What is Diamond Fluorescence?

Diamonds have many unique properties, including natural blue fluorescence under the black lights of a dance club. Some people seek diamonds that produce this unique effect of fluorescence, while others avoid it. Diamond fluorescence is the visible wavelengths emitted by diamond when excited by invisible radiation.Virtually all diamonds fluoresce when exposed to X-rays, and this forms the basis for the diamond’s identification and collection at mining sites. Fluorescence occurs in a third of all gem grade diamonds when they are exposed to the ultraviolet light produced by black lighting or other long-wavelength UV source. The UV light excites electrons in the diamond crystal, which then release this absorbed energy in the form of visible light of faint to very strong intensity. Once the light source is removed however, the fluorescence is no longer observed. If, in rare situations, light emission continues for a period after the exciting light has been turned off, the phenomenon is called phosphorescence. An example of this is the Hope diamond, whose color changes from blue to red when exposed to UV light then glows red momentarily after the UV light is turned off.

Recent studies have shown that blue fluorescence in any amount does not impact the face up appearance of a diamond; therefore, it is only the prevalent belief of the diamond traders and the consumers that causes less demand for diamonds with strong fluorescence and this brings the price down. In the 1950s, diamonds with fluorescence were sold at a premium, and were called “blue white” diamonds. Then in the 1970s, the use of black lights in the discos showed the diamonds’ fluorescence and the price of fluorescence diamonds dropped as did the demand for them. The presence and color of fluorescence and its intensity in a diamond are indicated on all GIA and AGS diamond grading reports.

GIA diamond reports and many other gemological lab reports indicate whether or not a diamond exhibits fluorescence, but have your diamond checked by your local independent jewelry appraiser for fluorescence this may help in identifying your diamond in the future.  Since UV radiation is a component of daylight and is also present in fluorescent lit rooms, diamonds with fluorescence can appear to slightly change color quite often. Fluorescence diamonds that produce a blue reaction are more desirable because the diamond usually appears whiter, or more colorless, under UV light sources. Fluorescence diamonds that fluoresce yellow appear even more yellow under some lighting conditions making these diamonds less desirable.

How does diamond fluorescence affect the value of a diamond?

Diamonds with a strong or very strong fluorescence are priced slightly lower than other diamonds of the same color grade and clarity grade. The visible effects of diamond fluorescence grades of inert, faint, negligible, and medium, can only be detected by a trained gemologist under very controlled lighting conditions. Blue fluorescence, if strong or very strong, may alter the appearance of a diamond with a high color grade (D-F) in a negative way.  For diamonds with very high color grade, D to F grade, strong fluorescence is believed to interfere with the flow of light and make the diamonds appear a little oily or murky. We recommend a grade of None to Faint blue fluorescence in colorless the diamonds with D to F color grades.

When shopping for a diamond, check to see if it has fluorescence.  If the diamond has blue fluorescence, it probably won't be a factor in the diamond's appearance unless the intensity is strong or greater, and even then rarely does blue fluorescence affect the beauty of a diamond. Diamonds in the color grade ranges that have more yellow (H and lower) may appear to have less yellow color due to the fluorescence, adding positively to the diamond’s appearance. The diamond trade will slightly discount prices of diamonds in the higher color grade category, while adding a very slight premium to those in the lower color grade category.