Fluorescence

Fluorescence is a characteristic in which a diamond glows when exposed to ultraviolet light. Fluorescence is caused by trace elements of other minerals trapped in a diamond's crystal structure. This occurs in maybe 20-30% of all diamonds.

The main reason fluorescence is important is that it can have a PROFOUND impact on the price of a diamond and it's ease of resalability. When a diamond absorbs ultraviolet light, it can temporarily turn the diamond into a chalky blue color or rarely a chalky yellow or white color. The GIA certificate will tell you the color a diamond fluoresces and the strength of the fluorescence. The range is none, faint, medium, strong and very strong. In terms of price, none is the best-case scenario. Faint would not impact the salability or appearance of a diamond unless it is a very high-grade diamond such as a 2 carat DIF. In this type of diamond, faint fluorescence might make it more difficult to sell even if the fluorescence is not discernible to the eye.

The best way to determine if a diamond has fluorescence or to simply check it out before you buy it, is to hold it under a black light. A jeweler should have one or you can buy a cheapie online. A meaningful exercise before buying a fluorescent diamond is to compare a fluorescent and non-fluorescent diamond of the same size, cut and color grade under 3 different lights- a black light, a regular office ceiling LED tube light, and sunlight. Here is what you will likely see. No difference between none and faint blue, a discernible difference between medium blue and faint under a black light, and a whopping difference between strong blue and faint under a black light. Under a regular office LED light, the differences will be discernable but modest, except maybe the strong blue stone might be more chalky looking. Regarding fluorescence and daylight: Ultraviolet light is present in the spectrum of daylight. Accordingly, a strong blue diamond glows blow and becomes less transparent in sunlight.

Some people (me for instance) like the impact that faint, or medium fluorescence has on a diamond's appearance, so the fact that it is cheaper is a bonus if I don't intend to resell it.