Process that produces a direct positive image on a silver-coated copper plate, invented by Louis-Jacques-Mandé Daguerre of France and Joseph-Nicéphore Niepce in the 1830s. In the process, a copper plate is coated with silver iodide and exposed to light in a camera, then fumed with mercury vapour and fixed with common salt in solution.

Source: Art & Architecture Thesaurus

http://vocab.getty.edu/page/aat/300053530