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The cyanotype, invented by Sir John Herschel in 1842, is one of the earliest and one of the most permanent of the photographic processes. The process, which uses iron salts, produces prints which are Prussian blue or cyan in colour hence the name cyanotype. It was the first photographic process used to illustrate a book. Anna Atkins, a botanist, published a book 'British Algae: Cyanotype Impressions Part I' in 1843 using photograms, preceding William Henry Fox-Talbot's 'The Pencil of Nature' by several months. Cyanotypes, or blueprints, were also used for copying architects and engineers drawing before the days of photocopiers.
Cyanotypes are easy and cheap to make requiring just two chemicals to make the light sensitive emulsion. They require no development or fixing other than washing in water. The chemicals are also relatively safe enabling the process to be used by children.
Materials and Method
The following chemicals and materials will be needed. A supplier list can be found at the end of the article.
- Ferric ammonium citrate (green)
- Potassium ferricyanide
- Scales accurate to 1 gram
- Two paper cake cases for weighing the chemicals in
- A graduate measure capable of measuring 100ml
- A syringe 2.5 or 5ml (available from a pharmacist)
- A small graduate with 1ml graduations
- Two 100ml or 250ml brown bottles (available from a pharmacist)
- A small glass
- Paper, such as watercolour or cartridge paper. Avoid papers labelled 'acid free' or 'buffered' as these contain alkalis which will make the image fade
- Invisible tape such as Scotch Tape
- A paint brush or a coating rod made from a glass stirring rod with the ends bent - carefully use a blowtorch & gloves
- Kitchen paper
- A printing frame or picture frame that can be easily opened and closed
- A source of UV light such as a tanning unit or the sun
- A suitable large format negative, one that will print on grade 0 or 1 paper.
