In some triplets the cement layer fluoresces brightly providing rapid identification. Many composite stones can be fairly easily identified as such in this manner. White synthetic spinels glow bluish-white, useful for rapidly picking them out in set jewellery. Natural amber glows patchily while ambroid may show swirls. Most synthetic rubies and emeralds fluoresce brighter red than most natural ones.
Synthetic rubies phosphoresce for ten seconds or so while the natural rubies are inert or nearly so.
Colourless, yellow and orange synthetic sapphire may fluoresce red due to chromium. Fresh water Biwa pearls glow bright yellow. Synthetic emeralds may phosphoresce a dull red while naturals are inert. Gilson synthetic emeralds glow bright red. Cultured pearls show a yellowish fluorescence, natural salt-water pearls are usually inert.