The cyanotype is a cameraless photographic process producing white silhouettes on Prussian blue. Invented by Herschel in 1842, learn how Anna Atkins made the first photo book.
Anna Atkins placed a piece of algae on paper coated with iron salts, pressed it under glass, and set it in the sun. When she washed the paper in water, the uncovered areas turned a deep, impossible blue. The algae, blocking the light, remained white. The result was a precise white silhouette of a seaweed specimen floating on a field of Prussian blue. She did this hundreds of times, and in 1843 she bound the results into a book: Photographs of British Algae: Cyanotype Impressions. It was the first book illustrated with photographs, and it appeared one year after the cyanotype process was invented.
The cyanotype is a photographic process invented by Sir John Herschel in 1842. Paper is coated with a solution of ferric ammonium citrate and potassium ferricyanide, then exposed to ultraviolet light. The light reduces the ferric iron to ferrous iron, which reacts with the ferricyanide to form Prussian blue, a deep blue pigment. Areas blocked from the light by an object placed on the paper remain white. The print is washed in water to remove the unexposed chemicals, and the blue image is permanent. No camera is required. No darkroom is required. The process is simple enough that it has been used as a teaching tool for children, and it is still practiced by artists today.
This entry covers how the cyanotype works, its invention, Anna Atkins's groundbreaking use of it, and why this blue process has survived for over 180 years.
The cyanotype is a printing-out process, meaning the image becomes visible during exposure rather than requiring chemical development. The chemistry is straightforward. Two solutions are prepared: one of ferric ammonium citrate and one of potassium ferricyanide. They are mixed in equal parts just before use and brushed onto paper. The paper is dried in the dark, placed in a contact printing frame with an object or negative on top, and exposed to sunlight or another UV source.
During exposure, ultraviolet light converts the ferric ammonium citrate to a ferrous salt. The ferrous iron reacts with potassium ferricyanide to form ferric ferrocyanide, known as Prussian blue. The longer the exposure, the deeper the blue. After exposure, the paper is washed in plain water. The unexposed iron salts dissolve away, leaving the white areas where objects blocked the light and the blue areas where light reached the coating.
The resulting image is monochromatic blue. There is no tonal range in the traditional sense. The blue is either present or absent, with some variation in density depending on exposure time. This limitation is also the cyanotype's strength. The blue is so distinctive and so permanent that the process has never been fully abandoned.
A 2024 article published in Applied Phycology described the cyanotype process and its use in science education, noting that Atkins's cyanotypes, now over 180 years old, still look pristine in museum collections. The article demonstrates how making cyanotypes can teach photochemical reactions, the importance of UV light, and the history of scientific imaging. Read the study at Taylor and Francis.
Sir John Herschel (1792-1871) invented the cyanotype in 1842. Herschel was a polymath: astronomer, chemist, and the man who first coined the word "photography" in 1839. He was also the one who suggested sodium thiosulfate as a photographic fixer to Talbot, making permanent photography possible. The cyanotype was one of several processes Herschel experimented with, and he invented it primarily as a way to reproduce drawings and diagrams cheaply.
The process did not catch on for fine art photography in the 1840s because the blue color was considered unsuitable for portraiture. But it found an unexpected application: the blueprint. In the 1870s, the cyanotype process was adopted for reproducing architectural and engineering drawings. The paper was coated, the drawing was placed on top as a transparent overlay, and the whole thing was exposed to sunlight. The result was a white-line image on blue paper: the blueprint. The word "blueprint" entered the English language as a synonym for any plan or design, and it comes directly from the cyanotype process.
The cyanotype was revived as a fine art process in the 20th century. Photographers like Robert Demachy and Edward Steichen experimented with it. In the contemporary era, the cyanotype has become one of the most popular alternative processes, practiced by artists who value its simplicity, its distinctive color, and its connection to the earliest days of photography.
Atkins is the photographer most closely associated with the cyanotype, and she was the first person to use the process to create a book. Photographs of British Algae: Cyanotype Impressions (1843-1853) was produced over ten years and contained hundreds of cyanotype photograms of seaweed specimens. Atkins learned of the process through her father, John George Children, who was a friend of Herschel. A 2024 article in the Linnean Society newsletter described the society's three volumes of Atkins's cyanotypes, containing 450 pages of handwritten text and photographic images. Read the article at The Linnean Society.
Herschel invented the process. His own cyanotypes were experiments rather than artworks, but his technical contribution is foundational. He discovered that the combination of ferric ammonium citrate and potassium ferricyanide produced a stable blue image when exposed to light, and that the image could be fixed with a simple water wash. No other photographic process is so chemically simple.
Dixon was Atkins's childhood friend and collaborator. An unpublished album of 74 cyanotypes by Atkins and Dixon, held at the Beinecke Rare Book and Manuscript Library at Yale, shows the two women expanding the process beyond algae to include lace, feathers, and flowering plants. A 2025 feature from Yale News described the album as blending scientific illustration with artistic exploration. Read the feature at Yale News.
Ware is a contemporary chemist and photographer who developed an improved cyanotype process in the 1990s using ferric ammonium oxalate instead of ferric ammonium citrate. The "new cyanotype" produces a deeper blue, faster exposure times, and better tonal range than Herschel's original formula. Ware's work demonstrates that even a 180-year-old process can be improved.
The cyanotype is one of the few 19th-century photographic processes still widely practiced. Its simplicity is the reason. You need two chemicals, water, paper, and sunlight. No darkroom, no enlarger, no expensive equipment. This accessibility has made it a favorite of art educators, hobbyists, and fine art photographers working in alternative processes.
A 2023 study published in the Journal of Chemical Education described the cyanotype process and its potential in chemistry education, demonstrating how making cyanotypes can teach students about photochemical reactions, oxidation-reduction chemistry, and the history of scientific imaging. Read the study at ACS Publications.
The cyanotype is one of several early photographic processes. It is contemporary with the daguerreotype and the calotype, but it is fundamentally different because it is a cameraless process, producing photograms rather than camera images. It is part of the broader category of alternative process photography. The cyanotype also relates to contact printing, since the process requires the object or negative to be in direct contact with the sensitized paper. For more on the history of photography, read our post on photography as fine art, or explore our guide to how to read an image.
The New York Public Library holds a copy of Atkins's Photographs of British Algae, one of only a handful of surviving copies. The Linnean Society of London holds three volumes of Atkins's cyanotypes. The Beinecke Rare Book and Manuscript Library at Yale holds the unpublished Atkins and Dixon album. The Victoria and Albert Museum in London has a collection of historical and contemporary cyanotypes.
When you look at a cyanotype, notice the depth of the blue. Prussian blue is one of the most lightfast pigments ever discovered, which is why Atkins's prints from the 1840s still look as blue as the day they were washed. For more on the broader context of early photography, read our entries on daguerreotype and calotype, or explore our post on documentary photography and the loaded image.
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