Research topics and interests

Structural characterization of the Prussian blue pigment

Structure of Prussian blue and XANES at Fe K edge of
	     PB-paper samples Prussian blue (iron hexacyanoferrate) is one of the first modern synthetic pigments and has been used in a wide variety of cultural artefacts, among them famous paintings from Watteau (1684-1721) or Van Gogh (1853-1890) and watercolors from Hokusai (1760-1849).
We are investigating the crystalline structures of Prussian blue by means of X-ray diffraction, X-ray absorption spectroscopy, Raman and FTIR spectroscopy. We emphasize particularly on identifying the disorders and structural features responsible for its color as well as its light and anoxia-induced fading. The inherent nature of this electrochromic pigment makes it particularly sensitive to radiation damage and one part of our research emphasizes on estimating, preventing, or even using this particularity.

Role of cellulosic substrate on the photoreduction of iron(III) hexacyanoferrate

Investigation of Prussian blue-substrate interactions by synchrotron techniques

When exposed to strong visible light or submitted to anoxic treatment, some paper artworks containing Prussian blue (cyanotypes, blueprints, stamps and watercolors) exhibit a discoloration of the pigment more or less pronounced. We confirmed previous studies that the general discoloration process implies the reduction of Prussian blue's ferric ions. Thanks to advanced synchrotron techniques, we could furthermore demonstrate the influence of the cellulosic substrate in which the pigment is embedded on its final sensitivity to photoreduce. We particularly highlighted the oxydation of the cellulose leading to a release of electrons facilitating the reduction of iron(III) hexacyanoferrate, and its role in playing as a reservoir of solvated cations that migrate within the Prussian blue structure upon reduction.

Collaboration: European research platform for ancient materials (IPANEMA, SOLEIL synchrotron, France), the Centre de Recherche sur la Conservation des Collections (CRCC, Paris, France) and the Smithsonian Museum Conservation Institute (MCI, Washington DC, USA).

Porosity and transport phenomena in archaeological corroded iron

3D image analysis and transport properties of porous corroded iron

Studies on long-term altered systems have shown that iron corrosion products developed in soil or in anoxia are organized in multi-layers with a thickness of several hundred microns to some millimeters depending on their age. They exhibit a significant porosity which varies with time and with location, especially near the metal interface. We could show that this porosity influences the penetration and migration of the electrolytes towards the metal, determines the amount and type of surface potentially reactive to the corrosion process and controls the transport of chemical species and thus the local chemistry. Within this context, we developed specific X-ray and neutron micro-tomographic image acquisition techniques at different scales (from micro to nano) together with 3D image processing tools and numerical simulations of diffusion and transport. This allowed us to acquire specific knowledge about the porosity of the corroded system at relevant and representative scales and the evolution of this porosity as a function of the nature of the corrosion layers.

This project is performed in collaboration with the Laboratoire Archéomatériaux et Prévision de l'Altération, (LAPA, CNRS-CEA, France).