<P> Albertus Magnus (1193 / 1206--80) discovered silver nitrate and noted that it could blacken skin . Silver nitrate would later be used as a light sensitive material in the photographic emulsion on photographic glass plates and film . </P> <P> Georg Fabricius (1516--71) discovered silver chloride, later used to make photographic paper . </P> <P> In 1614 Angelo Sala wrote in his paper Septem Planetarum terrestrium Spagirica recensio: "When you expose powdered silver nitrate to sunlight, it turns black as ink". He also noted that paper wrapped around silver nitrate for a year had turned black . </P> <P> Wilhelm Homberg described how light darkened some chemicals (photochemical effect) in 1694 . </P>

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