Influence of moisture content on colour of granular materials. Part I: experiments on yellow ochre

Abstract

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.

A Multi-Analytical Approach for the Characterization of Seventeenth Century Decorative Wall Paintings in Two Norwegian Stave Churches: A Case Study at Eidsborg and Heddal, Norway

“…It has been successfully applied for the analysis of artists' materials [9], painted artworks (e.g., murals, indigenous paintings etc.) [10][11][12] and reconstructions [13,14], as well as examining the mineralogical composition of modern [12,[15][16][17][18] and historic [15,19,20] ochres. The majority of these studies employ a multi-analytical approach, relying on a combination of XRD with various techniques including Scanning Electron Microscopy (SEM) [12,16,19,20], thermal analysis [11,16,18], Raman Spectroscopy [9,14,20], and Fourier Transform Infrared Spectroscopy (FT-IR) [9,11,14,16,19].…”

Does electro-osmosis work in moisture damage prevention? Applicability of infrared-based methods to verify water distribution under electric fields

“…This let us avoid specular reflectance contribution. That's because at high moisture content the reflected radiation is spatially heterogeneous and presents a maximum value due to specular contribution whereas at lower moisture content this effect is negligible (Monnard et al, 2016). The samples used in this second trial are described in Table 1.…”