Is Diamond Fluorescence Good or Bad?

What is diamond fluorescence? Is it good or bad? Should you buy (or not buy) a diamond because of it? These and other similar questions are often raised as diamond shoppers seek answers in making an informed buying decision.

You may be asking: What is diamond fluorescence? Fluorescence is the glow you sometimes see when an object emits visible light. Some diamonds fluorescence when they are exposed to ultraviolet (UV) rays from sources like the sun and fluorescent lamps. This can cause them to emit a bluish light or more rarely, a yellow or orangey light. Once the UV light source is removed, the diamond stops fluorescing. Not all diamonds fluoresce. Only about 25% to 35% of diamonds exhibit some degree of fluoresce.

GIA considers diamond fluoresce an identifying characteristic. It is not a grading factor like the GIA 4Cs (color, cut, clarity, and carat weight). GIA Diamond Grading Reports and Diamond Dossiers describe a diamond’s fluoresce by its intensity (None, Faint, Medium, Strong, and Very Strong) when compared to master stones used in the lab, If the fluoresce is Medium, Strong, or Very Strong, the color of the fluoresce will be noted.   

Some trade professionals think blue fluorescence enhances a diamond’s appearance, especially diamonds with higher grading. Bluish fluorescence can make a faint yellowish diamond appear more colorless in UV light, such as natural daylight. As a result, near colorless to faint yellow diamonds with a very strong to medium bluish fluorescence may have a slightly higher per carat price than similar diamonds that do not fluoresce.

The opposite is true for diamonds with higher color grades: diamonds in the D to H color range with a bluish fluorescence ae often considered less desirable by the trade. Some believe that a bluish fluorescence may cause a hazy or oily appearance in theses diamonds, but only if the fluorescence intensity is very strong. Not all diamonds with a very strong bluish fluorescence look oily, however, and they may sell for less than diamonds that do not have blue fluorescence.

Many jewelers have studied the effect of blue fluorescence on diamond appearance. The study was done by screening a large number of diamonds, assembling four sets of six diamonds, with each group representing a different color grade. The diamonds in each set were as similar as possible in all respects except the intensity of blue fluorescence. Diamond graders, trained professionals, and average observers viewed the diamonds in controlled conditions to make a judgement about their appearance.

It was noted that, for the average observer, such as the general public, no systematic effects of the blue fluorescence on the face-up appearance of the groups of diamonds were detected. Even experienced observers did not consistently agree on the effects of fluorescence from one stone to the next. Overall, blue fluorescence had a negligible effect on the face-up appearance of diamonds in the colorless or near-colorless grade ranges except for a slight improvement in the rare instances of very strong fluorescence intensity.

Fluorescence is neither good nor bad. A diamond’s beauty is int eh eye of the beholder. You may perceive fluorescence, or you not. You may like it, or you may not. If you are considering a diamond with bluish fluorescence, take the time to look at it under different kinds of lighting, including natural daylight, and compare it to other diamonds of the same color. See if you notice any difference.

Perhaps diamond fluorescence sparks so much conversation because its effect is so subjective. Opinions range across the spectrum. See if you notice it the next time you’re in a jewelry store- and then decide if it appeals to you. You should love what you end up buying. There’s no hard rule, so let your heart lead the way.

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