On maps and charts, the scale is usually printed beneath the title or in the legends in the form of a bar scale, representative fraction ( example: 1:24,000), or statement of equivalency ( One Inch = 500 miles). The ratio of distance shown on a map, globe, relief model, section, aerial photograph, or other cartographic item to its corresponding dimension on the ground or to another graphic representation. Click here to learn more about the process, courtesy of James M. Click here to see examples ( Getty Museum) and here to see another selection, courtesy of the Victoria & Albert Museum, London. They were superseded as a photographic medium by the albumen print, invented in 1850, which gave clearer definition. Salted paper prints are usually a warm brown color with limited tonal range. Glass negatives produced a much sharper image. Embedded in the fibers of the paper, rather than on a surface layer, the image appears grainy and mottled when affected by the texture and any imperfections in the paper negative. Because they are contact prints, salted paper prints are the same size as the negative. Placed inside a frame under a calotype or glass negative, the paper was exposed to ultraviolet light (sunlight) and then fixed by washing to dissolve the unexposed silver salts. Invented by William Henry Fox Talbot in 1840 as a result of his experiments with " photogenic drawing," salt prints were the earliest positive photographic prints, made by immersing a sheet of high-quality writing paper in a solution of sodium chloride (table salt) and coating one side with a solution of silver nitrate to produce light-sensitive silver chloride.
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