What is Sun Bleaching?

[kookbreaker]

Hello folks,

My store's window faces the sun for much of the day, so I have to make it a point to rotate the products that are in that window lest the sun bleach away any bright colors on the packaging.

Now, one thing I have in the window are a pair of the famous happy drinking birds:

http://i303.photobucket.com/albums/nn125/SpectrumSci/112.jpg

Now, the glass holding the fluid in the drinking birds is well sealed, but yet despite this, after some time in the sun the color in the fluid starts to fade! But where does it go? The fluid doesn't go anywhere, yet the color does!

I tried doing a web search and found that sun bleaching is a very undiscussed topic. Perhaps it has another name, but there is no entry to be found on wikipedia, or anywhere else.

Anyone got a clue?

[Delvo]

Big complex molecules tend to fall apart with hit with energy. If that happens to a molecule of dye or paint or such, then the resulting smaller molecules are not dye or paint anymore.

[TX50]

It's basically as "Delvo" says. The changes in the molecules affect their
ability to absorb and reflect certain wavelengths of light. Try searching
for "ultraviolet bleaching" to get more information.

[leon_heller]

Red seems to be affected more than other colours - red paint on cars fades much quicker, for instance.

Leon

[BenBurch]

...My store's window...

Never noticed you had a store. I buy stuff like that. Bookmarked!!!

[kookbreaker]

Never noticed you had a store. I buy stuff like that. Bookmarked!!!

Cool! :D

But sometimes this makes me think me think my marketing sucks, even among friends. :P

[kookbreaker]

Big complex molecules tend to fall apart with hit with energy. If that happens to a molecule of dye or paint or such, then the resulting smaller molecules are not dye or paint anymore.

OK, this makes more sense. I had thought the molecule was being evaporated, not broken.

[kookbreaker]

Red seems to be affected more than other colours - red paint on cars fades much quicker, for instance.

Leon

I've been noticing that. The red colored drinking birds fade mighty fast, while the blues hang on for a while.

[I Ratant]

Mere long-term exposure to the sun turns bones into dust out here in the desert.
Eats up the rubber in car tires.
Cracks and disintegrates plastics.
It will bleach the plastic films I cover my toy airplanes with, and make the side facing the sun become quite brittle, able to poke a finger through, while the other side stays stiff and firm.

[Evilgiraffe]

I think a tentative explanation could go along the lines of....

Red dyes work by absorbing blue light, conversely blue dyes will absorb red light. Photons of blue light have higher energies than red photons hence the red dye will absorb proportionally more energy from the light irradiating it.

In order to react and transform into something else, all molecules must pass through a high energy transition state and one way of getting there is to absorb a photon. The higher energy of blue photons puts red dye molecules in a higher excited state than red photons do to blue molecules, therefore from this higher excited state the red dye molecule is more likely to react and become something other than a dye than the blue molecule.

There are some hefty assumtions about the chemistry of the dyes involved but it seems plausible to me.

[BenBurch]

Cool! :D

But sometimes this makes me think me think my marketing sucks, even among friends. :P

Much rather buy from you than American Science and Surplus where I don't know anybody.

Some time next year, I plan to buy a 10" Dob so I'll be looking to you then. I used to make my own mirrors, but my time is worth $50/hr to me, and there is no way to make a decent telescope in less than 10 hours...

[FramerDave]

I deal with this a lot, since a big part of framing is an effort to preserve artwork in as close to its original state as possible. The worst part of fading comes from UV light in the 300-380 nanometer range. When you're dealing with art, somewhere around 97-98% of this portion of the spectrum can be blocked with the proper glass.

What Delvo mentioned is correct. UV energy will hasten the breakdown of molecular bonds in the dyes, causing the degradation of color. Other parts of the spectrum including visible light and infrared (heat) will do the same, but at a slower rate. Pigments are far less likely to break down and fade. And fading is a cumulative process. Low light over a long period of time can fade anything as much as harsh light in a short period of time.

And yes, red will always fade first. Anything blue is blue because it reflects light at that end of the spectrum, which would include UV light. Red absorbs it, meaning that it will fade faster. If you look at cheap artwork in cheap frames, especially at a fast food joint (because of the large windows and fluorescent lights) you'll see that they're usually nothing but shades of blue.

It might be worthwhile to get some quotes on UV-blocking window film. It'll help protect your stock and probably help lower your energy bills.

[Blackadder]

Edit: oh while I was typing this it seems Framer Dave already answered my question minutes before I asked!


I have an old calendar with nice pictures. I hung them on the walls of a place in my house that has direct sunlight most of the day. During the years all color has gone away except the Blue.

But I left them hanging since they are still pretty as blue black and white only.


Can somebody explain to me why all color has gone except the blue? Is that a logical event or could it have been another color if the pictures would have been printed in another ink.

[fuelair]

OK, this makes more sense. I had thought the molecule was being evaporated, not broken.
In a sealed sytem, even if evaporated (and iirc, evaporation on both the beak and in the sealed part is involved w/how the bird works) when the temp drops, the liquid (ether iirc - though probably not nowadays) recondenses. Oh, molecules do not evaporate they just get further apart as a function of the evaporation of the liquid the are part of.

[kookbreaker]

Much rather buy from you than American Science and Surplus where I don't know anybody.

There's a small irony, I do know folks at AS&S. :D


Some time next year, I plan to buy a 10" Dob so I'll be looking to you then. I used to make my own mirrors, but my time is worth $50/hr to me, and there is no way to make a decent telescope in less than 10 hours...

At the prices telescopes are going for these days mirror making has become a dying art. C'est la vie.

[kookbreaker]

In a sealed sytem, even if evaporated (and iirc, evaporation on both the beak and in the sealed part is involved w/how the bird works) when the temp drops, the liquid (ether iirc - though probably not nowadays) recondenses. Oh, molecules do not evaporate they just get further apart as a function of the evaporation of the liquid the are part of.

This is why I was confused. The liquid remains, but the color is gone. I had wondered if it was caused by evaporation, but the sealed system made that impossible.

I still am surprised there was no wikipedia page about this.

[ddt]

Red seems to be affected more than other colours - red paint on cars fades much quicker, for instance.


I have the impression that the more environmentally-friendly car paints that were introduced 15-20 years ago fade much quicker than the old ones.

Is this right? And if so, why? Do the newer pigments consist of less stable molecules?

[BenBurch]

... I still am surprised there was no wikipedia page about this.

I hereby empower you to make one!

[fuelair]

Try this for info: http://www.exploratorium.edu/snacks/dippingbird/index.html

[fuelair]

And this for the specific liquid currently in the bulb!!http://www.bbc.co.uk/dna/h2g2/A640865

[FramerDave]

I have the impression that the more environmentally-friendly car paints that were introduced 15-20 years ago fade much quicker than the old ones.

Is this right? And if so, why? Do the newer pigments consist of less stable molecules?

I don't know much, if anything, about car paint but I doubt that it contains pigments, mainly because of the price. Pigments in general are less likely to fade since they are composed of minerals for the most part and are inherently stable. For instance, lapis lazuli is a stone, iron oxide is used in some reddish colors, titanium dioxide is very stable and used in white paint and variations on carbon are often used in black paint or ink.

So the newer car paints may fade more quickly, but it's probably not because of pigments used.