What is fluorescence?

When a diamond absorbs ultra-violet light, it converts it into a visible glow or luminescence, called fluorescence. About 35% of all diamonds are fluorescence, and in most of them, the glow is blue. There are five fluorescence grades: None, Faint, Medium, Strong, and Very Strong.

How fluorescence is graded?

There are five fluorescence grades: None, Faint, Medium, Strong, and Very Strong. How does it affect the beauty and the value of the diamonds?

• Colorless (D, E, F) stones, strong or medium fluorescence decreases a diamond's transparency, light reflection, and retraction inside the stone. Under the influence of the daylight, the diamond looks "milky" or "cloudy." Such diamonds might be 30% cheaper, but the negative visual effect is not worth this "discount."
• In Near Colorless (G, H, I) stones, the negative effect is less noticeable, but still, I wouldn't recommend purchasing strong and very strong fluorescence diamonds.
• InLight Yellow (J, K, L, M)diamonds and other lower color grades, strong blue fluorescence may actually have a partial positive effect. The strong blue glow of the fluorescence partly neutralizes the yellow tint of the stone. It creates an effect called "double face": from the face-down position, the color of the diamond remains the same, but from the face-up position, the diamond's color looks one grade lighter (better). So, in this case, a K color diamond with strong fluorescence, set in a ring, will look like a J color stone, in simple words – one grade higher.

So, even though light reflection and retraction's negative effect remains, the fluorescence "improves" the apparent color in one grade.

What is the final conclusion?

In the case you look for Light Yellow diamonds (K, L, M, N) colors, you may consider buying a diamond with "None," "Faint," "Medium," "Strong" or "Very Strong" fluorescence. It will look one or two grades up "whiter," but transparency and play of light in the diamonds may look decreased, comparing to non-fluorescent stones. What is the conclusion? Choose "None" for Colorless (D, E, F) diamonds. Choose "None" or "Faint" (and in exceptional cases "Medium") for Near Colorless (G, H, I, J) diamonds. Leave the rest of the grades: "Strong" or "Very Strong" to those customers who didn't read this article...

That's all I wanted to tell you about.