Diamond Fluorescence - Good or Bad?

Many diamond consumers are often confused concerning how to treat diamond fluorescence. Is this a desired attribute or does diamond fluorescence indicate a defective and less valuable diamond? As it turns out, the diamond industry itself is up in arms about how to regard and judge the phenomenon of diamond fluorescence.

It is a well-known fact that the diamond gemstone is an extraordinary material. Diamonds are actually the hardest natural material on earth, highly thermo-conductive, and brilliantly beautiful. Many diamonds also emit a natural bluish glow when placed under ultraviolet lights, called fluorescence. Although not all diamonds possess this property, many diamonds glow under UV lights just like teeth or a white shirt might appear to glow under such lights. In fact, many diamonds emit a bit of this glow in natural light as well, since a small amount of UV rays are also present in natural light.

Diamond fluorescence will appear as a graded characteristic on every GIA certificate since fluorescence can affect the color quality of your diamond. For diamonds with a high color grade (near colorless to colorless, or D-F), fluorescence can give the diamond a cloudy or milky look, slightly suppressing the gemstone's brilliance.  Hence, in D-F color graded diamonds, fluorescence can lower diamond value and quality. However, it is important to keep in mind that it is relatively rare for fluorescence to have such a significant impact on the value of a diamond. In most cases, diamond fluorescence hardly impacts the brilliance of a diamond at all.

Generally speaking, the higher the quality and price per carat of a diamond, the more a high level of fluorescence lowers the diamond's value. Some experts advise consumers and buyers to avoid purchasing diamonds with intense fluorescence, suggesting that in its extreme form, the most prominent effect of diamond fluorescence reduces diamond brilliance and transparency.  

On the other hand, for diamonds with low color grades (near colorless to faint yellow, J-M), fluorescence can have the opposite effect and actually add to the value of a diamond, improving its color. When a diamond emits blue/white tones in daylight and under UV rays, these tones offset the diamond's yellow hues, which normally lower the gemstone's color grade. Therefore, in the case of diamonds with a low color grade, the lower the grade, the less of an effect the fluorescence will have on the price. Nonetheless, fluorescence is always mentioned on the diamond certificate and it has the potential of raising the diamond's color grade. For instance, if a diamond is slightly yellowish with an L color grade, but it is also fluorescent, the diamond certificate will state that the diamond is fluorescent and the color grade will rise to K.

There have been various claims regarding diamond fluorescence throughout the ages. In the 1990s, some diamond purists argued that diamonds which project fluorescence are less pure than diamonds that do not.  Others claim that high color graded diamonds (D-F) that don't project fluorescence are rarer than those that do. As a result, diamond fluorescence became a value-reducing attribute.

Martin Rapaport took these opinions into consideration and manifested them in his Rapaport Index, with diamond fluorescence negatively impacting diamond prices. Despite the Rapaport Index's substantial role in the diamond industry's pricing methods, many diamond experts and traders maintain that fluorescence cannot be determined as a negative attribute. As a result, many dealers have been rather indifferent towards the fluorescence phenomenon, not considering it an important factor in diamond pricing.

In 1997, the GIA decided to dig deeper into the issue by conducting a thorough study on the objective perception of diamond fluorescence. Instead of appointing diamond experts as the judges, common diamond consumers were asked to distinguish between fluorescent and non-fluorescent diamonds. Results showed that no clear distinction was made, thus the GIA stated that diamond fluorescence does not have a significant effect on the color transparency of diamonds. Furthermore, when diamonds were viewed in a table-up position (as in diamond jewelry showrooms), intense fluorescence actually enhanced the gemstones' color (though it did not affect transparency), while in a table-down position no clear effect was reported. This study was very enlightening for many diamond experts, strongly suggesting that diamond fluorescence should no longer be treated as a negative characteristic, nor should it have a significantly negative effect on diamond value.