The wet-collodion negative process, also known as silver monochrome negative process, was invented in 1851 by Frederick Scott Archer.

Compared to Daguerreotypes, the technique considerably reduced the pose time for picture-taking. In addition, thanks to the glass plate (matrix), it was possible to make multiple identical prints.

The process consisted in coating a glass plate, which had been cleaned and cut to the desired size beforehand, with a printing emulsion composed of cellulose nitrate (powdered cotton), ether and alcohol. After evaporation, the collodionized plate was dipped in a solution of silver nitrate, then transferred to a frame inside a lightproof box. It was then immediately exposed, i.e. while still wet, in the photographic chamber.
After exposure (to light), the latent image obtained was then developed in a pyrogallic acid or ferrous ammonium sulfate solution for a few seconds. The collodion plate was then fixed in sodium thiosulfate. Next it was washed and then dried by the heat of a flame. Finally, it was varnished in order to protect the collodion layer. Printing from a collodion negative plate was done by direct contact with light-sensitive albumen paper.

Practically all of the portraits that Félix Nadar took were done with the wet collodion technique.