Ask LH: Why Do Posters Turn Blue In The Sun?

Dear Lifehacker, Why do many printed signs and posters displayed in shop windows turn blue once the sun bleaches them? Is this a result of the sun's UV rays being preferentially harmful to certain colours or inks in the material or is it a chemical process related to the original printing of these posters? Thanks, Blueless

Picture: weegeebored

Dear Blueless,

Ever since reading your question, I've had that rubbish Eiffel 65 track Blue (Da Ba Dee) stuck in my head. ("Yo listen up, here's a story about a little guy that lives in a blue world. And all day and all night and everything he sees is just blue like him inside and outside!")

This officially makes you the worst person ever. But anyway...

We pitched your question to Dr Lachlan Yee, a Southern Cross University director who specialises in photochromic dyes. Here's what Yee had to say on the matter:

Red pigment in posters has a greater amount of frequency and therefore energy compared to blue pigment. It has been hypothesised by chemists and physicists that the high energy absorption destroys the pigment. Therefore you're going to get that fading back to blue because this is all that's left behind: the red pigment has died off. So basically, the red in the poster has absorbed all the high energy and subsequently degraded, leaving behind the blue pigments.

"I have a blue house with a blue window. Blue is the colour of all that I wear. Blue are the streets and all the trees are too. I have a girlfriend and she is so blue." Damn it, it's still stuck in my head! (Incidentally, we have no idea what that 'Captain Manja: Backside Can Do' poster is advertising. Frankly we're afraid to think.)

Cheers Lifehacker

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    You are a mean man Mr. Jager.
    A mean, mean (blue) man.

    Why did you have to mention that song? Now I have it in my head too!!

    "Red pigment in posters has a greater amount of frequency"

    What the??

    Probably should read:
    "Red pigments absorb more colours of a higher frequency"

    "This officially makes you the worst person ever."
    No, that'd be you. He only infected one person with that ear worm, whereas you managed to spread it to all your readers, who are now blue da ba dee da ba die die die!!!!!

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