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Sir John Herschel (1792-1871) was the first scientist to publish a description of the cyanotype process. In addition to being well-known as a astronomer, Herschel is also credited with the discovery of sodium thiosulphate as a means of fixing a photographic image on paper and preventing it from fading.

Herschel's wrote the following in his notebook now housed in the Science Museum, London:

Jan. 29 [1839]. Experiments tried within the last few days since hearing of Daguerre's secret and that Fox Talbot has also got something of the same kind... Three requisites: (1) Very susceptible paper; (2) Very perfect camera; (3) Means of arresting the further action.

Tried hypsulphite of soda to arrest action of light by washing away all of the chloride of silver or other silvering salt. Succeeds perfectly. Papers 1/2 acted on 1/2 guarded from light by covering with pasteboard, were when withdrawn from sunlight, then well washed in pure water - dried, and again exposed. The darkened half remained dark, the white half white, after any exposure, as if they had been painted in speia... Thus Daguerre's problem is so far solved.

Almost all photographic processes rely on Herschel's discovery. It was also Herschel who suggested the name "photography" instead of the previously used "photogenic drawing."

Cyanotype was the first photographic process to be used to illustrate a book. The first woman photographer, Anna Atkins, used cyanotypes to illustrate her book, Cyanotypes of British and Foreign Flowering Plants and Ferns. This was also the first book of printed photographs and text.

Sodium thiosulphate is erroneously known as sodium hyposulphite or hypo and was crucial to the development of photography and is still used in certain photographic techniques today. This method uses two simple compounds of iron to make light sensitive material. The print that results from this chemical is cyan blue in color, thus giving the process its name.


Cyanotypes use ultra-violet light or sunlight to expose the image.A chemical mixture is used to coat the paper and allowed to dry. An object or image is then exposed on the paper in sunlight. The paper is washed under cool running water and allowed to dry. The blue color ranges from pale to deep blue tones.

Herschel is also known for his development of the blueprint, a method for copying architectural drawings. Like cyanotypes, blueprint paper begins white and is then coated with light-sensitive chemicals. A translucent sheet on which the architectural diagrams have been drawn is placed over the paper; a strong light is then directed through the translucent sheet onto the paper. Those portions of the paper exposed to the light become blue when washed in water, while areas protected from light by the drawing's lines do not. The result is a white-line print on blue paper.


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