Combined macro X-ray fluorescence (MA-XRF) and pulse phase thermography (PPT) imaging for the technical study of panel paintings

Nina Deleu; Michaël Hillen; Gunther Steenackers; Gwen Borms; Koen Janssens; Katlijne Van der Stighelen; Geert Van der Snickt

doi:10.1016/j.talanta.2023.125533

Combined macro X-ray fluorescence (MA-XRF) and pulse phase thermography (PPT) imaging for the technical study of panel paintings

Talanta. 2024 Apr 1:270:125533. doi: 10.1016/j.talanta.2023.125533. Epub 2023 Dec 9.

Authors

Nina Deleu¹, Michaël Hillen², Gunther Steenackers², Gwen Borms³, Koen Janssens⁴, Katlijne Van der Stighelen⁵, Geert Van der Snickt⁶

Affiliations

¹ ARCHES Research Group: University of Antwerp, Antwerp, Belgium; AXIS Research Group: University of Antwerp, Antwerp, Belgium. Electronic address: nina.deleu@uantwerpen.be.
² InViLab Research Group: University of Antwerp, Antwerp, Belgium.
³ Royal Museum of Fine Arts Antwerp, Antwerp, Belgium.
⁴ AXIS Research Group: University of Antwerp, Antwerp, Belgium.
⁵ Research Unit Archaeology, Art History and Musicology: KU Leuven, Leuven, Belgium.
⁶ ARCHES Research Group: University of Antwerp, Antwerp, Belgium; AXIS Research Group: University of Antwerp, Antwerp, Belgium.

PMID: 38134817
DOI: 10.1016/j.talanta.2023.125533

Abstract

Museum staff usually relies on a proven combination of X-ray radiography (XRR) and infrared reflectography (IRR) to study paintings in a non-destructive manner. In the last decades, however, the research toolbox of heritage scientists has expanded considerably, with a prime example being macro X-ray fluorescence (MA-XRF), producing element-specific images. The goal of this article is to illustrate the added value of augmenting MA-XRF with pulse phase thermography (PPT), a variant of active infrared thermographic imaging (IRT), which is an innovative diagnostic method that is able to reveal variations between or in materials, based on a different response to minor fluctuations in temperature when irradiated with optical radiation. By examining three 16^th- and 17^th-century panel paintings we assess the extent in which combined MA-XRF and PPT contributes to a better understanding of two commonly encountered interventions to panel paintings: (a) Anstückungen (enlargement of the panel) or (b) substitutions (replacement of part of the panel). Yielding information from different depths of the painting, these two techniques proved highly complementary with IRR and XRR, expanding the understanding of the build-up, genesis, and material history of the paintings. While MA-XRF documented the interventions to the wooden substrate indirectly by revealing variations in painting materials, paint handling and/or layer sequence between the original part and the extended or replaced planks, PPT proved beneficial for the study of the wooden support itself, by providing a clear image of the wood structure quasi-free of distortion by the superimposed paint or cradling. XRR, on the other hand, revealed other features from the wood structure, not visible with PPT, and allowed looking through the wooden panels, revealing e.g. the dowels used for joining the planks. Additionally, IRR visualised dissimilarities in the underdrawings. In this way, the results indicate that PPT has the potential to become an acknowledged add-on to the expanding set of imaging methods for paintings, especially when used in combination with MA-XRF, IRR and XRR.

Keywords: Active IRT; Anstückungen; Bruegel; MA-XRF; Panel paintings; Pulse phase thermography.