Fluorescence is one of the least covered subjects in diamonds. Not something common in public knowledge, fluorescence with respect to diamonds means the gem’s tendency to reflect a soft fluorescent glow when put under UV light, also known as black light. While almost all diamonds are subject to this test once in the laboratory, only 30% of the roughs actually fluoresce.
In case you are wondering if it’s a good thing for a diamond to have fluorescence, that’d be a no. In fact, fluorescence in diamonds is deemed as a mark of imperfection. That explains why diamonds in the range of D, E and F that emit a fluorescent glow under UV are put up at a 15% slashed off price.
What’s a Fluorescent Glow Like?
A fluorescent glow in diamonds is a soft, blue glow. While it diminishes the value of top-grade diamonds, it works to the advantage of stones appearing between the range I and M color. The fluorescence of the stone makes them appear a shade or two brighter when exposed to a UV light source. That is the reason why stones from the said grades are sold for a very moderate premium.
Fluorescence is never a deciding factor in buying diamonds, unless of course you are talking very strong fluorescence. The effects it casts on the brilliance or fire of the stone is only negligible, so much so that it cannot be identified with naked eyes. However, caution should be exercised in this regard only when buying stones from the D to H grade. Stones in these categories do not have the kind of body color that can offset the level of fluorescence which is why they need to be as perfect as possible.
Fluorescence and Pricing
The fluorescence of a diamond makes a direct hit on its pricing. Pricing in this case is determined by two other factors, namely, color and clarity. However, when all three come together, the best combination wins the higher number while the poorest one scores the lowest. Those between D and F color are sold for up to 10% discount for strong fluorescence and 7% for medium glow. For G and H, the mark up starts at maximum 10% for very strong to 3% for medium. For I through M, the reduction is an even 2% for all the slots. It’s the stones in the Faint category that sells for least discounts.