Answer: Fluorescence is a phenomenon occurring in diamonds and other gemstones. The fluorescence that occurs naturally in a diamond arises from submicroscopic structures within the diamond when it is exposed to UV light. Blue is the most common color of fluorescence, but others colors are also possible.

On our GIA Gem Laboratory diamond grading reports, the strength of the fluorescence is noted as none, faint, medium, strong, or very strong. Beginning with medium, the color of the fluorescence will be noted (ex. blue, yellow, green, etc.). If fluorescence is faint, the report will not note the color. Blue is the most common color for a diamond to fluoresce.

GIA has extensively researched the subject of fluorescence and we published a detailed article describing our findings in the Winter 1997 issue of Gems & Gemology, entitled "A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds."

Back issues of Gems & Gemology can by ordered online, or by contacting our subscriptions department at (800) 421-7250, ext. 7142 or e-mail: dortiz@gia.edu.

Some jewelers believe that fluorescence is always an undesirable characteristic. However, GIA's research indicates that fluorescence is not necessarily negative, and in some cases, fluorescence actually has a positive effect by making a diamond appear whiter.

Some treatments can alter the fluorescence of a diamond. For more information on this, please follow the links on our HPHT treatment page.