Gum Bichromate – across the roof tops of Lucca, Tuscany, Italy

Getting to grips with the Gum Bichromate printing process.

Gum prints are produced by brushing onto a sheet of watercolour paper a gum arabic solution mixed with potassium dichromate and a water colour pigment. After drying the sheet is exposed to UV light through a negative in contact with the paper where the dichromate hardness the gum in proportion to the amount of UV it is exposed to. The print is then developed in warm water to wash away the unhardened gum . During development the gum can be manipulated with a brush, sponge or spray of water making each print a one of a kind and unique. Gum prints of more than one color are made by repeating the process with different colour pigments building up the print over several layers.