Cyanotype

Cyanotype is a photographic printing process that uses iron salts and ultraviolet light to produce images in Prussian blue.

Ferric ammonium citrate: A light-sensitive iron(III) salt used in cyanotype sensitizer solutions. It supplies iron that ultraviolet exposure converts into a more reactive form.
John Herschel: An English astronomer and chemist who made major contributions to photography and coined several photographic terms. He discovered cyanotype in 1842 while investigating iron-based photographic processes.
Botanical illustration: The visual depiction of plants, often made to document their forms and identifying features. Cyanotype contact prints recorded delicate plant structures without requiring a camera.
Salted paper print: A nineteenth-century photographic print made by sensitizing salted paper with silver nitrate. It creates brown or reddish-brown silver images rather than cyanotype’s iron-based blue.
Potassium ferricyanide: An iron-containing salt used with ferric ammonium citrate to make cyanotype sensitizer. It reacts with the exposed iron to form the blue image pigment.
Anna Atkins: An English botanist and photographer who published books illustrated with cyanotypes of algae and other plants. Her 1843 book used cyanotypes to record botanical specimens.
Photogram: A photographic image made by placing objects directly on a light-sensitive surface and exposing it to light. The process naturally produces photograms when objects are laid on sensitized paper.
Van Dyke brown: A photographic printing process that uses iron and silver salts to produce brown images. It shares contact-printing practice with cyanotype but forms a brown silver image.
Photoreduction: A chemical reduction caused by light, in which a substance gains electrons. Ultraviolet light reduces iron(III), initiating the image-forming reaction.
Photogenic Drawing: An early photographic process developed by William Henry Fox Talbot that produced images on sensitized paper. It was an influential paper-printing process that preceded cyanotype and used different light-sensitive chemistry.

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