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What Is Fluorescence in a Diamond?
Fluorescence is a type of luminescence, or light. Fluorescence in diamonds refers to their natural ability to emit a visible glow when they're exposed to ultraviolet (UV) light. When diamonds with strong fluorescence are placed under UV light sources, including natural sunlight, they typically emit a blue glow, and the intensity of the glow varies. Once the UV light source is removed, this glowing effect immediately stops.
This property isn't universal among diamonds. Research indicates that approximately 25-35% of all diamonds show some degree of fluorescence when exposed to UV light. Among these fluorescent diamonds, about 95% emit a blue glow, while the remaining small percentage produce other colors like yellow, green, red, purple, or orange.
What Causes Diamond Fluorescence?
Fluorescence in diamonds is created by trace elements that become part of the diamond during its formation deep within the earth. As diamonds crystallize over millions of years, small amounts of elements such as nitrogen, boron, or aluminum can become incorporated into the diamond's structure. The most common cause of blue fluorescence in diamonds is from the addition of nitrogen to the diamond’s crystal structure: When nitrogen atoms group together in a specific way, they form what's known as an N3 center. These special arrangements, or “luminance centers,” allow electrons to absorb UV light — and then release that energy as visible blue light.
Different elements create different fluorescence colors. While nitrogen typically produces blue fluorescence, other elements may create yellow, green, or reddish glows. Approximately 30% of natural diamonds have the unique arrangement of trace elements to display some noticeable degree of fluorescence, while the remaining diamonds lack the special arrangements needed to create visible fluorescence. This does not affect the diamond's structure or durability; it simply adds a captivating optical property that can enhance a diamond's unique character and beauty.
How Does Fluorescence Affect a Diamond?
The impact of fluorescence varies depending on intensity, color grade, and viewing conditions:
- Colorless diamonds (D-F): Fluorescence typically has no noticeable effect on appearance.
- Near-colorless diamonds (G-J): Strong and very strong blue fluorescence often enhances appearance by counteracting the faint yellow tint, making these diamonds appear whiter and brighter under strong UV light.
- Faintly yellow diamonds (K-M): Medium to strong blue fluorescence frequently improves these diamonds significantly by masking yellow tones and increasing apparent whiteness.
Diamond fluorescence manifests differently depending on the lighting environment, which can significantly impact your experience with the stone in everyday settings:
- Indoor Lighting: Most standard indoor lighting contains minimal UV light, making fluorescence virtually undetectable. However, some fluorescent bulbs and certain LED lights do emit small amounts of UV radiation, which might trigger a subtle glow in diamonds with medium to strong fluorescence.
- Outdoor Sunlight: Natural sunlight contains UV radiation, particularly on bright, clear days. In this environment, diamonds with strong to very strong fluorescence may exhibit their characteristic glow, potentially enhancing the appearance of diamonds with yellowish tints.
- Special Lighting Conditions: In venues with high UV content lighting (nightclubs, certain restaurants, and events with black lights), fluorescent diamonds will display their most dramatic effects, creating a distinctive and personalized experience with your jewelry.
Diamond Fluorescence Scale
The GIA grades diamond fluorescence on a five-point scale, from None to Very Strong. This assessment is made by examining the diamond under a specialized long-wave UV lamp in controlled lighting conditions. If the fluorescence is Medium, Strong or Very Strong, the color of the fluorescence will also be noted on the grading report. Here's what each grade means:
None
Diamonds with "None" fluorescence exhibit no visible glow when exposed to UV light. These diamonds are considered "non-fluorescent." Under normal lighting conditions, these diamonds appear identical to their counterparts with fluorescence.
Faint
Diamonds with "Faint" fluorescence exhibit a very slight glow under UV light. This level of fluorescence is usually not visible to the naked eye and requires specialized equipment to detect it. Faint fluorescence has virtually no impact on a diamond's appearance in normal lighting conditions.
Medium
"Medium" fluorescence describes a noticeable glow under UV light that may occasionally be visible in certain daylight conditions, particularly in outdoor settings with strong sunlight. This beneficial effect has led some consumers to specifically seek out diamonds with medium fluorescence.
Strong or Very Strong
Diamonds with "Strong" or "Very Strong" fluorescence emit a vibrant, pronounced glow when exposed to UV light. This intensity of fluorescence can be visible in natural sunlight and sometimes even in environments with high UV content.
Very strong fluorescence is particularly uncommon, appearing in less than 1% of diamonds. These diamonds require careful evaluation before purchase, as they may exhibit the most noticeable effects – both positive and negative – associated with fluorescence.
How to Tell if a Diamond Has Fluorescence
Fluorescence in diamonds remains invisible under standard indoor lighting conditions, making specialized methods necessary for detection. There are two reliable ways to determine if a diamond exhibits this unique property:
- Professional Certification: The most definitive method is to review the diamond's grading report from a reputable gemological laboratory such as GIA or IGI. These certificates specifically document fluorescence presence and categorize its intensity as None, Faint, Medium, Strong, or Very Strong, along with the fluorescence color.
- UV Light Examination: For a direct observation, view the diamond under a long-wave ultraviolet light (black light) in a darkened room. Fluorescent diamonds will emit a visible glow—typically blue, though occasionally yellow, green, or other colors depending on the specific crystal lattice defects present in the diamond.
Is Diamond Fluorescence Good or Bad?
Diamond fluorescence is neither inherently good nor bad. Diamond fluorescence is simply a natural characteristic that affects different diamonds in different ways, depending primarily on their color grade.
The Gemological Institute of America conducted a comprehensive study on diamond fluorescence and found that in most cases, observers could not detect any visual difference between fluorescent and non-fluorescent diamonds under normal lighting conditions. Many participants actually preferred the appearance of diamonds with medium to strong blue fluorescence.
When evaluating a diamond, it's best to judge each stone individually under various lighting conditions rather than making decisions based solely on the fluorescence grade on a certificate. What ultimately matters most is how the diamond looks to you.
