Francien Bossema: "In the museum world, I was the odd one out as a mathematician"

The KHMW Thesis Award for Interdisciplinary Research 2025 has been awarded to Francien Bossema. She obtained her PhD on 23 May 2024 at Leiden University for her PhD thesis 'Tailoring X-ray tomography techniques for cultural heritage research'.

Although formally based at the Centrum Wiskunde & Informatica (CWI) in Amsterdam as a PhD candidate, Bossema also conducted part of her research at the Rijksmuseum (Amsterdam), the British Museum (London), and the J. Paul Getty Museum (Los Angeles). Her cross-disciplinary approach is precisely what the KHMW Thesis Award for Interdisciplinary Research is intended to recognize.

Why would you investigate an art-historical object using X-rays?

‘The question always came from my colleagues at the Rijksmuseum. They had a three-dimensional object, such as a wooden sculpture or a knife sheath, and wanted to look inside it - for example, to determine its age. In the case of a wooden object, this can be done by analyzing the tree rings. Of course, you can’t just saw such a sculpture in half. That’s why we use X-rays. Just as in a hospital, you can use a CT scan in a museum to make a three-dimensional image of an object and digitally slice through it.’

That sounds logical. Hasn’t that been done yet?

‘Very little. Firstly, because CT scanners are usually designed for human use. The human body consists mostly of water, which X-rays can penetrate quite easily. Art objects, by contrast, often consist of multiple materials- wood, metal, paper, paint - and that makes it more complex. Also, unlike people, art objects come in vastly different shapes and sizes. Some are small, like a bead or a necklace, but others…’ Bossema gestures towards the fireplace in the Blue Room of the Hodshon House. ‘A mantelpiece like that, for example, isn’t something you can just place in an X-ray scanner.’

That's why Bossema works with laboratory setups where the X-ray source and the detector that captures the X-rays do not rotate around the patient, as in the medical world. 'With us, the object is on a rotation table and the source and detector remain stationary', she explains. 'That offers more possibilities. Another advantage is that we can achieve a higher resolution than with a medical CT scanner. That is necessary, because the features we want to see are often very small.'

What is your role in this as a mathematician?

‘As the object rotates, hundreds of X-ray images are taken that are combined into a CT scan. For the reconstruction, you need to know all the positions. Where is the source? By how many degrees has the object rotated between two images? Where is the detector in relation to the object and source. We – because I worked in a team – developed an algorithm to calculate all those parameters very precisely using small metal balls. Thanks to this, we were able to use the X-ray machine at the Rijksmuseum, which previously could only take two-dimensional images, to create three-dimensional CT scans. One benefit is that much larger objects can now be scanned within the museum’s setup. Another is that the objects do not need to be taken off-site, which is a significant advantage given their often fragile and valuable nature.’

What did you do at the British Museum?

‘The British Museum is one of the pioneers in this field. They have a beautiful, large CT scanner, which they have been using to study their collection for several years. We were allowed to use it to verify the accuracy of my calculations.’

And how was your collaboration with the J. Paul Getty Museum in Los Angeles?

‘I didn’t visit the museum during the research phase. We did the entire project, and the resulting article, online. They were behind the buttons of the machine, and I told them what I needed via Zoom. Last year, after completing my PhD, the museum invited me for an eight-week guest scholarship. That wasn’t enough time for a full research project, so I’m still in the process of finishing that.’

You have a bachelor’s degree in mathematics and physics at VU Amsterdam and a master’s degree in applied mathematics at Leiden. How did you end up in the museum world with such a background?

‘After secondary school, I found it difficult to choose a study, as I enjoyed many subjects. In the end, I chose mathematics. This PhD project was ideal for me because it allowed me to combine multiple disciplines and interests. Alongside mathematics, informatics and computer science, the work also touched on art history, dendrochronology, and museum studies.’

You also specialized in science communication during your master’s. Did that come in handy?

‘Absolutely! In an interdisciplinary project like this, clear communication is vital. The museum colleagues explain what they need, and then I sit with them in the scanning room all day. The scanning process is guided by their immediate feedback, so we can extract as much information as possible from the object.’

It sounds like you are a jack of all trades.

‘I’ve learnt a great deal from my colleagues over the past few years. My thesis consists of four published articles. The art-historical sections were largely written by my colleagues, while I was responsible for the technical parts. The conclusions about the art objects were drawn collaboratively, often after hours spent looking at the CT scans together.’

What, in your view, is the value of team science?

‘The largest part of this PhD thesis is based on team science. In 2021, we even won the NWO Team Science Award (from the Dutch Research Council for our project on Hugo de Groot's chest, for which we developed a new technique to scan larger objects. An interdisciplinary team contributed to each article. There were always at least one mathematician and one computer scientist, and often several curators or restorers from the museum. For me personally, team science is very important. For me personally, team science is crucial. I believe it boosts creativity and propels science forward.’

That sounds like quite the organizational feat.

‘It was. In most cases, I was the project lead, as it was my PhD research. I reached out to people and organized meetings to discuss the work. So yes, organizational skills are key. Planning is essential too. It can be tricky, because everyone has other commitments. It takes time and patience to get everything coordinated. But I found that everyone was very enthusiastic about the project, because it produced so much valuable new information.’

How do you feel about winning the KHMW Thesis Award for Interdisciplinary Research?

‘The crowning glory of my work! In that museum environment, I sometimes felt a bit like the odd one out. There I was the mathematician who always talked about algorithms. While among mathematicians I was the one who always wanted to talk about art. I took a unique position, and I enjoyed that. But to have my work recognized in this way is truly special.’

More information

Award ceremony programme and registration for 9 july 2025 (in Dutch), Haarlem

Source, with permission: KHMW interview (in Dutch; translation: CWI)