Fluorescence and Diamonds: A Love-Hate Relationship

What Is Fluorescence?

In short, fluorescence is the emission of visible light when a diamond is exposed to X-rays or ultraviolet (UV) radiation.  Roughly one third of all diamonds fluoresce to some degree.  Under the GIA grading system, diamonds are viewed in a special UV light box under long-wave UV light to assess the color and intensity of a diamond's fluorescence.  Then, one of five grades is assigned to the diamond:

  • None
  • Faint
  • Medium
  • Strong
  • Very Strong

Just like the GIA color grades, fluorescence grades encompass a range of intensities.  To prove this point, many people can notice very faint fluorescence in diamonds with a GIA grade of "None."  Besides assigning a grade commensurate with the intensity of the diamond's fluorescence, diamond graders also note the color that the diamond fluoresces.  The overwhelming majority of diamonds that fluoresce (97% in one GIA study) emit blue fluorescence.  Rarely one can find a diamond with yellow, white, or orange fluorescence.

The Effect of Fluorescence

Fluorescence is a difficult concept for many jewelry professionals to understand and explain to their clients.  Thus, the diamond industry has tended towards discounting diamonds with fluorescence grades above Medium.  Diamonds with higher fluorescence grades are more difficult to resell than those with a lower grade.  D, E, and F-color diamonds with no fluorescence command premium prices in the diamond market.  It is said that fluorescence can cause colorless diamonds to look hazy or milky in daylight, as ultraviolet radiation is present in normal daylight.  On the opposite side, blue fluorescence can improve the apparent color of a diamond with a color grade of J or below because it offsets the yellow tint of the stone.  In order to get the best value in a diamond, we recommend our clients purchase diamonds with fluorescence grades of None to Faint.

The Ugly Truth

To test the true affect of fluorescence on apparent diamond color, GIA performed an experiment where trained diamond graders, diamond industry professionals, and average consumers were shown diamonds of varying fluorescence.  The average consumers preferred diamonds that fluoresce over those that do not.  Even the trained diamond graders were mixed in their preferences of the diamonds.  Indeed, when GIA was developing its grading report, fluorescence was meant as an identifying characteristic and not as a grading factor.  GIA has determined that, at best, fluorescence has a "weak" impact (positive or negative) on the apparent color of a diamond.  But since the jewelry industry steadfastly maintains its own views on diamond fluorescence, those are the views that affect diamond value on the market.

Originally posted by me to LibertyDiamonds.com on 4/6/2010.

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