Cyanotype

Herschel’s (John - 1792-1871) interest in botany, born during his time in the Cape Colony, was put to use in his photographic experiments. Herschel began to experiment with floral dyes, using the petals of fresh flowers in the place of the silver salts to produce photographic papers. He would crush the flower petals to pump in a marble mortar, sometimes with the addition of alcohol. The juice expressed by squeezing the pump into clean linen or cotton cloth was spread on paper with a flat brush, and dried in the air…….

One of his color processes used an iron pigment known as Prussian blue rather than vegetable dyes. This process dubbed by Herschel the “cyanotype,” became the most commercially valuable of the paper photographic methods in 1840s, and survived into the twentieth century as the basis of the architect’s blueprint. By washing paper with a solution of ferric ammonium citrate, an iron salt, Herschel created photographic paper highly sensitive to the action of light. After half an hour or an hour’s exposure to sunshine, followed by a wash in a solution of yellow potassium ferrocyanate, a white image would appear on a bright blue background.

This cyanotype process led to the publication of the first book to use photography: Anna Atkin’s ‘Photographs of British Algae: Cyanotype Impressions” first part published in 1843 ….

During the summer of 1843 Atkins began working on a book about algae, using the cyanotype method of photography. In her preface she explained that “the difficulty of making accurate drawings of objects as minute as many of the Algae and Confervae, has induced me to avail myself of Sir John Herschel’s beautiful process of Cyanotype. …Pages 235 to 237


John Herschel: en.wikipedia.org/wiki/John_Herschel