Van Dyke Brown process.
The Vandyke brown print is based on the first iron-silver process, the argentotype, invented in 1842 by the English astronomer, Sir John Herschel. Both processes utilize the action of light on ferric salts and their chemistry is very similar. The Vandyke process gets its name from its similarity in color to the deep brown pigment used by the Flemish painter Van Dyck.
In Vandyke a suitable paper is coated with a solution containing ferric ammonium citrate, silver nitrate and tartaric acid, using either rod or brush. When dry, the sensitized paper is exposed by contact printing to a negative under an ultraviolet light source.
Exposure may be done in a contact-printing frame, in a vacuum frame, or even by simply placing the negative and sensitized paper under a sheet of thick glass.
After exposure, the paper is developed in plain water, toned, fixed, washed and dried.