to a
very strong intensity. Having fluorescence does not hinder the durability of the stone however it can sometimes
cause a diamond to appear blue or milky. Of course you are not under a black light often, if at all, however you
do go out in sunlight which will also cause the diamond to have a similar blue hue. When you see fluorescence on
your diamond report it is always something to inquire about with a gemologist. You always want to know all the
side effects whether positive or negative.