Cyanotype
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A cyanotype of algae by 19th century botanist Anna Atkins
Sir John Herschel (1842) Experimental cyanotype of an unidentified engraving of a lady with a harp, Museum of the History of Science
Architectural drawing blueprint, Canada, 1936
Cyanotype postcard, Racine, Wis., c. 1910

The cyanotype (from Ancient Greek: κυάνεος, kyáneos 'dark blue' and τύπος, týpos 'mark, impression, type') is a slow-reacting, photographic printing formulation sensitive to a limited near-ultraviolet and blue light spectrum, the range of 300 nm to 400 nm, known as UVA radiation.[1] It produces a monochrome, blue-coloured print on a range of supports, and is often used for art and reprography in the form of blueprints. For any purpose, the process usually uses two chemicals – ferric ammonium citrate or ferric ammonium oxalate, and potassium ferricyanide, and only water to develop and fix. Announced in 1842, it is still in use.

History

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The cyanotype process was discovered,[2] and named thus, by Sir John Herschel, who in 1842 published his investigation of light on iron compounds,[3] expecting that photochemical reactions would reveal, in a form visible to the human eye, the infrared extreme of the electromagnetic spectrum detected by his father William Herschel and the ultraviolet or "actinic" rays that had been discovered in 1801 by Johann Ritter. Though Johann Wolfgang Döbereiner had published in 1831 in German on the light-sensitivity of ferric oxalate,[4][5] of which Herschel became aware during his visit to Hamburg, it is too lightly toned to form a satisfactory image and would require a second reaction to make a permanent print.[6]

Alfred Smee had in 1840 used electrochemistry to isolate a pure form of potassium ferricyanide,[7] which he sent to Herschel, whose innovation was to use the ammonium iron(III) citrate or tartrate, then commercially available as an iron tonic and also introduced to him by Smee, for photographic purposes. He mixed the ammonium ferric citrate in a 20% aqueous solution, with 16% of the potassium ferricyanide, to make the sensitizer for coating plain paper. Exposed to sunlight, the ferric salt is reduced, then combines with the ferricyanide to yield ferric ferrocyanide – Prussian blue (also known as Turnbull's blue, or Berlin Blue in Germany).[8] Intensifying and fixing is achieved simply by rinsing the print in water in which unexposed sensitizer and reaction products are readily soluble.

Anna Atkins, a friend of the Herschel family, over 1843–61 and with the assistance of Anne Dixon, hand-printed several albums of botanical and textile specimens, especially Photographs of British Algae: Cyanotype Impressions,[9] effectively the world's first photographically illustrated books.[10] After the Antarctic Ross expedition (1839–1843), John Davis, artist and naturalist on the expedition, made or commissioned some cyanotypes in 1848 from seaweeds collected on the voyage.[11] Also in the Antipodes, Herbert Dobbie, in imitation of Atkins, produced a book New Zealand ferns: 148 varieties, but with double-sided pages of cyanotype prints, in 1880.[12]

John Mercer in the 1850s used the process for printing photographs onto cotton textiles, and discovered means of toning the cyanotype violet, green, brown, red, or black.[8]

As with all of his photographic inventions, Herschel did not patent his cyanotype process. Chemist George Thomas Fisher Jr. quickly disseminated information on the new medium internationally in his popular 50-page manual Photogenic manipulation in 1843, containing plain instructions in the theory and practice of the arts of photography: calotype, cyanotype, ferrotype, chrysotype, anthotype, daguerreotype, and thermography,[13] which the following year was translated into German and Dutch. The medium was immediately taken up and perfected by notable photographic practitioners of the time, including William Henry Fox Talbot[14] and Henry Bosse. The latter, in making fine presentation albums of bridges and structural steel, foresaw an appropriate effect in colour; the intense blues of his refined cyanotypes from large glass plates were printed on fine French paper 37 cm x 43.6 cm, and watermarked Johannot et Cie. Annonay, aloe's satin and leather bound.[15][16][17]

Commercial use came only in 1872, the year after Herschel's death. Marion and Company of Paris were first to market the cyanotype, under the proprietary name of "Ferro-prussiate", for reprography of plans and technical drawings and to advantage due to its low cost and simplicity of processing, which required only water. In this application and with the manufacture of blueprint papers, it remained the dominant reprographic process until the 1940s.[8] During the 217-day Siege of Mafeking of the town of Mafeking (Mafikeng) in South Africa during the Second Boer War from October 1899, the process was used to print stamps and banknotes.[1]

The simple technology of the cyanotype, though, remained accessible in the nonindustrial realm and contributed to folk art; Francois Brunet notes the cyanotypes on cloth used by American home quilt-makers after 1880,[18] and Geoffrey Batchen cites 30 or more early cyanotyped family snapshots on cloth, sewn into pillow slips or quilts, in the collection of Eastman House.[8] Sandra Sider perpetuates this tradition in her own quilt-making and as a proponent for increased museum acquisitions of art quilts.[19]

The cyanotype produced negatives, reversing the darks and lights of the image or object exposed on it, but Herschel also contrived a version, though more complex, to produce positives, which he hoped would aid in his ambition to achieve images of full natural colour. Its difficulties were overcome by Henri Pellet in 1877 in his gum arabic iron cyanofer direct positive photographic tracing method,[6][20] which he commercialised.[21]

Process

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Herschel's formula and method

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In a typical procedure, equal volumes of an 8.1% (w/v) solution of potassium ferricyanide and a 20% solution of ferric ammonium citrate are mixed. The overall contrast of the sensitizer solution can be increased with the addition of about 6 drops of 1% (w/v) solution potassium dichromate for every 2 ml of sensitizer solution.[citation needed]

This mildly photosensitive solution is then applied to a receptive surface (such as paper or cloth) and allowed to dry in a dark place. Cyanotypes can be printed on any support capable of soaking up the iron solution. Although watercolor paper is a preferred medium, cotton, wool, anodized aluminium, and even gelatin sizing on nonporous surfaces have been used. Care should be taken to avoid alkaline-buffered papers, which degrade the image over time.

An image can be produced by exposing sensitised paper to a source of ultraviolet (UV) light (such as sunlight) as a contact print. The combination of UV light and the citrate reduces the iron(III) to iron(II). This is followed by a complex reaction of the iron(II) with ferricyanide. The result is an insoluble, blue pigment (ferric ferrocyanide) known as Prussian blue.[22] The exposure time varies widely, from a few seconds in strong direct sunlight, to 10–20 minute exposures on a dull day.

After exposure, the paper is developed by washing in cold, running water; the water-soluble iron(III) salts are washed away. The parts that were exposed to UV turn blue as the water-insoluble Prussian blue pigment remains in the paper, which gives the print its typical blue color.[22] The blue color darkens upon drying.

Improved formula

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The ingredients for the process have remained mostly unchanged since its inception in 1840.[23] In 1994, Mike Ware improved on Herschel's formula with ammonium iron(III) oxalate, also known as ferric ammonium oxalate, to replace the variable and unreliable ammonium ferric citrate.[24] It has the advantage of being made up as a convenient single stock solution with a good shelf-life that does not nourish mould growth. The solution is well-absorbed by paper fibres, so it does not pool on the surface or result in a tackiness, which may adhere to negatives. The paper better retains the pigment, with little of the Prussian blue image being lost in the washing stage, and exposure is shorter (ca. 4-8 times) than the traditional process. The cyanotype solution, even once its excess is washed off with water, remains photo-sensitive to some degree. A print that has been stored or displayed in bright light will eventually fade, the light causing a chemical reaction that changes the Prussian blue of the cyanotype to white. Storing the cyanotypes in darkness reverses the process,restoring them to their original vibrancy.[25]

Different composition levels of ferric ammonium citrate (or oxalate) and potassium ferricyanide result in a variety of effects in the final cyanotypes. Mixtures of half ferric ammonium citrate and half potassium ferricyanide produces a medium, even shade of blue that is most commonly seen in a cyanotype. A mix of one-third ferric ammonium citrate and two-thirds potassium ferricyanide produces a darker blue, and a more high-contrast final print.[26]

Disadvantages of the Ware formula are a higher cost, more complicated preparation, and a level of toxicity.[27]

Printmaking

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A paprika branch (Chilie) with leaves, cyanotype as a photogram, exposed (left) and developed (right).

The simplest kind of cyanotype print is a photogram, made by arranging objects on sensitised paper. Fresh or pressed plants are a typical subject, but any opaque to translucent object will create an image. A sheet of glass presses flat objects into close contact with the paper, resulting in a sharp image. Otherwise, three-dimensional objects or less-than-perfectly flat ones create a more- or less-blurred image depending on the incidence and breadth of the light source.

Chemigrams are variants of photograms. The cyanotype solution is applied, poured, or sprayed irregularly. A variant of action painting results from repeated washing and application, placing objects on top.

More sophisticated prints can be made from artwork or photographic images on transparent or translucent media. The cyanotype process reverses light and dark, so a negative original is required to print as a positive image. Large-format photographic negatives or transparent digital negatives can produce images with a full tonal range, or lithographic film can be used to create high-contrast images.

The cyanotype may be combination-printed with gumoil,[28] or with a gum bichromate image, in which, for full-colour imaging from colour separations, it may form the blue layer; or it may be combined with a hand-painted or hand-drawn layer.[29]

Toning

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Cyanotype, toned with tannin, tea, and coffee; left side – bleached with washing soda before toning, picture of flower made with Image Creator

In a cyanotype, blue is usually the desired color, but a variety of alternative effects can be achieved. These fall into three categories – reducing, intensifying, and toning.[30] It is common to bleach prints before toning them, but also possible to achieve different effects by toning prints without bleaching.[31]

  • Bleaching processes are ways of decreasing the intensity of the blue. Sodium carbonate, ammonia, borax, Dektol photographic developer, and other chemicals can be used to do this. Household bleach is also effective, but tends to destroy the paper base. How much and how long to bleach depends on the image content, emulsion thickness, and what kind of toning is being used. When using a bleaching agent, controlling the bleaching process by washing in clean water as soon as the desired effect is achieved, to prevent loss of detail in the highlights is important.[32]
  • Intensifying processes strengthen the blue effect. Chemicals used are hydrogen peroxide or mild acidic substances – citric acid, lemon juice, vinegar/acetic acid, etc.[30] These can also be used to speed up the oxidation process that creates the blue pigment.
  • Toning processes are used to change the color of the iron oxide in the print.[30] The color change varies with the reagent used. A variety of agents can be used, including various types of tea, coffee, wine, urine, tannic acid, or pyrogallic acid, resulting in tones varying from brown to black.[33] Most toning processes will to some extent tint the white parts of a print.

Long-term preservation

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One of the most robust of Victorian print technologies, cyanotypes are quite stable on their own, but in contrast to most historical and present-day processes, the prints do not react well to basic environments.[34] As a result, it is not advised to store or present the print in chemically buffered museum board, as this makes the image fade. Another unusual characteristic of the cyanotype is its regenerative behavior: prints that have faded due to prolonged exposure to light can often be significantly restored to their original tone by simply temporarily storing them in a dark environment.[35][36]

Cyanotypes on cloth are permanent but must be washed by hand with non-phosphate soap[37] so as to not turn the blue to yellow.

Cyanotype in artistic practice

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Artistic potential

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The cyanotype's success as a form of artistic expression lies in its capacity for manipulation or distortion.[38] It produces distinctive effects and is versatile,[27] enabling prints to be made on a wide variety of surfaces,[24] including paper, wood, fabric,[39] glass, Perspex, bone, shell and eggshell, plaster and ceramics,[26][40] and at any scale; to date 2017, the largest is 276.64 m2 (2977.72 ft2), created by Stefanos Tsakiris in Thessaloniki, Greece, on 18 September 2017.[41] Robin Hill in 2001 exhibited Sweet Everyday, a 30.5 m (100 ft) cyanotype enwrapping Lennon, Weinberg, Inc.'s Soho gallery, and evoking wavy brushstrokes by placing ordinary shopping bags on photo-sensitive paper exposed to light.[42] For photographic negatives or positives enlargement directly onto the emulsion is not feasible due to the low sensitivity of the emulsion (except with a solar enlarger), so requires contact printing at 1:1 ratio. The low sensitivity permits progress to be inspected in a printing frame during exposure. Consequently and because of its long exposure scale it suits most negatives whether of high or low contrast. As a recognisably 19th century technology, artists like John Dugdale use it to evoke, or to critique, Victorian aesthetics and social constructs.[25]

The artist is not restricted to the reproduction of existing photographic negatives. Prints can be made of three-dimensional objects, utilising the ability of the objects to be placed on top of the photosensitive material. Once exposed to light, the final print is of an outline of an item[26] with internal detail where they allow light, depending on their relative transparency and exposure, to filter through; Anna Atkins' botanical cyanotypes sharply register the more transparent segments of a petal or leaf.[43] An object original, used to make a cyanotype photogram, including the human figure for example, is reproduced at actual size. Robert Rauschenberg's and Susan Weil's collaborative cyanotypes, including Untitled (Double Rauschenberg), c. 1950[44] were made by both artists lying down, hands held, on a large piece of photosensitive paper (treated with cyanotype chemicals). The resulting prints of their bodies in various poses are currently part of the Museum of Modern Art's permanent collection.[38] In France, from the end of the 1970s, Nancy Wilson-Pajic made cyanotype photograms of everything from a broken windshield to herself (Falling Angels), and eventually several long series of museum collections and of Haute-Couture robes by Christian Lacroix and other designers. The results have been shown all over the world and are in major institutions and public collections.

The blue hue naturally associates symbolically with sea or sky.[45] As German photographer Thomas Kellner notes of his 1997 Cubist multi-pinhole portraits of porcelain dolls; "I am specially happy with the blue colour in this series as the blue has a different depth in the background than a black print. Blue is still infinite, whereas black usually has the character of ending."[46] The negative form may be disorienting or surreal;[26] while white is often used to frame or highlight a central subject in many artistic media, the opposite may be true in the cyanotype, requiring the artist to adapt their ideas to the effect.[25]

Equally important is the expressive potential of the application of emulsion using brush, squeegee, roller or cloth, or by stamping, for calligraphic effect.[26]

The cyanotype process is quite flexible, and it can be scaled up to incredible sizes. For example, in 2017, Stefanos Tsakiris created a 276.64 square meter cyanotype in Thessaloniki, Greece. The print, which holds the world record for the largest cyanotype print, was made to help teach people about cyanotype photography and increase environmental awareness.[47]

Artists

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Nineteenth century

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Self portrait of Linley Sambourne modelling (10 January 1895) for Punch cartoon 'Quite English, You Know!
Anna Atkins, Photographs of British Algae: Cyanotype Impressions, cyanotype, 1843-53

Britain

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Anna Atkins, who was also an accomplished watercolorist, in her cyanotype botanical specimens, is considered the first to make art with the medium[48] in which the sea plants appear suspended in an oceanic blue,[49] and while her hundreds of images satisfy a scientific curiosity, their aesthetic quality has served as inspiration for cyanotype artists ever since.[43][50]

Cyanotype photography was popular in Victorian England, but became less popular as photography improved.[51] By the mid-1800s few photographers continued to exploit its accessible qualities and at the Great Exhibition of 1851, despite extensive displays of photographic technology, only a single example of the cyanotype process was included.[1][52] Peter Henry Emerson exemplified the British attitude that cyanotypes were unworthy of purchase or exhibition with his assertion that: "No one but a vandal would print a landscape in red, or in cyanotype."[53]

Consequently, the process devolved to the proofing of domestic negatives by hobbyist photographers and to postcards, though another British scientist, Fellow of the Royal Astronomical Society[54] Washington Teasdale,[55] delivered hundreds of lectures throughout his lifetime and was among the first to illustrate them with lantern slides, and, up to 1890, to record his experiments and specimens, used the cyanotype, a collection of which is held at the Museum of the History of Science, Oxford.[56]

Edwin Linley Sambourne used cyanotypes as an archive of reference images for his Punch cartoons.[57]

France

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Curators and practitioners in France embraced the process. Caricaturist, illustrator, writer and portrait photographer Bertall (born Charles Albert, vicomte d' Arnoux, comte de Limoges-Saint-Saëns) as partner of Hippolyte Bayard was commissioned in the 1860s to make cyanotype portraits from glass negatives for the Société d'Ethnographie for their publication Collection anthropologique.[58] While artistic in execution they also satisfy with the scientific interests of the group as each subject is photographed nude with front, back and profile views, not in the field but in his studio. The project also takes advantage of the ease of making multiples of cyanotypes for the publication[59] Henri Le Secq's cyanotypes, which he made after he gave up photography after 1856 to continue painting and collecting art, were reprints of his famous works and made around 1870 as he was afraid of possible loss due to fading. He gave the reprints dates of the original negatives, some of which are still in good condition.[1] They are well-represented in French collections.[8] From the early 1850s through the 1870s Corot, with associated artists working in and near the town Barbizon adopted the hand-drawn cliché-verre, and though most were printed on salted or albumenized paper, some used the cyanotype.[60]

United States

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In the US the medium persevered into the 20th century. Eadweard Muybridge made cyanotype contact prints of his animal locomotion sequences,[61] and Edward Curtis' ethnographic cyanotypes of native North Americans are preserved in the George Eastman House.

Pictorialism

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Edward Steichen (1904) Midnight Lake George or Road into the Valley – Moonrise.
Bertha Evelyn Jaques, Untitled, c. 1900, cyanotype, NGA 136408

Pictorialists, throughout Europe and other western countries, in efforts to have photography accepted as an art form, emphasised handcraft in printing, in imitation of painting and drawing, and drew on Symbolist subject matter and themes. Many of the practitioners were respected amateurs whose work was rewarded in a system of international 'salons' run by such organisations as the Camera Club of New York, and competition promoted an elevated level of technical experimentation with all of the then-current processes, such as calotypy, cyanotypy, gum printing, platinum printing, bromoil and Autochrome colour.[62]

Clarence White's impeccable domestic and plein-air pictures are indebted in their bold composition to his contemporaries the painters Thomas Wilmer Dewing, William Merritt Chase and John White Alexander. His labor-intensive process entailed developing the negatives then making tests on cyanotype, playing with dimensions, proportions, and other variables, before making a print in platinum, which he then meticulously and expressively retouched. Alfred Steiglitz in White's portrait of him (1907) held in Princeton University Art Museum, appears gloweringly critical in the cyanotype print preserved there.[63]

At the turn of the century, painter-photographer Edward Steichen, then associated with Alfred Steiglitz who promoted the Photo-Secession and Pictorialism through his Camera Work (1903–1917) produced prints of Midnight Lake George now held in The Alfred Stieglitz Collection: Photographs at the Art Institute of Chicago where in 2007 scientific examination of the prints and his records concluded that cyanotype had been incorporated in their predominant gum bichromate over platinum production.[64] Steichen argued provocatively in the first issue of Camera Work that "every photograph is a fake from start to finish, a purely impersonal, unmanipulated photograph being practically impossible."[64]

Photo-Secessionist Franco-American Paul Burty-Havilland, involved through marriage with the Lalique company, evinces a Japonisme in his moody cyanotype portraits and nudes made between 1898–1920.[65] Another American Pictorialist Fred Holland Day made cyanotypes of youths, nude or in sailor suits, in 1911, that are held in the Library of Congress,[66] and French artist Charles-François Jeandel printed his erotic imagery of bound women in his painting workshop in Paris and then in Charente 1890–1900.[67]

The more traditional American printmaker Bertha Jaques, aligned with the antimodernist views of the late Victorian Arts and Crafts movement, from 1894 produced more than a thousand cyanotype photographs of wildflowers.[68]

Impressionism

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American artist Theodore Robinson painted in Giverny 1887–1892, contemporaneous with Monet of whom he made a portrait in cyanotype, and of the haystacks that Monet famously painted. He noted that "Painting directly from nature is difficult as things do not remain the same; the camera helps to retain the picture in your mind."[69] He often drew a grid over his cyanotypes or albumen prints to assist transferring the composition, with compositional amendments, onto canvas, though conscious that "I must beware of the photo, get what I can of it and then go." His photographic imagery is held in the Canajoharie Library and Art Gallery and the Terra Foundation for the Arts.[69][8]

Modernism

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Arthur Wesley Dow's modernist approach was influential on the Pictorialists in the eloquently simple compositions of his New England environment, like Pine Tree (1895),[70] a cyanotype, related to his interest, while studying in France, in the flat, decorative qualities of Japanese art and that of Les Nabis.[71]

In Europe, Josef Sudek, the 'Poet of Prague' sometimes employed the cyanotype to impressionist effect during the early Modernist period.

Milan-born photographer, printmaker, painter, set designer and experimental film-maker, Luigi Veronesi, well-informed about the international debate on abstraction, was impressed with the abstract potential of the photogram. He participated in a 1934 exhibition in Paris with the international group of abstract artists 'Abstraction-Création', through which he met with Fernand Léger. He drew inspiration from Léger's Ballet Mécanique, Surrealism via the Metaphysical painting of Georgio de Chirico, and fellow photographer Giuseppe Cavalli with whom, convinced of the essential 'uselessness' of art, in 1947 he founded a group named La Bussola (The Compass). Influenced by Constructivist theories (and politically aligned with Communism), Veronesi used the cyanotype photogram after 1932 as a means of revealing metaphysical qualities in objects.[72][73]

Late modern

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Catherine Jansen (1981) The Blue Room, cyanotype on fabric, mixed media.

In a 2008 essay A.D. Coleman perceived a return of the legacy Pictorialist methods being applied in art photography from 1976,[62] a tendency represented in Francesca Woodman's late cyanotypes and in contact prints by Barbara Kasten and Bea Nettles.[74] Weston Naef, curator of photography at the J. Paul Getty Museum in Los Angeles, in a 1998 New York Times article by critic Lyle Rexer, confirmed that "Looking back at [photography's] pioneers, today's artists see a way to restore expression to an art beguiled by technology," referring to the loss of 'intimacy' in digital imaging to account for artists' attraction to daguerreotypes, tintypes, cyanotypes, stereopticon images, albumen prints, collodion wet plates; all physical and 'hands-on' methods.[75] Artists David McDermott and Peter McGough, who met in the East Village New York art scene of the 1980s, and until 1995 took the phenomenon to the extreme of reconstructing themselves as Victorian gentlemen, adopting the lifestyle and documenting it and their possessions using vintage cameras and materials, first inspired by their discovery of the cyanotype, and dating their contemporary works in the nineteenth century.[76]

Contemporary

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Indigo XII, Kate Cordsen. Cyanotype on handmade paper

Since 2000 around 10 books, and in growing numbers, are published each year in English in which 'cyanotype' appears in the title, compared to only 95 in total from 1843 to 1999.[77] Though it has been an artform since its inception, the numbers of artists now employing the cyanotype process have burgeoned, and they are not solely photographers. In the book of the 2022 British exhibition Squaring the Circles of Confusion: Neo-Pictorialism in the 21st Century eight contemporary artists: Takashi Arai, Céline Bodin, Susan Derges, David George, Joy Gregory, Tom Hunter, Ian Phillips-McLaren and Spencer Rowell employ the craft of photography for postmodern purpose, including the cyanotype.[78]

International

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Many were included in the first American international survey of the cyanotype in 2016; the Worcester Art Museum's Cyanotypes: Photography's Blue Period[45] which displayed uses of the medium that extend well beyond the utilitarian contact-printing of negatives; Annie Lopez stitched together cyanotypes printed on tamale paper to create dresses; Brooke Williams tea-toned her cyanotypes, adjusting their color to accord with her story as a Jamaican American woman; and Hugh Scott-Douglas experimented with photograms and abstraction.

In 2018, the New York Public Library exhibited the work of nineteen contemporary artists who employ the medium. Mounted 175 years after Anna Atkin's first book of cyanotypes, British Algae, the exhibition was titled Anna Atkins Refracted: Contemporary Works.[79]

Amongst others currently working in, or with, cyanotype are;

United States

[edit]

Christian Marclay who suggests musical scores in his grids of cassette tapes or their unspooling.

Kate Cordsen applies Japanese aesthetics and non-Cartesian perspective in her mural-scale cyanotype landscapes.

Betty Hahn was early to incorporate cyanotype with other art media including hand-painting with embroidery as a feminist statement[80]

Meghann Riepenhoff reprises Anna Atkins by exposing her prepared papers underneath the waves, so light filters through moving sand, shells, and water currents.[45][81]

Canada

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Canadian Erin Shirreff translates her sculptural interests into large-scale cyanotype photograms of temporary three-dimensional compositions in her studio with hours-long exposures during which component forms are moved, added or subtracted for transparent effect.[82]

Germany

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German artist Marco Breuer abrades cyanotype prints on watercolour paper in representations of the passing of time.

Iceland

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Icelandic artist and filmmaker Inga Lísa Middleton employs the cyanotype for nostalgic representations of her homeland, and as a symbolic colour in imagery alerting audiences to an emerging catastrophe in the marine environment.[citation needed]

United Kingdom

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British-born American resident Walead Beshty's Barbican Art Gallery installation of 12,000 cyanotype prints traces a visual time line from October 2013 to September 2014 in a work called A Partial Disassembling of an Invention Without a Future: Helter-Skelter and Random Notes in Which the Pulleys and Cogwheels Are Lying Around at Random All Over the Workbench, produced from each object from the artists' studio being exposed on cyanotype-coated found paper, card or wood.[citation needed]

World Cyanotype Day

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World Cyanotype Day (WCD) is celebrated on the last Saturday of September. Since 2015, it has brought together global community of artists to share prints and celebrate the cyanotype process.[83]

See also

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References

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Further reading

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia
from Grokipedia
The cyanotype is a photographic printing process that produces distinctive Prussian blue images through the photochemical reaction of iron salts exposed to ultraviolet light, invented by British astronomer and chemist Sir John Herschel in 1842.[1] Herschel developed the technique as a simple, low-cost method for reproducing notes and diagrams, naming it "cyanotype" from the Greek words for "blue" and "print" due to the characteristic color formed by the insoluble ferric ferrocyanide (Prussian blue) pigment.[2] The process begins by coating a surface, typically paper, with an aqueous solution of ferric ammonium citrate (as a photosensitive iron(III) compound) and potassium ferricyanide, which remains stable until exposed to UV light; upon exposure, the iron(III) reduces to iron(II) in illuminated areas, which then react to form the blue complex there, while unexposed areas remain soluble.[3] After exposure, the print is rinsed in water to remove unreacted chemicals, revealing a negative image in shades of blue against a white background, often using contact printing (photograms) without a camera or enlarger. Early adoption included botanical illustration by Anna Atkins, a British photographer and botanist who, starting in 1843, produced Photographs of British Algae: Cyanotype Impressions, the world's first book illustrated entirely with photographs, documenting over 400 species of algae through direct impressions of specimens.[4] By the 1870s, cyanotypes found widespread industrial application in reprography, particularly for architectural and engineering blueprints, as the process allowed inexpensive duplication of large technical drawings on sensitized paper.[2] Though largely superseded by modern copying technologies in professional contexts, cyanotype endures in contemporary art and education for its accessibility, environmental simplicity (requiring no silver halides or toxic developers), and striking aesthetic, inspiring artists to explore themes of nature, abstraction, and ephemerality.[5]

Fundamentals

Definition and Characteristics

A cyanotype is a monochromatic photographic printing process that produces images in Prussian blue on substrates such as paper or fabric. Developed as one of the earliest non-silver halide methods, it relies on the photoreaction of iron salts to form an insoluble blue pigment known as ferric ferrocyanide.[6] The process, invented in 1842 by British astronomer John Herschel, enables the creation of detailed, continuous-tone prints through direct contact exposure. Key characteristics of cyanotypes include high sensitivity to ultraviolet light, particularly in the 300–450 nm range, with peak response around 360 nm, allowing exposure using sunlight or artificial UV sources. As a contact printing technique, it requires placing a transparency, object, or negative in direct contact with the sensitized surface to produce a one-to-one scale image, resulting in sharp details where light cannot penetrate. The signature cyan-blue hue arises from the ferric ferrocyanide pigment, which imparts a vibrant, non-fading color to the final print.[7] Unlike silver-based processes, cyanotypes achieve permanence without chemical fixing; excess unexposed salts are simply rinsed away in water, leaving a stable image resistant to further light degradation. Historically, the cyanotype earned the nickname "blueprint" due to its widespread use in the late 19th and early 20th centuries for reproducing architectural and engineering drawings, where opaque lines on the original negative yielded white lines against a blue background.[8] This distinguishes it from modern blueprints, which utilize the diazo process—a chemical method producing similar blue-tinted copies but with greater speed and convenience for large-scale reproduction.[9] The basic workflow of cyanotype production involves coating a receptive surface with the iron-based sensitizer, drying it in subdued light, exposing it to UV radiation to initiate the photoreaction, and washing the print to remove solubles and reveal the image.[7] This straightforward sequence underscores the process's accessibility and enduring appeal in photographic practice.

Chemical Basis

The cyanotype process relies on two primary chemicals: ammonium ferric citrate, which serves as the UV-sensitive iron(III compound, and potassium ferricyanide, which provides the ferricyanide ions necessary for pigment formation.[10][2] These are typically mixed in aqueous solutions to form a light-sensitive coating. The photochemical reaction begins when ultraviolet (UV) light irradiates the coated surface, inducing a reduction of Fe(III) to Fe(II) within the ammonium ferric citrate complex through a ligand-to-metal charge transfer process.[11][12] This Fe(II) then reacts with ferricyanide ions ([Fe(CN)6]3-) from potassium ferricyanide, reducing them to ferrocyanide ions ([Fe(CN)6]4-). The resulting ferrocyanide ions subsequently combine with remaining Fe(III) ions to produce an insoluble precipitate of Prussian blue, chemically known as ferric ferrocyanide or iron(III) hexacyanoferrate(II).[13][14] This overall reaction can be represented by the balanced equation:
4Fe3++3[Fe(CN)6]4Fe4[Fe(CN)6]3 4 \text{Fe}^{3+} + 3 [\text{Fe}(\text{CN})_6]^{4-} \rightarrow \text{Fe}_4[\text{Fe}(\text{CN})_6]_3
[15]
UV light, particularly in the UVA range (around 365 nm), drives this electron transfer because the ferric citrate complex strongly absorbs UV radiation, exciting electrons and facilitating the reduction; visible light has minimal effect due to weak absorption in that spectrum, preventing significant reaction without UV exposure.[16][12] Handling these chemicals requires standard laboratory precautions, as both ammonium ferric citrate and potassium ferricyanide exhibit low acute toxicity but can cause skin or eye irritation upon direct contact.[17] Potassium ferricyanide contains cyanide in a stable complex that does not readily release free hydrogen cyanide under normal conditions, rendering the final cyanotype prints non-toxic and stable for handling.[18][19]

History

Invention by Herschel

In 1842, British astronomer and chemist Sir John Frederick William Herschel invented the cyanotype process while experimenting with iron salts for reproducing his scientific notes and diagrams.[20] His primary motivation was to develop a simple, permanent method for reproducing his extensive scientific notes and botanical drawings, rather than for general photography, addressing the need for accurate copies without manual redrawing.[5][1] Herschel's original formula involved mixing equal parts of two solutions: one of ammonium ferric citrate and one of potassium ferricyanide, which were then applied to paper as a light-sensitive coating.[20][21] In early tests, he exposed the coated paper to sunlight under contact negatives or transparent drawings, resulting in the formation of insoluble Prussian blue (ferric ferrocyanide) in the exposed areas, while the unexposed regions remained soluble and washed away with water to reveal white images on a deep blue background.[20] Herschel coined the term "cyanotype" for this process, deriving it from the Greek words for "blue" (kyanos) and "impression" (typos), highlighting its distinctive Prussian blue coloration.[1] Herschel detailed his discovery in the paper "On the Action of the Rays of the Solar Spectrum on Vegetable Colours, and on Some New Photographic Processes," published in the Philosophical Transactions of the Royal Society in 1842, where he described the cyanotype as a stable, non-silver alternative for precise copying.[22] This publication marked the formal introduction of the process to the scientific community, emphasizing its utility for archival reproduction over artistic imaging.[2]

19th-Century Developments and Popularization

Following Sir John Herschel's 1842 invention of the cyanotype process, he further developed its applications for creating photograms—camera-less images formed by placing objects directly on sensitized paper—and for duplicating written notes and drawings, demonstrating its utility as a simple copying method for scientific records.[5] Herschel's experiments emphasized the process's permanence and ease, allowing stable blue images to emerge upon exposure to light and development in water, which laid the groundwork for broader adoption beyond initial laboratory use.[2] In 1843, English botanist Anna Atkins pioneered the cyanotype's artistic and scientific application by producing Photographs of British Algae: Cyanotype Impressions, the first book illustrated entirely with photographic images, featuring over 400 hand-printed cyanotype photograms of seaweed specimens to accurately depict their forms without the distortions of hand-drawing.[23] Atkins self-published the work in installments through 1853, collaborating with her friend Anne Dixon on many plates, and distributed copies to fellow scientists, marking the process's early role in natural history documentation.[24] The cyanotype spread to continental Europe and the United States in the mid-19th century, with French chemist Michel Eugène Chevreul conducting experiments around 1840 on the light sensitivity of Prussian blue, observing that the pigment paled and released cyanogen gas when exposed to sunlight in an airtight chamber, which contributed to understanding the chemical reactions underlying the process.[25] In France, the technique influenced early photographers exploring non-silver processes, while in the US, adoption began among scientific and amateur circles by the 1870s, with photographers like Henry Peter Bosse using cyanotypes to document landscapes and engineering projects along the Mississippi River in the 1890s, adapting Herschel's method for topographic surveys.[26] By the 1870s, cyanotypes gained prominence in engineering and architecture as an efficient alternative to hand-tracing drawings, enabling quick reproduction of technical plans on sensitized paper exposed under sunlight or artificial light.[27] This practical shift, driven by the process's low cost and reliability, replaced labor-intensive methods and supported industrial growth, particularly in reproducing blueprints for construction and machinery.[28] Key advancements included the introduction of commercial blueprinting machines in the 1880s, such as the first Swiss-made device exhibited at the 1876 Philadelphia Centennial Exposition, which automated exposure and washing to produce uniform copies of large architectural plans at scale.[2]

Process

Materials and Preparation

The traditional cyanotype process requires two primary light-sensitive chemicals: ammonium ferric citrate (preferably the green grade for its stability) and potassium ferricyanide, along with distilled water as the solvent and a suitable substrate such as acid-free watercolor paper or natural fabric like cotton.[29] These materials are chosen for their ability to form a photosensitive emulsion that produces the characteristic Prussian blue upon exposure and development.[21] Protective equipment, including nitrile gloves, is essential during handling to avoid skin contact with the irritant chemicals, and all preparation should occur in subdued light or darkness to prevent unintended exposure.[21] Preparation of the sensitizing solution begins with creating two stock solutions separately. Solution A consists of 25 grams of ammonium ferric citrate dissolved in 100 milliliters of distilled water, resulting in a 25% solution; Solution B is made by dissolving 10 grams of potassium ferricyanide in 100 milliliters of distilled water, yielding a 10% solution.[29] These stock solutions are stable for several months when stored in amber glass bottles away from light, but the working sensitizer—formed by mixing equal parts of Solutions A and B immediately before use—should be prepared fresh and used within a few hours to maintain efficacy, as it turns greenish-yellow upon mixing and degrades over time.[21] Coating the substrate involves applying the mixed sensitizer evenly to one side of the paper or fabric using a soft hake brush for broad coverage, a glass rod for uniform thin layers, or immersion dipping for complete saturation, depending on the desired print size and texture.[21] The coated material is then dried thoroughly in a dark, dust-free environment, such as a light-tight box or under a red safelight, for 30 minutes to several hours until tack-free, ensuring the emulsion adheres well without cracking during exposure. For contact printing, a negative image is prepared on a transparent medium, typically by printing a digital positive (inverted to negative) onto inkjet transparency film or acetate sheets using an opaque black ink to block UV light where tones are desired.[21] This negative is placed in direct contact with the dried coated surface, secured under glass in a printing frame to prevent shifting, allowing UV light to pass through transparent areas and expose the emulsion selectively. Essential equipment includes a reliable UV source—such as direct sunlight on a clear day or artificial UVA lamps (e.g., 365 nm wavelength)—for exposure, along with shallow developing trays large enough to accommodate the print for rinsing in running distilled or tap water to remove unexposed chemicals.[21] Additional tools like a contact printing frame and hygrometer help control humidity, which can affect coating consistency, while pH-neutral blotting paper aids in final drying.

Exposure and Development

The exposure process in cyanotype printing begins by placing a photographic negative, transparency, or physical object in direct contact with the light-sensitive coated surface, typically paper or fabric, to create a contact print. This assembly is then secured under glass or another transparent material to ensure even contact and exposed to ultraviolet (UV) light, which initiates the photochemical reaction forming the Prussian blue image in the exposed areas. Sunlight serves as the traditional and most common UV source, with exposure times generally ranging from 5 to 20 minutes in direct midday sun, depending on conditions; artificial UV lamps or exposure units require longer durations, often 30 minutes to several hours, to achieve comparable results.[30][31][32] Several factors influence the exposure time and quality, including the intensity of the UV light, ambient humidity, and the freshness of the chemical coating, as higher humidity can slow the reaction and older solutions may require extended exposure. Overexposure tends to produce deeper, darker blue tones but risks loss of detail in highlights, while underexposure results in weak, pale images that may not fully develop. To determine optimal timing, practitioners often create test strips by progressively uncovering sections during exposure, allowing adjustment based on the desired density.[33][34][35] Following exposure, development reveals the image by rinsing the print in running water, which dissolves and removes the unexposed iron salts, leaving the insoluble Prussian blue prussiate in the exposed regions to form the permanent cyan image. This step typically lasts 5 to 20 minutes, or until the water runs clear and the highlights appear white, ensuring all residual chemicals are cleared to prevent ongoing reactions. Gentle agitation aids uniformity, and distilled or soft water is preferred to avoid mineral deposits that could affect clarity.[36][37] After development, the print is air-dried flat on a clean surface or screen to prevent distortion, warping, or uneven fading, with the image darkening to its final intensity over 24 hours as residual moisture evaporates. Heat sources like hair dryers should be avoided, as they can accelerate uneven drying and alter tones.[38][39] Common troubleshooting issues include uneven coating, which leads to blotchy or streaked results due to inconsistent chemical application, often resolved by using a rod or brush for uniform spreading during preparation. Solarization, a reversal effect where tones invert and highlights turn lighter or greenish, arises from extreme overexposure and can be mitigated by monitoring test exposures closely.[40][41]

Toning and Alternative Techniques

Toning cyanotype prints involves immersing the fully developed and washed print in chemical solutions to modify the characteristic Prussian blue color, typically after a brief bleaching step to lighten the image and facilitate the reaction.[36] Common toning agents include tannic acid, which produces warm brown tones through the formation of iron tannate complexes, citric acid for subtle purple hues, and tea infusions for sepia-like effects.[10] These processes alter the print's texture as well, often yielding a more matte or aged appearance.[42] The chemical basis of toning relies on the partial decomposition of Prussian blue (ferric hexacyanoferrate(II)) during bleaching, which releases ferric ions that then bind with polyphenolic compounds in the toner, such as tannins, to create new colored iron-polyphenol complexes like iron tannate.[10] For instance, tannic acid reacts with iron(III) hydroxide intermediates to form stable, brownish pigments, shifting the image from intense blue to earthier tones while preserving the structural integrity of the print.[25] This reaction is pH-dependent, with alkaline bleaches like sodium carbonate enhancing the ion release for more dramatic color changes.[36] Historical toning recipes from the 19th century expanded the cyanotype's palette beyond blue, with British chemist John Mercer pioneering mordant toning by bleaching prints and treating them with organic dyes to achieve varied hues.[2] Borax or potassium oxalate solutions, followed by toning with potassium thiocyanate, were used to produce bluish-lilac tones by forming iron complexes after a mild bleach.[2] These methods, documented in early photographic manuals, allowed practitioners to customize images for artistic or practical purposes, such as enhancing contrast in blueprints.[25] Alternative techniques extend toning by incorporating additional steps or materials to achieve unique effects, such as multiple exposures on toned prints to introduce subtle color variations through differential light sensitivity of remaining iron compounds.[25] Fabric printing with cyanotype emulsions followed by toning adapts the process for textiles, where agents like tannic acid not only color the image but also fix it to fibers for durable results.[43] Layering gum bichromate over a cyanotype base enables multi-color prints, as the gum's dichromate sensitivity allows pigmented emulsions to build upon the blue underlayer for vibrant, hand-blended results.[44] Modern variations emphasize eco-friendly and accessible approaches, such as using household items like coffee grounds for brown eco-toning, where caffeic acid acts similarly to tannins in binding iron ions without synthetic chemicals.[43] These methods reduce environmental impact while offering reproducible tones, often combined with natural bleaches like vinegar to control intensity.[42] A method for toning cyanotypes green uses potassium permanganate combined with common salt. The solution is prepared by dissolving 5 g of common salt in 1 L of water, then adding 2 g of potassium permanganate and mixing thoroughly. The finished, washed cyanotype print is immersed in the solution for a few seconds, rinsed quickly in water, and the process repeated once or twice if needed; excessive toning risks posterization or destruction of tonal values. The print is then washed for 15 minutes in water. This technique often produces a strong yellow discoloration on the paper and is unreliable and capricious. Undiluted potassium permanganate is toxic by ingestion and accelerates combustion; great caution is required in handling.[45]

Technical Variations

Improved Formulas

In the late 20th century, chemist Mike Ware developed an improved cyanotype formula known as the "New Cyanotype" to address limitations in Herschel's original recipe, such as variable sensitivity and acidity from ferric ammonium citrate.[46][47] This single-solution sensitizer replaces the citrate with ammonium iron(III) oxalate, combined with potassium ferricyanide, and optionally includes a small amount of ammonium dichromate to enhance contrast and extend the shelf-life of the sensitizer.[48] The preparation involves dissolving 30 g of ammonium iron(III) oxalate trihydrate in 30 ml of purified water at approximately 50°C, adding 0.1 g of ammonium dichromate (optional), then incorporating a solution of 10 g potassium ferricyanide dissolved in 20 ml of purified water at approximately 70°C; the combined hot solutions are stirred, cooled to about 20°C for at least 2 hours, filtered, and diluted to a total volume of 100 ml with purified water, resulting in a stable, non-acidic mixture with indefinite shelf life.[46][49][50] The photochemical mechanism in Ware's formula relies on the enhanced reduction of the iron(III) complex upon UV exposure, as shown in the equation:
Fe(C2O4)33+hνFe2++products \text{Fe(C}_2\text{O}_4\text{)}_3^{3-} + h\nu \rightarrow \text{Fe}^{2+} + \text{products}
This step generates ferrous ions that react with ferricyanide to form Prussian blue (ferric ferrocyanide), yielding prints with deeper blue tones and superior contrast compared to traditional methods.[50] The formula's design promotes archival quality with minimal density loss over time.[51] Key advantages include significantly reduced exposure times—typically 2 to 6 minutes in direct sunlight or 20 to 30 minutes under UV lamps—versus 10 to 45 minutes for the original formula, alongside lower toxicity due to the elimination of citric acid's corrosiveness.[52][53][54] Ware's formula, first published in 1995, has become widely adopted for its consistency and ease of use in alternative photography.[49]

Sensitometric Characteristics

Mike Ware's cyanotype processes provide sensitometric details primarily via exposure scale (ES, the log exposure range for useful tonal separation), with no explicit gamma values reported. Contrast is adjustable, affecting the effective ES. The Simple Cyanotype (introduced in 2019) allows ES adjustment from ~1.8 (high contrast, pH ~8) to ~2.7 (low contrast, pH ~4), with medium at ~2.3 (pH ~6). Dmax ~1.5. Longer ES indicates lower contrast and extended tonal scale.[55] The New Cyanotype requires negative density range of at least 1.8 log units for full tonal scale (up to 2.6 with citric acid to reduce contrast). Proper acid development (e.g., HCl) achieves ~1.8 logE range for smooth, long tonal scale.[47] The traditional/Classic Cyanotype accommodates negative density range ~1.0–1.2 due to tonal loss in processing, resulting in shorter scale and reduced contrast.[29] Other variants include citrate-oxalate hybrids, which blend ferric ammonium citrate and oxalate to achieve balanced sensitivity and tonal range, offering a compromise between the original's familiarity and the New Cyanotype's speed without full replacement of components.[56] These modifications maintain compatibility with traditional toning while improving overall performance.[48]

Digital and Modern Adaptations

In contemporary cyanotype practice, digital negatives have revolutionized image control by allowing artists to generate precise positives from scanned or digital originals. These negatives are created by inverting the image in software such as Adobe Photoshop, adjusting density curves to optimize contrast and exposure for the cyanotype's spectral sensitivity, and printing onto transparent inkjet films using desktop printers. This method enables reproducible results from any digital source, bypassing the limitations of traditional film negatives.[57] UV LED exposure units provide consistent indoor alternatives to sunlight, addressing variability in natural light conditions. These units, typically emitting at 365-395 nm wavelengths, deliver uniform UV radiation via arrays of LEDs housed in lightboxes, reducing exposure times to 5-15 minutes depending on intensity and distance. Such setups ensure predictable outcomes in controlled environments, facilitating year-round production without weather dependence.[58][59] Hybrid processes integrate cyanotype with digital technologies to expand scale and versatility. For instance, artists scan cyanotype prints for digital enhancement or composite layering in software before reprinting enlarged versions via projected UV exposure or direct digital-to-analog transfer. This approach combines the organic textures of hand-coated emulsions with computational precision, enabling large-format works and multi-process collages.[60] Eco-friendly adaptations minimize environmental impact through reduced chemical use and natural alternatives. Water-based chemistry reductions involve diluting traditional sensitizers or employing single-solution formulas that require less ferricyanide, while post-exposure development relies on hydrogen peroxide accelerations instead of extended rinsing. Botanical toning with plant extracts, such as tea tannins or wood ash bleaches, replaces synthetic mordants, yielding sustainable color variations from deep indigos to earthy tones.[61][47] Post-2000 developments emphasize accessibility via open-source resources and educational kits. Mike Ware's New Cyanotype formula, introduced in the late 1990s and widely adopted since, offers a stable, single-bottle sensitizer that simplifies preparation and enhances archival qualities, shared freely through technical publications. Commercial kits from suppliers like Bostick & Sullivan and Jacquard provide pre-measured components for beginners, while open-source tutorials and formulas on educational platforms support K-12 integration, blending art with chemistry curricula. In 2025, events like World Cyanotype Day, themed "Cultivating Community," and exhibitions such as "Expanded Cyanotypes: New Directions in Cyanotype Making" at the Griffin Museum of Photography (March–April 2025) have further democratized the process, fostering community-driven innovations in workshops and online forums through advanced digital hybrids and sustainable techniques.[47][48][62][63][64]

Applications

Artistic Practices

Cyanotype's artistic potential lies in its cameraless photogram technique, which enables the creation of abstract forms by directly placing objects on light-sensitive paper, capturing intricate textures and silhouettes such as those of plants, lace, or everyday items exposed to sunlight.[65] This process produces ethereal, high-contrast images that emphasize shadow and form, offering artists a direct, experimental approach to abstraction without the mediation of a lens.[66] Artistic techniques with cyanotype often involve layering multiple exposures to build complexity, such as overlapping transparencies or objects to create depth and narrative sequences within a single print.[67] Scale variations expand its expressive range, from intimate book illustrations—echoing early photobooks—to large-scale murals that immerse viewers in expansive blue landscapes.[68] Integration with other media enhances versatility; artists combine cyanotypes with painting, drawing, or digital elements, toning the blue emulsion with inks or dyes to introduce color and hybrid textures.[69] In modern practice, cyanotype's appeal stems from its accessibility and low cost, requiring only sunlight, basic chemicals, and everyday materials, making it ideal for democratic, hands-on creation amid digital saturation.[70] Sun printing particularly suits environmental themes, allowing artists to document ecological motifs like flora and decay directly from nature, fostering reflections on sustainability and impermanence.[71] Feminist artists have revived the process to reclaim its legacy, drawing on pioneers like Anna Atkins to explore themes of women's historical exclusion from scientific and artistic spheres through botanical and abstract imagery.[72] The 2020s have seen a photobook revival, with works like Mandy Barker's Photographs of British Algae: Cyanotype Imperfections (2025) using the technique to critique plastic pollution via decayed organic forms, blending archival aesthetics with contemporary urgency.[73]

Non-Artistic Uses

Cyanotype has been extensively employed in engineering and architecture for reproducing technical drawings as blueprints, serving as the dominant reprographic method from the 1870s until the early 1940s.[2][74] This process allowed for inexpensive, contact-printed copies of plans, maps, and schematics directly from originals, facilitating efficient dissemination in construction and design fields.[6] Although largely supplanted by diazo-based whiteprints in the 1940s and later by xerographic methods, cyanotypes are valued for their inherent lightfastness and non-fading properties when properly processed, aiding in the archival preservation of historical materials.[2][75] In botany and scientific documentation, cyanotype enables the creation of detailed photograms of plant specimens, akin to those pioneered for herbarium records, providing accurate, shadow-based representations for taxonomic and ecological studies.[76][77] Modern applications extend to UV sensitivity research, where the process's photochemical reaction—converting ferric ions to Prussian blue under ultraviolet exposure—serves as a detector for measuring UV radiation intensity in environmental and material science experiments.[78][79][80] For instance, cyanotype-coated papers quantify UV transmission through filters or fabrics, aiding studies on photodegradation and solar protection efficacy.[79] As an educational tool, cyanotype supports hands-on STEM curricula by demonstrating principles of photochemistry, light sensitivity, and chemical reactions in accessible classroom settings.[62] Commercial kits provide pre-sensitized materials for students to produce prints using sunlight, integrating lessons in biology, physics, and chemistry without specialized equipment.[81] These activities, suitable for grades K-12, emphasize experimental design and observation, such as testing UV blockers, while fostering interdisciplinary connections to environmental science.[62][71] Beyond these, cyanotype finds utility in textile applications through direct printing on fabrics, where the iron-based sensitizer bonds to natural fibers like cotton, yielding durable blue patterns for patterned cloths or experimental dyeing.[82] In libraries and archives, it historically facilitated low-cost copying of documents, manuscripts, and maps, preserving textual and illustrative content before digital alternatives emerged.[2] In 21st-century biotechnology, adaptations of the cyanotype reaction—leveraging Prussian blue formation—enable sensitive detection in assays, such as single-cell bacteria identification via photoactivated nanoparticle aggregation for rapid microbial mapping.[83] Prussian blue analogs further support protein visualization in electrochemical biosensors, enhancing specificity in diagnostic platforms.[84]

Preservation

Long-Term Stability

Cyanotype prints exhibit inherent stability under controlled conditions, but their long-term durability is primarily compromised by fading mechanisms involving the photochemical reduction of the image-forming Prussian blue (ferric ferrocyanide) to colorless or soluble Prussian white (ferric ferrocyanide hydrate). This reversion is initiated by exposure to ultraviolet (UV) and visible light, where photons provide energy for electron transfer, breaking down the complex into soluble iron salts that can leach from the print.[6] The process is reversible to some extent, as faded prints can partially regain color when stored in the dark, allowing reoxidation of the ferrocyanide.[85] However, high humidity accelerates this degradation by promoting hydrolysis of the Prussian blue complex, while atmospheric pollutants such as sulfur dioxide enhance oxidative damage, leading to uneven bleaching and potential mold growth in humid environments.[86] Several factors during and after processing influence the archival quality of cyanotype prints. The pH of the washing water is critical; neutral to alkaline conditions (pH 7.5–8.5) during rinsing can cause up to 18% loss in image density due to partial dissolution of the Prussian blue, whereas slightly acidic distilled water (pH 6–6.5) limits loss to about 5% by stabilizing the ferrocyanide.[6] Formulas using ammonium ferric oxalate instead of the traditional ammonium ferric citrate yield more stable prints, as oxalate avoids leaving hygroscopic organic residues that yellow over time or sensitize the image to further fading; oxalate-based variants also exhibit greater resistance to humidity-induced degradation.[47] Additionally, selecting unbuffered, acid-free archival papers prevents alkaline migration that could destabilize the emulsion, ensuring the support does not contribute to long-term discoloration or brittleness.[87] In optimal dark storage conditions—cool (around 18°C), low humidity (40–50% RH), and free from pollutants—untoned cyanotype prints demonstrate substantial longevity, with historical examples remaining intact for over 170 years without significant degradation. Toned variants, where the Prussian blue is converted to more insoluble metal ferrocyanides, exhibit even greater permanence, resisting both light and environmental stressors for extended periods.[6] Cyanotypes exhibit high sensitivity to light, fading faster than the most sensitive Blue Wool Standard (#1) on the ISO Blue Wool Scale (ISO 105-B02), indicating poor light fastness and requiring strict limitations on display exposure.[88]

Conservation Methods

Cyanotype prints require careful storage to mitigate their sensitivity to light and environmental factors. They should be housed in unbuffered, acid-free folders or enclosures made from materials such as polyester or polypropylene to avoid contact with alkaline substances, which can accelerate fading of the Prussian blue image.[85] Optimal storage conditions include a stable temperature range of 15-20°C and relative humidity of 40-50%, with complete avoidance of direct or intense light exposure, particularly ultraviolet (UV) wavelengths.[89] Low UV lighting in storage areas further protects the prints from gradual degradation, ensuring long-term stability without the need for frequent intervention.[85] Proper handling is crucial to prevent physical damage and chemical contamination. Conservators recommend wearing clean cotton gloves during any manipulation to eliminate the transfer of skin oils, which can lead to localized discoloration or staining on the sensitive surface.[89] Additionally, matting with acid-free, lignin-free boards provides essential support, reducing abrasion from stacking or movement and allowing safe interleaving of multiple prints in storage.[85] For restoration of existing works, faded areas resulting from light exposure can often be revitalized through controlled oxidation. Placing the print in a dark, oxygen-rich environment for several weeks to months allows the soluble ferric ferrocyanide complex to convert back to stable Prussian blue, reversing the fade without chemical additives.[90] Alternatively, immersion in a dilute hydrogen peroxide solution (typically 1-3%) can accelerate this process, restoring intensity in a matter of hours while minimizing risk to the emulsion; the print must then be thoroughly rinsed and dried. Digitization using high-resolution scanning or photography serves as a complementary backup strategy, creating archival digital surrogates that preserve the work's appearance for study and reference without handling the original.[89] Professional conservation techniques extend these practices for institutional collections. UV-filtering glazing or acrylic sheets are applied to framed displays to block harmful wavelengths while permitting viewing, significantly extending the lifespan of exhibited pieces.[91] For paper supports affected by acidity from aging, deacidification baths using non-aqueous magnesium-based solutions may be used selectively, applied only to margins or backing to neutralize acids without exposing the image to potentially fading alkaline conditions.[92] A notable case study involves the conservation of Anna Atkins' "Photographs of British Algae" cyanotype volumes held in major museums, such as the Victoria and Albert Museum and the Natural History Museum. These institutions employ climate-controlled vaults with the aforementioned temperature and humidity parameters, combined with custom solander boxes for dust protection and periodic non-invasive monitoring to address minor fading through dark storage revival techniques, ensuring the survival of these pioneering works.[93]

Notable Practitioners

19th-Century Pioneers

Sir John Herschel, the inventor of the cyanotype process in 1842, extended its utility beyond initial experimentation by applying it to practical tasks in his astronomical work, particularly for copying and reproducing detailed notes and diagrams with precision and permanence.[2] His method, which fixed images using hyposulphite of soda, allowed for reliable duplication of complex scientific records, marking an early adoption in scholarly documentation.[1] Anna Atkins, a British botanist, became one of the earliest adopters of cyanotype for artistic and scientific illustration, self-publishing Photographs of British Algae: Cyanotype Impressions in 1843, recognized as the first book illustrated entirely with photographs.[23] Through direct contact printing of algae specimens on sensitized paper, Atkins produced over 400 meticulous images across three volumes by 1853, demonstrating the process's potential for accurate botanical representation without camera mediation.[4] Her work not only advanced photographic publishing but also highlighted cyanotype's accessibility for non-professional practitioners.[94] In France, Alphonse Louis Poitevin advanced cyanotype toward commercial viability in the 1860s by developing ferro-gallate variants for reproducing translucent documents, enabling efficient large-scale printing of plans and illustrations.[74] His innovations in photosensitive compounds facilitated the process's transition from laboratory curiosity to industrial tool, particularly in lithography and document duplication.[95] From the 1880s, American surveyors and engineers adopted cyanotype for mapping and plan reproduction, using it to create durable copies of land surveys and architectural drawings, as evidenced in early manuscript traces and nautical charts. This practical application underscored the process's affordability and sunlight-driven simplicity, supporting expansion in civil engineering projects across the United States.[8]

20th- and 21st-Century Artists

During the 1920s and 1930s, Modernist and Surrealist artists adapted cameraless techniques, with Man Ray's rayographs serving as influential photograms that inspired later cyanotype experiments by evoking dream-like abstractions through direct light exposure.[96] Surrealists integrated such processes into their work to capture subconscious imagery, though cyanotype's blue tonality was more commonly adopted in subsequent revivals rather than direct 1930s applications.[97] Contemporary artists have revitalized cyanotype for cameraless landscapes and thematic explorations. Abelardo Morell, a Cuban-American photographer, employs cyanotype alongside camera obscura methods to create inverted projections of environments, blending historical processes with modern spatial illusions in series like his tent camera works.[98] Binh Danh integrates cyanotypes into ecological narratives, printing directly onto leaves and historical sites to address themes of memory, war, and environmental fragility, as seen in his Civil War memoranda and national park daguerreotypes/toned cyanotypes.[99][100] In the 2020s, cyanotype has intersected with activism and digital innovation. Artists like Susan Hoffman Fishman employ it to visualize climate impacts, creating mixed-media cyanotypes of global sinkholes to highlight geological instability from environmental change.[101] Mandy Barker uses cyanotype photograms to document fashion waste accumulation in oceans, raising awareness of plastic pollution and consumerism's ecological toll.[102]

References

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