What Is Diamond Fluorescence?

Answer

Diamond fluorescence is the visible light some diamonds emit when exposed to ultraviolet light. Approximately 25%-35% of diamonds submitted to the GIA show some fluorescence, with blue being the most common color. According to expert gemologist Beth West fluorescence “is an incredibly natural phenomenon that has been used by gemologists historically for centuries as a key identification tool.” While fluorescence by itself does not determine whether a diamond is natural or lab grown, West confirms that the “rich Caribbean blue hue is very characteristic of a natural diamond”.

Key takeaways

Diamond fluorescence is visible light emitted by some diamonds when exposed to ultraviolet light.

GIA rates diamond fluorescence from None to Very Strong.

More than 95% of fluorescent diamonds submitted to GIA fluoresce blue.

Fluorescence usually has little noticeable effect on a diamond’s appearance.

Fluorescence alone cannot help tell whether a diamond is natural.

What is the diamond fluorescence grading scale?

Diamond fluorescence is an identifying characteristic, not a quality grade. According to the GIA, the intensity of a diamond’s reaction to long-wave UV light is rated as None, Faint, Medium, Strong or Very Strong. For Medium and above ratings, the color of the fluorescence is also recorded.

The grading scale describes the intensity of the reaction, not whether fluorescence is good or bad. GIA research also found that fluorescence has no noticeable effect on the appearance of most diamonds. In rare instances, diamonds with extremely strong fluorescence may appear hazy or oily, although GIA notes that this effect is uncommon. These effects should not be confused with diamond clarity (opens in a new window), which describes inclusions and blemishes.

GIAs Fluorescence Grading Scale Image 1 Credit GIA IG — GIA’s fluorescence grading scale

How do you test for diamond fluorescence under UV light?

Diamond fluorescence can be seen by shining ultraviolet light on the diamond and then observing the visible light it emits. The GIA records fluorescence under long-wave UV, which is similar to the ultraviolet wavelengths present in daylight.

The test shows whether a diamond fluoresces and the color of that reaction. Blue is the most common color, although diamonds can also fluoresce yellow, orange, green, white or red. A basic UV test will reveal the reaction, but laboratories use additional testing alongside fluorescence to determine whether a diamond is natural or lab-grown.

Different natural diamonds under ultraviolet light — Various natural diamonds under ultraviolet light

Do natural and lab-grown diamonds fluoresce differently?

Natural and lab-grown diamonds can both fluoresce, but their fluorescence responses can differ. Natural diamonds that fluoresce often respond more strongly to long-wave UV. Lab-grown diamonds can respond more strongly to short-wave UV.

The color of the glow can differ too. In natural diamonds, fluorescence is overwhelmingly blue, with yellow, white and other colors seen only rarelyⁱ. Lab-grown diamonds show a wider range of colors when gemologists examine them with the deep-UV imaging used in laboratories. Lab-grown diamonds created with CVD often fluoresce green to blue, or orange to red, frequently in a striped or banded pattern.

These differences come from variations in impurities and defects in their crystal structures, influenced by how the diamonds formed. Specialized UV testing can reveal different fluorescence patterns that help gemologists investigate a diamond’s origin.

It’s important to note that fluorescence is not conclusive on its own. Some modern CVD-grown diamonds can display fluorescence that resembles natural diamonds, so laboratories use additional testing to confirm origin.

FAQs

Is diamond fluorescence good or bad?

Diamond fluorescence is not inherently good or bad. The GIA reports that it has no noticeable effect on the appearance of most diamonds. In some cases, blue fluorescence can make a diamond that has a yellowish tint look more colorless in daylight. Fluorescence is not one of the 4Cs of diamonds (opens in a new window) and is recorded separately on a GIA grading report.

Does a diamond glow in the dark?

Diamonds stop fluorescing as soon as the UV light is removed. If a diamond keeps glowing afterwards, this is called phosphorescence. It’s uncommon in natural diamonds (opens in a new window) but frequently observed in lab-grown diamonds, particularly those produced using the HPHT method. The lingering glow can last for seconds or even minutes.

Do lab-grown diamonds fluoresce?

Yes, lab-grown diamonds can fluoresce under UV light. However, their fluorescence can look different from natural diamonds in terms of brightness, color and pattern. Gemologists use these differences when analyzing natural vs. lab-grown diamonds (opens in a new window).

Does fluorescence mean a diamond is natural?

No. Both natural and lab-grown diamonds can fluoresce. This characteristic alone does not confirm a diamond’s origin. A diamond grading report (opens in a new window) can confirm whether a diamond is natural or lab-grown.