When people talk about diamonds, the 4Cs—cut, color, clarity, and carat weight—usually take center stage.
They’re the key factors that shape how a diamond looks and how much it costs. But seen on grading reports is another detail that doesn’t get as much attention: diamond fluorescence.
Fluorescence is a natural effect where a diamond glows under ultraviolet (UV) light. Most often, that glow is a soft blue, but other colors can also appear.
Diamond fluorescence has been the subject of debate for years because some believe it improves a diamond’s look, while others see it as a drawback.
With this being said, it isn’t the biggest factor that influences looks or value, but, since diamonds are a large emotional and monetary investment, it’s still something worth knowing about.
In this article, we’ll discuss the basics of fluorescence: what causes it, how it affects appearance and value, and how you can factor it in the search for your next stone.
What Causes Diamond Fluorescence
It’s a well-known fact that diamonds are made out of carbon. One thing often overlooked, though, is that carbon isn’t the only thing that’s present within a diamond’s crystal lattice.
During the creation of diamonds deep within the earth, trace elements like boron or nitrogen can get trapped inside the stone.
It’s these trace elements that are the cause of fluorescence; when exposed to UV light, they make the diamond give off a glow.
According to the Gemological Institute of America (GIA), diamond fluorescence is actually quite common. About 25 - 35% of natural diamonds fluoresce, with around 95% of them showing up as blue, and the other 5% showing up as other colors like green or yellow.
How Diamond Fluorescence Is Graded
Fluorescence is one of the characteristics recorded on the GIA’s grading reports. Like seen in scale gradings of attributes like color or clarity, fluorescence is described on a scale in terms of its strength
The grading scale includes:
- None - no fluorescence
- Faint - minimal fluorescence under UV light
- Medium - noticeable fluorescence under UV light, a trained eye may be needed
-
Strong - obvious and significant fluorescence under UV light
- Very Strong - intense fluorescence under UV light
- If the fluorescence is medium or higher, the color of the glow is also noted, which is usually blue.
As mentioned above, while other colors like green or yellow exist, they’re rare.
To keep the grading consistent, tools specifically meant to measure fluorescence are used in precise settings to ensure the diamond is viewed under controlled UV light, giving a control to measure against.
How Fluorescence Can Affect a Diamond’s Appearance and Value
For the vast majority of diamonds, fluorescence doesn’t have any noticeable effect on appearance under normal lighting.
That said, there are a few perspectives that some jewelers have that’s worth knowing about.
Lower Color Grades and Fluorescence
In diamonds with lower color grades (I–M), where more yellow is present, some gemologists believe that blue fluorescence can actually help reduce the tint and make the stone look a little whiter. This comes from basic color theory—when yellow and blue light mix, the result appears closer to white.
Because of this school of thought, in cases of diamonds with lower color grades, diamonds with high degrees of fluorescence may be priced a bit higher than their low or non-fluorescent counterparts.
Higher Color Grades and Fluorescence
At the other end of the scale, very high color grades (D–F) are already icy white. Some jewelers note that strong fluorescence in these stones can sometimes have a hazy or oily look. While the reasoning makes sense, a GIA study found that only about 0.2% of diamonds show this effect, making it extremely rare.
For this reason, diamonds in the higher color grades with strong fluorescence can be priced a bit lower than those without it.
Conclusion
Fluorescence is an interesting part of a diamond’s identity, but it’s not nearly as important as the characteristics outlined by the 4Cs. For most diamonds, it won’t have any noticeable effect in everyday scenarios.
With this in mind, when shopping, think of fluorescence as an extra detail rather than a deciding factor. Focus first on cut, color, clarity, and carat weight, since those are what have the most impact on a diamond’s sparkle and overall appeal.
If fluorescence is listed on a grading report, the best way to know if it matters for you is to see the diamond in person.
At Paul’s Jewelers, we have a team of GIA graduate gemologists who would be more than happy to help you on your diamond journey. Our team can walk you through the details of a diamond, and show you how different stones look side by side - fluorescence or not. Stop by our showroom at your convenience, and see why we’ve been Milwaukee’s favourite jewelers for over 50 years.
