The daguerreotype was the first practical photographic process, invented in the late 1830s by the French theatrical designer Louis Jacques Mandé (1789–1851) and widely used in portraiture until the mid-1850s. A brass plate coated with silver was sensitized by exposure to iodine vapor and exposed to light in a camera for several minutes. A weak positive image produced by mercury vapor was fixed with a solution of salt. Hypo soon replaced salt as the fixing agent and after 1840 gold (II) chloride was used to intensify the image.