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For millennia, we mostly had to make do with natural pigments and dyes, but in the last 300 years or so, chemical synthesis has revolutionized the colors of our world.

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Prussian blue


Nowadays, we have everything from bright blue cars to green cupcakes and pink phone cases, but our lives weren’t always so full of rainbows.

For millennia, we mostly had to make do with natural pigments and dyes, which were dug out of the Earth or taken from plants. And while white chalk is great for cave painting, it doesn’t work so well for multi-colored clothes.

If you want flashy colors that’ll last — but don’t want to spend a ton of time or money harvesting them from nature — turn to chemistry. And in the last 300 years or so, chemical synthesis has revolutionized the scientific, art, and fashion worlds. One of the first pigments made in a lab was Prussian blue.

It was created in Berlin around 1706, and was famously used to dye the uniforms of the Prussian army. The color was included when Crayola debuted their crayons in 1903, and it still appears in crayon packs today. You just might know it by a different name, since it’s been called ‘midnight blue’ since 1958.

Now, the details of the discovery are a little fuzzy, but the story goes: a paint maker by the name of Diesbach was trying to cook up a red pigment from some scale insects. But he borrowed some chemicals from a labmate that happened to be contaminated with iron, and got a dark blue color instead. The color of something depends on how that object absorbs and reflects light.

A red apple, for instance, looks red to us because it reflects the long wavelengths of red light, and absorbs the rest. But a blue shirt is reflecting shorter wavelengths of blue light. Or, because of complementary colors, something can appear blue because it only absorbs the color of light that’s opposite on the color wheel: orange.

White light is a mixture of all colors, so when one gets taken away, you basically perceive what’s left — the complementary color. There are different reasons why a pigment might reflect or absorb certain wavelengths. With Prussian blue, it’s because of iron and something called charge transfer.

The pigment actually has two differently-charged iron atoms that will absorb orange light and use that energy to move an electron from one iron atom to the other. And because of complementary colors, it ends up looking blue. Diesbach’s mistake was serendipitous because at the time, a lot of blue pigments faded, like indigo.

Or they were super expensive, like ultramarine, which was made by grinding up semi-precious stones shipped from Afghanistan. Prussian blue was cheap and durable, so all of Europe wanted it: for clothes, stamps, and in their fine art. It was a smash hit, and not just for its looks.

Because Prussian blue can bind metals like cesium or thallium, the pigment has had a second life as a drug to treat people for heavy metal contamination. Another highly sought-after pigment was discovered while trying to make medicine. Specifically, quinine, a natural drug that was used to treat malaria. 150 years after the invention of Prussian blue, there still was no easy way to make purple.

The ancient Romans got purple from Mediterranean snails, but it took a lot of them to make much dye, which meant the color was real expensive. So when an 18-year-old chemistry student in London named William Henry Perkin was tinkering with a molecule from coal tar, a sticky type of distilled coal, and failed to make quinine, he was still excited. Because, instead, he stumbled upon a bright purple substance that could permanently dye fabric.

He called it mauveine. Mauveine is an organic pigment, made mostly of carbon, hydrogen, and nitrogen. So it’s not purple because of metals, but because of the way electrons are distributed when organic compounds form rings.

Carbon rings are only possible when every other carbon is held together with a double bond. That means electrons are constantly moving across all of the bonds, in a kind of hexagonal donut cloud. They’re pretty easy to excite with yellow light, so that’s what gets absorbed.

And because purple is the complement to yellow, the pigment looks purple! Now, if you think color discovery is just a thing of the past, think again. In 2009, a grad student at Oregon State University was heating up some manganese oxide and other chemicals to around 1200 degrees Celsius in hopes of generating a new, super efficient electronic material.

He hadn’t made the next silicon, but he did create the first new blue pigment in two centuries. It was a bright blue, and because it was made at such high temperatures, the scientists knew it had to be a pretty stable chemical. Along with oxygen, the pigment was made of just three elements: yttrium, indium, and manganese.

So it was named YInMn blue. The key to the color is the how the manganese atoms are ordered within the crystal structure: they sit inside little pyramids surrounded by some oxygens. Because of the pyramidal shape, the manganese electrons are repulsed by different amounts by the oxygens, so they have different energies.

That means there’s some wiggle room to get excited, so the electrons can absorb a lot of light. YInMn absorbs red and green light really well, but still reflects blue light, so it’s a vibrant blue. It’s also non-toxic and reflects heat, which means it doesn’t just look pretty — it could be used to paint roofs and keep houses cool.

The same team has since reported that if they add zinc and titanium, they can make purples. And if they replace the manganese atoms with copper or iron, they can make greens or oranges with similar properties. This year, Crayola decided to honor YInMn blue by giving it a coveted spot in its 24-pack of crayons.

But, like Prussian blue, it’s going to be renamed first. Which, y’know, makes sense for marketing, but means kids might miss out on some cool chemistry. Thanks for watching this episode of SciShow!

If you like these mashups between science, history, and art, check out our video where Michael explains 10 times we sacrificed our health for the sake of fashion.