Cyanotype

Cyanotype is an old monochrome photographic printing process which gives a cyan-blue print.

The English scientist and astronomer Sir John Herschel discovered this procedure in 1842. Though Sir John Herschel is perhaps the inventor of the cyanotype process, it was Anna Atkins, a British scientist, who brought the process into the realm of photography. She created a limited series of cyanotype books that documented ferns and other plant life. By using this process, Anna Atkins is regarded as the first woman photographer.

The process uses two chemicals:

Ammonium iron(III)citrate
Potassium ferricyanide

They result in a photo-sensitive solution when dissolved in water, which is used to coat a material (usually paper). A positive image can be produced by exposing it to a source of ultraviolet light (such as sunlight) with a negative. The UV light reduces the Iron(III) to Iron(II). This is followed by a complex reaction of the Iron(II) complex with ferricyanide. The result is an insoluble, blue dye (Ferric ferrocyanide) known as Prussian blue.

The developing of the picture takes place by flushing it with flowing water. The water-soluble Iron(II) salts are washed away, while the non-water-soluble Prussian Blue remain in the paper. This is what gives the picture its typical blue color. The process was popular in engineering circles well into the 20th century. The simple and low-cost process enabled them to produce large-scale copies of their work, referred to as blueprints.

Contents

1 The Process
2 Long-term preservation
3 References
4 External links

The Process

As always, be smart with chemicals. While the chemicals involved in this process aren't anything to be scared of they could cause some irritation of the skin and will very surely irritate mucous membranes. Be careful and wear something you wouldn't mind having blue stains on. They will happen.

Cyanotypes are very easy and inexpensive to make. All you need is Ferric Ammonium Citrate (Green), Potassium Ferricyanide, a receptive surface for the print (paper, cloth, etc.) and sunlight.

Cyanotype Stock Solution A:

80 grams Potassium Ferricyanide
1 liter water
Slowly mix water with crystals. Store in brown glass bottle with a good cap on it.

Cyanotype Stock Solution B:

200 grams Ferric Ammonium Citrate
1 liter water
Slowly mix water with crystals. Store in brown glass bottle with a good cap on it.

Optionally: Enhancing Bath

60 ml household Hydrogen Peroxide
1 liter water
Mix ingredients.

Once your solutions are mixed up, mix equal parts of Solutions A and B in a dimly lit area. Once mixed the emulsion is photosensitive, but not so sensitive that you can't mix them in a well lit room. Apply the emulsion to the printing surface either with a glass stirring rod or a paintbrush. If you use a paintbrush, use one without any metal on it as metals will react with iron in the emulsion and this could cause problems later on. Let the emulsion dry on the surface in as dark an area as possible.

Once dry, take it outside and make your exposure. Traditionally people have used large format negatives and litho film to make photo prints or everyday objects to make photograms. UV light is what makes the emulsion change color, so the sun is usually the most readily available source of light. Other exposure systems exist, but they are expensive.

Your print will be done when the emulsion that is not obscured by your printing materials has turned a steel-grey-blue color. What constitutes a complete exposure is a matter of opinion and the UV saturation of sunlight varies at different altitudes, so do tests to figure out what will work under your circumstances. 10-20 minute exposures on bright, sunny days are average.

When you have exposed your print, take it back inside and wash it under running water until all the yellow stain is gone. Let it dry and it will gradually turn a deeper blue. If you don't want to wait for it to darken on its own, put the print in the enhancing bath for a few seconds. You will see it "blue up" immediately.

A note on print surfaces - Watercolor paper works best, but cyanotype emulsion is very flexible and can be successfully printed on more or less any clean surface that will soak up water. The best surfaces are natural fibers such as cotton, wool and of course wood pulp. The emulsion can also be mixed into gel mediums and other acrylics. If you wish to print on to a nonporous surface you will first need to get the surface as clean as you can and then size the surface with gelatin. Emulsion can be coated onto the gelatin sizing layer.

Long-term preservation

In contrast to most historical and present-day processes, cyanotype prints do not like basic environments. So it is not a good idea to store or present the print in chemically buffered museum board. This will cause the image to fade. Another unusual characteristic of the cyanotype is its regenerative behaviour: 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.

References

Atkins, Anna, with text by Lynn J. Schaff. Sun Gardens: Victorian Photograms. New York; Aperture, 1985.
Blacklow, Laura. (2000) New Dimensions in Photo Processes: a step by step manual. 3rd ed.
Ware, M. (1999) Cyanotype: the history, science and art of photographic printing in Prussian blue. Science Museum, UK

External links

[Information on the Photogram]
[Cyanotype by Mike Ware]
[Mike Ware's New Cyanotype] - a new version of the cyanotype that address some of the classical cyanotypes short comings
[Cyanotypes.com - a free information centre with articles and galleries on the cyanotype process]
[The Cyanotype process]
[The Cyanotype process II]

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