Schulze is best known for the discovery that certain silver salts, most notably silver chloride and silver nitrate, darken in the presence of light, and for using those effects to capture temporary photographic images. 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.
^Susan Watt (2003). Silver. Marshall Cavendish. pp. 21–. ISBN978-0-7614-1464-3. Retrieved 28 July 2013. "... But the first person to use this property to produce a photographic image was German physicist Johann Heinrich Schulze. In 1727, Schulze made a paste of silver nitrate and chalk, placed the mixture in a glass bottle, and wrapped the bottle in ..."