Diamond Fluorescence: Bad or Good, Especially Strong Blue?

Fluorescence is a photoluminescent phenomenon in which a diamond emits visible light when exposed to ultraviolet (UV) radiation.

When a diamond is exposed to UV light in natural sunlight and artificial lighting sources such as fluorescent lamps, some of the electrons within the diamond's structure are excited to higher energy levels, known as photoexcitation. These electrons absorb energy from the UV light and move to higher energy states. After a brief period, the excited electrons return to their original, lower energy states, releasing the absorbed energy in light. This emitted light is typically in the visible spectrum, with blue being the most common color observed.

The specific cause of diamond fluorescence can vary and is still the subject of ongoing research. One proposed explanation is the presence of trace elements or impurities within the diamond crystal lattice, such as nitrogen or boron. These impurities can interact with light in complex ways, influencing a diamond's fluorescence properties.

Our Key Observations

• Fluorescence in most diamonds does not significantly affect their overall appearance.
• Fluorescence can help buyers on a budget save 5 to 15%.
• In some cases, fluorescence can negatively impact a diamond’s appearance. Avoid diamonds with fluorescence that look hazy, oily, or cloudy.
• Blue fluorescence can make near colorless diamonds appear colorless. For example, H color diamonds with medium blue fluorescence can look colorless to the naked eye.
• Strong blue fluorescence is not always detrimental; some diamonds, like an M color diamond we observed, can appear near-colorless due to very strong blue fluorescence.
• High color grade diamonds, such as D or E color diamonds, often have blue fluorescence.
• Always check the dealer's return policy to ensure you can return the diamond if necessary due to its fluorescence or for other reasons.

This price discount breakdown by fluorescence type in a diamond below is our best estimation based on its corresponding color. The discount percentage will change depending on the size of the stone and how negatively fluorescence influences it, especially if it makes it look dull or hazy.

The price discount associated with fluorescence in diamonds is not fixed, as its impact on brilliance varies. Typically, D and E color diamonds with fluorescence receive a higher discount, while F and G colors may see smaller discounts in the faint range but larger ones in the medium-to-strong blue range. For H, I, and J colors (up to Z), fluorescence can enhance the diamond's appearance, often reducing or eliminating discounts. Since blue complements yellow, fluorescence may make these diamonds appear whiter.

As confirmed in this GIA study, most consumers cannot detect fluorescence, and many diamonds with fluorescence retain similar brilliance to those without. Some stones may appear milky or hazy, but this can occur in diamonds without fluorescence as well. The key consideration is the diamond's appearance—if fluorescence does not affect it, a buyer could benefit from the 4-15% discount. We suggest discounts of up to 2% for faint, 5% for medium, 12% for strong, and 18% for very strong blue fluorescence.

Fluorescence can be an advantage, especially for diamonds with a yellow tint (H, I, J colors or lower), as blue fluorescence makes them look whiter. The intensity of fluorescence also matters; faint to medium levels usually do not harm brilliance, while strong fluorescence might. However, most diamonds with fluorescence are discounted due to perception, even if their beauty is unaffected. Detecting fluorescence is harder under indoor lighting but may be more visible in sunlight.

The picture below shows how diamonds that emit different types of fluorescence look in regular settings. 

Over the past decade, approximately 25% to 35% of diamonds submitted to GIA exhibited some level of fluorescence, with less than 10% showing any noticeable effect on appearance. This effect, however, is not always negative and can sometimes enhance the diamond's brilliance. In over 95% of cases, the fluorescence appears blue, which can make yellow-tinted diamonds look more colorless since blue complements yellow.

Key Stats from GIA’s Study

• Fluorescence Occurrence: Out of 26,010 diamonds reviewed, 9,175 (35%) exhibited some fluorescence.
• Faint Fluorescence: Of the 9,175 diamonds with fluorescence, 3,465 (38%) had faint fluorescence, considered the lowest level of blue fluorescence (faint, medium, strong, or very strong blue).
• Medium to Strong Fluorescence: 5,710 diamonds (62%) displayed blue fluorescence at intensities from medium to very strong. While 97% of these had blue fluorescence, 3% fluoresced other colors such as yellow, white, and orange.
• D-to-F Range Diamonds: Of 11,901 diamonds in the D-to-F color range, 3,250 showed fluorescence.

Key Findings

• For average buyers, no consistent effect of fluorescence on appearance was observed.
• Even expert graders disagreed on the impact of fluorescence in their evaluations.
• Diamonds with strong blue fluorescence were often perceived to have a higher color grade than they actually did.
• Most observers have observed no significant link between fluorescence and diamond clarity.

What would be my best choice between no fluorescence or faint/medium blue fluorescence?
Generally, no fluorescence is preferred. However, blue fluorescence benefits diamonds with lower color grades, such as H, I, or below. In these cases, it enhances the appearance by making the diamond appear whiter. Avoid fluorescence in D to G color diamonds, although faint fluorescence can be acceptable for G color.

Why is fluorescence perceived negatively?
Fluorescence is not as straightforward as other factors like carat weight or color. Because of this uncertainty, buyers often assume the worst and prefer to avoid it for safety.

What about fluorescence in D to F color diamonds? Why should it be avoided?
In most cases, fluorescence in D to F diamonds does not negatively affect the stone. However, in rare instances, it can give the diamond a bluish hue. While some may prefer this effect, most opt to avoid it in colorless diamonds.

Is strong blue fluorescence bad?
Strong blue fluorescence is often seen as a negative, but this perception is not always accurate. It can enhance H or lower color grade diamonds, making them appear whiter by balancing yellow tones. However, in D to G color diamonds, it may detract from the stone’s appearance. Viewing the diamond in person is important to judge the effect or ensure a return policy is in place.

Do all diamonds fluoresce?
No, not all diamonds fluoresce. GIA found that only 25-35% of the 26,000 diamonds they analyzed exhibited fluorescence.

Can fluorescence be seen with the naked eye or in any lighting?
You might notice fluorescence in bright sunlight or under UV light, such as in a tanning bed. Once UV exposure is removed, fluorescence is no longer visible.

Can fluorescence be easily detected?
No, it is difficult for even trained gemologists to detect fluorescence without high-tech tools.

Why is fluorescence not a grading factor like the 4Cs?
While GIA recognizes fluorescence as an identifying characteristic, it is not a major grading factor. While it can be helpful in certain diamonds, it is generally considered a minor negative in colorless diamonds.

Is fluorescence only blue in diamonds?
Blue is the most common form of fluorescence, but diamonds can also fluoresce in yellow, orange, red, white, and green. These other colors are less desirable than blue.

How bad is strong blue fluorescence?
Strong blue fluorescence can affect the diamond's color grade differently. It is not always negative, particularly in lower-grade diamonds, where it can enhance appearance. However, colorless diamonds may cause a cloudy or bluish effect. It is best to inspect the diamond in person to see how fluorescence impacts its look.

Does fluorescence affect a diamond's durability?
No, fluorescence does not impact a diamond's structural integrity or durability.

How can fluorescence work to my advantage?
Fluorescence can help you get a discount of 4% to 10% without compromising quality. For faint fluorescence, expect up to a 2% discount; for medium blue, 5%; for strong blue, 12%; and for very strong blue, up to 18%. In diamonds graded H to L or lower, medium blue fluorescence may enhance the diamond's appearance. Faint fluorescence is also a way to save money without losing brilliance. Ensure you have a return option when buying diamonds with fluorescence to avoid unwanted effects.

What is the range of fluorescence in GIA grading reports?
GIA grading reports list fluorescence as none, faint, medium blue, strong blue, very strong blue, yellow, and green. Blue is the most common and desirable form.

What are common misconceptions about fluorescence?
Two key misconceptions are about the color and strength of fluorescence. A diamond with blue fluorescence often appears whiter, so do not be alarmed, particularly in H to J color diamonds. Fluorescence may be viewed negatively in higher color grades (D to E). Strong fluorescence can sometimes cause a milky or cloudy look under certain lighting conditions. Always check with your diamond dealer about the specific effects of fluorescence on the stone you're considering.

• About Fluorescence - GIA
• The Effect of Blue Fluorescence on the Appearance - GIA
• A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds - Gems and Gemology
• Measurement and Characterization of the Effects of Blue Fluorescence on Diamond Appearance - GIA.