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Daguerreotype of the 1843 Nantes flood by an unknown photographer. Courtesy of Charles Isaacs Photographs, inc., New York.
Both daguerreotype and calotype methods of image making were replaced in the 1850s by the wet collodion process.
From G. Tissandier, A History and Handbook of Photograph, 1878.
Merck litmus paper, 1934
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