When valuing and determining the quality of a diamond, one characteristic that can puzzle diamond buyers is the significance of diamond fluorescence. Whilst not all diamonds fluoresce, it can alter the price of a diamond by up to 10% - so it’s worth understanding exactly what diamond fluorescence is and how it impacts a diamond and its value. 

Diamond fluorescence

Diamonds under ultraviolet light. Photo by James St John

Diamond fluorescence is the degree to which a diamond will emit a soft, typically blue glow when placed under an ultraviolet (UV) light. A diamond will only fluoresce if there were traces of the element boron present in the earth when the diamond was undergoing the process of crystallization. In reality, only 30% of diamonds have this quality, so for most diamonds, fluorescence isn’t an applicable property. Additionally, whilst sunlight contains UV rays, the UV levels are usually too low to affect the appearance of a diamond to the naked eye.

Whilst the Gemological Institute of America (GIA) doesn’t consider the fluorescence of a diamond to be a grading factor, or in other words one of the 4Cs, the institute does note it as an identifying characteristic. Hence, they have a grading scheme for diamond fluorescence with four distinct tiers of fluorescence intensity. The most fluorescent diamonds are rated as ‘very strong’ whilst the weakest are rated as ‘faint.’ Interestingly, however, the GIA qualified the significance of diamond fluorescence in 1997 when they established a test in order to determine the impact of the trait. They asked 46 observers, ranging from non-industry individuals to long-standing experts, to compare a selection of diamonds that differed only in their degree of fluorescence. The test found that non-industry observers could see no difference between the same diamonds with different levels of fluorescence. The experts' valuations came out very mixed, but it was generally found that diamonds with a high fluorescence were rated higher for their color when viewed table up. The GIA concluded that whilst the effect of fluorescence was as a whole negligible, it was not only most visible on stones with a low quality of color, but also improved their appearance.

But how does fluorescence specifically affect the color of a diamond? Some jewelers believe that fluorescence can make a diamond look milky or hazy and because of this, high-quality diamonds with a D-F rating receive up to a 10% markdown. However, the distinct bluish glow can also make yellower diamonds look whiter and thus offset their discoloration. As a result, I-M diamonds with high fluorescence can receive a higher valuation.

So, diamond fluorescence certainly isn’t the key thing to consider when purchasing a diamond because its effects aren’t usually visible to the naked eye, but it’s useful to consider if you are opting for a lower quality stone, alternatively if you would like a higher quality stone for a lower price. At 64Facets, we only use diamonds with minimal fluorescence to ensure that the color and clarity of our high-quality diamonds is never compromised.

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