Some diamonds react to ultraviolet (UV) light by emitting a visible glow, a phenomenon known as fluorescence. When exposed to light sources like a black light or natural sunlight, these diamonds temporarily glow or appear to change color. This characteristic stems from the diamond’s unique composition and structure.
Understanding Diamond Fluorescence
Fluorescence means a diamond emits visible light under ultraviolet light. This effect is temporary, lasting only as long as the diamond remains exposed to the UV light source. Once the UV light is removed, the diamond immediately stops glowing and returns to its original appearance.
The most common color of diamond fluorescence is blue, appearing in approximately 95% of fluorescent diamonds. However, diamonds can also fluoresce in other hues, including yellow, green, orange, red, white, and pink, though these are less common. The glow’s intensity varies from a faint shimmer to a strong, distinct luminescence.
The Science Behind the Glow
A diamond’s ability to fluoresce results from specific trace elements or structural defects within its crystal lattice during formation. These elements absorb ultraviolet light energy and re-emit it as visible light, creating the characteristic glow. Nitrogen is the most common impurity responsible for blue fluorescence.
When nitrogen atoms are arranged in particular configurations, such as the N3 center (a group of three nitrogen atoms around a vacancy), they produce a blue glow under UV light. Other impurities like boron can lead to different colors, such as yellow or red fluorescence. Hydrogen and other structural anomalies also contribute to various fluorescent colors.
Impact on Diamond Appearance and Value
Fluorescence can subtly influence a diamond’s appearance, particularly in certain lighting conditions. In diamonds with a faint yellowish tint, blue fluorescence can sometimes make the stone appear whiter or more colorless in natural daylight, which contains UV light. This occurs because blue is the complementary color to yellow, neutralizing some undesirable yellow tones.
Gemological laboratories, such as the GIA (Gemological Institute of America), grade fluorescence based on its intensity under long-wave UV light, using categories like None, Faint, Medium, Strong, and Very Strong. For most diamonds, fluorescence has no noticeable impact on transparency or beauty. Only in a small percentage of cases (fewer than 0.2% of GIA-submitted diamonds) does strong fluorescence cause a cloudy or milky appearance.
Regarding value, fluorescence’s impact is nuanced. Diamonds with high color grades (D-F) exhibiting strong blue fluorescence might sometimes sell at a slight discount due to a perception of haziness, even if none is present. Conversely, for lower color grades (I-M), medium to strong blue fluorescence can be desirable as it enhances their apparent color, sometimes leading to a slight premium. Ultimately, the effect on value is often less significant than other factors like cut, clarity, and carat weight.
Distinguishing Natural vs. Lab-Grown Diamonds
UV reactivity, specifically fluorescence, can indicate differences between natural and lab-grown diamonds, though it is not a definitive test. Both natural and laboratory-created diamonds can fluoresce, sharing the same fundamental physical and chemical properties. However, their fluorescence characteristics often differ due to distinct formation processes and impurity profiles.
Natural diamonds tend to fluoresce more strongly under long-wave ultraviolet light. Lab-grown diamonds, particularly those produced by High-Pressure High-Temperature (HPHT) or Chemical Vapor Deposition (CVD) methods, may show different fluorescence patterns or react more strongly to short-wave UV light. For instance, HPHT diamonds can exhibit a cruciform pattern, while CVD diamonds might show a striped pattern. While these differences provide clues, professional gemological testing with specialized equipment is necessary for conclusive identification of a diamond’s origin.