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.
Some of the new hydrothermal and flux-melt products however act very much like natural stones under all stimulation. It is necessary to review the literature to find references to new developments. The Verneuil Process, pp. All rights reserved internationally.