Missions

18-month post-doctorate funded by the DIM PAMIR (https://www.pamir.fr/projets-soutenus/deep-purple/) on the analytical characterization of a dye produced from certain lichens, the orchil. This extracted dye, generally reddish-purple in colour, is used as a substitute for Tyre purple in dyeing and painting. However, the analysis of the colouring material in the 11th century Mont Saint-Michel manuscripts has revealed a much wider range of colours for this dye, from pink to brown or violet. The brown tint raises questions: is it the original colour or the result of the dye degradation? In the case of the Mont Saint-Michel manuscripts, both hypotheses seem likely depending on the illuminations. This project focuses on three questions related to the colour of this dye. A first axis will deal with the manufacturing process of this dye during which we will try to identify the parameters allowing to obtain the different shades observed and to link the colour to the molecular composition of the dye. A second axis will focus on the study of the light degradation of this dye by trying to determine its degradation kinetics and mechanisms. Finally, the impact of the degradation on the signals collected by the main non-invasive techniques will be examined in order to ensure the reliability of the identification of this dye despite its alteration.

Activités

- Extraction of dye from orchil lichen and preparation of mock-up using traditional techniques in collaboration with a professional illuminator.
- Analysis of mock-up using non-invasive spectral techniques (Raman, fluorescence and reflectance spectroscopies).
- Implementation of an HPLC protocol for molecular characterization of the extracted dye from lichens and from the mock-up.
- Monitoring of degradation (light ageing in climatic chamber) by HPLC and by spectral techniques used previously.
- Spectroscopic analysis of BnF illuminated manuscripts to broaden the corpus and see if a link can be made between hues, state of preservation and recorded signals.

Compétences

For this research project, the team is looking for candidates with a solid background in organic chemistry, analytical chemistry, biochemistry or materials science. Skills in liquid chromatography coupled with mass spectroscopy and in electronic (UV-Vis, fluorescence) and/or molecular (Raman) spectroscopy are expected. Experience with dyes and/or heritage materials will be an advantage. The post-doctoral fellow will benefit from the skills of his supervisors in these various techniques, but is expected to be a driving force behind the experimental set-up, and to carry out the analyses himself on model samples produced in collaboration with a professional illuminator. Analyses on BnF manuscripts will be carried out by the post-doctoral fellow with the help of the CRCC team (notably those involved in the Mont Saint-Michel manuscript analysis project). Candidate should be able to work well with large team and travel to several sites. Finally, an ability for precise, meticulous work will complete their profile.

Contexte de travail

The postdoctoral fellow will work at different sites:
- CRC (Centre de Recherche sur la Conservation) at the Museum National d'Histoire Naturelle, Paris 5ème, for the preparation, ageing and spectral analysis of mock-up
- At the ICP (Institut de Chimie Physique, Université Paris-Saclay) on the Orsay IUT campus, for molecular characterization of the dye by HPLC.
- Occasionally at the LRMH (Historical Monuments Research Laboratory) in Champs-sur-Marne.
- At the BNF (Richelieu site), for the analysis of illuminated manuscripts using portable instrumentation.
The postdoc will be supervised by Anne Michelin at the CRC in the "Color and Visual Effects" team, whose activities focus on light/matter interaction and the analysis of color materials using spectroscopic techniques, and Witold Nowik at the LRMH, a specialist in coloring materials, including orchil, both in terms of the properties that enable them to be used, their ageing, and their characterization using chromatographic techniques. Sylvie Héron at ICP will contribute her expertise and guidance in HPLC coupled with mass spectrometry. Laurianne Robinet, CRC research engineer and coordinator of the « Étude Matérielle des Manuscrits Anciens du Mont Saint-Michel » project, will contribute to scientific exchanges. Charlotte Denoël, head of the medieval manuscripts department at BnF, is involved in various projects relating to the materiality of collections, notably on the use of orchil in medieval manuscripts, and will contribute her expertise on both collections and illumination techniques and materials. Joël Boustie, President of the AFL - Association Française de Lichénologie - and Professor at the Institut des Sciences Chimiques de Rennes, will share his knowledge of lichen metabolites and his access to this raw mater Lastly, Siloë, the illuminator, will share her expertise on the techniques and materials involved in the dye manufacturing process and its use in painting to create mock-up.