Thread by @kakape

People often ask me what I find so fascinating about blue and what it has to do with science, so here‘s a story about one particular blue from right here in Berlin:
#TuesdayisBluesday

Around 1706 alchemists in Berlin accidentally discovered a new blue. Johann Jacob Diesbach was working in the lab of Johann Konrad Dippel trying to make a red pigment, carmine. But he used some potash contaminated with animal blood by Dippel and ended up with a blue pigment.

They quickly realized the blue was stable and easy to make and that meant it was worth a fortune. Because good blue pigments were rare. Ultramarine, for instance, was laboriously made from lapis lazuli (shipped most prominently from the Badakshan region) and incredibly expensive.

Artists quickly adopted the new hue and it became known as Prussian blue or Berlin blue. You can see it in any museum: Gainsborough used it, as did Picasso. It’s in Van Gogh's Starry Night and it is one of the pigments used in Hokusai’s famous print The Great Wave off Kanagawa

(It also left its mark in German literature: In TheodorFontane’s “Frau Jenny Treibel”, the husband is the owner of several Prussian Blue factories. “What are all the cornflowers in the world compared with a Prussian blue factory?” he asks at one point.)

Scientists, of course, wanted to know what exactly this substance was and so for many years they investigated the chemical makeup of Prussian Blue trying to figure out the chemical components that produce the color.

A French chemist, Pierre-Joseph Macquer, eventually managed to break down the pigment into two parts: an iron salt and and an unknown acid. Because of its origin this acid became known as prussic acid. It’s other name also references its blue origin: hydrogen cyanide.

The cyanide ion is simple, one carbon and one nitrogen atom. And it is deadly. In human cells it basically interferes with the use of oxygen leading people to suffocate even though their blood is full of oxygen.
It became a staple of crime novels. But it didn’t stay in fiction.

Cyanide was used as a gas in the WWI. It was used to execute people in gas chambers. And in Germany it was developed into Zyklon B, the poison Nazis used to carry out their mass murder in extermination camps.
What started as a beautiful new blue had spawned a cruel weapon.

But that isn’t the whole story either. Prussian Blue yielded a poison but it also ended up, of all things, a medicine to treat poisoning.
Today it is on the WHO’s List of Essential Medicines as a treatment for instance for radioactive caesium poisoning.

There is a LOT more to the story of Prussian Blue.
For instance: it is the origin of the term “blueprint", because it is the compound you end up with in an early copying process developed by the English astronomer John Herschel.

So this is one story that I tell when people ask me about my fascination with Blue. From alchemy to poison to medicine: These compounds have incredible, fascinating, tragic stories.
And if you want more reasons to be fascinated by Blue, I have a whole book full of them for you...