O LÁPIS DA NATUREZA

Informação recebida do Centro Interuniversitário de História da Ciência e Tecnologia (na imagem, litografia de Constantin Guys, 1805-1892):

Vai realizar-se a primeira Conferência CIUHCT (Pólo Lisboa) do presente ano lectivo. Dia 28 Outubro, 17h, FCUL, sala a anunciar.

"Prussian blue, or the pencil of nature",

Pierre Laszlo, Ecole polytechnique, Palaiseau, France, and University of Liège, Belgium, “Cloud’s Rest,” Prades, F-12320 Sénergues, France. (pierrelaszlo@usa.net)

Prussian blue, the synthetic pigment invented in the eighteenth century, has had many uses, including the blueprint and Caselli’s pantelegraph (1861), an ancestor of the fax machine. This lavishly illustrated talk will focus on applications to the visual arts. The novel blue pigment, used in paints (e.g. ,Vincent van Gogh) and in inks, enjoyed much use for watercolors.

In mid-nineteenth century, the French artist Constantin Guys, Baudelaire's friend, routinely sketched a scene or a character with Prussian blue ink, obtained from Parisian suppliers. It would be transferred to a lithographic engraving for a magazine such as L’Illustration: such articles illustrated by Guys’s work using Prussian blue antedated the photographic reports
familiar to us.

The astronomer John Herschel (1792-1871) devised in 1842 the cyanotype, a photographic process using paper treated with photosensitive Prussian blue. Upon light exposure, and subsequent fixation with sodium thiosulfate, durable images result. One of its inventors, William Henry Fox Talbot (1800-1877), came up in 1844 with the metaphor of “The Pencil of Nature” for the ability of photography to capture natural scenes, in their realistic truth— or so he construed. A joint friend of Fox Talbot and of Herschel, Anna Atkins (1799-1871), took to cyanotypes with scientific rigor and with enthusiasm. The daughter of the chemist-zoologist John George Children (1777-1852), she was brought up in the presence of many of the leading English chemists at the time, including Humphry Davy. She devised numerous photograms, of a similar type as Man Ray for instance would make famous in the first half of the twentieth century. She embarked on a botanical project, of awesome magnitude, of thus recording the morphology of a wide variety (424 different specimens) of algae. "The difficulty of making accurate drawings of objects as minute as many of the Algae and Conifera, has induced me to avail myself of Sir John Herschel's beautiful process of Cyanotype, to obtain impressions of the plants themselves," she wrote in october 1843. The resulting book, British Algae: Cyanotype Impressions, was the very first to be photographically illustrated and printed, between 1843 and 1853.

I shall present and comment upon her compositions, attempting to delineate the artistry from the science. Prussian blue thus highlights Socrates’s definition of the beautiful as the useful.

References
- Ludi, A., "Prussian Blue, an Inorganic Evergreen", Journal of Chemical Education 1981, 58, 1013.
- Barbara H. Berrie, “Prussian Blue.” In Artists’ Pigments: A Handbook of
their History and Characteristics, vol; 3, National Gallery of Art, Washington DC, 1997, 191-217.
- Dunbar, K. R. and Heintz, R. A., "Chemistry of Transition Metal Cyanide
Compounds: Modern Perspectives", Progress in Inorganic Chemistry, 1997, 45,
283-391.
- Prakash R. Somani and S. Radhakrishnan, "Electrochromic response in polypyrrole sensitized with Prussian Blue", Chemical Physics Letters, 1998 292,218 - 222
- Peter Frederick, Creative Sunprinting, Focal Press, NewYork, 1980.