Gum Bichromate
Pigment, gum, and dichromate—painterly photography.
Hardened gum arabic holds watercolour pigment in proportion to UV exposure. Pictorialists layered colours for impressionistic effect.
You paint a mix of watercolor pigment and a light-sensitive gum onto paper, expose under a negative, and rinse — the unexposed parts wash away.
- ▸Light hardens the gum. Hardened gum holds onto pigment; unhardened gum dissolves.
- ▸You can layer different colors one at a time for painterly photos.
- ▸Looks halfway between a photograph and a watercolor painting.
History
Mungo Ponton discovered dichromate's light sensitivity in 1839; the gum process was refined by Robert Demachy and Heinrich Kühn around 1900 as a Pictorialist tool to make photographs look like paintings.
Process
- 01
Mix gum arabic, ammonium dichromate, and watercolour pigment.
- 02
Coat paper and dry quickly in the dark.
- 03
Contact-print under a negative in UV light.
- 04
Develop face-down in water; unhardened gum washes away.
- 05
Re-coat and re-print with new colours for layered images.
Strengths
- +Any colour palette
- +Hand-finished feel
- +Layerable
Limitations
- −Dichromate is toxic
- −Tricky registration
- −Soft detail
Sources & citations
References for the history and process described above.
- 01Gum Bichromate Process — Alternative Photography
- 02Pictorialism — The Metropolitan Museum of Art — Heilbrunn Timeline