CNN  —  A century ago, the scientist and inventor George Washington Carver filed two patents related to his new method for making paints and stains from Alabama’s clay. He had discovered the iron-rich soil could be used in a chemical reaction with a potassium compound and nitric acid to produce a vibrant blue pigment. It was a familiar hue: Prussian Blue, as it is known, had already changed the course of art history around 1705 when a paint maker in Berlin accidentally discovered its chemistry.

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