Daguerreotype

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Daguerreotype

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The daguerreotype /dəˈɡɛrɵtaɪp/ (French: daguerréotype) process (also called daguerreotypy), introduced in 1839, was the first publicly announced photographic process and the first to come into widespread use. By the early 1860s, later processes which were less costly and produced more easily viewed images with shorter exposure times had almost entirely replaced it. A small-scale revival of daguerreotypy among photographers interested in historical processes was increasingly evident in the 1980s and 1990s and has persisted into the 2010s.The daguerreotype image is formed on a highly polished silver surface, most commonly this is upon a metal substrate like copper, but in the 19th century brass was also used, also daguerreotypes can be made on pure silver sheets. There were two methods used in plating the silver to copper - electroplating and Sheffield plate where the silver and copper are bonded under pressure and with annealing.In the nineteenth century method of polishing the silver surface is polished with a buff (covered with a hide or velvet) using first rotten stone, then jeweler's rouge and then lampblack. By the light of a safelight the silvered plate is exposed to halogen gases. Firstly iodine (from iodine crystals at room temperature) and then exposure to bromine fumes to accelerate the sensitivity of the light-sensitive silver halide coating. Exposure to Chlorine) fumes can also be used. The plate is then carried to the camera in a light-tight plate holder. Withdrawing the protective dark slide exposes the sensitized surface to the image projected within the dark camera by the lens, creating an invisible latent image on the plate which is then developed to visibility by fuming it with heated mercury. In the Becquerel variation of the process the plate is only sensitised with exposure to Iodine and then developed by exposing it to red filtered light. After development, the light sensitivity of the plate is arrested by removing the remaining silver halide with a mild solution of sodium thiosulfate (Daguerre's initial method was to use a hot saturated salt solution). To give the image a warmer tone and physically reinforce the powder-like silver particles of which it is composed, a gold chloride solution is pooled onto the image and the plate is briefly heated over a flame, then drained, rinsed and dried. Even after this gilding treatment, the image surface is still very delicate and the silver is subject to tarnishing from exposure to the air, so the plate must be kept under glass in a sealed enclosure.The distinguishing visual characteristics of a daguerreotype are that the image is on a bright (ignoring any areas of tarnish) mirror-like surface of metallic silver and it will appear either positive or negative depending on the lighting conditions and whether a light or dark background is being reflected in the metal.Several types of antique images, most commonly ambrotypes and tintypes but sometimes even prints on paper, are frequently misidentified as daguerreotypes, especially if they are in the small, ornamented cases in which daguerreotypes were usually housed. The name "daguerreotype" correctly refers only to one very distinctive image type and medium, produced by a specific photographic process that was in wide use only from the early 1840s to the late 1850s.