What is Diamond Fluorescence?

Diamond fluorescence is a lesser known feature of a diamond that often raises big questions. Because it’s not well understood, fluorescence is usually talked about in terms of being good or bad. Well, just as every other feature creates a unique picture for every diamond, the same can be said for fluorescence. So, let’s talk about what you should know about diamond fluorescence and why you may find it in your perfect diamond.

What to Know About Diamond Fluorescence

Diamond fluorescence is caused by trace amounts of an element that reacts to UV light being trapped inside a diamond’s crystal structure. Three elements will cause fluorescence in diamonds: aluminum, nitrogen, and boron. If any amount of these elements is present and absorbed over the millions of years it takes to form a natural diamond in the earth, then that diamond will fluoresce.

The term diamond fluorescence refers to the bluish glow some diamonds exhibit under ultraviolet (UV) light. In other terms, it’s the visible light that a diamond emits when exposed to UV rays, which are an essential part of daylight. In more than 95% of diamonds that exhibit fluorescence, the visible color is blue.

While blue is by far the most common color that a diamond will fluoresce, in rare instances the color could be yellow or red as well. The color of the fluorescence plays an important role in the overall appearance of the diamond. We’ll discuss the impact in greater detail later in the article because as with most things about diamonds, there are nuances to fluorescence.

In GIA studies, the clear majority of diamonds had no widely noticeable effect on their appearance regardless of strength of fluorescence. Additionally, these studies found that the average person viewing diamonds could not determine a difference between a diamond with fluorescence and one without.

Approximately 30% of diamonds exhibit fluorescence to some degree. While the GIA takes note of fluorescence as an identifying characteristic, it’s not considered a grading factor like the 4Cs. When the GIA describes fluorescence, the diamond is given a level of intensity of None, Faint, Medium, Strong, or Very Strong on the certification.

Having an understanding of what diamond fluorescence is, how it appears, and how it’s documented is an important baseline for making the best choice in a diamond. Next, we’ll dive deeper into the nuances of how fluorescence can impact a diamond and tips for using the feature to your advantage for a smart investment.

How Does Fluorescence Impact a Diamond?

The textbook thinking on fluorescence is that it is a flaw, but we believe there’s nuance to consider with fluorescence. A lot of personal opinions from jewelers and diamond suppliers can get wrapped up in a discussion about fluorescence. So, it’s important to remain objective and view how fluorescence can be both good and bad.

Most of the time, fluorescence is invisible in daylight. In fact, GIA research has shown that certified diamond graders cannot perceive fluorescence without a black light. Also, for the average observer, none were able to recognize any blue fluorescence when presented with diamonds known to fluoresce. So with that in mind, let’s talk about how choosing a diamond with fluorescence could be a great choice.

Some fluorescence actually enhances the look of the diamond by making it appear brighter. In the industry, this is often called good fluorescence. Not only can good fluorescence make the diamond look brighter, it can also improve visible color. Since most color in a diamond is yellowish in nature, a blue fluorescence will cancel that out, resulting in a more colorless appearance.

So for example, a K color diamond with good medium fluorescence can make the diamond look just as white/colorless as a G or H color diamond. We think that makes this a perfect combination because you pay for a K color diamond, but get the look of a G color diamond. We think this stone has great value.

Times when fluorescence is considered to negatively or neutrally impact a diamond’s quality typically fall into three categories:

Very Strong blue fluorescence. These diamonds have a high likelihood of appearing hazy or milky.

Strong to Medium blue fluorescence doesn’t usually impact the look of a diamond.Within the high color spectrum (D to G), these diamonds generally trade at a discount to those without fluorescence, because the fluorescence is considered an unknown factor that may negatively impact the stone’s appearance. For diamonds in the lower color spectrum (I to M color), good fluorescence will add a premium to the diamond, while bad fluorescence that makes the diamond look lackluster will trade at a discount.  

Faint fluorescent diamonds are generally traded as if they have no fluorescence. However, for diamonds in the colorless spectrum (D to F color), where purity is prized and prices are driven in large part by its rare supply, faint fluorescent diamonds will trade at a slight discount to diamonds with no fluorescence.  

When considering a diamond with fluorescence, it’s important to view the diamond in multiple light sources. This can be done in person or online with a skilled jeweler who can give you detailed feedback about if and how the stone changes in appearance. The bottom line is that the diamond that you choose should look brilliant, regardless of its fluorescence intensity.  

Many fancy-colored diamonds will also exhibit fluorescence, and in this instance, the effect has the potential to enhance the color of the stone if the stone is the same color as the fluorescence. For example, in yellow diamonds exhibiting yellow fluorescence, the overall look of the stone will be a more intense hue of yellow.

As a final note on fluorescence, lab-grown diamonds (other than fancy color lab-grown diamonds) never have fluorescence. We think in time this fact could make fluorescence in a natural diamond a more desirable and valuable trait since it serves as a natural differentiator to lab-grown diamonds.

In the end, it’s most important for you to be happy with the diamond you choose. You’ll want to be looking at it every day, so choosing one that first meets the guideline of being appealing to your preferences is key. After that, a specialist can help guide you in making the best diamond investment, with or without fluorescence.

Have questions? We're happy to help.