Cyanotype
Based on Wikipedia: Cyanotype
The Color of Blueprints
In 1950, two young artists in New York City stripped down, held hands, and lay together on an enormous sheet of chemically treated paper. When sunlight hit the paper around their bodies, it turned a deep, vivid blue—except where their forms blocked the light, leaving ghostly white silhouettes. Robert Rauschenberg and Susan Weil had just made one of the most striking artworks of the twentieth century using a technique invented more than a hundred years earlier. Those prints now hang in the Museum of Modern Art.
This is the cyanotype. The name comes from the Greek words for "dark blue" and "impression," and it's the reason we call architectural plans "blueprints." But before it became synonymous with construction drawings and engineering documents, the cyanotype was something far more interesting: an early photographic process that let anyone with two chemicals and some sunlight capture images of the world in brilliant Prussian blue.
A Father-Son Discovery Story
The cyanotype emerged from a family obsession with invisible light.
In 1800, the astronomer William Herschel—famous for discovering the planet Uranus—was studying sunlight with a prism when he noticed something strange. The thermometer he'd placed just beyond the visible red end of the spectrum showed a temperature increase. He had discovered infrared radiation: light our eyes cannot see, but our skin feels as heat.
The following year, a German physicist named Johann Ritter went hunting for invisible light at the other end of the spectrum. He found it. Beyond violet, there existed rays that could trigger chemical reactions even though they were invisible. He called them "chemical rays." We call them ultraviolet.
Decades later, William Herschel's son John became fascinated by these hidden forms of light. Could chemistry make the invisible visible? In 1842, he published his experiments on how light affects iron compounds, hoping to find a way to capture both his father's infrared rays and Ritter's ultraviolet ones in a form human eyes could actually see.
He didn't quite achieve that goal. But he stumbled onto something remarkable.
Two Chemicals, One Blue
The cyanotype process is elegantly simple—almost suspiciously so, given what it produces.
You need just two ingredients. The first is ferric ammonium citrate, an iron compound that was sold in the 1840s as a health tonic. The second is potassium ferricyanide, a bright red crystalline substance that had recently been isolated in pure form by a chemist named Alfred Smee, who sent samples to Herschel.
Mix these two chemicals in water. Brush the mixture onto paper. Let it dry in the dark.
Now expose it to sunlight.
Ultraviolet light—the same invisible rays Ritter discovered—transforms the iron in the solution. The ferric iron (which has three positive charges) gets reduced to ferrous iron (with only two). This ferrous iron then reacts with the ferricyanide to form a compound called ferric ferrocyanide.
You probably know it by another name: Prussian blue.
This is one of the first synthetic pigments ever created, discovered accidentally in Berlin around 1706 when a paint maker contaminated his materials with animal blood. The resulting blue was so intense and so stable that it revolutionized painting. Artists could finally depict blue clothing and blue skies without bankrupting themselves on ultramarine ground from lapis lazuli.
In the cyanotype process, this same vivid pigment forms directly in the paper fibers wherever light has struck. Rinse the paper in plain water, and the unexposed chemicals wash away, leaving behind a brilliant blue image against a white background. No darkroom. No developing chemicals. Just sunlight and water.
The World's First Photographically Illustrated Books
John Herschel, true to the gentlemanly scientific tradition of his era, did not patent his invention. He simply published his findings and moved on to other experiments. This meant anyone could use the technique—and someone extraordinary did.
Anna Atkins was a botanist and a friend of the Herschel family. She had learned about the new process directly from its inventor, and she immediately recognized its potential for something Herschel hadn't considered: scientific documentation.
Beginning in 1843, Atkins embarked on an eighteen-year project to create detailed images of British algae. Her method was the photogram: she placed actual specimens directly onto sensitized paper and exposed them to sunlight. The algae blocked the light, leaving white silhouettes against a deep blue field. Every delicate filament, every branching frond, reproduced itself with perfect accuracy.
With help from her friend Anne Dixon, Atkins hand-printed several volumes of Photographs of British Algae: Cyanotype Impressions. These books predate the works usually credited as the first photographically illustrated publications. Atkins had quietly produced something unprecedented: a scientific reference work where the illustrations weren't drawings or engravings interpreted through an artist's hand, but direct impressions of the specimens themselves.
The cyanotype's ability to capture botanical subjects continued to inspire. In 1880, a New Zealand printer named Herbert Dobbie produced a book of 148 fern varieties using the same technique, with cyanotype prints on both sides of each page.
How Blueprints Got Their Name
For thirty years after its invention, the cyanotype remained largely a curiosity—a technique for artists and scientists, but not a commercial product.
That changed in 1872, the year after John Herschel died.
A company in Paris called Marion and Company realized that the cyanotype had one overwhelming advantage for reproducing technical drawings: it was absurdly cheap. The chemicals cost almost nothing. The "developing" process was just water. You didn't need expensive equipment or specialized training.
They began selling pre-coated paper under the proprietary name "Ferro-prussiate" for copying architectural plans and engineering drawings. The process was perfect for this application. You could take a technical drawing rendered in dark lines on translucent paper, lay it over the sensitized sheet, expose it to sunlight, and wash it in water. Minutes later, you had an exact copy: white lines on a blue background.
These copies became known as blueprints.
The term stuck even as the technology changed. By the 1940s, diazo printing and later xerography replaced the cyanotype for technical reproduction. But we still call architectural plans blueprints, even though they haven't been blue for decades. The word became a metaphor: a blueprint for success, a blueprint for change. The cyanotype's linguistic legacy outlived its commercial dominance.
Emergency Currency and Quilted Memories
The cyanotype's simplicity made it invaluable in unexpected circumstances.
During the Second Boer War, the British garrison at Mafeking in South Africa found itself under siege for 217 days, from October 1899. Cut off from supply lines and running low on everything, the besieged forces needed currency and postage stamps. They turned to cyanotype printing—one of the few reproduction methods possible with minimal equipment and readily available materials. Mafeking siege stamps and banknotes, printed in that distinctive blue, became collector's items.
But the most touching applications were domestic. After 1880, American quilters discovered they could print cyanotypes directly onto fabric. Family photographs—portraits of children, pictures of beloved homes—were transferred onto cloth and sewn into quilts and pillow slips. The Eastman House museum collection contains dozens of these fabric cyanotypes, tender artifacts of people who wanted their memories to be literally wrapped around them.
This wasn't high art. It was folk craft, the simple technology of the cyanotype democratizing image-making in ways the grand portrait photographers of the era never imagined.
The Chemistry of Transformation
One of the strangest properties of the cyanotype is that it can heal itself.
If you leave a cyanotype print in bright light for extended periods, it will eventually fade. The Prussian blue breaks down chemically, turning white. Most photographic processes, once faded, are gone forever.
Not the cyanotype.
Put that faded print in a dark drawer for a while, and something remarkable happens: the blue comes back. The chemical reaction reverses in darkness, and the image restores itself to something close to its original vibrancy. This regenerative quality makes cyanotypes among the most durable of all nineteenth-century photographic technologies.
The prints have one peculiar vulnerability, though. They react badly to alkaline environments. Most archival museum boards are chemically buffered to be slightly basic, which helps preserve most artworks. But this buffering will slowly destroy a cyanotype. The print must be stored on acid-free but unbuffered materials—a counterintuitive requirement that has tripped up more than one well-meaning conservator.
Fabric cyanotypes present their own challenges. The blue is permanent on cloth, but you must wash these pieces by hand using non-phosphate soap. Phosphates turn the blue to yellow, ruining the image.
Beyond Blue
The Prussian blue of a standard cyanotype is striking, but artists have long sought other colors.
As early as the 1850s, a chemist named John Mercer discovered that cyanotypes could be toned—chemically transformed to produce violets, greens, browns, reds, and even blacks. The blue iron compound could be converted to other substances with different hues, expanding the palette available to artists.
The process works in stages. First, you might bleach the print, reducing the intensity of the blue using sodium carbonate, ammonia, or even ordinary household bleach (though bleach tends to destroy the paper along with the image). Then you tone it, introducing new chemicals that change the color of the iron compounds. Tea produces warm brown tones. Wine can create purples. Tannic acid yields deeper browns approaching black. Even urine has been used historically as a toning agent.
Intensification works in the opposite direction, strengthening the blue. Hydrogen peroxide or mild acids—citric acid, lemon juice, vinegar—speed up the oxidation that creates the blue pigment and deepen the final color.
By adjusting the original formula, you can also control contrast. Equal parts of the two chemicals produce a medium, even blue. More potassium ferricyanide creates darker blues and higher contrast. More ferric ammonium citrate gives lighter, softer results.
The New Cyanotype
For over 150 years, the basic cyanotype formula remained essentially unchanged from Herschel's original recipe. Then in 1994, a British scientist named Mike Ware decided to improve it.
The traditional ferric ammonium citrate has always been problematic. Different batches vary in composition and reliability. The solution doesn't keep well and can grow mold. It tends to pool on the paper surface rather than soaking into the fibers, which means it can stick to negatives during contact printing.
Ware substituted ferric ammonium oxalate—a related but more stable compound. His new formula could be mixed as a single stock solution with a long shelf life. It absorbed better into paper, produced sharper images, and required exposures four to eight times shorter than the traditional process.
There are tradeoffs. The Ware formula costs more, requires more careful preparation, and introduces some toxicity that the original process lacks. But for serious practitioners, the improved consistency and shorter exposure times often outweigh these disadvantages.
Making Pictures Without Cameras
The simplest cyanotype is a photogram—an image made without any camera at all.
You place objects directly on sensitized paper, expose it to light, and the objects leave their silhouettes. Anna Atkins's botanical studies were photograms. So were Rauschenberg and Weil's life-sized body prints.
The technique rewards experimentation. A sheet of glass pressed over flat objects creates sharp-edged shadows. Three-dimensional objects produce softer, more ambiguous forms depending on how the light wraps around them. Transparent or translucent materials—pressed flowers, feathers, lace—create complex gradations as they filter different amounts of light through to the paper.
Some artists push the medium further with chemigrams: they apply the cyanotype solution irregularly, pouring or spraying it across surfaces, then selectively expose and wash the results in a kind of chemical action painting.
For photographic images—reproducing actual photographs rather than shadows of objects—you need a negative. The cyanotype reverses tones, so a standard photographic negative produces a positive print. Large-format negatives work best because the cyanotype's low light sensitivity makes enlargement impractical; you typically contact-print at a one-to-one ratio, with the negative pressed directly against the sensitized surface.
The Scale of Art
Because you can sensitize almost any absorbent surface, cyanotypes have been made on astonishing substrates: paper, wood, fabric, glass, plexiglass, bone, shell, eggshell, plaster, ceramics. The only requirement is that the material can soak up the iron solution.
And because you're contact printing rather than projecting through a lens, there's theoretically no limit to size.
In 2001, the artist Robin Hill created Sweet Everyday, a cyanotype stretching thirty meters—about a hundred feet—that enwrapped an entire gallery in New York's Soho neighborhood. She made the image by placing ordinary shopping bags on photosensitive paper, producing wavy patterns that surrounded viewers on all sides.
That wasn't the record for long. In 2017, Stefanos Tsakiris created a cyanotype in Thessaloniki, Greece, measuring nearly 277 square meters—about the size of a tennis court.
At the other extreme, the long exposure times required by the cyanotype's low sensitivity have their own advantages. You can open a contact printing frame during exposure to check your progress, something impossible with faster photographic processes. The extended exposure scale also means the process handles both high-contrast and low-contrast negatives gracefully.
Why Blue?
The color itself carries meaning.
Blue suggests water, sky, depth, distance. Artists working with cyanotypes often lean into these associations. Nancy Wilson-Pajic, a French artist working from the late 1970s, made cyanotype photograms of everything from shattered windshields to haute couture gowns by Christian Lacroix—all rendered in that characteristic blue that seems to float between physical object and ethereal impression.
The process also serves as a deliberate anachronism. It's recognizably nineteenth-century technology, and artists like John Dugdale use it precisely to evoke—or to critique—Victorian aesthetics and the social constructs of that era. In an age of digital photography and instant image manipulation, choosing to work with sunlight and iron salts and washing your prints in water represents a conscious step backward into a slower, more physical relationship with image-making.
The Democratization of Images
In 1843, the year Anna Atkins began her algae books, a chemist named George Thomas Fisher Jr. published a fifty-page manual titled Photogenic manipulation. It contained instructions for seven different early photographic processes: calotype, cyanotype, ferrotype, chrysotype, anthotype, daguerreotype, and thermography. The book was translated into German and Dutch the following year.
Fisher's manual represents something important: the moment when photography stopped being a secret known only to its inventors and became knowledge available to anyone who could read. The cyanotype was among the most accessible of these early processes—cheap, forgiving, requiring no specialized equipment.
This accessibility has never really disappeared. Today you can buy cyanotype kits for children, premixed solutions for artists, and detailed formulas for chemists who want to mix their own. The process that John Herschel published in 1842 is still being used in 2024, essentially unchanged in its fundamentals.
The materials cost almost nothing. The chemistry works reliably. The results are beautiful and durable. And on a sunny afternoon, anyone with some ferric ammonium citrate, some potassium ferricyanide, a brush, some paper, and an interesting object to place on it can make an image that will last for generations.
That's a remarkable legacy for a failed experiment in making invisible light visible.