Why do colors fade in the sun? And not just fabrics but also painted and plastic items?
In: Chemistry
“Colors” are due to dyes, molecules that reflect (or re-emit) radiation in the wavelength of the colors you see.
That happens because of the way the electrons in the molecule interact with the light and these light-interacting electrons are usually part of double bonds.
When UV radiation from the sun hits these molecules over time, the double bonds break so the dye molecule doesn’t interact with light anymore (becomes faded).
Some dyes don’t have double bonds (like Van Gogh’s yellow, CdS, which is toxic) and they also fade due to chemical reactions started by the light. However, these are mostly older substances that aren’t really used industrially anymore.
Car paint doesn’t fade as easily because it has fillers, anti-corrosives (molecules that prevent the dyes from fading) and because it demand the use of more durable dyes, especially since car surfaces get hotter (and dyes fade faster if it’s hotter). Car surfaces are also metallic, so they naturally reflect part of light anyway.
Source: I’m a chemical engineer working on light-activated molecules for my dissertation.
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