Van Dyke brown is a printing process named after Anthony van Dyck.
It involves coating a canvas with ferric ammonium citrate, tartaric acid, and silver nitrate, then exposing it to ultraviolet light. The canvas can be washed with water, and hypo to keep the solutions in place. The image created has a Van Dyke brown color when it’s completed.
The Van Dyke brown process was patented in Germany in 1895 by Arndt and Troost.