Diamonds possess hidden properties that become apparent under specific lighting conditions. These unique characteristics reveal more about a diamond’s formation and composition.
Diamond Fluorescence Explained
Diamond fluorescence describes the emission of visible light by a diamond when it is exposed to ultraviolet (UV) radiation. This temporary glow occurs only while under UV light, ceasing once the light is removed. Approximately 25% to 35% of natural diamonds exhibit some degree of fluorescence, with blue being the most common color. Diamonds can also fluoresce in other colors, including yellow, green, orange, red, or white, depending on their specific composition.
The intensity of this glow varies significantly, ranging from faint to very strong. Gemological laboratories typically assess diamond fluorescence using long-wave UV light, also known as black light. This light has wavelengths generally between 350nm and 400nm. The visual effect of fluorescence is usually subtle and often imperceptible to the average observer in normal viewing conditions.
The Science Behind the Glow
Diamond fluorescence stems from specific trace elements and structural defects within the diamond’s crystal lattice. Impurities incorporated into their carbon structure act as “activators” that absorb UV energy and then re-emit it as visible light, creating the glow.
Nitrogen is the most common trace element responsible for blue fluorescence, found in about 75% of all diamonds. Boron, another trace element, is less common but can cause yellow, orange, or green fluorescence. When these elements absorb UV light, their electrons are excited to a higher energy state. As they return to their stable state, they release the absorbed energy as a photon of visible light.
Implications for Diamond Appearance and Identification
Diamond fluorescence can influence a diamond’s visual appearance, particularly in specific lighting conditions. Strong blue fluorescence can make a diamond with a faint yellowish tint appear whiter or more colorless by neutralizing the yellow hue, especially in lower color grades (I to M). Conversely, in rare instances, extremely strong fluorescence might cause a diamond to appear milky, hazy, or oily. However, this affects fewer than 0.2% of fluorescent diamonds. For most diamonds, fluorescence does not noticeably impact transparency or brilliance.
On diamond grading reports, such as those from the GIA, fluorescence is noted by its intensity (None, Faint, Medium, Strong, Very Strong) and, if medium or stronger, the color. While not one of the traditional “4 Cs” (carat, cut, color, clarity), fluorescence can influence a diamond’s market value. Diamonds with very strong fluorescence, particularly in higher color grades, may sometimes be priced lower due to perceived haziness. In lower color grades, blue fluorescence can occasionally command a slight premium due to its whitening effect.
Fluorescence also serves as a tool for gemologists in identifying diamonds. Its presence and characteristics help distinguish natural diamonds from synthetic (lab-grown) diamonds, which often exhibit different patterns or colors. It can also assist in identifying diamonds that have undergone certain treatments. However, relying solely on fluorescence for identification is insufficient, as some synthetic diamonds can mimic natural fluorescence, requiring more advanced testing methods.