What is Diamond Fluorescence?

Jan 20th 2023

What is Diamond Fluorescence?

You’re starting the New Year off right with some much-needed research on diamond engagement rings. Yes, it’s time to propose to your wonderful partner. But as you’re poring over diamond certificates, you’re still confused on one particular topic: diamond fluorescence.

The term “fluorescence” usually indicates brightness, so you probably want the most fluorescent diamond you can find, right? Not exactly. Diamond fluorescence actually has nothing to do with the stone’s sparkle. There’s plenty more to understand, and we’re here to help you learn more.

What is Diamond Fluorescence?

To put it simply, diamond fluorescence refers to the way in which the gems respond to long-wave ultraviolet (UV) rays. Here’s an example. When sunlight hits certain diamonds, they tend to glow in various colors, primarily blue.

But not all diamonds display fluorescence. According to the Gemological Institute of America (GIA), roughly 25-35% of diamonds show some form of fluorescence. That’s based on the thousands of gems that have been submitted to GIA for evaluation in the past several years.

Now, you’re probably wondering whether these diamonds look like fancy color diamonds. Again, not exactly. Of the diamonds that have the ability to glow while out in the sun, only about 10% display enough fluorescence to alter the stones’ appearance. We’ll dig into more of this later.

So, what causes certain diamonds to glow? Sometimes, traces of chemical elements, like nitrogen, get trapped inside of the diamond crystals as they form, which causes slight variations in the gem’s composition. However, this ultimately doesn’t affect the stones’ durability. They still score a perfect 10 on the Mohs Hardness Scale — a scale that ranks the durability of diamonds, gemstones and other minerals.

*Pro Tip: Both natural and lab grown diamonds can exhibit fluorescence. You might even find diamonds that glow in yellow, orange and red hues under UV light, but it’s rare.

How is Diamond Fluorescence Graded?

If you know a thing or two about diamonds, you might already be familiar with their color scale, which features letters of the alphabet for grading. Stones given D through F rankings are colorless and valuable while Z-rated gems have light yellow or brown tones and are therefore least desirable.

But diamond fluorescence is measured on a different scale and usually doesn’t influence diamonds’ overall color. Here’s a breakdown of the full scale.

None: This rating is pretty self-explanatory. It simply means that a diamond doesn’t glow when exposed to UV rays. It also means that any traces of chemical elements in the stone aren’t significant enough to produce fluorescence.

Faint: You’ll likely see a soft, subtle glow when diamonds with faint fluorescence are placed under UV light. That’s because these gems contain small amounts of chemical elements that cause fluorescence.

Medium: When UV rays hit these diamonds, they give off a stronger glow than stones labeled as “faint.”

Strong: As you might expect, gems categorized in this group exhibit a deep glow of blue, yellow, orange or red.

Very Strong: As the highest ranking on the scale, “very strong” gems display a remarkably bright shade of colored glow.

*Pro Tip: Fluorescence rankings of “medium,” “strong” and “very strong” might impact a diamond’s appearance, so keep an eye out for this on diamond reports as you’re engagement ring shopping.

What Diamond Fluorescence Rating Should You Pick?

It honestly depends on your taste! A GIA study on fluorescence found that shoppers tend to prefer diamonds that range from medium to strong fluorescence. And here’s a great trick: It might not always be possible to get your hands on valuable, colorless diamonds (those that range from D through H on the color scale). But if you come across a medium or strong fluorescent diamond, make sure that it has a lower color grading — roughly between the letters I and N. 

Why not opt for a gem with a high color grade and “very strong” fluorescence? These diamonds can occasionally appear cloudy with a grayish tint. In fact, some jewelers don’t even carry “very strong” stones as a result.

*Pro Tip: Before purchasing, check your diamond under various types of lighting to make sure that it still looks stunning! It’s also helpful to compare with other diamonds that have similar color grades.

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