The water is suspected of remobilizing pigments of prehistoric painting into small worm-like heaps named vermiculations. To preserve these artworks, the moisture content of pigments must be monitored. Due to the fragility of the paintings and the technical constraints on the in-situ measurements, colour measurement is proposed as a noninvasive way to access humidity. This study aims at characterizing more precisely the influence of the moisture content on the optical behaviour of yellow ochre. The light reflected by the surface of drying ochre is measured with a gonio-spectroradiometer. A scenario is proposed: the water saturation at high moisture contents is connected to the presence of a specular radiation which brings a loss of chromatic information. The evaporation of water brings the disappearance of the specular radiation and the augmentation of the diffuse radiation. These first results are promising for the development of a non-destructive in situ method of moisture measurement.

In some fields, it's important to control the moisture content of granular materials without any invasive method. Moisture content is suspected to play a role in the occurrence of some unwanted phenomena like remobilization of particles on rock walls in caves for example. The hygrothermal conditions are important as they can modify the moisture content of the granular materials on the wall leading to a humidification or at the contrary to a drying of the powder. In this study, optical measurements are used to characterize a wet powder during its drying process. Different steps of this dynamic drying process are modelled and thanks to an adaptation of the existing Melamed's model of scattering of light by a particulate medium, simulation results are compared with instrumental measures. The modelling of such a system allows the estimation of moisture content of a granular material and brings information about the localization of water in the particulate medium.