The capacity of diamonds, colored gemstones, and pearls to emit visible light when exposed to higher energy wavelengths. In diamonds and colored gemstones, this occurs when their atoms react to long- and short-wave ultraviolet rays. In pearls, this occurs when some of their elements react to x-rays. Fluorescence is measured for identification purposes and described on a scale from inert (none) to very strong. Its presence can also help to confirm a pearl’s cultured origin.