Wet collodion is a Victorian photographic process, first suggested by Frederick Scott Archer in 1851. Collodion (gun cotton dissolved in ether and alcohol) is salted with cadmium bromide and flowed onto a glass or a blackened metal plate. When the collodion has set, the plate is sensitised in a bath of silver nitrate, placed in the plate holder of a view camera and exposed while still wet.
After brief development in an iron-based developer and fixing (traditionally in potassium cyanide, although modern ammonium thiosulphate fixers do the job) the plate is washed, dried and varnished. If the image is made on glass, the reverse is painted black to give a positive image.