A mobile instrument for in situ scanning macro-XRF investigation of historical paintings

TLDR

Scanning macro‑XRF is becoming a key tool for analyzing historical paintings, enabling elemental maps that reveal hidden layers and inform conservation, but its use has been limited by the absence of commercial instruments. We present the first commercially available XRF scanner for paintings. The scanner, comprising an X‑ray tube and a silicon‑drift detector mounted on a motorized stage, images 80 × 60 cm areas with dwell times below 10 ms, lateral resolution under 100 µm, count rates over 1000 cps / mass % for Ti–Mo, and detection limits of 100 ppm for 1‑s measurements. Its performance is illustrated by a case study of a Govert Flinck painting, demonstrating the instrument’s spectrometric figures of merit.

Abstract

Scanning macro-X-ray fluorescence analysis (MA-XRF) is rapidly being established as a technique for the investigation of historical paintings. The elemental distribution images acquired by this method allow for the visualization of hidden paint layers and thus provide insight into the artist's creative process and the painting's conservation history. Due to the lack of a dedicated, commercially available instrument the application of the technique was limited to a few groups that constructed their own instruments. We present the first commercially available XRF scanner for paintings, consisting of an X-ray tube mounted with a Silicon-Drift (SD) detector on a motorized stage to be moved in front of a painting. The scanner is capable of imaging the distribution of the main constituents of surface and sub-surface paint layers in an area of 80 by 60 square centimeters with dwell times below 10 ms and a lateral resolution below 100 μm. The scanner features for a broad range of elements between Ti (Z = 22) and Mo (Z = 42) a count rate of more than 1000 counts per second (cps)/mass percent and detection limits of 100 ppm for measurements of 1 s duration. Next to a presentation of spectrometric figures of merit, the value of the technique is illustrated through a case study of a painting by Rembrandt's student Govert Flinck (1615–1660).