The first practical photographic process, announced in 1839 by the Frenchman Louis Daguerre. A copper plate coated with polished silver was made light-sensitive with iodine vapor, which formed silver iodide on its surface. After exposure in the camera, the image was developed with mercury vapor and then fixed with a salt solution.
Daguerreotypes are extremely sharp and detailed. Their main weakness is that each one is a unique positive image on metal. There is no negative, so it cannot be copied easily. The calotype of William Henry Fox Talbot made multiple prints possible.
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