Diamond fluoresces in all colours, the fluorescence may be analyzed with a spectroscope in some cases for identification. When cooled with dry ice or liquid nitrogen some diamonds show fluorescence lines at 415.0 nm and 504.0 nm. Irradiated diamonds may show a line at 594.0 nm which is diagnostic. Diamonds that fluoresce bright blue show a yellow phosphorescence when held in cupped hands after the light is turned off - the only blue fluorescing gemstone to do so. Photographs of the pattern and colour of fluorescing diamond set jewellery may serve to identify it for insurance or other purposes.
Many stones show similar reactions as to long wave.
Synthetic blue sapphires show a greenish or white-blue glow, synthetic white stones a deep blue glow, naturals in both cases are usually inert. Some yellow sapphires fluoresce green at the surface. If suitable precautions are taken synthetics examined with a lens while fluorescing will often show curved structure lines. Benitoite which resembles sapphire fluoresces bright blue while natural sapphires are inert. Synthetic rubies and emeralds both often glow brighter red than their natural counterparts.