What Is a Cyanotype?
The camera-less printing process from 1842: how sunlight and two iron salts turn paper Prussian blue, and how an algae catalogue became the first photo book.
A photograph made with sunlight, two chemicals and no camera at all.
How do you take a photograph without a camera?
A camera exists to focus light. A cyanotype skips that job entirely: the subject itself lies flat on a sheet of paper coated with a light-sensitive iron solution, held down under glass, and the sun does the rest. Wherever light reaches the coating, a chemical change begins; wherever the object casts its shadow, nothing happens. A rinse in plain water then washes the unchanged coating away, leaving a white, life-size silhouette on a ground of deep blue.
Photographers call this contact printing, and an image made this way from a physical object is a photogram. Because the object must touch the paper, a cyanotype can never enlarge or shrink anything — every fern frond and feather prints at exactly its real size. That constraint is also the charm: the print is a direct physical record of a thing, not a picture of it.
The short version
- No camera: a cyanotype is a contact print — the object lies directly on coated paper and blocks the light, so the image is always life-size.
- Two chemicals: ferric ammonium citrate and potassium ferricyanide; ultraviolet light converts them into the insoluble pigment Prussian blue.
- Water develops it: a plain rinse washes the unexposed coating away — no developer, no fixer.
- Invented in 1842: Sir John Herschel devised it as a copying tool; a year later Anna Atkins used it to make the first book illustrated with photographs.
Two chemicals, sunlight and water: where the blue comes from
The coating is a mix of two solutions: ferric ammonium citrate and potassium ferricyanide. Brushed onto paper and dried, it is a pale yellow-green, and it responds mainly to ultraviolet light — which sunshine delivers in quantity while ordinary household bulbs deliver almost none.
Ultraviolet light pushes the iron in the coating from its ferric state to its ferrous state. The converted iron then reacts with the ferricyanide half of the mix and forms an insoluble blue compound locked into the paper fibres. The unexposed coating, by contrast, stays fully water-soluble — which is why development needs nothing but a rinse. Five to ten minutes in cool water carries the yellow chemistry away and leaves the blue bound in the paper.
The print that comes out of the wash is not finished changing. Over the next day the image oxidises into Prussian blue — the same pigment sold in artists' paint tubes — and visibly deepens as it dries.
Why did Herschel invent it — and who actually used it?
Sir John Herschel, the astronomer and chemist, worked out the process in 1842 after investigating the light-sensitivity of iron salts. He wasn't chasing art: he wanted a cheap way to duplicate his own notes and tables. Lay a page over sensitised paper, expose it to the sun, and a legible copy appears — pale lines on blue.
The process found its largest audience not in photography studios but in drawing offices. For decades, architects and engineers duplicated technical drawings as cyanotypes because it was a fast, inexpensive way to copy a full-size plan — which is why blueprints are blue, and why the word survives long after the process left the drawing office.
Anna Atkins and the first book of photographs
In 1843, a year after Herschel devised the process, the botanist Anna Atkins — a family friend of both Herschel and the photography pioneer William Henry Fox Talbot — began using cyanotypes to document her collection of seaweeds. Her aim was scientific, not artistic: the standard manual of British algae, published in 1841, had no illustrations, and such fine, translucent specimens were difficult to draw reliably. Laid directly on sensitised paper, the algae printed themselves.
The result, Photographs of British Algae: Cyanotype Impressions, appeared in its first instalment in October 1843 and is regarded as the first book illustrated with photographs. Atkins issued it in parts over roughly a decade and made every page photographically — even the captions and text pages are cyanotypes of her handwriting. Around 20 copies are known to survive, and on the strength of the book Atkins is often credited as the first woman photographer. She was cataloguing specimens, not making art — and that is precisely what gives the plates their unforced, modern beauty.
What beginners hear — and what's actually true
Myth: you need a darkroom to make cyanotypes.
Reality: the coating reacts to ultraviolet light, not ordinary room light. A dim room away from windows is enough for coating and drying the paper — practitioners work under normal tungsten household light and only keep the paper away from daylight and fluorescent tubes.
Myth: there is one correct exposure time.
Reality: exposure runs from about two minutes in strong midday sun to half an hour or more under cloud or an artificial UV lamp, depending on the light, the coating and the paper. Experienced printers judge by colour — the exposed coating shifts from yellow-green to a bronzed grey-blue — or run a covered test strip rather than trusting anyone else's timing.
Myth: a pale print out of the wash means you failed.
Reality: the blue keeps developing after the rinse, deepening noticeably as the print oxidises in the air over the next day. A print that looks washed-out but intact will darken on its own; only an image that dissolves in the water was genuinely underexposed.
What it takes to try one
The barrier to entry is unusually low for a photographic process. The two chemicals are sold as a small kit you mix with water, or you can buy paper already coated and skip the chemistry altogether. Beyond that you need objects worth printing, a sheet of glass from a picture frame, a sunny windowsill or garden, and a tray of water. Everything fits on one beginner cyanotype setup list, and none of it assumes prior experience.
The one genuine decision is your light source. Strong sun prints in minutes and costs nothing, but it varies with season and weather — which is why many printers eventually weigh sunlight against a UV lamp for repeatable results.
Frequently asked questions about cyanotypes
Do you need a camera to make a cyanotype?
No. A cyanotype is a contact print: an object or a film negative lies directly on the sensitised paper and blocks the light. The paper records the shadow, so the image is always the same size as the thing that made it.
Why are cyanotypes blue?
The exposed coating converts into Prussian blue, an insoluble iron pigment formed inside the paper fibres — the same pigment used in artists' paint. The colour is the image itself rather than a dye added afterwards, which is why untoned cyanotypes are always some shade of blue.
How long does a cyanotype take to expose?
Anywhere from about two minutes in strong midday sun to thirty minutes or more under an overcast sky or an artificial UV lamp. The reliable guide is colour, not the clock: expose until the coating turns from yellow-green to a bronzed grey-blue, then rinse. Including the wash, a print is usually finished within the hour.
Why did my print wash away in the water?
It was underexposed. Only coating that has received enough ultraviolet light converts to the insoluble blue compound; everything else is water-soluble by design and rinses out. Give the next print more light — weak sun, UV-filtering glazing over the print or a low-powered lamp are the usual culprits.