In 1851 the Wet Collodion Process was introduced by Frederick Scott Archer. In this process a glass plate was coated with wet collodion and then sensitized by dipping it into a bath of silver nitrate, then while still wet it was placed in the camera and an exposure was made. The plate was then immediately developed, while still wet, to form the negative.
The wet collodion process was also used to make another form of photograph. The Ambrotype. These ambrotypes were simply a wet collodion negative viewed with a dark background (sometimes a black lacquer or black velvet) behind them.
In 1853 the wet collodion process was used with black enameled iron and these were called Ferrotypes or Tin types. Smaller tintypes were called Gemtypes.
These ferrotypes or tintypes were very popular in America and were not introduced to Europe until the late 1870's and were then classed only as a beach photographer's novelty.