Stratigraphic mapping of paintings by multispectral reflectography

Abstract

Despite recent technological advances, it is currently not possible to uniquely and noninvasively measure the micrometric thickness of pictorial layers in paintings. The presence of optically opaque materials (pigments) severely limits the detection capability, as it hinders the penetration of the probe's near-infrared radiation, typically employed for this purpose. In our previous work, we explored the possibility of using diffuse reflectance spectroscopy (DRS) to achieve stratigraphic information about painting materials. We showed that the thickness of pictorial layers can be quantified by the intensity of the spectral reflectance factor measured at a given wavelength in the infrared, i.e., an easily detectable spectral feature. In the present work, we extend the previously proposed method by applying multispectral reflectography to measure new ad hoc prepared pictorial samples and a mock-up simulating a Mondrian painting. We thus demonstrate that it is possible to obtain 2D and 3D stratigraphic maps of the pictorial layer over large areas with the same measurement time and spatial resolution as multispectral scanning reflectography.

Combined Scanned Macro X-Ray Fluorescence and Reflectance Spectroscopy Mapping on Corroded Ancient Bronzes

“…An intrinsic limit of the techniques used in this work is the evaluation of the volumes investigated: in XRF analyses, the thicknesses investigated typically depend on the atoms that make up the material and on their absorption of X radiation; otherwise, reflectance spectrometry is generally indicated as a superficial technique even though we know that in the infrared range, from about 800nm onwards, scattering phenomena are possible which allow us to excite and obtain information on the deeper layers, in the order of micrometres [54]. However, the joint use of techniques that employ different volumes of analysis can lead to obtaining information relating to the inhomogeneity of the sample, which is a typical factor in the context of cultural projects and all those processes of uncontrolled natural degradation, such as the case of patina formation.…”