In 1839, Talbot devised an improved process to form a negative picture on transparent paper coated with silver salts. Such an image still required an exposure of at least a minute, but many positives could be made from a single negative image by exposing a second light-sensitive sheet through the negative image itself. Talbot called these images calotypes, from the Greek for"beautiful." This method of converting a negative to a positive is the basisfor modern photography, and for this reason Talbot is considered to be one of the two founders of photography. The announcement of Daguerre's process in France moved Talbot to present his"photogenic drawing" to the Royal Society in 1839. By the autumn of 1840, Talbot had discovered that gallic acid sped up the development of latent images,and in 1841 he patented his perfected process, now calling it the Talbotype. He developed a way to speed up the exposure of images by coating the photographic paper repeatedly with alternate washes of salt and silver, then exposing the paper in a moist state. This vastly reduced the exposure time required for portraits, and the agonizing effort required to remain still during a sitting was eliminated.
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