Cyanotype
Blueprints made of sun and iron salts.
Anna Atkins used cyanotype to publish the first photo book—of British algae. Coat paper, lay objects, expose to sunlight, rinse to a deep Prussian blue.
You coat paper with a light-sensitive blue chemistry, lay objects on it, then put it in the sun. Wash with water and you get a Prussian-blue photogram.
- ▸No darkroom needed — just sunlight.
- ▸Wherever light hits the paper, it turns blue. Wherever something blocked the light, it stays white.
- ▸Rinsing in plain water 'develops' and fixes the image.
History
Sir John Herschel invented the cyanotype in 1842. Anna Atkins's 'Photographs of British Algae' (1843) was the first book illustrated entirely with photographs. Engineers later adopted it for blueprints; artists revived it as a contact-printing medium.
Process
- 01
Mix ferric ammonium citrate and potassium ferricyanide in equal parts.
- 02
Coat watercolour paper with the solution in dim light; let dry.
- 03
Place a negative or object directly on the dry paper.
- 04
Expose to UV/sunlight for 5–20 minutes until image darkens.
- 05
Rinse in water; the image oxidises to its final Prussian blue.
Strengths
- +Inexpensive
- +Non-toxic
- +Permanent prints
- +Beautiful blue tonality
Limitations
- −Single colour only
- −Long exposures
- −Humidity-sensitive
Sources & citations
References for the history and process described above.
- 01Anna Atkins and the First Photo Book — The New York Public Library
- 02Cyanotype Process — Science Museum Group
- 03John Herschel and the Cyanotype — Royal Society