Even today, with the limitless paint colors at our disposal, you’ll likely see mostly red barns while driving down a country road. The reason for this, remarkably, has to do with the byproducts of dying stars.
As Google employee Yonatan Zunger explained on his Google+ profile, barns have historically been painted red because red paint is the cheapest. But to really dig deep and get to the bottom of why that is, you have to “go all the way to the formation of matter itself,” he writes. The foundation of red paint relies on iron oxide, an organic compound that reflects reddish-orange light while absorbing yellow, green, and blue light waves. On our planet, there’s tons of it, and we have the natural process of nuclear fusion to thank.
Zunger lays out all the details his blog post, explaining,
“The only thing holding the star up was the energy of the fusion reactions, so as power levels go down, the star starts to shrink. And as it shrinks, the pressure goes up, and the temperature goes up, until suddenly it hits a temperature where a new reaction can get started. These new reactions give it a big burst of energy, but start to form heavier elements still, and so the cycle gradually repeats, with the star reacting further and further up the periodic table, producing more and more heavy elements as it goes. Until it hits 56. At that point, the reactions simply stop producing energy at all; the star shuts down and collapses without stopping…
So it’s because of the details of nuclear fusion—the particular size at which nuclei stop producing energy—that iron is the most common element heavier than neon. And as we saw before, you have to be a d-block element to make a decent pigment, which means that iron is going to be, by far, the most plentiful pigment for any species which lives on a star that isn’t about to blow up. And it’s going to bond to oxygen, the most plentiful thing around in planetary crusts for it to bond to (only hydrogen and helium are more common, and they tend to evaporate), to form iron oxides: those rich, red ochres that we mix with oils to form a cheap, stable, red paint.”
So the next time you’re driving through the country or walking past a bold accent wall, remember that it took a massive astronomical event to get there.
