In diamonds, fluorescence is an attribute that is observed when the diamond exposed to invisible ultraviolet (UV) rays. Under normal lighting conditions, a diamond’s fluorescence is not detectable to the eye. However, if a diamond is naturally fluorescent, it will emit a soft colored glow when viewed in ultraviolet light. This glow will last as long as the diamond is exposed to the UV light. Fluorescence is not dangerous to the diamond or the wearer, nor does it compromise the structural integrity of the diamond. It is simply a fascinating quality that occurs naturally in some diamonds.
On a GIA diamond grading report, fluorescence refers to the strength or intensity of the diamond’s reaction to the UV light. The GIA scale uses the following grades: None, Faint, Medium, Strong, Very Strong. Beginning with the grade of Medium, the fluorescence grade will also include the color, e.g., “Medium Blue”. The most common color of fluorescence is blue, but other colors are possible depending on the trace elements within the diamond’s crystal structure.
Does Fluorescence Matter?
The first and most important thing to remember is that fluorescence is almost always an invisible property of the diamond. In the vast majority of situations, fluorescence has no impact at all on the visual beauty of a diamond. But for the grade on the diamond’s certificate, the typical diamond wearer will never see the fluorescence of their diamond in the course of a lifetime. This is true of diamonds with a grade of Faint or Medium fluorescence. In fact, diamonds in the near colorless and faint yellow ranges that exhibit some fluorescence will actually face up whiter than stones of equal color without fluorescence.
The GIA has done extensive research on diamond fluorescence and has confirmed these facts. In 1997, they published an article on the topic, which can be found here. Beginning in 2009, GIA began including explanatory information on fluorescence with the GIA report, a copy of which can be viewed here.
In extreme cases of fluorescence – typically graded Strong or Very Strong – the diamond may appear to have an oily or milky appearance. To a casual observer, it may appear that the diamond is dirty or cloudy. These diamonds should be avoided because the presence of this extreme fluorescence detracts from the beauty of the stone.
So why then do some recommend avoiding any type of fluorescence? The simple answer to that question is laziness. It is easier to tell a customer that “fluorescence is bad and you should avoid it” than it is to actually educate them on the facts. The bottom line on fluorescence is that in the Faint and Medium Blue ranges, it is not a characteristic that should cause great concern to you as a buyer.
