The story
The pigment was discovered circa 1700 in the German state of Prussia by a paint-maker named Diesbach.
Etymology from Wiktionary, CC BY-SA 4.0.
Prussian blue
Today it means: An insoluble dark, bright blue pigment, ferric ferrocyanide (equivalent to ferrous ferricyanide), used in painting and dyeing, and as an antidote for certain kinds of heavy metal poisoning. Full definition →