Johann Heinrich Schultz
Johann Heinrich Schultz is credited with the discovery that certain silver salts, most notably silver chloride and silver nitrate, darken in the presence of light. In an experiment conducted in 1724 he determined that a mixture of silver and chalk reflects less light than untarnished silver. Though his discovery did not provide the means of preserving an image - the silver salts continued to darken unless protected from light - it did provide the foundation for further work in fixing images by such researchers as Thomas Wedgewood and Sir Humphrey Davy.