We’re all familiar with the 4Cs of diamonds – cut, color, clarity and carat weight. But diamonds also possess a quality called fluorescence that’s part of the evaluation and assessment of a diamond. It’s actually called photo-luminescence and it’s caused by small amounts of the chemical boron in the diamond. It’s activated by UV light.

It’s graded by how much blue there is in the diamond – None, Faint, Medium, Medium blue, Strong, Strong Blue and Intense Blue. At one time, this was a highly-prized quality in a diamond and the demand for a blue-white diamond was high. The blue indicated the fluorescence of the diamond, while white was a reference to the overall color of the body of the stone. This has decreased over time as consumer preference shifted towards the more colorless stones.

The tide of public preference may be shifting back to the blue-white diamond, but you want to be sure, when buying a diamond, that you examine it under a variety of conditions, such as sunlight and fluorescent light, as well as a jeweler’s black light. Some diamonds with a fluorescent quality can become hazy in daylight or even glow out on the dance floor!

Colorless diamonds have become increasingly rare and expensive. The color grades of D (flawless) to G are going to be hard to come by at a reasonable price. If you’re buying a diamond with a color grade of H or higher, some fluorescence may actually be a good attribute for it and increase your stone’s value and attractiveness, as the blue fluorescence can offset any other gradations in the stone, such as a yellowish tone.

Although some diamonds have a yellow or orange fluorescence, most reputable jewelers will recommend against a diamond with this quality, unless you’re buying a colored diamond in the same hue, as a similar fluorescence will enhance and intensify that color.