Even though it’s only been about a century that fluorescence in diamonds has been looked at seriously, fluorescence in nature has been catching our eye for quite a bit longer. It’s everywhere in the form of jellyfish, coral, butterflies, parrots, plants, crude oil, and minerals.
The easiest way to think about fluorescence is to imagine the glow of jellyfish in the deep blue sea or a neon sign on a starlit night. The more complex way to imagine it is to envision a diamond that appears to glow or change colors when exposed to ultraviolet light.
Even though fluorescence is often too subtle to be seen by the naked eye, it’s something to consider when matching diamonds for one piece of jewelry. Colorless diamonds with the same color grades can look not quite right if their fluorescence’s are wildly different.
The same irregularities due to the presence of boron and nitrogen that give us fancy colored diamonds is also what gives a colorless diamond its fluorescence.
Diamonds can have a fluorescence of many different colors including red, yellow, pink, green, orange, and blue-green. By far the most common color is blue, caused by trace elements of nitrogen and aluminum. An excellent example of this is the 127.01 carat octagonal Portuguese Diamond with a “Very Strong” blue fluorescence. The moniker is from famed jeweler and former owner Harry Winston.
By far, the rarest color in fluorescence is red. A magnificent example is one of the most famous gems in the world: the 45.52 carat blue Hope Diamond with an unusual orange-red fluorescence.
Lucky for colorless diamonds, that blue fluorescence can sometimes help a colorless diamond with a yellow tint look whiter than its actual color grade.
Only about one-third of colorless stones have fluorescence. And of those diamonds with fluorescence, they are just as likely to be of the highest quality as not. For the two-thirds of diamonds that have no fluorescence, they will get a grading of “None.”
For those that do have fluorescence, they are graded from “Faint” to “Very Strong.” Most on the low end of the grading scale can’t be seen with the naked eye and might only impact a diamond’s brightness rather than the color. In some cases, “Very Strong” fluorescence can cause a milky haze that causes a stone to lose its transparency.
A diamond’s fluorescence is determined by what minerals were present during their crystallization. When put under an ultraviolet light, these trace minerals react to being put under the light by emitting a glow that is called fluorescence. A diamond with no trace minerals won’t absorb ultraviolet light and thus won’t emit a colorful glow.
It’s important to note that fluorescence doesn’t point to the structural integrity of a stone. Whether a diamond has it or not, it’s still a diamond with the same durability as any other diamond.
Because the sun emits ultraviolet light, the effects of fluorescence can be duplicated in daylight. Even though our eyes can’t pick up on those ultraviolet rays, the stone definitely does. This can lead to diamonds with a strong fluorescence having a milky haze when in the bright sun. Because of this, some stones with strong fluorescence can go for less than stones with all other factors being equal, but with “None” or “Faint” fluorescence. Whatever the fluorescence is in your diamond, it’s important to see the stone in different types of light as well as having each diamond in any one piece of jewelry having matching fluorescence.