Photographic Processes Chemistry 103, Spring 2001 Daguerreotype Dominant photographic process used in America, 1840-60 1. Photographic plate was made by plating Ag on Cu and then…

Daguerreotype. Dominant photographic process used in America, 1840-60 1. Photographic plate was made by plating Ag on Cu and then polishing surface 2. Ag-surface was made sensitive to light by exposing to iodine vapors to form AgI:.. 3. Exposed daguerreotype was exposed to heated Hg to form an amalgam with silver in places exposed to light. Amalgam is the image. 4. Unexposed AgI was removed by washing with water and sodium thiosulphate solution:… 5. After 1841, gold toning was done by immersing fixed plate in gold chloride solution to yield a protective coat of gold metal on the mercury amalgam surface. Tintype or Ferrotype , patented by Hamilton Smith in the US in 1856, was particularly popular during the Civil War. These prints contain no tin, but use an iron plate, usually coated with a black varnish (of linseed oil, asphaltum, and lampblack) to yield a surface referred to as a “japanned surface.” The plates were inexpensive and more robust than the ambrotype so that the final tintype could be sent through the mail or carried in a pocket. The chemistry involved is identical to that of the ambrotype. The iron sheet was, however, much thinner than the glass of the ambrotype, contrary to what is shown in Figure 3. Calotype Negatives. The chemistry involved in producing the calotype is identical to that of the salted paper prints made in the Chemistry 103 lab: paper is sensitized by forming a silver halide on it by sequential dipping in a halide salt solutions and silver nitrate. William Henry Fox made these salted papers more light sensitive by additions of gallic acid. The papers were exposed to light to form an image, developed, and then fixed with sodium thiosulfate. In contrast to the salted paper print, the calotype was waxed to make the paper translucent. To make a print, the calotype negative was placed on top of more photo paper (sensitized with silver halide) and allowed to develop in sunlight. Albumen Prints , first described by Blanquart Evrard at the French Academy of Sciences in 1850. Albumen papers were the dominant printed material by 1855 and the most common process from 1860-1885. Albumin paper uses a printing-out process (POP0, meaning that the image is formed by light alone, not developed chemically from the invisible latent image. Albumin papers were coated with egg white containing either ammonium chloride or sodium chloride. The papers were then sensitized by dipping them in silver nitrate. Prints were made by putting the negative in contact with the albumin paper and exposing to sunlight. Collodion negatives were generally used to print albumin papers. The chemical reactions involved in producing the images are identical to those used in salted paper prints. Albumen prints generally are warm browns, purplish- brown or black. They can often be identified from the crackle pattern developed as the albumen emulsion aged…

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