Cyanotype is a monochrome photographic procedure that produces a negative copy of the original in a Prussian blue color , called a blueprint .

The name copy the ferroprusiato was widely used in copying architectural plans until appeared copies heliographic ( Diazed ) that were revealed with ammonia vapors and had a reddish color, and no longer required rinse programs . In the 1980s, the latter were overtaken by xerographic prints , which no longer required tracing paper originals.

With the advancement of computer systems, modern printers print from a file run in a computer-aided design (CAD) program. The blueprints have been reduced to the artistic realm.

Sir John Hersche an English astronomer invented this procedure in 1842 . Although Herschel devised it, it was British botanist Anna Atkins who immediately put it into practice. Atkins published a series of books where she was documenting ferns and other plants. The illustrations were bluish copies(cyanotypes), allowing her to document them without drawing. For her British Algae series of 1843, Anna Atkins is considered the first female photographer.

The process uses two chemical compounds:

  • Iron (III) ammonium citrate

  • Potassium ferricyanide

This mixture results in a photosensitive solution, which is used to coat a material. By exposing the negative image it to an ultraviolet light source (such as sunlight) we got the positive. Ultraviolet light reduces iron (III) to iron (II). This is followed by a complex reaction of iron (II) with ferricyanide. The result is a blue (cyan) water-insoluble substance.

In a normal procedure, are mixed in equal amounts: 8% solution of potassium ferricyanide and a 20% solution of ammonium iron (III) citrate. This photosensitive solution is applied to a surface like paper. It can be left to dry in the dark or to make the process faster with a tumble dryer somewhere where UV rays will not penetrate. Cyanotypes can be printed on any surface capable of absorbing the iron solution. Although paper is the preferred medium, other materials have been used.

By exposing the surface to ultraviolet light, the iron in the exposed areas is reduced, turning the paper to the blue (cyan) color that gives the procedure its name. The color change depends on the amount of light, but acceptable results can be obtained after a 10-20 minute exposure on a sunny day. Prints can be made with large format negative and lithographic film, or any everyday object can be used to produce a still . After a final rinse that removes the photosensitive substances from the paper and only the blue dye formed in the image remains. The Prussian Bluenewly formed needs to be oxidized to achieve final color and contrast. It naturally oxidizes with atmospheric oxygen, but the process can be sped up by immersing the print in a 3% solution of hydrogen peroxide ( hydrogen peroxide).



CYANOTYPES ON PAPER OUTDOOR - 15 MIN OR MORE (always check the uv power on website)

The digital image is converted to negative using photoshop (see blog how to make a negative) and the negative is printed on a transparent acetate sheet (DO NOT USE CHEAP ACETATE) then the negative is superimposed over the sheet treated with liquid cyanotype. In this case we expose at the sun. Exposure time: 25 minutes


exposure time : 25 min


I used exactly the same technique but for exposure I used uv box that reduced the time. Uv rays being much stronger inside the box than the outdoor ones.

exposure time : 4 min


exposure time : 4 min

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