Preußisch Blau

In 1704, Berlin colormaker Johann Jacob Diesbach was attempting to make a red pigment—Florentine lake—using potash, iron sulfate, and cochineal. His potash was contaminated with animal blood (supplied by alchemist Johann Conrad Dippel, who used it in his experiments). Instead of red, Diesbach produced a deep, brilliant blue. He had accidentally created iron ferrocyanide, the first purely synthetic pigment.

The new color was called Prussian blue (Preußisch Blau) after the Kingdom of Prussia, where it was discovered. It was also called Berlin blue. The recipe was published in 1724 by John Woodward in the Philosophical Transactions of the Royal Society. Within decades, Prussian blue was available across Europe at a fraction of the cost of ultramarine, which required grinding lapis lazuli imported from Afghanistan.

Prussian blue transformed painting. Before 1704, blue was the most expensive color on a painter's palette. Ultramarine cost more than gold. Now any painter could afford a rich, deep blue. Hokusai used Prussian blue for his Great Wave off Kanagawa (1831). Picasso's Blue Period (1901-1904) relied on it. The sky in European painting changed color after 1704—it became deeper, more accessible, more present.

Prussian blue has a medical use that connects to its origins in blood chemistry. It is the standard treatment for thallium and radioactive cesium poisoning. The pigment binds to the metals in the gut and prevents absorption. After the Chernobyl disaster in 1986, the Soviet government distributed Prussian blue to affected populations. The first synthetic color became a life-saving antidote.