What is fluorescence in a diamond?

As one of the lesser-known characteristics of a diamond, fluorescence is commonly misunderstood. In reality, diamond fluorescence is a simple, natural effect appearing in roughly 30% of all diamonds that causes them to glow under ultraviolet light (UV). Diamond fluorescence is most often blue, but it can manifest in a wide array of colours including yellow, orange, red, white or green.

In a small percentage of diamonds (less than .02%), fluorescence can give the stone a cloudy or oily look, and some consider this to be an undesirable trait. In other cases, fluorescence can give certain diamonds on the colour spectrum a whiter appearance, which is perceived as a positive. That’s why it takes a little more digging to understand if strong fluorescence in a diamond is good or bad.

Diamond fluorescence scale and the GIA

The Gemmological Institute of America (GIA) does not factor in diamond fluorescence to determine quality, like it does with the 4Cs – colour, cut, clarity, and carat. Instead, the GIA uses fluorescence as an identifying characteristic that aids in distinguishing one stone from another. GIA grading reports label the intensity of diamond fluorescence as follows:

• None: No glow at all under a UV light.
• Faint: Very light glow under a UV light.
• Medium: A glow is prevalent under a UV light.
• Strong or Very Strong: A profound glow is clearly seen under a UV light.

How to use diamond fluorescence to your advantage

Higher grade. Lower price.

Colour, which is one of the 4Cs, is utilized by gemmologists to help determine the quality of a diamond. On the high end of the colour spectrum are colourless diamonds labeled D-F. When a diamond in the colour range of D-F has Strong to Very Strong fluorescence it’s not uncommon to see discounted pricing. This happens because many people automatically assume that a high fluorescence rating means that a diamond will have a hazy or oily appearance. And though this effect is rare, this negative association can still decrease a diamond’s perceived value.

Improve perceived colour

Interestingly, fluorescence can give the perception of improved colour to diamonds in the colour range of H-K. Diamonds that fall in this range often contain a faint yellow hue, and when counteracted by a Medium or Strong blue fluorescence, the combination can help make them look whiter.

Blue Nile and the GIA

All Blue Nile loose diamonds have been analyzed and graded for quality by the GIA, one of the most respected and accurate labs in the diamond industry. That’s why, given the controversy around this characteristic, it’s probably best to take advice on diamond fluorescence directly from the GIA:

“GIA studies show that for the overwhelming majority of diamonds, the strength of fluorescence has no widely noticeable effect on appearance. In the GIA Fluorescence Study, it was found that the average person could not make a distinction between a diamond with fluorescence and a diamond without. In many instances, observers prefer the appearance of diamonds that have Medium to Strong fluorescence. In rare cases, some diamonds with extremely strong fluorescence may appear hazy or oily; fewer than 0.2% of the fluorescent diamonds submitted to GIA exhibit this effect."