Fluorescence in diamonds is a common phenomenon that can range from faint to strong blue. While faint blue fluorescence does not significantly affect the color and clarity of diamonds, strong blue fluorescence can interact with the yellow hue in lower color grade diamonds, resulting in a milky appearance, low brilliance, and reduced value. Therefore, strong blue fluorescence may not be desirable for diamonds.

However, strong blue fluorescence typically has a negligible effect on the appearance of diamonds in the colorless and near-colorless color grade ranges (D to J). Nonetheless, there are rare instances where the strong blue intensity of fluorescence can strongly affect diamond color. In this article, we will explore the causes and effects of strong blue fluorescence in diamonds and whether it is considered good or bad.

Key Takeaways

  • Strong blue fluorescence in diamonds can result in a milky appearance, low brilliance, and reduced value.
  • Strong blue fluorescence typically has little effect on diamonds in the colorless and near-colorless color grade ranges.
  • In rare instances, strong blue fluorescence can strongly affect diamond color.

What is Strong Blue Fluorescence in a Diamond?

Diamond fluorescence is the glow seen off diamonds when exposed to UV light, including black light and sunlight. Up to 30 or 35% of diamonds fluoresce, and as much as 99% of the time, they give off a blue light. However, there are rare instances when diamonds give off other colors such as yellow, white, green, orange, or red.

The Gemological Institute of America (GIA) classifies diamond fluorescence into 4 primary grades: None, Faint Fluorescence, Medium Fluorescence, Strong, and Very Strong Fluorescence. Strong blue fluorescence is a term used to describe a diamond that emits a strong blue glow under UV light.

While fluorescence can enhance the color features of some diamonds, it can lower the quality of high-grade diamonds. In many cases where diamonds have strong blue fluorescence, the diamond can appear cloudy, hazy, or milky. This haziness can lead to a price drop, and the diamonds may not always be the best varieties.

Overall, strong blue fluorescence in a diamond can be a desirable feature for some buyers, while others may prefer diamonds without any fluorescence or with only faint fluorescence. It is important to consider the individual characteristics of each diamond and how they may affect its appearance and value.

Fluorescence Grade
No fluorescence observed
Faint fluorescence, visible under UV light
Moderate fluorescence, visible under UV light
Strong fluorescence, visible under UV light
Very Strong
Very strong fluorescence, visible under UV light

What Causes Blue Fluorescence in a Diamond?

Blue fluorescence in a diamond is caused by the interaction of trace minerals, such as nitrogen and boron, with UV light. These minerals are naturally occurring substances that are present in the diamond during the crystallization process. Fluorescence occurs in the submicroscopic structures within the carbon crystals and the trace minerals that are deep within the crystals. Nitrogen is the most prevalent mineral that contributes to fluorescence, although boron also plays a role. The blue color is a result of the interaction between the minerals in the diamond and sunlight or UV light.

Diamond Fluorescence Strong vs. Strong Blue

Diamond fluorescence is a crucial factor to consider when buying diamonds. The difference between strong and strong blue fluorescence is significant, and it impacts the appearance and value of the diamond.

When you look at a diamond with strong blue fluorescence, the blue color is highly visible under UV light. The fluorescence can make the diamond look brighter and whiter, which enhances its beauty and value. However, this effect is only observed in diamonds with a lower color grade, such as I-grade diamonds.

On the other hand, strong fluorescence without blue can negatively impact the diamond’s brilliance. When a diamond has strong fluorescence without blue, it can appear milky and hazy, reducing its value. This effect is commonly observed in diamonds with D-G color grades.

In summary, strong blue fluorescence can enhance the beauty and value of a diamond, while strong fluorescence without blue can negatively impact its brilliance and reduce its value. It is essential to consider the fluorescence level and color when buying diamonds to ensure that you get the best value for your money.

Fluorescence Level
Impact on Diamond
Strong Blue
Enhances brightness and whiteness
Can make the diamond appear milky and hazy

Strong Blue Fluorescence Diamond Good or Bad?

When it comes to diamonds, the presence of strong blue fluorescence can be a double-edged sword. The fluorescence can enhance the whiteness of lower-grade diamonds with yellow inclusions, especially in well-lit areas. However, the effect diminishes as the distance from the light source increases, so the diamond may not look as good outside of the store.

In terms of diamond quality, strong blue fluorescence may not always be a good thing. Diamonds with very strong fluorescence are often devalued, making them a bargain only for those shopping for D-graded diamonds. Additionally, blue-white diamonds may appear milky and lack the sparkle of transparent or bright white diamonds, which are more highly valued.

The cloudiness caused by strong or even medium fluorescence can also be problematic. Buyers are encouraged to avoid diamonds in the DEF color grades, as the high fluorescence can make the diamonds look hazy and milky, reducing their value. However, in almost colorless diamonds in the J-M grades, the bluish tint from strong fluorescence cancels out any faint yellow hue, resulting in colorless and bright sparkling diamonds.

Overall, the fluorescence of a diamond can greatly affect its value and appearance. For those concerned about the value of their diamond engagement ring, it is important to consider the fluorescence and color grade. Higher grades, such as I-M, can increase the value of the diamond by canceling out yellow undertones and leaving behind brighter, higher-quality diamonds.


When it comes to purchasing diamonds, buyers are often faced with the decision of whether or not to choose fluorescent diamonds. While fluorescence can add to the diamond’s beauty, it is important to remember that the color, cut, clarity, and carat weight are the most important factors to consider. For those looking for the best value for their money, it is recommended to choose diamonds that are graded high for color and clarity properties. However, for those on a budget, fluorescent diamonds can provide a cheaper option without sacrificing quality. It is important to note that the strong blue fluorescence can either enhance or detract from the diamond’s color properties. Ultimately, buyers should consider their budget and personal preferences when making a decision on whether or not to choose fluorescent diamonds.