Monika Fabijanczyk explained the 'Van Dyke Brown' process in her course at the Gallery of Photography, Dublin. It is an early photographic process so named becuase the print colour resembled a brown paint named after Flemish painter Van Dyke.
The chemicals Ferric Ammonium Citrate, Tartaric Acid & Silver Nitrate are mixed to create an emulsion which is painted onto a base material such as thibk card, material such as canvas or even light coloured wood.
It is then exposed to a negative in UV light which gives an orange-brown image, then developed in water darkening the image somewhat before being dipped into a fixing solution. It is here that the image turns a rich chocolate brown.
A very interesting printing technique and wonderfully explained by the tutor. The image is from a wet-collodium glass plate negative used by Monika in her demonstration.