Improved radiographic methods for the investigation of paintings using laboratory and synchrotron X-ray sources

Abstract

It is generally known that radiographic inspection of 15-17th century paintings can easily be done with a polychromatic X-ray source using a voltage between 20 kV and 40 kV in combination with classic X-ray films. Unfortunately, the spatial structure of numerous 19 th and early 20 th century paintings cannot be visualized with conventional radiography due to several reasons such as the use of lead white grounds or low absorbing pigments. Radiographic images are blurred or worse, they do not contain the picture of the painting. During the last decades, many technological innovations have been introduced in the field of radiography but their possibilities in cultural heritage have not been explored in full detail. In our investigation we used phosphor imaging plates, energy dispersive detectors and CCDcameras in combination with synchrotron radiation and conventional X-ray tubes in order to improve the quality of radiographic images. Several promising techniques that could improve the quality of radiographs of paintings were identified.

Old traces, read anew – ‘The Reading Hermit’ painting in the light of X-ray fluorescence

“…Like for the improved radiographic methods presented by O. Schalm et al 16 the presence of a lead-white grounding does seem to blur neither the XRF-plots nor the NAR images as it would in conventional X-ray radiography.…”

Mobile depth profiling and sub-surface imaging techniques for historical paintings—A review

“…Their instrument proved capable of separating support and paint layers in the energy dispersive radiography of a mock-up of a 19th century painting. Schalm et al compared different radiographic techniques in an attempt to enhance the contrast obtained [66]. Next to electron emission radiography (see above) and dichromatic radiography at synchrotron sources, an experimental set-up for energy resolved radiography was described.…”

“…Recently a dedicated X-ray source, emitting a monochromatic fan beam, was described [84]. Other groups used K-edge imaging at synchrotron radiation sources [66,85].…”

“…Given the strong absorbance of electrons in paint layers the images obtained are dominated by surface paint layers with covered layers making only minor contribution. Electron emission radiography has also been subject to a recent comparison of radiography techniques [66].…”

In situ macro X‐Ray fluorescence scanning on a Leonardo da Vinci portrait

“…For example, by performing X‐ray radiography (XRR), some pigments, such as copper, iron or manganese, are poorly visible when the preparatory layer is lead‐based, due to the high mass attenuation coefficient of lead that maximizes the contrast for lead distribution and obscures the low and medium Z elements in the pigment distributions. This effect occurs also when the painting support is made of a strongly absorbent material (as wood) [6–9] . Contrary to XRR analysis, neutron‐based imaging techniques as neutron activation autoradiography (NAAR) represent a very suitable tool for the visualization of elements such as manganese, copper and mercury, due to their susceptibility to activation.…”