Introduced in France in 1839, the daguerreotype was the first commercially successful photographic process. Noted for its great detail, the one-of-a-kind daguerreotype image is a silver-mercury alloy, formed on a highly polished, silver-coated copper plate. Initially, exposure times were long, up to thirty minutes, but once they were reduced, the process became popular for portraiture. The daguerreotype image can appear as a negative at certain viewing angles and is distinguished by its mirror-like surface and grayish-white tones, the latter often enhanced with delicate hand-coloring. Daguerreotypes are vulnerable to abrasion and tarnishing and were therefore housed in cases, under glass. The process is still occasionally used by contemporary photographers and artists.