Diamond Fluorescence: When to Avoid It, Especially Very Strong Blue

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

When a diamond is exposed to UV light, which is present in natural sunlight as well as in artificial lighting sources such as fluorescent lamps, some of the electrons within the diamond's structure are excited to higher energy levels. This process is known as photoexcitation. The 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 the form of 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 a 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 the fluorescence properties of a diamond.

Our Key Observations

• Fluorescence in most diamonds does not affect the overall appearance of the diamond.
• Blue fluorescence can help make near colorless diamonds look colorless. We have seen H color diamonds with medium blue fluorescence that look colorless to the naked eye.
• Strong blue fluorescence is not necessarily bad. Many diamonds with strong blue fluorescence are not adversely affected by it. Once, we observed an M color diamond looked like a near colorless diamond because of very strong blue fluorescence.
• It is common for high color grade diamonds to have blue fluorescence, such as D or E color diamonds.
• Fluorescence can be an ally because it can reduce the price of a diamond by 5 to15%.
• In some cases, diamond fluorescence may affect the overall appearance of a diamond. Avoid diamonds with fluorescence that look hazy, oily, or cloudy.
• Inquire about the dealer's return policy and ensure you can return the diamond because of its fluorescence or for any other reason.

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 how big the stone is and how negatively fluorescence influences it, especially if it is making it look dull or hazy.

The estimated price discount should not be viewed as absolute as it might change from diamond to diamond and the degree to which fluorescence affects brilliance positively or negatively. Generally speaking, buyers will get a higher discount on D and E color diamonds with fluorescence. In F and G colors, the discount may be lower in the faint range but higher in the medium-to-strong blue range. In the H, I, and J colors (even up to Z), you may not get any discounts because the fluorescence can positively influence the brilliance of the diamond. As mentioned earlier, blue is a complementary color to yellow and might make such stones look whiter than their actual color grade.

As confirmed in GIA’s study, consumers will often not be able to detect the presence of fluorescence in a diamond. Furthermore, most diamonds with fluorescence can have as much brilliance as those without. A diamond's milky, hazy, and oily appearance can also be found in stones with no fluorescence.

The most important factor in a diamond is its appearance; if you are happy with its appearance, do not worry about fluorescence. Instead, enjoy the 4-15% discount you may get when you buy a diamond with fluorescence. We believe the discount should be up to 2% for faint fluorescence, up to 5% for medium blue, 12% for strong blue, and 18% for very strong blue.

Fluorescence does not have the same impact on all diamonds; it might be a positive factor in some cases. Here are some scenarios when fluorescence might work in your favor:

Price: Since fluorescence is perceived as a negative factor universally without being dealt with on a case-by-case basis, it presents an opportunity for a buyer to grab an exceptional diamond at a discounted price.

Positive effects: Blue fluorescence is frequently beneficial in diamonds with a yellow tint (H, I, J colors or lower grades). This is because blue compliments yellow and makes a diamond appear whiter than its color.

Level of intensity: Fortunately, the intensity with which a diamond emits fluorescence is not the same. While stronger vigor often leads to a higher negative impact, lower intensity ranges, i.e., faint or medium blue, usually do not drastically harm a diamond's brilliance.

It does not hurt all diamonds the same way: In some cases, fluorescence might make a diamond look overly dull or oily; in others, it might not impact the visual appearance. However, most diamonds with fluorescence get discounted because of the perception problem, even if it does not affect their beauty.

The picture below shows how diamonds that emit different types of fluorescence look in regular settings. It is hard to distinguish between diamonds with no fluorescence and those that emit fluorescence while inspecting them with the naked eye. Observing this effect is harder under indoor lighting, though it may be easier to detect under sunlight.

Of the diamonds submitted to GIA over the past decade, around 25% to 35% exhibited some fluorescence level. In under 10% of these diamonds, fluorescence affected the appearance of the diamond. However, this effect is not necessarily harmful and can sometimes complement a diamond’s brilliance. The visible color is blue in more than 95% of the diamonds exhibiting fluorescence. Since blue is a complementary color to yellow, tinted diamonds look more colorless.

Key Stats from GIA's Study

None or No Fluorescence: After reviewing a random sample of 26,010 diamonds, GIA found that only 9,175, or 35%, exhibited some level of fluorescence. 

Faint Fluorescence: After reviewing a random sample of 26,010 diamonds, GIA found that only 9,175, or 35%, exhibited some level of fluorescence. Of the 9,175 diamonds, 3,465, or 38%, reported faint fluorescence. Please note that GIA considers faint fluorescence the lower end of blue fluorescence, e.g., faint blue, medium blue, strong blue, and very strong blue.

Medium to Very Strong Blue Fluorescence: After reviewing a random sample of 26,010 diamonds, GIA found that only 9,175, or 35%, exhibited some level of fluorescence. Of the 9,175 diamonds, 62% or 5,710 had blue fluorescence, ranging from medium to very strong blue. While 97% of these fluoresced blue in varying intensities, 3%, or 162 stones, fluoresced other colors, such as yellow, white, and orange.

Of the 11,901 diamonds in the D-to-F range evaluated in the study, 3,250 fluoresced.

Key Findings of the GIA Study

1. For average buyers (consumers), no systematic effect of fluorescence was observed.
2. Even experienced observers or graders did not agree on the effect of fluorescence on the stones they were given to evaluate.
3. Diamonds with strongly blue-colored fluorescence were perceived to have a higher grade than their actual color grade.
4. Most observers did not find any connection between fluorescence and diamond clarity.

What would be my best choice if I could pick between no or faint/medium blue fluorescence?

Generally, no fluorescence is preferred. However, blue fluorescence is helpful and recommended in H, I, and lower-color diamonds. If you can, avoid it in D to G color diamonds. Faint fluorescence is also acceptable for G color.

Why is fluorescence perceived negatively?

Because it is not a black-and-white topic such as carat weight or color, buyers need clarity about how to go about fluorescence. Hence, they generally try to be on the safe side and assume the worst.

What about fluorescence in D to F color diamonds, and why should it be avoided in such a range?

In most cases, fluorescence in D to F color diamonds does not negatively impact the stone. However, it can make the diamond look bluish in very few cases, so most people prefer to avoid it. Some prefer the bluish hue of white diamonds, so that might be your preference.

Is strong blue fluorescence bad?

You could get fortunate with strong blue fluorescence. People assume it is a super negative factor and avoid it, but it is not bad in H and lower color grade diamonds. It can help them look much whiter than their color since blue complements yellow. However, it can be somewhat negative in D to G color diamonds. Therefore, make sure you see the diamond in person to determine how the fluorescence affects it or have a solid return policy if you buy a D to G color diamond with strong or very strong blue fluorescence.

Do all diamonds fluoresce?

No! When GIA analyzed about 26,000 diamonds, only 25-35% exhibited some level of fluorescence.

Can fluorescence be seen with the naked eye or in any lighting?

You might see fluorescence under bright sunlight or in places with strong UV rays, such as a tanning bed. Once the source of UV rays is removed, you cannot see the fluorescence.

Can fluorescence be easily identified and detected?

No, it is tough for trained gemologists to see it. Most gemologists use high-tech tools to determine a diamond's degree of fluorescence.

Why is fluorescence not a grading factor like the 4Cs?

While GIA considers fluorescence an identifying characteristic in a diamond, we believe it is a significant price and quality factor. It can be helpful in certain diamonds but is generally a slight negative factor in colorless ones.

Is fluorescence only blue in diamonds?

While blue is the dominant color in fluorescence, there are also yellow, orange, red, white, and green colors. However, the latter colors are usually less desirable and least preferred than blue.

How bad is strong blue fluorescence?

We have explained this in detail in this guide. It generally depends on the color grade and is not always a negative influence. You will have to look at it case by case and inspect the diamond in person. You might end up lucky and get an extra discount while also getting a diamond with strong blue fluorescence with no adverse effect.

Can diamond fluorescence make a diamond less durable?

No, fluorescence does not influence the durability of a diamond; the diamond's structural integrity remains intact.

How might fluorescence work to my advantage?

• You may get a 4% to 10% discount on your diamond purchase without compromising quality. We believe the discount should be up to 2% for faint fluorescence, 5% for medium blue, 12% for strong blue, and 18% for very strong blue.
• Medium blue fluorescence might enhance the color of your diamond if it is within the H-L range or higher.
• Faint fluorescence will also help you save money on your diamond without losing its overall brilliance.
• When buying a diamond with fluorescence, make sure you have the option of returning it to be on the safe side.

What is the range of diamond fluorescence in GIA grading reports?

None or no fluorescence, medium blue, strong blue, very strong blue, faint, yellow, and green. Blue is the most common form of fluorescence in diamonds.

What are the misconceptions about fluorescence?

Some websites discuss fluorescence as a negative factor for diamonds. The two most misunderstood concepts in fluorescence are color and strength. A diamond will look whiter if it fluoresces blue. Do not panic if the diamond fluoresces blue; it is not as harmful in the H to J color range. Most high-color grades, such as D-E, often have blue fluorescence, a negative factor.

The fluorescence grade ranges from None to Very Strong. Diamonds with very strong fluorescence tend to have a milky look even under everyday lighting conditions. A diamond might rarely appear dirty or cloudy to a typical observer under very strong fluorescence. A good rule of thumb would be to double-check with your diamond dealer about the effect of fluorescence on the diamond you are considering purchasing. Avoid buying a diamond with intense fluorescence in terms of strength.