Red paint is one of the most common colors for buildings around the world. In America, most barns are painted red. Most public buildings in India, including railway stations, post offices and other large spaces are painted red as well. In fact, most buildings from British-era India are red in color.
This is because traditionally, red paint was cheaper than all other colors. Red paint is mostly composed of red ochre. It is basically ferric oxide – a compound of iron and oxygen. Ferric oxide is also the rust that forms on our iron objects, giving it the rusty red color. Red ochre is one of the oldest pigments used by man. It is also one of the most readily available, because iron makes up around 5% of the Earth’s crust and oxygen makes up a whopping 46.6%. Red paint is cheap because of the abundance of red ochre, which can be found in huge quantities all over the world.
How is that related to dying stars?
To answer that, we need to remind ourselves how stars work. Stars are born out of huge clouds of hydrogen gas, called nebulae.
As the hydrogen atoms in a nebula become attracted to each other, they form a huge ball of gas (like Jupiter or Saturn). If the ball of gas is really massive, the gravitational force is enough to bring the hydrogen atoms very close to each other. This starts a special type of reaction, called nuclear fusion. Four nuclei of hydrogen (each of which are made up of one proton) come together and form a nucleus of helium (two protons and two neutrons). This generates a huge amount of energy. (In fact, we use this same process to make hydrogen bombs.) This causes the huge ball of gas to become a star, and start emitting heat and light, just like our Sun.
One of the mechanisms for fusion is the proton-proton chain reaction, which occurs in stars like our Sun. Heavier stars have a more complex mechanism called the CNO cycle. This process goes on for millions of years, but in the end, almost all the hydrogen in the core of the star gets used up. If the star is massive enough, it then starts to fuse helium into heavier elements. When all the helium is used up, it fuses lithium, and then carbon. As each lighter element is used up, the star starts fusing the heavier elements available to it. Each heavier element is used up faster than the last one and the star keeps spiraling downwards until it hits the magic number of 56. 56 is a very special number for a nucleus. When nuclei that have less than 56 nucleons (i.e., proton and neutrons) bind, they will release energy. If they have more than 56 nucleons, they will lose energy. 56 is the last stop in the nuclear fusion process. And which element has this magic number of nucleons? You guessed it.
Once a massive star has reached the iron stage, it does not have many options. It starts rapidly collapsing until the pressure is released in a huge explosion. This is called a supernova, and it can produce more light than an entire galaxy. A supernova is also where the elements heavier than iron are formed, although in very small quantities.
So what does this have to do with red paint on Earth?
Earth and the entire Solar System have been formed from a nebula that has been left behind by supernovae a very long time ago. This is the reason we find heavy elements on the Earth today. It is also the reason for the abundance of iron in terrestrial planets like Earth. Iron is also a very reactive metal, as anyone with iron instruments can tell you. Back in the early days of our planet, the atmosphere contained gases like carbon dioxide and water vapor, but no free oxygen. Therefore, the iron on the Earth’s crust was present as a metal and did not rust at all. However, with the emergence of life, plants started releasing oxygen into the air. This caused the iron to rust and form iron oxide. Thus, iron oxide became one of the most common rocks on the planet.
Because iron oxide is so easy to procure, red paint became one of the cheapest paints available. This was long before advances in chemistry would allow us to make our own pigments in any shade that we want. Builders looking for a cheap paint to protect their buildings from the weather turned to red ochre.