An accidental discovery in a Berlin laboratory found its way into Rococo paintings and Japanese woodblock prints. How did this colour travel so far, and what made it different from earlier blues? Evie Hatch traces the story of Prussian Blue, from eighteenth-century Europe to Japan’s nineteenth-century “blue revolution”. She explores its unusual chemistry, remarkably modern marketing campaign and early problems with fading, and asks why it is often called the first modern synthetic pigment. Th...