Cyanotype
This is a technique for making prints in which the image source (such as an item, a negative, or a specimen) is put directly on the light-sensitive print paper (covered with iron salts), which is then treated after being exposed to direct light. It is easy to see the areas where the light has oxidized the surface of the paper because of the characteristic blue hue. In 1842, Sir John Herschel came up with basis for the procedure that architects would later use to create blueprint drawings of structures.
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