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The cyanotype process for making prints was invented by Sir John Herschel in 1842 and came from his discovery of the light sensitivity of iron salts. A sheet of paper was brushed with iron salt solutions and dried in the dark. The object to be reproduced - a plant specimen, a drawing or a negative - was then placed on the sheet in direct sunlight. After about 15 minutes a white impression of the subject formed on a blue background. The paper was then washed in water where oxidation produced the brilliant blue - or cyan - that gave the process its name. |
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