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FLUORESCENCE
Fluorescence is a natural phenomenon that occurs in some diamonds when they are exposed to ultraviolet light. The reaction can cause the diamond to emit visible light, which disappears once the UV source is removed.
On a GIA report, fluorescence describes the strength of a diamond’s reaction to long-wave ultraviolet light. UV light is also naturally present in daylight, which means fluorescence can in some cases influence how a diamond appears under different lighting conditions.
WHAT IS FLUORESCENCE?
When a diamond is exposed to ultraviolet light, certain structural characteristics within the stone can cause it to emit visible light. This phenomenon is known as fluorescence.
The effect is present only while the diamond is exposed to UV light. Fluorescence should therefore not be considered part of the diamond’s actual body color, but rather as a separate optical characteristic.
On a GIA report, fluorescence is stated separately from the diamond’s other quality characteristics.
HOW DOES FLUORESCENCE AFFECT A DIAMOND’S APPEARANCE?
For the vast majority of diamonds, fluorescence has no clearly visible effect on the diamond’s appearance.
GIA studies have shown that the average observer is generally unable to distinguish between a diamond with fluorescence and a comparable diamond without it. In some cases, diamonds with Medium or Strong fluorescence were even preferred visually.
Blue fluorescence can be particularly relevant in diamonds with a yellowish tint, as blue and yellow are complementary colors. Under lighting conditions containing UV, blue fluorescence can therefore make some diamonds appear less yellow.
In very rare cases, extremely strong fluorescence may cause a diamond to appear slightly hazy or oily. According to GIA, this occurs in fewer than 0.2% of the fluorescent diamonds they have examined.
HOW COMMON IS DIAMOND FLUORESCENCE?
Fluorescence is relatively common. According to GIA, approximately 25-35% of submitted diamonds display some degree of fluorescence.
For the majority, however, the reaction is limited. GIA states that only around 10% of fluorescent diamonds are graded Medium, Strong or Very Strong, where fluorescence may potentially influence the diamond’s visual appearance.
In more than 95% of diamonds that fluoresce, the visible fluorescence is blue. Blue is therefore by far the most common fluorescence color, although diamonds can also fluoresce in other colors, including orangy yellow, yellow, orange, red, white and green. These colors occur far less frequently.
HOW DOES GIA GRADE DIAMOND FLUORESCENCE?
GIA grades fluorescence according to the strength of a diamond’s reaction to ultraviolet light:
None - No observable fluorescence
Faint - Weak fluorescence
Medium - Noticeable fluorescence
Strong - Strong fluorescence
Very Strong - Very strong fluorescence
IS DIAMOND FLUORESCENCE GOOD OR BAD?
Fluorescence should not automatically be considered either positive or negative.
A diamond’s overall visual appearance is more important than fluorescence considered in isolation. Cut, color and the lighting conditions in which the diamond is viewed can all have a greater influence on its appearance.
This is particularly true for natural fancy color diamonds, where color is one of the diamond’s most important characteristics. In these diamonds, fluorescence should always be evaluated in relation to the individual color and overall visual appearance rather than solely by the fluorescence grade stated on the GIA report.
