Under strong light, soluble dichromates react with gum acacia (or ‘arabic’), rendering it insoluble in water. By incorporating artists' pigments in the colloidal layer, a ‘painterly’ contact-printing process results. Invented by Poitevin in 1855, and popularized as ‘Photo-aquatint’ by Alfred Maskell and Robert Demachy in 1894, it usually involves several applications of layers of pigmented, dichromated gum, interspersed with reregistration under the negative, exposure, and development with water. Gum bichromate is a popular ‘alternative process’, inexpensive but expressive, offering great manipulative control over images in watercolour, and the possibility of three-colour printing.
— Mike Ware
Bibliography
- Scopick, D., The Gum Bichromate Book (1991)
