HPHT-treated type I diamonds of various colors may exhibit unusually intense fluorescence at the facet edges and junctions. This effect, here named the “fluorescence cage,” is observed with a fluorescence microscope as a luminous network on the diamond’s surface. It was not observed in untreated diamonds or colorless type IIa HPHT-treated diamonds. This fluorescence pattern is believed to result from a high concentration of HPHT-induced optical centers, which remain on facet edges after repolishing.
