About 1831 French painter Louis Jacques Mandé Daguerre made photographs on silver plates coated with a light-sensitive layer of silver iodide. After exposing the plate for several minutes, Daguerre used mercury vapors to develop a positive photographic image. These photographs were not permanent because the plates gradually darkened, obliterating the image. In the first permanent photographs made by Daguerre, the developed plate was coated with a strong solution of ordinary table salt. This fixing process, originated by British inventor William Henry Fox Talbot, rendered the unexposed silver-iodide particles insensitive to light and prevented total blackening of the plate. The Daguerre method produced an unreproducible image on the silver plate for each exposure made. = each exposure made.