UV Lamp Exposes Heat-Treated Gems

One of the easiest and quickest ways gem dealers and gemologists can determine if a stone has been heat-treated is with ultraviolet (UV) fluorescence. Now there are two affordable tools that can help make a first determination.

The compact yet powerful ENF-260Cand ENF-280C ultraviolet lamps supply both long-wave UV (365nm) and short-wave UV (254nm). The ENF-260C is equipped with two 6-watt tubes, one long-wave and one short-wave.  It has a unique LONGLIFE™ filter glass that ensures higher initial UV intensity and is extremely resistant to solarization. The ENF-280C is similar in design but features two 8-watt tubes. Both lamps have rugged aluminum housings and are available in 120V/60Hz, 230V/50Hz and 100V/50-60Hz versions.

Under magnification, the lamps’ short-wave UV will display chalky fluorescence in heat-treated rubies and sapphires. Although these chalky segments may have colors similar to the gem being tested, they will appear lifeless or dull. Since fissures in emeralds are often enhanced with oils and resins, many of these will fluoresce under the lamps’ long-wave UV light. Under the UV light and magnification, the treated segments often show entirely different colors from the rest of the gem.