Sunday, September 18, 2011

Why do veins appear blue?

I’d like to straighten out an incorrect statement that I made in a previous post and in my book on color.

On page 156, I said that in the region surrounding the lips, “there are relatively more veins carrying blue deoxygenated blood,” It turns out to be a misconception that blood turns blue when it loses its oxygen contact.

Yet veins deep below the skin certainly do appear blue. Why, then has no one seen blue blood? I had always assumed the answer was that if when a vein is cut open, the blood immediately turns red on contact with air.

In fact, blood is always red (or at least a deep maroon color) when it is deoxygenated.

What’s going on here? The scientific answer involves a lot of factors, but according to Wikipedia, on light Caucasion skin at least, “veins appear blue because the subcutaneous fat absorbs low-frequency light, permitting only the highly energetic blue wavelengths to penetrate through to the dark vein and reflect off. A recent study found the color of blood vessels is determined by the following factors: the scattering and absorption characteristics of skin at different wavelengths, the oxygenation state of blood, which affects its absorption properties, the diameter and the depth of the vessels, and the visual perception process.”

PDF of scientific paper
Wikipedia on Veins
Good summary by
Science on the subject  
Color and Light: A Guide for the Realist Painter
Previously on GJ: Three Color Zones of the Face

Photo from We Heart It.
Thanks, Myke!


MrCachet said...

And here I thought the only people whose veins appeared blue - were Bluebloods!

Jason Peck said...
This comment has been removed by the author.
Jason Peck said...

Ive read that Bouguereau, painted veins with straight Viridian, and then scumbled translucent layers of the local skin tone over the Viridian to recreate the effect of blue veins. Ive tried it myself, and the effect is very believable. Ive tried other colors with bad results. The Viridian seems to work best.

Has anyone else tried this?

Chibi Janine said...

Don't feel bad about the mis-information I was told this by a biology teacher of all people :)

brownbird said...

I'll correct my copy immediately =:o)

Liz Mooney said...

My veins appear more green, is that related to my skin tone?

Cindy Skillman said...

This is funny to me. I've seen a lot of venous blood, and it's a dark, dull red immediately on leaving the body. Yet for some reason I still believed the deoxygenated blood thing. In fact, if I remember correctly, we were even told this in nursing school. So despite the clear evidence of my eyes, I believed what I had been taught. I find that so typical of so many things. It's easy to deceive ourselves, isn't it?

I suppose, relatively speaking, venous blood is "bluer" than arterial blood (which is astonishingly and sometimes alarmingly red -- alarming when you weren't expecting to see it!).

That said, even venous blood in a living person's veins contains a LOT of oxygen. I have noticed, though, that if the blood is from a corpse (on removing an IV, for example), it can be so dark as to appear almost (though not quite) blue.

James Gurney said...

Thanks, Cindy, We're benefiting from your experience with corpses, which is way beyond mine. And what you say is true. I remember when I was a kid someone told me that all clouds came from factory smokestacks, and it took me many years to say, "Hey, wait a minute!"

Liz, Bouguereau must have gotten the color right, at least for your veins.

Fantasio said...

Sometimes things are as easy as they seem. The external elastic tissue from a blood vessel is of a blue color, depending on the thickness of the fibrous connective tissue around it, the blue shines through. The smaller or finer the vessel, the more violet and finally red does it appear underneath the skin.

According to this illustration: and some observations from pathology (NCIS, C.S.I.:) imagery.

EvanDouglas said...

While it is true that the venous blood vessels carry a lower oxygen concentration than their blood, it is not because they look blue in your skin.


The Art of Kevin Wueste said...

This past week my fellow art nerd (tm) Anna and I have been talking about Rayleigh scattering, Tyndall and Mie scattering of pigments. The book (which is intense and dryer than desert sand in, uh, the desert: "The Physics and Chemistry of Color; The 15 Causes of Color" by Kurt Nassau 2nd ed 2001 talks about this very phenomena: "Veins show blue because they provide the dark background for surface scattering. (Tyndall blue).. thank you for the update! Have truly learned from and enjoyed your book! - Kevin

Adam Davis said...

Artist Douglas Flynt has a great blog post of his own concerning the "blue vein" phenomenon. You guys may find this interesting as well!