A confocal X-ray fluorescence microscope was built at the Cornell High Energy Synchrotron Source (CHESS) to obtain compositional depth profiles of historic paintings The microscope consists of a single-bounce, borosilicate monocapillary optic to focus the incident beam onto the painting and a commercial borosilicate polycapillary lens to collect the fluorescent X-rays The resolution of the microscope was measured by scanning a variety of thin metal films through this confocal volume while monitoring the fluorescence signal The capabilities of the technique were then probed using test paint microstructures with up to four distinct layers, each having a thickness in the range of 10–80 microns Results from confocal XRF were compared with those from stand-alone XRF and visible light microscopy of the paint cross-sections A large area, high-resolution scanner is currently being built to perform 3D scans on moderately sized paintings

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Development of confocal X-ray fluorescence (XRF) microscopy at the Cornell high energy synchrotron source

Often, just micrometers below a painting’s surface lies a wealth of information, both with Old Masters such as Peter Paul Rubens and Rembrandt van Rijn and with more recent artists of great renown such as Vincent Van Gogh and James Ensor. Subsurface layers may include underdrawing, underpainting, and alterations, and in a growing number of cases conservators have discovered abandoned compositions on paintings, illustrating artists’ practice of reusing a canvas or panel. The standard methods for studying the inner structure of cultural heritage (CH) artifacts are infrared reflectography and X-ray radiography, techniques that are optionally complemented with the microscopic analysis of cross-sectioned samples. These methods have limitations, but recently, a number of fundamentally new approaches for fully imaging the buildup of hidden paint layers and other complex three-dimensional (3D) substructures have been put into practice. In this Account, we discuss these developments and their recent practical appl...

Photon-based techniques for nondestructive subsurface analysis of painted cultural heritage artifacts.

Recent developments in spectroscopic imaging techniques for historical paintings - A review

A model for the confocal volume of 3D micro X-ray fluorescence spectrometer

A historical self-portrait painted by Sir Arthur Streeton (1867-1943) has been studied with fast-scanning X-ray fluorescence microscopy using synchrotron radiation. One of the technique's unique strengths is the ability to reveal metal distributions in the pigments of underlying brushstrokes, thus providing information critical to the interpretation of a painting. We have applied the nondestructive technique with the event-mode Maia X-ray detector, which has the capability to record elemental maps at megapixels per hour with the full X-ray fluorescence spectrum collected per pixel. The painting poses a difficult challenge to conventional X-ray analysis, because it was completely obscured with heavy brushstrokes of highly X-ray absorptive lead white paint (2PbCO(3)·Pb(OH)(2)) by the artist, making it an excellent candidate for the application of the synchrotron-based technique. The 25 megapixel elemental maps were successfully observed through the lead white paint across the 200 × 300 mm(2) scan area. The sweeping brushstrokes of the lead white overpaint contributed significant detrimental structure to the elemental maps. A corrective procedure was devised to enhance the visualization of the elemental maps by using the elastic X-ray scatter as a proxy for the lead white overpaint. We foresee the technique applied to the most demanding of culturally significant artworks where conventional analytical methods are inadequate.

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Alexis Fuentes Rodriguez

Papers

Three-dimensional micro-XRF investigations of paint layers with a tabletop setup