ambrotype definition

A photograph that causes a positive image on a sheet of glass utilizing the wet plate collodion method.  It was first used in the 1850s in the United States.  The method was invented by Frederick Scott Archer but ambrotypes utilized the plate image not as a negative, but as a positive.  James Ambrose may be credited with coining the term "ambrotype"; he took out many patents in regards to the process.