The Precursors: Johann Heinrich Schulze
During the Middle Ages, alchemists had noticed the darkening of silver salts when exposed to the light and used them to colour various materials such as wood and ivory. However, it was at the time of the Renaissance that alchemists discovered silver chloride, when a certain Fabricius noticed in 1566 that it turned dark blue in the light.
The first scientific study on the reactions of certain chemical compounds of silver was published in 1727 by Johann Heinrich Schulze, a German professor of anatomy interested in chemistry, who was certainly the first to establish that light reacts on silver salt and thus opened the way to photography.
Johann Heinrich Schulze (Josef Maria Eder, Geschichte der Photographie, Halle, 1890)