February 15

What Color Should a Diamond be Under UV Light? | How Is Fluorescence Interpreted?


Author: David Kopelman

Key Takeaways

  • A diamond's color varies between yellow and greenish-blue depending on the fluorescence type.
  •  Fluorescence in diamonds refers to a glow type that occurs just after exposure to ultra violet light.
  • All diamonds don't fluoresce blue; some fluoresce a different color.
  • Any existence of fluorescence in a diamond negatively affects its value.

What Color Should a Diamond be Under UV Light?

Diamonds are fine-looking stones that have captivated many jewelry enthusiasts for diamond's sparkle and brilliance. However, there's another feature of them that isn't, in most cases, talked about, which is diamond fluorescence.

Do you know that diamonds glow in an array of colors under ultraviolet light? If you’re looking to know what color a diamond should be under UV light, go through the following sections.

Aside from learning what a fluorescent diamond is, you’ll also know how and why some types of diamonds can glow in black light. You'll also discover how to use this concept to your advantage when purchasing a diamond engagement ring.

What is Diamond Fluorescence?

Fluorescence is the effect that UV lights have on a diamond. It originates from incorporating certain chemical impurities and natural elements like aluminum, nitrogen, and boron during the formation process.

a diamond under the UV light

Electrons from these natural elements and chemical impurities absorb a certain percentage of UV lights, causing them to release protons in order to convert to their natural state. When you see a natural diamond glow, you’re witnessing its fluorescence.

A diamond with medium or faint fluorescence can have a slight haziness appearance. In most cases, fluorescence diamonds glow blue. Naturally sourced diamonds exhibit light yellow, yellow gold, or white fluorescence less often.

Natural diamonds with very strong fluorescence appear hazy, milky, or cloudy to the naked eye. Out of hundreds of colored diamonds, only 10% have a certain level of fluorescence.

Types of Diamond Fluorescence

The Gemological Institute of America grades a diamond with fluorescence based on intensity. With that in mind, here are the grades on the fluorescence diamonds scale from worst to best.

  • Very strong fluorescence: Natural diamonds with very strong fluorescence show a saturated or prominent hue when under black light.

  • Strong fluorescence: Real diamonds with strong fluorescence exhibit an intense or strong blue hue under ultraviolet light.

  •  Medium fluorescence: Naturally sourced diamonds with medium fluorescence show a strong blue hue under ultraviolet light. Unlike diamonds with very strong and strong fluorescence, diamonds with medium fluorescence are usually not detectable to the naked eye.

  • Faint fluorescence: Diamonds with faint fluorescence have a slight fluorescence amount. They aren't detectable to the naked eye and exhibit a subtle blue glow under black light.

  •  Non-fluorescence: GIA grades diamonds without fluorescence as non-fluorescence.

How Does Fluorescence Affect Diamond Value and Color Grade?

Any existence of fluorescence negatively affects a diamond's quality and value to some extent. The greater the diamond fluorescence, the more it negatively affects the monetary value of the piece of jewelry. Jewelers and diamond sellers usually discount high-color diamonds with very strong fluorescence, between 5% and 40%, compared to similar diamonds in the non-fluorescence category.

The prices of white diamonds, with the same features and characteristics, can vary massively depending on the fluorescence amount available. A milky appearance that very strong or strong fluorescence causes affects the diamond's brilliance and the color grade of a diamond. 

Lower color grades aren't affected similarly to higher color ranges. While a diamond’s fluorescence never increases the value of a piece of jewelry, the presence of any level of fluorescence in a diamond between J, K, and L color grades can fool a buyer into seeing an attractive color.

A medium blue fluorescence diamond color can counteract any yellowish tint a real diamond may have. In some cases, it makes it appear whiter, and in the end, this’ll increase the color grade of the diamond. Fluorescence can make a diamond have a blue color, shine, and sparkle than a raw diamond as long as it lacks fluorescent properties.

diamonds under UV light

Is Diamond Fluorescence Good or Bad?

Whether a fluorescent diamond is bad or good primarily depends on your preferences. Here are some points that might help you judge how bad or good fluorescent diamonds are.

  • Fluorescence in a real diamond reduces yellowness and creates whiteness, therefore, color J can sometimes look like color I in direct sunlight. If you want to buy diamonds with lower color grades anywhere between I, J, K, and L, consider purchasing them with strong/medium/faint fluorescence instead of non-fluorescence.
  • Diamonds with fluorescence are cheaper.
  • A fluorescent diamond sometimes exhibits haziness, and it might have an oily appearance in orangey light or daylight.

Medium and Strong Blue Fluorescence: What is the Difference?

The term blue with fluorescence in the jewelry world refers to the fluorescence color of a given diamond. If you have been a diamond fan for a long time, you might have also come across medium and strong blue diamonds. 

A medium or strong blue diamond glows blue when sourced to ultraviolet light. Most labs use the terms negligible and loose diamond to describe non-fluorescent diamonds.

Are All Diamonds Fluoresce Blue?

Not all diamonds fluoresce blue, some of them glow yellow, purple or greenish-blue. The second most common color in the industry is yellow, which has the opposite impact of a blue diamond during the process of color grading. Rarer fluorescence colors are red, magenta and green.

different diamond fluorescence

Do Lab Diamonds Glow in Ultraviolet Lights Like Real Diamonds?

Just like naturally sourced diamonds, lab diamonds can display fluorescence. The submicroscopic structures available within the rock crystal during the growing process cause this effect. 

Blue fluorescence is the most common color in lab diamonds due to the existence of aluminum, boron, and nitrogen impurities. Lab-grown diamonds can also exhibit rarer colors of fluorescence, including white and orange.

Do Natural Diamonds Glow Purple Under Black Light?

Natural diamonds don’t glow purple under black-lighting, but some minerals show this property. Fluorite, for example, can often exhibit purple color under black lighting, where it glows brightly.

Final Thoughts: Is this a Reliable Test to determine if a Diamond is Real or Fake?

There is a lot of unproven information on the internet that claims you can know if a diamond is fake or real based on fluorescence. You should never use fluorescence to determine if a diamond ring is real or not. 

While most diamonds don’t fluoresce, approximately a third of naturally sourced diamonds do. Many other gemstones and minerals display fluorescence, so don't use this phenomenon to identify whether a diamond is fake or real.

FAQs about Fluorescence in Diamonds

Why do my Diamonds Look Blue under UV Light?

Your diamonds look blue under ultraviolet light since the minerals inside them are blue. Also, remember blue is the most common color in terms of diamond fluorescence.

Why Does My Diamond Look Green under UV Light?

Your diamond’s fluorescence is green mainly because of phosphorescence. The luminous green phosphorescence makes it look green when exposed to UV or any other visible light.

What Color do Diamonds Show under UV Light?

The most common color when it comes to diamond fluorescence is blue. Almost all fluorescent diamonds glow blue since they have blue crystals in them.

Do Naturally Sourced Diamonds Glow Under Ultraviolet Light?

Diamonds glow when exposed to UV or visible light, and in most cases, they produce a blue glow.

About the Author:

David Kopelman

In every article I write, I share my experience as a GIA Graduated Gemologist so that you learn everything about diamonds and other precious stones.

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