Research topics and interests

Pigment-Substrate-Environment

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 the substrate on the photoreduction of Prussian Blue

When exposed to strong visible light or submitted to anoxic treatment, some artworks containing Prussian blue exhibit a discoloration of the pigment more or less pronounced. The general discoloration process implies the reduction of Prussian blue's ferric ions. We have already demonstrated the influence of the substrate in which the pigment is embedded, on its final sensitivity to photoreduce. This projects aims at better characterizing the capacity of the substrate to modify the Prussian blue crystalline structure and alter its fading behavior.

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).

Long-term corrosion in iron-based materials

Porosity and transport phenomena in archaeological corroded iron

3D visualization of the
	     corrosion interface

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. 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, acquiring 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 is essential.

This project aims at developing an approach based on the coupling of high resolution 3D visualization of corroded iron layers with numerical simulations of diffusion and transport. We will develop porosity characterization and simulation tools based on X-ray computer tomographic (CT) data of archaeological and model iron artefacts. This project is performed in collaboration with the Laboratoire Archéomatériaux et Prévision de l'Altération, (LAPA, CNRS-CEA, France).