Rebecca Morelle’s Aug. 4, 2016 article for BBC (British Broadcasting Corporation) News online describes an intriguing piece of research into artists and how they work,
A hidden portrait by the French Impressionist painter Edgar Degas has been revealed by scientists.
Researchers in Australia used powerful X-rays to bring to light the painting of a young woman concealed beneath a work called Portrait of a Woman.
The researchers believe the subject is Emma Dobigny, who appeared in other Degas paintings.
Dr Daryl Howard, a co-author of the study, told BBC News: “I think what is really exciting is that we have now been able to add one more Degas artwork for the world to see.”
Morelle describes how the second portrait deteriorated such that a previous painting on the canvas was becoming perceptible and how scientists were able to ‘peel’ back the original to see what lay beneath,
It had long been known that Degas’ portrait of a woman wearing a black bonnet and dress, which he painted in the late 1870s, covered an earlier painting.
A ghostly impression of the composition appears as a dark stain on the sitter’s face, and over the years has become more prominent as the oil paint thinned.
Conventional X-rays revealed the outline of another image was lurking beneath, but without scraping away the outer painting, the researchers required a much more powerful technique to show any detail.
For that, they used the Australian Synchrotron, a huge accelerator that generates more powerful X-rays, to peer beneath the top layers of paint.
They were able to detect the metallic elements in the pigments that Degas had used in his underlying artwork.
Dr Howard, from the Australian Synchrotron, said: “Each element has its own unique signature, and so that gets collected.
“And what we do is analyse that data and build up these ‘elemental maps’. And that allows us to image all the different pigments used in the painting.”
Through this they were able to see in colour and in remarkable detail Degas’ hidden work: a portrait of a woman with auburn hair.
Apparently, Degas had a tendency, in his early paintings, to give his models pixie-like (longish and pointed) ears. Unusually, he has incorporated some of the features of the first painting into the second painting.
Getting back to the science, the technique used to ‘uncover’ the first painting is nondestructive (many techniques used in conservation are destructive as scrapings are required) and more powerful than previous x-ray techniques used to uncover artists’ secrets.
Here’s a link to and a citation for the paper,
A Hidden Portrait by Edgar Degas by David Thurrowgood, David Paterson, Martin D. de Jonge, Robin Kirkham, Saul Thurrowgood, & Daryl L. Howard. Scientific Reports 6, Article number: 29594 (2016) doi:10.1038/srep29594 Published online: 04 August 2016
This paper is open access but for anyone who doesn’t have the time to read it, here’s a bit from the paper’s Discussion section (Note: Links have been removed),
We are not aware of any other current analytical technique that could have achieved such an imaging outcome for this painting. The data generated by this study has provided a better understanding of the artist’s technique. The 60 μm [micrometre] spatial resolution allows us to observe with confidence that a majority of the hidden sitter’s face has been achieved as one action. However the disproportionate and blurred form of the ears is indicative of several attempts to achieve the final proportions and features. Degas is reported as having painted “pixie” like ears at about this period46. By examining single elemental maps of the painting it is possible to observe such a “pixie” like ear shape (e.g., Mn and Fe, Fig. 3) which appears to have been reworked to a more conventional form (e.g., Co and Hg, Fig. 3). Careful study of the data reveals numerous intricacies of painting technique and brush stroke direction of the underpainting. It reveals stylistic information and elemental composition information that is unlikely to be reproducible by persons attempting to copy a work, and the technique has strong potential for application in authentication studies4,5.
Consideration has been given to the properties of synchrotron radiation, and the research group used visible and chemical observation to look for radiation-induced change in preliminary experiments. Pigment binder matrices were studied by Fourier Transform Infrared (FTIR) spectroscopy before and after extended X-ray exposure at the XFM beamline, and spectroscopic changes were not detected. No evidence for any chemical or physical change was observed for radiation doses 10,000 times that reported for this study, which is in accord with recent findings by other research groups using intense radiation sources47,48.
This study has successfully demonstrated a virtual reconstruction of a hidden portrait by Edgar Degas and has delivered a better understanding of his work and artistic practices. The authors propose that the unfolding technological developments for examining artwork using synchrotron radiation-based techniques will significantly impact the ways cultural heritage is studied for authentication, preservation and scholarly purposes. We anticipate that the high quality outcome presented here and the propagation of the rapid-scanning XRF detector technology used will further stimulate growing interest in the better understanding of our cultural assets. Parallel work using portable XRF systems7 is demonstrating that a version of the technique is becoming viable (at substantially reduced spatial resolution and increased data collection time) outside of a synchrotron facility, raising a strong likelihood that precedents being set at synchrotron facilities will directly influence emerging field-based technologies. Until recently XRF large area scanning facilities were built in-house, and this had limited the technique’s availability. With the introduction of commercial large scanning area instruments on the market49, the technique has the potential to expand rapidly.
And here’s just a bit from the paper’s Methods section (Note: Links have been removed),
The scanning XRF mapping of the painting Portrait of a Woman was performed at the X-ray fluorescence microscopy (XFM) beamline of the Australian Synchrotron31. The X-ray fluorescence was acquired with the Maia 384A detector array, which integrates the sample stage motion with continuous fly scanning, leading to zero data readout overhead50,51. An incident excitation beam energy of 12.6 keV was used to circumvent intense fluorescence from the Pb L absorption edges, which would originate primarily from the painting’s Pb-based ground layer and thereby limit detection sensitivity to other elements in the pictorial paint layers. The low-energy sensitivity of the detector is limited to approximately 4 keV, thus Pb-M fluorescence (~2.3 keV) was not detectable for example. The energy resolution of the detector is 375 eV at Mn Kα.
The artwork was fitted to a custom manufactured cradle for scanning. The painting was placed approximately 13 mm from Maia detector rather than the optimal distance of 10 mm, since the painting was not perfectly flat. The painting is shown mounted at the XFM beamline in Supplementary Material Fig. S1. A 426 × 267 mm2 area was raster-scanned at 16.4 mm s−1, providing a dwell time of approximately 3.7 ms per 60 × 60 μm2 pixel and yielded a 31.6 megapixel data set in 33 h. Given the 10 × 10 μm2 incident beam size used, the average time an area of the painting was in the beam was 0.6 ms. The average incident flux on the painting was 1.5 × 109 photons s−1.
For art historians, conservationists, scientists, and people like me (the curious), this is pretty exciting stuff.
I recommend reading Morelle’s piece for anyone who finds the science a little hard going as she does an excellent job of describing the science and the art.