Modern Prussian Blue is light-fast, chemically inert, and chromatically rich, so much so that it is still on modern painters’ palettes, for artists in oils and watercolors. When Bob Ross loaded up his palette, he always included Prussian Blue, which he favored for winter skies. It is also cheap, because easy to manufacture. For this reason, it was the blue used in blueprints, and, by the late nineteenth century, was the standard blue in Japanese blue woodblock prints. Hokusai’s Great Wave is one such print. It is also one of the last pigments which is also a medicine. The very word drug used to refer equally to pigments and medicines; it is now just about only Prussian Blue which is still part of the standard medical toolkit. Prussian Blue is used in histology, as a non-toxic stain for soft tissues, and as a remedy or cure for forms of radiation poisoning, taken in pill form. Other drugs can perform these functions; it is just that Prussian Blue is easy to make.