Cyanotype

Henri Le Secq. Farmyard Scene. GEH.

The cyanotype process was discovered by the physical scientist, inventor, and architect of early photographic processes John Herschel in 1842 (Ware, Herschel's Cyanotype: Invention or Discovery 371). The cyanotype is a contact-printing process that produces an image in Prussian blue when the sensitized material is exposed to ultraviolet light. One of several fetching aspects—besides the striking Prussian blue—of the cyanotype is that the chemicals used are essentially harmless and inexpensive and a fixed image can be achieved with a water bath.

            The cyanotype process differs from other processes of the time in that it was not a silver-nitrate process and instead is the effect of UV on ferric salts. Chemists had long known about the chemical creation of Prussian blue since its discovery was first published in 1724. The story of its discovery is worthy of an essay itself, but in short the artist Heinrich Diesback of Berlin discovered it in 1704 when he purchased some tainted potash from a notorious alchemist and used the ash in an attempt to  make a crimson pigment (Ware, Prussian Bleu: Artists' pigment and Chemists' Sponge 612). 

Herschel, John. Lady with a Harp. 1842. The Oxford History of Science Museum.

            In 1842 Herschel was in efforts to create colored images. With the assistance of a colleague in the Royal Society—Albert Smee—he was given the bright red complex salt, potassium ferricyanide. To his astonishment when Herschel exposed a paper coated with an aqueous solution of potassium ferricyanide to the summer sun his paper turned Prussian blue (Ware, Prussian Bleu: Artists' pigment and Chemists' Sponge 617).  Herschel furthered his discovery—again with the help of Smee—with the addition of ammonium ferric citrate to the photosensitive solution, substantially shortening the exposure time.

Chemistry

Ammonium iron (III) citrate and potassium ferricyanide:
UV causes a photochemical redox reaction in the iron complex, whereby the iron (III) is reduced to iron (II) and the citrate is oxidized initially to acetone di-carboxylic acid:
2Fe³⁺(aq) + C(OH)COOH(CH₂COOH)₂(aq) à 2Fe²⁺()aq) + CO(CH₂COOH)₂(aq) + CO₂(g )+2H⁺(aq)
The iron (II) then couples with ferricyanide to precipitate Prussian blue in a density proportional to the quantity of photons absorbed:
Fe²⁺(aq) + [Fe^III(CN)₆]^3-(aq) à Fe^III[Fe^II(CN)_6]^-(s) (Ware, Prussian Bleu: Artists' pigment and Chemists' Sponge 617).
Herschel’s Original formula consisted of two solutions. Solution A was 20g of ferric ammonium citrate to 100 ml of water and Solution B was 16g potassium ferricyanide to 100 ml of water. These two solutions were then mixed in equal proportions to create the sensitizer (James 151).

People of Note

Pillow made up of 30 cyanotype images on cloth sewn together. GEH

The cyanotype was never used as frequently as any of the silver-nitrate processes and was mostly used by amateur photographers. Today the cyanotype is a popular process among amateur photographers because it is inexpensive and easy to learn.

Atkins, Anna. Photographs of British Algae. 1843. Detroit Institute of Arts.

            Anna Atkins was the first person in history to use a photographic process to catalogue a collection of objects and publish them in book form. In 1843 Atkins published British Algae: Cyanotype Impressions (Naef 24). Atkins’ cyanotype photograms are spectacularly rich both scientifically and artistically. Atkins’ gift was to choose a subject—algae—both simple and incredibly diverse, what her photograms revealed was a glimpse of both truth and beauty.

Bosse, Henry. Pine Bend. 1891. Minneapolis Institute of Arts Collection.

            In the 1870s Henry P. Bosse—trained as a cartographer, draftsman, painter, and engineer set off to document the 850 miles or shoreline and the accompanying States along the Mississippi river, using only the cyanotype process (Naef 64). The cyanotype process was then currently commercially available and was being utilized to duplicate materials—maps and architectural materials. Bosse travelled aboard the riverboat General Barnard—the very same boat that Twain rode around the same time (Naef 64).  As Bosse travelled down river he took photographs of the river, the cities and towns along side, and the lives of the people that utilized the Mississippi.

Preservation

A sensitized cyanotype solution is applied directly to the medium so it lacks a binding layer and avoids binder-related deterioration issues. Overall the cyanotype has less degradation issues than silver materials in the 19^th century.

            The paper support used has the inherent flaws of the time period it came from and may experience foxing and can be brittle.

B.T. Babbitts Soap. GEH

            The Prussian blue will fade when exposed to light but will partially revive when stored in the dark. Images will also fade when stored in alkaline conditions; therefore alkaline-buffered enclosures should not be used (Reilly 43).

Link to me creating a cyanotype using Herschel's process

Works Cited

James, Christopher. The Book of Alternative Photographic Processes. 2nd Edition. New York: Delmar Cengage Learning, 2009.

Naef, Weston. Photographers of Genius at the Getty. Los Angeles: The J. Paul Getty Museum, 2004.

Reilly, James M. Care and Identification of 19th-Century Photographic Prints. Rochester: Eastman Kodak Company, 2009.

Ware, Mike. "Herschel's Cyanotype: Invention or Discovery." History of Photography 22.4 (1998): 371-379.

—. "Prussian Bleu: Artists' pigment and Chemists' Sponge." Journal of Chemical Education 85.5 (2008): 612-621.