Cyanotypi

Cyanotypi, commonly known as cyanotype or blue printing, is a photographic printing process that produces images in blue tones. It relies on iron-based salts that react to ultraviolet light to form Prussian blue, a ferric ferrocyanide pigment.

The typical process coats paper or fabric with a mixture of ferric ammonium citrate and potassium ferricyanide. After drying in a dark environment, an object or photographic negative is placed on the coated surface and the sheet is exposed to sunlight or another UV source. Exposed areas form a blue image while unexposed areas remain pale. The print is then washed in water to remove unreacted salts, revealing a stable blue image.

History and use: Cyanotype was devised by Sir John Herschel in 1842. It gained prominence in the 1840s and 1850s, notably through botanist Anna Atkins, who used it for plant illustrations. The technique also earned the common name blueprint because it was widely employed to reproduce technical drawings for engineers and architects.

Contemporary practice: Today cyanotypes are used by photographers and artists as a low-cost, non-silver printing method. They can be produced on paper or fabric and may be toned with tea, coffee, or other agents to shift the color toward greenish or sepia tones. Many makers use digital negatives to control exposure and ensure reproducible results.