flourescent diamond rough under UV light
Photo courtesy of Alrosa

What is fluorescence?
Fluorescence in diamonds is the soft glow a diamond can emit when exposed to ultraviolet light. Fluorescence occurs when a substance absorbs the energy from a source of electromagnetic radiation, usually ultraviolet (UV) light, and is then immediately released by the material, as visible light, in a continuous “in and out” flow of energy. This natural phenomenon is not only beautiful, but also rare!

How rare is fluorescence?
Conditions must be just right as a diamond forms over billions of years, deep within the Earth, to produce fluorescence. Of the diamonds previously seen at AGS Laboratories, just under 15% of diamonds have displayed some fluorescence. The diamond’s rarity increases as the fluorescence intensity increases. Diamonds with very strong fluorescence are the rarest. Less than 6% of the diamonds submitted to AGS Laboratories have medium to very strong fluorescence, with less than 0.5% displaying very strong fluorescence.

How does AGS Laboratories grade fluorescence?

AGS Laboratories looks at diamond fluorescence differently. We grade fluorescence from the top-down view of the diamond (known as “face-up”). We do this because diamonds are set face-up, and this is the best way to get the true picture of how your diamond appears as it’s set in jewelry. The other significant difference where AGS Laboratories has pioneered looking at diamond fluorescence is our grading scale for the intensity of the glow.

The commonly used scale in the jewelry industry uses six categories: None, Very Faint, Faint, Medium, Strong, and Very Strong. At AGS Laboratories, we decided to include None, Very Faint, and Faint into one grade, “Negligible.“ Why? Because fluorescence in these small ranges have little impact on how the diamond appears face-up, so our scale has only four grades: Negligible, Medium, Strong, and Very Strong.

AGS fluorescence grading scale

What colors do diamonds fluoresce?
The most common color for a diamond’s fluorescence is blue. Other colors include yellow, green, orange, and even red or pink. Colors other than blue are much rarer, representing under 1% of diamonds previously seen at AGS Laboratories!

Why do diamonds fluoresce?
Fluorescence in diamonds is caused by a specific arrangement of atoms in the diamond’s crystal structure. Over 98% of natural diamonds contain minute traces of nitrogen. When conditions are right, the nitrogen atoms form perfect triangular patterns (called “N3 centers”), which interact with light in a remarkable way. Diamonds with sufficiently high quantities of N3 centers absorb and transform UV “black light” into a soft blue glow. This phenomenon is fun and beautiful to observe and serves as a unique indicator of your diamond’s natural origins.