Gum bichromate printing — often simply called gum printing — is one of the most beautiful historical and alternative photographic processes.
Unlike most traditional photographic techniques, it does not rely on the light sensitivity of silver or iron salts. Instead, it uses the unusual properties of chromium salts, which cause organic colloids to change their properties when exposed to light.
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| “Syria”, photograph by Radosław Brzozowski Vienna gum bichromate print |
How Does Gum Bichromate Printing Work?
A layer of gum arabic sensitised with dichromate loses its natural solubility when exposed to light.
Gum arabic is a natural resin obtained from acacia trees. When a pigment — for example lamp black or watercolour paint — is added to the sensitised gum layer, exposure to light produces an image that can later be developed in water.
One of the great advantages of gum printing is that the image can also be modified manually in many different ways.
The printer can remove unwanted areas, alter contrast, add further layers and build up colour gradually. The final image may be naturalistic or completely expressive and surreal.
It is no coincidence that gum printing is regarded as one of the classic noble photographic processes. Few other historical techniques offer such freedom for creative expression and direct manipulation of the image.
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| “Syria”, photograph by Radosław Brzozowski Vienna gum bichromate print |