Non-Invasive and Non-Destructive Examination of Artistic Pigments, Paints, and Paintings by Means of X-Ray Methods

Abstract

Recent studies are concisely reviewed, in which X-ray beams of (sub)micrometre to millimetre dimensions have been used for non-destructive analysis and characterization of pigments, minute paint samples, and/or entire paintings from the seventeenth to the early twentieth century painters. The overview presented encompasses the use of laboratory and synchrotron radiation-based instrumentation and deals with the use of several variants of X-ray fluorescence (XRF) as a method of elemental analysis and imaging, as well as with the combined use of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Microscopic XRF is a variant of the method that is well suited to visualize the elemental distribution of key elements, mostly metals, present in paint multi-layers, on the length scale from 1 to 100 μm inside micro-samples taken from paintings. In the context of the characterization of artists' pigments subjected to natural degradation, the use of methods limited to elemental analysis or imaging usually is not sufficient to elucidate the chemical transformations that have taken place. However, at synchrotron facilities, combinations of μ-XRF with related methods such as μ-XAS and μ-XRD have proven themselves to be very suitable for such studies. Their use is often combined with microscopic Fourier transform infra-red spectroscopy and/or Raman microscopy since these methods deliver complementary information of high molecular specificity at more or less the same length scale as the X-ray microprobe techniques. Since microscopic investigation of a relatively limited number of minute paint samples, taken from a given work of art, may not yield representative information about the entire artefact, several methods for macroscopic, non-invasive imaging have recently been developed. Those based on XRF scanning and full-field hyperspectral imaging appear very promising; some recent published results are discussed.

Photodegradation Kinetics of Alkyd Paints: The Influence of Varying Amounts of Inorganic Pigments on the Stability of the Synthetic Binder

“…This phenomenon was also previously confirmed by 3D, SEM microscope, and multivariate results. As reported in the literature (Del Federico et al, 2006;Janssens et al, 2016;René de la Rie et al, 2017), artificial ultramarine blue (PB29) has a significant loss of its blue color when mixed with alkyd resin after light irradiation. This effect is probably due to the chromophoric S-anions release after the opening of the sodalite cages of pigment, leading to the discoloration of the pigment itself.…”

A prototype handheld X-ray diffraction instrument

“…Naturally, a very wide range of materials are encountered in the field as a whole and the use of HHXRD would need to be targeted to specific material types such as metallic artefacts. The application of nondestructive techniques is increasingly important in archaeometry studies (Young, 2012;Janssens et al, 2016) and instrument portability is also a crucial advantage (Chiari, 2008). Curators are reluctant to allow artefacts to leave the museum/collection and HHXRD devices could also be taken to archaeological sites to improve conservation decisions.…”

Macro X‐ray fluorescence imaging spectroscopy of the suggested Santi di Tito's portrait of Galileo Galilei

“…MA‐XRF imaging is a non‐invasive methodology that provides high‐resolution elemental maps of paintings (Alfeld & Broekaert ; Alfeld & de Viguerie ; Janssens et al ). Its power to turn up new information on painting techniques, pigments, pictorial process, conservation state, attribution, and authenticity is well established.…”