Diamond Looks Blue in Sunlight – Is It Real One?

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You are outside looking at your new diamond ring, probably admiring it for the umpteenth time, and you realize it is looking decidedly blue today. You have never seen it this color before. Why is it a blue color in the sunlight, yet it looks colorless indoors, you wonder?

Your IGI certificate proves its authenticity and states the piece has no fluorescence. Before curiosity is taken over by doubt, allow us in this post to explore possible reasons for the color, and set your mind at ease or give you a reason to go back to the jeweler!

What Color Should a Diamond Be in Sunlight?

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An excellently cut diamond will sometimes show blue, purple, grey, or darker colors in direct sunlight. The cuts and facets determine how much light a diamond reflects and how much it leaks out. A well-cut stone will reflect a lot of light, making it appear dark to the human eye.

This appearance in the sunlight should not be mistaken for the Gemological Institute of America-GIA color grading system. This is determined by the presence of chemical impurities and structural defects integral to the stone.

On the GIA’s color-grading scale, the less color a diamond has, the better it is. The system grades from colorless to light yellow or brown.

The look is also not fluorescence, as this has a different effect. Fluorescence is a result of trace amounts of boron and nitrogen in the diamonds.

Fluorescence causes the diamond to glow when the stone is exposed to UV light. The color from direct sunlight sits inside the piece. Although the sun has UV rays, they rarely cause fluorescence in a stone.


Why Does My Diamond Look Blue In Sunlight?

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Most diamonds take on a dark blue or grey reflection in direct sunlight. Your diamond looks blue in direct sunlight as it reflects the sky.

When the sun is bright and the sky is a clear blue, the inside of a well-cut stone will reflect the blue color of the sky.

You will notice this does not happen if the sky is overcast by clouds or if you move to the shade. This is also one of the reasons why photographs of products on sale are typically taken in the shade, away from direct sunlight. Continuous diffuse lighting is the best.

Fluorescence could also make your diamond glow blue in the sunlight. This is not a color from the stone’s reflective properties, but a diamond’s tendency to produce a glow in ultraviolet light. 

Roughly 30% of all diamonds fluoresce to some extent, most in blue. Of these, only diamonds with very strong fluorescence will glow in the sunlight.

Other than white diamonds, there are blue diamonds, which are a type of diamond that exhibits the same characteristic properties of the mineral with the additional blue color in the stone.

They owe their color to trace amounts of boron that taint the crystalline lattice structure. If yours is a blue diamond, then it will appear blue in most lights.


How Does Sunlight affect Diamond Fluorescence?

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It is important to note that UV rays from sunlight will not affect most diamonds with fluorescence. Only stones with very strong fluorescence, which is about 0.6% of all diamonds, will show in sunlight by glowing.

The glow will be in the color blue, and very rarely in other colors such as yellow, orange, white, or red.

Fluorescence is associated with the presence of nitrogen atoms. It is treated as an identifying factor rather than a performance characteristic. In some cases, fluorescence can lower the value of a stone.


How Should a Diamond Look in Sunlight?

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The way diamonds look in different kinds of light is diverse and can be complicated. The look depends on the light source, the diamond color, and the diamond’s cut. The cut of the diamond is the most important factor when it comes to how it performs in light. 

The best-cut, clear, colorless diamond will look the darkest in sunlight. This comes as a surprise to most of us, who expected it to be a dazzling white.

There is a scientific explanation for the dark look: it boils down to our physiology, so follow closely. First, sunlight consists of very small, very bright pinpoint lights.

An ideal cut diamond will reflect a few of the intensely bright flares in direct sunlight. When you look at a diamond in the sun, it is equivalent to staring directly at the sun.

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Looking straight at the sun is not good for your eyes, so your pupils react by dilating to protect your eyes. The result is that the diamond appears dark due to the limited light that your pupils are allowing into your eyes.

Crushed ice diamonds will appear a lighter color in sunlight compared to ideal-cut stones. This is because crushed ice diamonds have many more facets.

In sunlight, the smaller facets on the stone split up the few flashes into multiple smaller sparkles, making it less intense for the eye, so it looks less dark by comparison.

If you want to see the beauty of your diamond in the sun, the best way is under a leafy tree if you can. The leaves filter the sun’s pinpoint lights, providing just enough shade for your pupils not to constrict the light going into your eyes.

This way, you will be able to see your diamond in all its glory, see it sparkle, and enjoy the display of colors all around you.

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One of the ways to tell if a diamond is real or fake is by looking at how it sparkles. A real diamond will sparkle white or gray on the inside (its brilliance) when held up to the light.

It will reflect rainbow colors (its fire) onto other surfaces. A fake will show rainbow colors inside when the stone is held up to the light.


Related Q&A

Why Does My Diamond Look Dark in the Sunlight?

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We perceive diamonds to be dark in sunlight because of the reaction of our pupils to the bright reflection from the diamond. The best-cut diamonds will look the darkest in sunlight.

While in reality, diamonds reflect a lot of light in sunlight, the dark color is totally due to our physiology. When our eyes are exposed to bright light, the pupils dilate.

This diminishes our perception of brightness in our immediate foreground and background, making bright things look darker, hence diamonds look darker in sunlight.


Why Does My Diamond Look Grey in the Sunlight?

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A grey hue is one of the dark appearances that a diamond can have in sunlight. This is one indication that your stone is a diamond with a good cut.

The color grey is due to your eyes’ moderation of the light to protect themselves from the damaging effects of the extremely bright light that is reflected by the diamond.

Your diamond’s cut and polish greatly influence the light performance of your diamond. When the light goes into the diamond, it is either reflected or leaked from the stone.

The reflected light produces brilliance, making it look bright, while the light that leaks out is unseen. The level of grey, from light to dark grey, is determined by the intensity of the light reflected by the diamond. The better the cut, the darker the diamond will appear.



A real diamond can look blue in sunlight. It can also look grey or dark. This is, however, not enough proof that a stone is a diamond.

When it comes to a true diamond’s reaction to light, a true diamond will sparkle white or grey on the inside when held to the light, and reflect rainbow colors onto other surfaces.

A fake will show rainbow colors inside. However, this is just one of the tests. A qualified jeweler can help you establish the authenticity of any stone.

Hey! I finally find the Answer!