How Does Diamond Fluorescence Affect Price and Color?


Summary
Standard lighting for diamond color grading changed in 2008, from a daylight-equivalent with little ultraviolet (UV) to one with significant UV. This entirely changes the age-old advice about diamond fluorescence. Learn how fluorescence alters color and price, then decide for yourself if a fluorescent diamond is the right choice for your engagement ring.
Reading time: 5 min 31 sec
diamond fluorescence - diamond engagement ring
Is this diamond fluorescent? Without a blacklight it’s impossible to tell. Only very strongly fluorescent diamonds show a change in color from sunlight to artificial lights. “Diagonal Diamond,” photo by Cory Denton. Licensed under CC By 2.0.

What is Diamond Fluorescence?

Sometimes, tiny amounts of impurities in diamonds can cause them to glow or luminesce under UV light. UV diamond fluorescence occurs in about 35% of colorless (white) diamonds and can be faint or very strong. (Fluorescence is a type of glow that occurs almost immediately after exposure to UV light).

In most cases, diamonds fluoresce blue. This cancels out the slightly yellowish color in most diamonds, resulting in a whiter appearance in sunlight. In artificial light, there’s little UV intensity more than a few inches from the light source.

Diamond Fluorescence and Lighting

Knowing how UV affects diamonds, gemologists originally set a lighting standard for color grading without a UV component. However, in 2008 the standard changed. Diamond colors are now graded under a daylight-equivalent light bulb with a UV component. This means that the effect of fluorescence is built into the color grade!

For diamond grading, the UV component is about 30 microwatts/cm², similar to a bright, sunny day in summer with a UV index of ten! So, fluorescence isn’t going to make your diamond appear whiter. In fact, if you spend most of your time indoors, more than a few inches from a light bulb, the diamond will look worse than its color grade.

Note that this is the exact opposite of explanations you’ll find elsewhere, where they assume diamond grading still occurs in UV-free lighting.

How Does Fluorescence Affect Color Grade?

For very strong blue fluorescence, diamonds can have a color two grades better than their color under non-UV lighting. Strong blue fluorescence may be at most one grade different, and medium a half grade. The effects of faint fluorescence are negligible.

Ultimately, you’re unlikely to notice these slight changes in color grade. Try sorting diamond colors in this impossible quiz!

Compare these diamonds side-by-side. © James Allen. Used with permission.

Diamond Fluorescence, Color, and Price

However, you may notice the difference in price! Fluorescent diamonds are discounted compared to those with no fluorescence.

We compiled a table of the average prices of 1-ct excellent-cut VS2 diamonds from the Blue Nile database at different color grades and fluorescence levels. Since there are relatively few fluorescent diamonds, some of these averages may be skewed. If you’re considering a fluorescent diamond, compare the price to the non-fluorescent averages in this table.

diamond fluorescence - table of 1ct prices by color and fluorescence strength

Notice that D-color diamonds with strong fluorescence have similar prices to non-fluorescent H-color diamonds four color grades lower! Meanwhile, a strongly fluorescent I-color costs about the same as a non-fluorescent J. Fluorescence doesn’t affect all diamond prices equally!

Cloudiness in Fluorescent Diamonds

Strongly fluorescent diamonds have another drawback: cloudiness. Though this effect doesn’t occur in all fluorescent diamonds, it’s essential to take a good, closeup look at the stone prior to buying.

diamond fluorescence - cloudy cushion cut F VS2 Strong Fluorecence
This F-color cushion-cut diamond has strong fluorescence and exhibits a milky, hazy appearance. © James Allen. Used with permission.

Cloudy or milky effects are most common in strongly fluorescent diamonds but can also occur in diamonds with medium fluorescence. It’s very rare, however, to find it in faintly fluorescing diamonds.

Cloudiness is more common in higher color grades, so it’s best to avoid strong and medium fluorescent diamonds in D, E, and F color diamonds.

Not All Diamonds Fluoresce Blue

Though blue is the most common color for diamond fluorescence, some diamonds fluoresce a different color.

Yellow is the second most common color, and it would have the opposite effect of a blue diamond during color grading. So, a diamond with strong yellow fluorescence might be given one lower color grade than it appears in an environment without UV. It would look slightly better indoors, where you likely spend most of your time! Again, this is the opposite of most advice, which assumes that grading occurs without UV.

Rarer fluorescence colors include green, magenta, and red. Very strong fluorescence in these colors may make a diamond appear darker. Any degree of fluorescence lower than this in these colors will likely have no effect on a diamond’s color grade, since they aren’t complementary to yellow.

The Aurora Diamond Collection is an extensive collection of colored diamonds. Some of these diamonds fluoresce unusual colors, and others not at all. Photos of the Aurora Pyramid of Hope under white and ultraviolet lighting by Waerloeg. Licensed under CC By-SA 3.0.

Recommendations for Diamond Fluorescence

Ultimately, you’re unlikely to notice the slight changes in color due to UV fluorescence in diamonds. However, diamonds with “Very Strong” fluorescence may have a noticeable shift and should be avoided.

If you’re following our advice and sticking to lower color grades, strong fluorescence may mean that the diamond is a little off-color in non-UV-emitting lights. However, faint and medium fluorescence will give you a discount with no detriment to color.

For the highest color grades, be sure to check diamonds with strong and medium fluorescence for a milky or oily appearance. Keep in mind that you could always return the stone if it doesn’t meet your expectations.

In G and H color diamonds, milkiness is less common and fluorescence can offer a significant discount.

In the end, it’s up to your personal preference if you’d like a fluorescent or non-fluorescent diamond in your engagement ring.

Buying Fluorescent Diamonds Online

When searching online, be sure to buy from a reputable dealer with excellent, up-close images. You’ll want to check any fluorescent diamond for color and cloudiness before choosing it for diamond jewelry.

Both James Allen and Blue Nile provide closeup 360° videos of their diamonds, allowing you to see clarity imperfections, color, and cloudiness — something most online dealers don’t do.

However, for those shopping for an engagement ring, you’ll find that James Allen provides a greater selection of settings, so you’re sure to find something you’ll love!

If you’re frustrated finding the right diamond for your tastes and budget, consider using a custom jeweler such as CustomMade. With their expertise, they can steer you toward the perfect center diamond for your engagement ring!

About the author
Addison Rice
A geologist, environmental engineer and Caltech graduate, Addison's interest in the mesmerizing and beautiful results of earth's geological processes began in her elementary school's environmental club. When she isn't writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.
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