Why is Diamond Fluorescence Important?
Fluorescence is an important but often overlooked feature that will affect the glow of some diamonds in direct sunlight or certain lighting conditions. About one third of all diamonds are fluorescent and this glow can be blue, red, yellow, or in extremely rare cases, orange or blue-green. Of all cases, roughly 97% are blue fluorescent diamonds so this is really the only type you will need to consider. Diamond fluorescence is not part of the traditional '4 Cs' grading scale (color, carat, clarity, or cut). It is far less important than the four main grading scales but it can raise or lower (usually lower) the value of a diamond so it is something we recommend every prospective diamond buyer should understand.
A detailed video on Fluorescence in Diamonds
What Is Fluorescence?
Diamond fluorescence refers to the degree that a diamond will seemingly change colors under ultraviolet light conditions. UV light is not directly visible to the human eye but is present in direct sunlight and also emitted in lesser degrees from certain types of lamps or light bulbs such as a fluorescent light. Diamond fluorescence is caused by trace elements or other irregularities such as long-term exposure to radiation that can tamper with the carbon structure of the stones. The type of trace elements will directly affect the color of fluorescence. For example, nitrogen and aluminum will produce blue fluorescence which makes up the vast majority of fluorescent diamonds.
Diamond fluorescence at low to moderate levels is usually undetectable by the naked eye. In these ranges, it will not noticeably affect the color of the diamond although it can affect its tone (brightness). Under high UV light conditions, a strong blue diamond fluorescence can appear slightly hazy or milky with the bright blue glow. However, diamond fluorescence remains it's own distinct (and subjective) category. It is not clearly good or bad and does not affect the carat weight or any other grade of the diamond. Diamond fluorescence has a specific grading scale that describes both the magnitude (from faint to strong) as well as the color that it fluoresces at under UV lighting conditions. If there is no color listed, always assume blue fluorescence.
Blue diamond fluorescence from left to right: Faint, Medium, Strong, Very Strong
Is Diamond Fluorescence Bad?
Even today, there is no clear consensus on whether diamond fluorescence is desirable or undesirable. Some consider fluorescence a form of impurity while others say that it enhances the uniqueness of each stone. The debates have also led to changing prices of fluorescent diamonds, sometimes unpredictably.
In fact, diamond fluorescence can improve the appearance of diamonds in lower color grades. Thomas M. Moses, Ilene M. Reinitz, Mary L. Johnson, John M. King, and James E. Shigley originally published their report on blue diamond fluorescence through GIA in 1997. However the report has since been lost or moved on GIA's site and is inaccesable. By request, we have included a copy of the original report:
In short, for colorless diamonds, fluorescence is more often seen as lowering the stone's value as it can make them look slightly hazy or impure under UV light. However, diamond fluorescence can also improve the color grade of faintly colored diamonds. For example, a stone with a yellowish tinge can appear closer to colorless if it exhibits blue fluorescence. Keep this that important fact mind if you are considering a dimaond at a lower color grade. Also be aware that fluorescence can vary in different types of light.
Diamond fluorescence can also play a major role in the stones jewelers choose for their arrangements. For example, a setting of several diamonds can have an unbalanced and unattractive appearance if each of its stones fluoresce differently. Therefore, in diamond arrangements consisting of multiple gemstones, minimal diamond fluorescence is highly desirable.
Diamond Fluorescence: The Bottom Line
Not surprisingly, some people do prefer highly fluorescent diamonds, regardless of color. Whether or not diamond fluorescence is desirable comes down to personal preference and one's own perception. If you prefer diamond fluorescence or simply don't care, you should opt for a stone with high levels of fluorescence. In general, higher fluorescence will lower the price of a stone. However, the 'real life' effect is actually very slight and even a highly fluorescent diamond will not be detectable in most normal conditions.
In any case, regardless your stand towards fluorescence, be sure to keep it in mind when looking for or comparing diamonds. Diamond fluorescence can have a very real effect on the stone's price.