Cyanotype
Cyanotype is an iron-salt photographic process invented by John Herschel. It became historically important through Anna Atkins’s botanical books and later through blueprint reproduction, while contemporary artists value its direct contact image and characteristic blue.
Herschel’s 1842 process
The English scientist and astronomer John Herschel described the cyanotype process in 1842 while investigating light-sensitive iron compounds.
Unlike silver-based photographic processes such as the daguerreotype and calotype, cyanotype forms its characteristic image through iron chemistry and Prussian blue. The process is generally used as a contact print, meaning the object or photographic negative is placed directly against sensitized paper rather than enlarged through a lens.
Cyanotype in images
Selected visual references help connect the article to surviving works, objects, places, documents or practical examples related to this subject.
Anna Atkins and botanical books
Anna Atkins used cyanotype to record algae by placing specimens directly on sensitized paper and exposing them to light. Her Photographs of British Algae, begun in 1843, is one of the earliest books illustrated photographically and the first major publication to use cyanotype systematically. The specimens block light and appear as pale silhouettes against blue, preserving delicate branching forms with exceptional clarity. Atkins combined scientific classification, collecting and image-making rather than using the process simply for decorative photograms.
Contact image and tonal reversal
In a simple photogram, areas receiving more ultraviolet exposure become blue after processing, while covered areas remain light. A photographic negative reverses tone so that the resulting cyanotype reads as a positive image. Because it is a contact process, the final image size normally matches the negative or object. Surface texture, paper absorbency and exposure all affect density and edge. Contemporary cyanotype practice often uses plants, lace, transparent objects or large digital negatives to exploit this direct scale relationship.
Blueprint reproduction
Cyanotype became widely used for copying architectural and engineering drawings because it was inexpensive and could reproduce line drawings at full scale. The familiar term 'blueprint' comes from this application. Later diazo and reprographic technologies replaced cyanotype for most professional drawing reproduction, but the blue image remained culturally associated with technical plans. This commercial history is separate from Atkins’s botanical work but depends on the same basic photographic principle.
Conservation and contemporary use
Cyanotype images can be sensitive to alkaline environments and prolonged intense light, and their iron chemistry differs from silver photographs. Good storage uses stable materials and controlled display. Contemporary artists have revived the process because it requires no camera, can work at large scale and produces a color strongly unlike ordinary photographic grayscale. Safe practice should follow modern photographic-material guidance; historical formulas should not be treated casually just because the process is more accessible than many nineteenth-century techniques.
More context, examples and technical detail
This section moves beyond the introductory account into the material, historical and interpretive details that make Cyanotype worth studying in depth.
Iron chemistry and the Prussian-blue image
The cyanotype process was invented by John Herschel in 1842. Paper or another support is coated with iron salts, exposed to ultraviolet light through a negative or object, and washed in water. The exposed chemistry forms ferric ferrocyanide—Prussian blue—creating a blue-and-white image. The process requires no silver, making it relatively inexpensive and chemically distinctive from many nineteenth-century photographic methods.
Because objects can be laid directly on sensitized paper, cyanotype is especially suited to photograms.
Anna Atkins and the first photographically illustrated books
Botanist Anna Atkins used cyanotype to record algae and later ferns by placing specimens directly on coated paper. Beginning in the 1840s, she assembled the prints into volumes such as Photographs of British Algae. These books are among the earliest sustained uses of photography for scientific illustration and are often described as the first books illustrated with photographic images. The specimens become pale silhouettes against intense blue, turning scientific classification into striking graphic design.
Prussian blue, sunlight and Anna Atkins
The cyanotype process was introduced by the scientist John Herschel in 1842. Paper or fabric is sensitized with iron salts, exposed to ultraviolet light under a negative or object and then washed, producing a characteristic Prussian-blue image. Anna Atkins used the process almost immediately to make photograms of algae for her book Photographs of British Algae, often cited as the first photographically illustrated book. Cyanotype later became useful for copying technical drawings, giving rise to the architectural “blueprint.” Its continued popularity in art and education comes from the process’s relative simplicity, direct contact imagery and intensely recognizable color.
Anna Atkins used cyanotype to record algae by placing specimens directly on sensitized paper and exposing them to light.
In a simple photogram, areas receiving more ultraviolet exposure become blue after processing, while covered areas remain light.
Cyanotype became widely used for copying architectural and engineering drawings because it was inexpensive and could reproduce line drawings at full scale.
Cyanotype images can be sensitive to alkaline environments and prolonged intense light, and their iron chemistry differs from silver photographs.
The cyanotype process was invented by John Herschel in 1842.
Botanist Anna Atkins used cyanotype to record algae and later ferns by placing specimens directly on coated paper.
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