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Monday, May 16 • 9:30am - 10:00am
(Photographic Materials) Photochromatic images of Edmond Becquerel: where do the colours come from? Tracks in the understanding of the origin of their colours

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Edmond Becquerel (French physicist, 1820-1891) introduced in 1848 the first colour photographs called by himself, “photochromatic images”. Among the first images was the recording of the solar spectrum he produced by directly projecting it onto a sensitized silver plate [1, 2]. At least, two examples of this solar spectrum image are kept in museum collections, one at the Musée Nicéphore Niépce (Châlon-sur-Sâone, France) and the other one at Musée des arts et métiers (CNAM, Paris). However photochromatic images are still light sensitive and have to be kept in the dark [3]. Becquerel wrote he had not yet "been able to arrest the subsequent action of diffused light which gradually destroys the images" [4]. Despite many attempts, Becquerel and other followers such as Abel Niépce de Saint Victor (1805-1870) who revisited Becquerel's process in the 1850s and the 1860s, never managed to make them light stable. The long exposure times required to produce the image and its light instability prevented the diffusion of the process among the public at large. A small number of photochromatic images have survived till today. The recent rediscovery of a batch of these early colour photographs in the archives of the National museum of natural history in Paris has brought a new interest for this process in particular to better understand the origin of the colours. Interestingly, if many hypotheses have been stated, the origin of colours has never been clearly demonstrated, and even scientifically re-explored since the 19th century, except a first study in 1999 [5]. A preliminary study funded by “Sorbonne Universités” and gathering different laboratories is endeavouring to reexamine those intriguing images. Our paper will describe this initiative, from the production of photochromatic images following Becquerel's publications to its analysis. The direct printing-out positive colour images are prepared in a very simple way that requires no development: a polished silver plate is sensitized by a chlorine solution and then exposed to the light in the camera. We studied parameters described by Becquerel to play a role in the formation of the images: the preparation of the silver plate, the thickness of the sensitized layer, the visible spectral bandwidths of the exposure, etc. We examined the relationship between the image microstructure and its optical properties. The microstructure of the coloured plates, the sensitized layer thickness, its morphology, and its porosity, as many characteristics that control the colours were investigated by using electron microscopies. Our multi-scale approach, from the naked-eye view to a sub-microscopic scale, will help us to relate the macro and micro-images to the reflectance properties measured with UV-Visible reflectance spectroscopy. This leads to a better understanding of the origins of the colours. [1] E. Becquerel. Annales de Chimie et de Physique, 22:451–459, 1848. [2] http://www.museeniepce.com/index.php/collections/enjeux-de-la-photographie/L-utopie-photographique. [Online; accessed21-Aug.-2015] [3] B. Lavédrine and J.-P. Gandolfo. L’autochrome Lumière. Secrets d’atelier et défis industriels. Paris : CTHS, 2009. [4] E. Becquerel. Photographic and Fine Art Journal, 8:8, 1855. [5] M. Kereun, Mythes et réalités autour de la fixation des couleurs héliochromiques. Mémoire de DEA, CNAM, 1999.

avatar for Christine Andraud

Christine Andraud

Professor, Centre de Recherche sur la Conservation / MNHN

Marie-Angelique Languille

Dr., Centre de Recherche sur la Conservation des Collections
Marie-Angélique Languille is conservation scientist at the Centre de recherche sur la conservation where she has been appointed for leading the photographic material section. In 2008, she got a PhD in physical chemistry, more specifically in surface science applied to catalysis... Read More →

avatar for Bertrand Lavedrine

Bertrand Lavedrine

Professor, Centre de Recherche sur la Conservation des Collections / MNHN
Bertrand Lavédrine received the doctoral degree from the Faculty of Humanities, University of Paris I Panthéon-Sorbonne, with the thesis in Art and Archeology, and got a Master degree in organic chemistry. In 1983, he was appointed to carry-out scientific researches on the preservation... Read More →

Edouard de Saint-Ours

Student, Centre de Recherche sur la Conservation / CNRS

Jean-Marc Frigerio

Professor, Institut des Nanosciences de Paris / UPMC
avatar for Saskia Vanpeene

Saskia Vanpeene

Conservation scientist, Centre de Recherche sur la Conservation / CNRS

Monday May 16, 2016 9:30am - 10:00am EDT
Room 516 CD