Sir John Herschel invented the cyanotype in 1842. The process depends on the
photochemical reduction of ferric salts into ferrous salts leading to the formation of Prussian blue, an iron-based pigment. The process was used sporadically throughout the 19th century and more frequently in the twentieth century for the reproduction of architectural plans and technical drawings, called “blueprints."

This project is made possible by a grant from the U.S. Institute of Museum and Library Services, grant number MA-10-13-0194.

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