The Kallitype is a hand-crafted, archival process that goes back 175 years. The process uses iron and silver based compounds to coat the paper, and various types of developers. The photographer here uses mainly sodium citrate. The image is contact printed by placing a negative that is the size of the final print on the paper that has been coated and then dried, then exposed under UV light. The print is then developed, toned, fixed and cleared/washed.
These prints are toned in a palladium or gold solution, which replaces the original silver in the print with that noble metal. This is done for two reasons: first, it changes the color of the print to a deeper brownish/black and second, it makes the print archival and protects it from fading. In fact, Kallitypes toned in palladium or platinum are indistinguishabe from palladium or platinum prints, both visually and chemically. In fact, many "platinum" prints in museums are probably kallitypes, as "platinum" prints were more prestigeous due to perceived archival qualities. When processed correctly, Kallitypes are every bit as archival as platinum prints.
Each print is handmade and therefore unique.