What Is Diamond Fluorescence?

Fluorescence is one of the numerous factors to consider when purchasing a diamond. However, unlike the 4 Cs (color, cut, clarity, and carat), fluorescence is not as easy a concept for most of us to grasp. For example, before I began my diamond education, I thought fluorescence was desirable because high fluorescence seems like it should provide more brilliance and shine. Under some circumstances, this is true; however, fluorescence is considered a flaw. Therefore, higher levels of fluorescence result in lower prices.

At this point, you may be confused by my statement that a high level of fluorescence can sometimes result in increased brilliance. This situation only occurs with diamonds of mid to lower color grades (“I” color or below). As you know from my article on the 4 Cs, I recommend “I” colored diamonds as a happy medium between price and beauty. They have a slight yellow tint, but not enough to detract from the stone’s overall appearance. At this color grade, stones can be brilliant both with or without fluorescence. Therefore, it is your preference whether or not to select a stone with fluorescence in the “I” color range.

If you select a color below "I," fluorescence typically increases brilliance. In contrast, fluorescence can have the opposite effect on diamonds of a color above “I.” For diamonds in the higher color grades, if any haziness is present, fluorescence can potentially amplify it, making the diamond appear cloudy. This haze or milkiness is typically much more visible under natural sunlight. Therefore, when purchasing a stone, I always recommend viewing it in sunlight before purchasing it. Most jewelry stores are happy to accommodate such requests; however, you can expect to be escorted outside and closely scrutinized during your outdoor viewing.

How to Identify Diamond Fluorescence

Now that you have a general understanding of fluorescence and how it can impact the brilliance and visual clarity of stones of various colors, how can you tell whether a stone has fluorescence? First, you always want to view the certification. Organizations such as the Gemological Institute of America (GIA) will provide certifications to accompany diamonds they have evaluated, so this should be your first stop when determining fluorescence. There are other certification agencies, such as the American Gem Society (AGS) and the International Gemological Institute (IGI); however, it is important to recognize that each organization does not have the same level of grading criteria. Therefore, do your research before completely trusting the certifier. That being said, GIA is the most well-recognized and respected, so you cannot go wrong if it is a GIA-certified diamond.

In addition to examining the diamond certification, if you are like me, you want some proof. Fortunately, when it comes to fluorescence, it is easy to determine whether a diamond does or does not exhibit fluorescence. The only tool you will need is a black light. When observed under a black light, diamonds with fluorescence will exhibit a bluish glow. The higher the fluorescence, the brighter this glow will be. In contrast, diamonds with no fluorescence will not exhibit any color when placed under a black light.

Is diamond fluorescence good or bad?

While diamond fluorescence can potentially amplify haziness in high color grade diamonds, in most cases, fluorescence will have minimal impact on the appearance of the stone, especially if the fluorescence is faint. For strong and very strong fluorescence, there is the potential to increase the brilliance of the lower color grades and have a negative impact on the higher color grades. While buying a diamond with fluorescence is a potential way to lower costs, ensure you view the stone under natural light to see the impact of the fluorescence. The best judge for determining whether it is good or bad is using your own eyes to view the diamond in question. If the diamond is high quality, has an excellent cut and very slight inclusions, then fluorescence will likely not have much impact. At that point, if there is no visible impact of fluorescence, the choice is largely personal.

If the thought of having a diamond that glows under a black light intrigues you, and there are no negative visible impacts of the fluorescence for the diamond you are purchasing, then the choice is yours. On a positive note, if you ever drop some small diamond jewelry, such as earrings, on the carpet or in the car, fluorescence can make them easier to find. Simply grab a black light, turn down the lights, and start your search. In contrast, you will be unaided in your search for a diamond with no fluorescence.