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Techniques & Tools Spectroscopy

X-Ray Visionary

How did you get into X-ray techniques and art analysis?

 X-ray-based techniques fit naturally into the world of art analysis because they allow non-destructive analysis of historical objects or materials. But I didn’t start out in the art sector – in fact, I got into X-ray-based methods right at the very start of my career, during my master’s thesis on automated data reduction of X-ray fluorescence spectra. My mentor at that time was Piet Van Espen, now part of our research group. In the early days, I was in history and the chemistry of historical materials. I  started collaborating with archaeologists, which led to a more concrete project on the analysis of archaeological glass. It turned out that the city of Antwerp has a lot of historical glass from the 16th and 17th centuries, and we worked with a local archaeologist to trace the trade and local manufacture of glass.

And that led you to art?

I gradually became more interested in museum collections, especially historical museums, and finally ended up dealing with fine art objects. Again in Antwerp, there were art-historical Rubens specialists who were not only interested in how this master painted, but also in the materials he used. Another notable change was that about 15 years ago, miniaturization revolutionized the x-ray analysis world; the relatively large and cumbersome lab instrumentation had a new partner: portable and battery-operated X-ray fluorescence (XRF) equipment (the early forms of handheld XRF instruments). Because we could bring the instrumentation to the material to be examined, we were able to irradiate a square cm of a painting and figure out indirectly which pigments were used.

What’s the added value of such measurements in the art world?

When I first started, people in the art-historical world were not terribly aware of the type of materials each painter was using. Such knowledge can be highly relevant in art authentication. Normally, painters of around the same time use the same set of pigments, so it’s not possible to prove that a painting belongs to certain painter, but it’s quite easy to prove the opposite: for example, if you find a type of yellow that can only have been used by a 19th century painter, it’s not a Rubens! Such analysis can easily be performed with portable XRF – and, most importantly, it can be done in a non-destructive manner.

What kind of people do you have in your group?

Our group has around 25 people now and, perhaps most interestingly, my colleague Karolien de Wael is an electrochemist, who works on highly specific analyses – essentially using electrochemical sensors as detector. She is, of course, very familiar with redox reactions, which is what causes painters’ pigments to change color. We combine her electrochemical experience and sensitive methods of detection with our high-end X-ray analysis experiments in paint samples. Normally, if you want to investigate whether a painter’s pigment is going to undergo spontaneous reaction, you have to age it in an artificial aging chamber for several months; when it changes color, you can start analyzing the degradation process. With electrochemistry, we can dramatically speed up that kind of analysis. Four people in the group are dealing specifically with photo degradation, and three or four more researchers are interested in developing advanced analytical methods, usually combining several modes of analysis – or constructing mobile instrumentation we can take into museums. The rest of the group don’t necessarily work on art analysis, but rather in food or environmental application areas.

What are your most rewarding research moments?

Well, the whole field is both rewarding and fascinating. We take our analytical equipment (often instrumentation we have developed ourselves) to the museum, and we really get up close with masterpieces – normally, you are not allowed to touch! And because we’re working with X-rays, the works of art are usually moved somewhere private, like a conservation workshop. Then, we can be alone with very famous works of art – a unique moment of exclusive intimacy; you can talk directly to the art – or rather, via our instruments, the art works talk to us! Scanning usually takes several days, so it allows us to photograph and look at the work of art in a way that we will never experience again; it’s a very stimulating aspect of these undertakings. Sometimes we discover completely unknown aspects of a work of art; for example, we may find that Rubens has decided to paint over something he didn’t like or want. It’s very exciting that, four hundred years later, we can make such decisions visible again. And that insight allows art historians to understand Rubens’ frame of mind at the time – what he originally intended and why he decided to change his mind.

Such new knowledge must thrill art historians too...

It’s great gift to give! The art historians we work with usually know these paintings very well indeed and may have been studying them for twenty years or more. By doing our chemical imaging analysis, we give them extra information that can sometimes completely change their view of the work, which is very rewarding for us also. Such enriching interactions really define the essence of analytical chemists – often working hard to achieve other people’s goals.

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About the Author
Koen Janssens

Koen Janssens is Full Professor, general and analytical chemistry, and Vice-Dean, Faculty of Sciences, at the University of Antwerp, Belgium.

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