Prussian Blue, Berlin Blue, Or Chinese Blue is a dark blue transparent, and very powerful staining color, used solely for tinting. There are at least three distinct kinds of Prussian blue depending upon the method of manufacture and the materials used. The ordinary prussian blue is made by adding ferrous sulphate (copperas) solution to a solution of yellow prussiate of potash. The precipitate formed is oxidized by dilute nitric acid or chloride of lime. After washing, it is treated with hydrochloric acid and again washed with water.

Prussian blue, when pressed or rubbed, should show a coppery hue in the lump. The best for painters and artists use, is the insoluble variety. This color is destroyed by heat and will not withstand the action of alkalies, moreover, sunlight will cause it to fade more or less. It is largely adulterated for the pure article is somewhat expensive.