The Valuing of diamonds, requires an assessment of each of the four Cs (cut, colour, clarity and carat weight). But a fifth factor-fluorescence-often plays a role in the pricing and marketability of diamonds.
Fluorescence is a trait that is greatly misunderstood. It’s often perceived by members of the trade and consumers as a negative trait, it is usually a positive one. Fluorescence almost always makes diamonds look better in overall colour appearance. Although this sounds like a good thing, some in the trade believe this means that they are paying for a higher grade than the true grade of the diamond. Sales have been lost, and unnecessary discounts given, on diamonds that possess only beautiful qualities.
Tracing the source
Fluorescence is the caused by trace impurities in the diamond. Approximately one-third of all gem-quality diamonds fluoresce, usually blue, But white, yellow, green, orange, and very occasionally red also may be witnessed. Pink diamonds may fluoresce a bright orange. Author of ‘The Micro World of Diamonds’, John Koivula states, “In natural diamonds, the reaction on exposure to long-wave ultra-violet radiation is virtually always stronger than the corresponding short-wave reaction.”
When a diamond is viewed in lighting that contains ultraviolet such as daylight the appearance is almost always improved by fluorescence. The excellent high-colour Russian diamonds which were highly publicized during the last two decades have a higher percentage of fluorescence in the medium-to-strong blue range than diamonds from other sources, which is one of the reasons they look so good.
Eric Bruton author of Diamonds discussed false white stones in his book: “If a stone has blue fluorescence and a tinted yellow body colour, the colours being complementary may cancel each other so that in some conditions the stone appears white. The experienced grader will recognize such stones because their colour grade appears to vary in different light intensities. A white light free of ultra-violet will disclose the true body colour, and an ultraviolet lamp will disclose the fluorescence.”
On GIA Gem Trade Laboratory grading reports, fluorescence is categorized by level of strength: None, Faint, Medium, Strong, or Very Strong. When fluorescence is faint, it’s listed without noting the colour of fluorescence while other levels of fluorescence are noted along with the colour. However, GIA lists fluorescence on grading reports as an identifying characteristic rather than a grading factor.
The 1997 winter issue of Gems & Gemology presented results of a visual observation experiment regarding fluorescence. Trained graders, trained professionals and untrained observers viewed diamonds in various lighting conditions and positions. They observed diamonds that fluoresced as well as those that were inert. Not surprisingly, most observers perceived the diamonds with strong blue fluorescence as having better colour appearance.
The study, which also analyzed a large sampling of data on diamonds submitted to the lab, found that about 35% of all diamonds exhibit florescence. Of those that fluoresced, 62% were medium to very strong and of those 97% were blue.
Consider the absurdity of this statement: “This diamond exhibits fluorescence. That means that in UV light such as sunlight, your diamond will look better. Therefore I have to charge you less.” Actually, some in the trade believe a premium is justified on lower-colour diamonds improved by fluorescence. But if lower-colour diamonds deserve such a premium, why don’t white diamonds that look even whiter because of fluorescence deserve a discount?
In The Micro World of Diamonds, John Koivula writes, “By far the most common ultraviolet fluorescence colour in diamonds is light blue, some-times referred to as a blue-white colour. Weak fluorescence reactions are relatively common, but strong blue fluorescence is much more unusual.”
Courtesy JLK magazine