A palette of colours on a silver plate: that is what the world's first colour photograph looks like. It was taken by French physicist Edmond Becquerel in 1848. His process was empirical, never explained, and quickly abandoned. A team at the Centre de recherche sur la conservation (CNRS/Muséum National d'Histoire Naturelle/Ministère de la Culture) has now shone a light on this, in collaboration with the SOLEIL synchrotron and the Laboratoire de Physique des Solides (CNRS/Université Paris-Saclay). The colours obtained by Edmond Becquerel were due to the presence of metallic silver nanoparticles, according to their study published on 30 March 2020 in Angewandte Chemie International Edition.
However, when the coloured plates were examined, metallic silver nanoparticles were revealed in the matrix made of silver chloride grains -- and the distributions of sizes and locations of these nanoparticles vary according to colour. The scientists assume that according to the light's colour (and therefore its energy), the nanoparticles present in the sensitised plate reorganise: some fragment and others coalesce. The new configuration gives the material the ability to absorb all colours of light, with the exception of the colour that caused it: and therefore that is the colour that we see. Nanoparticles having properties related to colour is a phenomenon known to physicists as surface plasmons (3), electron vibrations (here, those of the metallic silver nanoparticles) that propagate in the material. A spectrometer in an electron microscope measured the energies of these vibrations to confirm this hypothesis.
Victor de Seauve, Marie-Angélique Languille, Mathieu Kociak, Stéphanie Belin, James Ablett, Christine Andraud, Odile Stéphan, Jean-Pascal Rueff, Emiliano Fonda, Bertrand Lavédrine. Spectroscopies and electron microscopies unravel the origin of the first colour photographs. Angewandte Chemie, 2020; DOI: 10.1002/ange.202001241
The first colour photographs were created by a process introduced by Edmond Becquerel in 1848. The nature of these photochromatic images colours motivated a debate between scientists during the XIXth century, which is still not settled. We present the results of chemical analysis (EDX, HAXPES and EXAFS) and morphology studies (SEM, STEM) aiming at explaining the optical properties of the photochromatic images (UV‐visible spectroscopy and low loss EELS). We rule out the two hypotheses (pigment and interferences) that have prevailed since 1848, respectively based on variations in the oxidation degree of the compound forming the sensitized layer and periodically spaced photolytic silver planes. A study of the silver nanoparticles dispersions contained in the coloured layers showed specific localizations and sizes distributions of the nanoparticles for each colour. These results allow us to formulate a plasmonic hypothesis on the origin of the photochromatic images colours.
Victor de Seauve, Marie-Angélique Languille, Saskia Vanpeene, Christine Andraud, Chantal Garnier, Bertrand Lavédrine. Replication and study of the colouration of Edmond Becquerel's photochromatic images. submitted to arXiv, 2020 [link]
Edmond Becquerel's process of making photochromatic images, which are the first colours photographs, is still poorly understood. In particular, the origin of the colours of these images gave rise to a long-lasting debate, starting from the publication of Becquerel in 1848 until the end of the 19th century. This photographic process was replicated in the laboratory, and the colouration of the sensitized plates was studied by means of visible spectroscopy. A comprehensive description of the sensitization routes that were adapted from Becquerel's writing is given. The study of the exposition step allowed us to gain insights in the colouration mechanisms of the sensitized plates, and to compare between the two sensitization routes developed by Becquerel in terms of spectral sensitivity and colour faithfulness. The so-called "electrochemically sensitized" samples were found to be more sensitive and to reach a larger chromatic space than the "immersion-sensitized" ones. Finally, a reproducible way of creating coloured samples is suggested.
| Subjects: | Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci) |
| Cite as: | arXiv:2001.05250 [physics.app-ph] |
| (or arXiv:2001.05250v1 [physics.app-ph] for this version) |
