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.

In this post, we answer the most frequent questions about diamond fluorescence to help you choose your perfect diamond.

1. What is diamond fluorescence?

Fluorescence is the glow you sometimes see when an object emits visible light. Some diamonds fluoresce 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 orangy light. Once the UV light source is removed, the diamond stops fluorescing.

2. Do all diamonds fluoresce?

No. Only about 25% to 35% of diamonds exhibit some degree of fluorescence.

3. Is there a diamond fluorescence grade?

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

Learn more about how GIA Diamond Grading Reports describe diamond color and fluorescence.

Fluorescing diamonds

Blue is by far the most common fluorescence color in diamonds when they are exposed to longwave UV rays. Copyright: GIA and Harold & Erica Van Pelt. Courtesy: Harry Winston, Inc.

4. Will diamond fluorescence make a yellow diamond look whiter?

Some trade professionals think blue fluorescence enhances a diamond’s appearance, especially diamonds with I to M color grades. 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 are often considered less desirable by the trade. Some believe that a bluish fluorescence may cause a hazy or oily appearance in these diamonds, but only if the fluorescence intensity is very strong. Not all diamonds with very strong bluish fluorescence look oily, however, and they may sell for less than diamonds that do not have blue fluorescence.

If you’re not yet familiar with the 23 color grades on the GIA Color Scale, you can learn more about them with the GIA Diamond Color Chart.

Diamond brooch

This comet design brooch of gold set with colorless and fancy colored diamonds showers sparks when exposed to UV light. Photo: Andrew Quinlan/GIA

5. Can an average person tell the difference between diamonds that do and don’t fluoresce?

GIA has studied the effect of blue fluorescence on diamond appearance. The Institute screened a large number of diamonds, assembling four sets of six diamonds, with each group representing a different color grade (E, G, I, and K). 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 judgment about their appearance.

Here is what GIA found: “For the average observer, meant to represent the jewelry buying public, no systematic effects of 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.”

Simply put, blue fluorescence had a negligible effect on the face-up appearance of diamonds in the colorless or near-colorless grade ranges (grades D through J) except for a slight improvement in the rare instances of very strong fluorescence intensity.

If you’d like to dig deeper into the science, read GIA’s research findings on diamond fluorescence.

Group of diamonds

On the left, a group of seven diamonds under daylight-equivalent illumination. On the right, the same diamonds fluorescing under long-wave UV illumination. Photo: Kevin Schumacher/GIA

6. Is diamond fluorescence good or bad?

Fluorescence is neither good nor bad. A diamond’s beauty is in the eye of the beholder. You may perceive fluorescence, or you may 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.

Diamond brooch

This beautiful brooch contains several diamonds that fluoresce under longwave UV illumination.

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.

Now that you know more about fluorescence, you probably want to dig deeper into light’s effect on another aspect of diamond quality. Read on to learn how light affects a diamond’s cut appearance.

Main Image Copyright: GIA and Harold & Erica Van Pelt. Courtesy: Harry Winston, Inc.