Professor Paul Bellendorf, Institute of Archaeological Sciences, Monument Sciences and Art History, University of Bamberg, Germany, focuses on the intersection of cultural heritage and climate change. Dr. Vera Koester spoke with him for ChemistryViews about the work of a building preservation scientist, the effects of climate change on old buildings, and how he came to his field from materials science.
Can you say a bit about your work? How do you uncover the problems you deal with? How do you determine the phenomena that are affecting a particular building?
The problems find us. It is the other way around.
Unfortunately, there is no direct English translation of our German subject, Restaurierungswissenschaften, so we call it building preservation science. Our work is in the field of heritage sciences. So we are looking mainly at buildings. Our questions concern, for example, the historic condition of a building, the historic inventory, such as a painting on the wall or the mortar that was used to create the building, and all the materials related to our research. We work with almost any material in the building’s composition.
As part of this, we look at everything that has happened to the building during the time from when it was built until today. So this involves not only the materials themselves, but also the deterioration processes, the preservation materials that were used in the past, and all the other factors that have affected the building, such as its environment. For example, the SO2 concentration, which was very high in the past, had an effect on buildings.
It sounds like you need a huge amount of knowledge about many different materials and historical conditions and so on. How do you manage that? Do you work in an interdisciplinary team or do you know a little bit about everything?
We know a little bit about everything and all of our projects are interdisciplinary. Because for us it’s not only the building and the knowledge about the materials that are important but also its history. So we work with historians and art historians all the time. And then, of course, we also have a background in chemistry and materials science.
It’s like solving a puzzle with many pieces, and at the end we hopefully have more information about the building and the history of the object. A bit like the work that a detective does.
Since we are dealing with historic buildings and unique objects, our main problem is that our samples are extremely small. We usually have only one attempt to perform an analysis, and then we have to deal with the information we got from a very tiny sample. That’s a challenge. Also, we can’t use many different analytical methods. That makes the work very challenging as well. At the same time, it makes it very interesting because each sample and each building is unique. We don’t do anything like large-scale screening, so we don’t do 2000 samples a month and check the composition of that.
So instead of large-scale screening it’s more like detective work to figure out what’s going on?
Yes, it is. Soon we will have a new professorship in the application of what we call forensic building preservation science. We work very closely with the tools and approaches that are used in detective work, so we share some similarities with that field — but generally there’s not as much blood involved.
Ah, okay, that makes it much nicer.
You studied materials science. When you started, was it already clear where your path would lead, or was it a decision that developed over the course of your studies?
As a child, I imagined studying archaeology or something like that. So I had a personal interest in history. After graduating from high school, the question was what I should study. Everybody said that if you study archaeology, you have to be very good with old languages, and I am not good at languages. So I decided to study materials science. I think it is a very interesting subject. Actually, it’s a mixture of different subjects: It’s physics, it’s math, it’s chemistry, and all these things combined with a main focus on the material. When I finished my materials science studies, I said, okay, I don’t want to spend the rest of my life working in quality assurance or something like that. I went back to my original field of interest and I did a master’s degree in heritage sciences. In a way, it was like going back to my original childhood idea.
Lots of your work today concentrates on climate change and how it affects buildings. What are the challenges there?
It’s a new subject that we started when I came to Bamberg two years ago. Climate change is everywhere and, of course, it also affects our buildings. For us, the question was what will happen to our buildings when we change the climate, when we change the temperature and especially the humidity. Climate change and its impact on cultural heritage is already a problem today in historic gardens and parks, for example. It is getting drier; the trees need more water and are dying. In some cases, you’re not able to plant the original kind of trees or plants because it’s too dry in the summer months. These same processes also affect our locations and their inventory.
In the project we are running at the moment, for example, we’re looking at the effects on indoor climate conditions. The indoor climate is, of course, influenced by the outdoor climate. In Saxony-Anhalt in particular, we have had a problem with very dry summers three years in a row. Now the question is how the inventory in the buildings is influenced by this dryness. We have a change in humidity, which becomes especially problematic with hydroscopic materials like wood and other organic materials. If you take a piece of wood and you dry it, it gets smaller, it gets cracks, and when you put water on it again, the cracks are still there. So we have permanent damage and a long-term problem here. Our vision is to find solutions that avoid these damages to historic materials.
Is that possible?
Definitely, because of climate-change predictions. We know from calculations that the climate in Central Europe will change within the next 50 or 100 years. Of course, these are forecasts, so we don’t know exactly how things will develop. But if it is calculated that humidity will drop, we need to take some preventive measures to avoid lowering the humidity inside certain buildings. A very simple approach might be to not open the doors and the windows in churches when it is dry outside.
This sounds very easy and clever, but you need to understand the process behind it and pass the information on to the people responsible for opening and closing the doors of a church. To illustrate this for you with an example: In the spring, like now, it gets warmer in Germany. If you have a cold cellar and open the window, warm air, which can hold more water than cold air, comes into the cellar. It mixes with the cold air in the basement and can no longer hold all the water. As a result, you have the water on the cold wall and then you get mold in the basement. This is a very simple process that we know from our daily life.
Buildings and churches have always experienced these changes in temperature and humidity because we have summer and winter months. Currently, we only have data on these processes from the spring and autumn; there is still no awareness of this problem in the summer months. It is necessary to get more information about it.
The problem lies in the extreme changes in temperature and humidity, and these changes are getting larger. At the same time, buildings are getting older. So I can imagine that there are more and more things to repair. Is there a limit at some point where we have to say that we won’t be able to maintain some things?
Maintaining buildings is always a question of money. You need money to renovate your building, to refit it, or to keep it up to date so that you can use the building.
For the problem we discussed earlier regarding low humidity in a church, there is a very simple solution: Install a system that evaporates water – an air conditioner to heat, cool, humidify, and dry the interior. But all four of these processes need energy, and until we have solutions to get it 100 % from renewable energy sources, we are reinforcing the process of climate change. So it’s a cycle.
In terms of cultural heritage, we encounter these problems not only with historic buildings but also, for example, with museums. Museums are often air conditioned. Here another big issue is how we can build a green museum and at the same time comply with the very strict environmental conditions you need in many museums. So, overall, there are many challenges in the field of building preservation science, because we cannot put a big glass dome around our historic buildings. Of course, the buildings must be in the environment and must interact with the environment. These issues don’t always have a great deal to do with chemistry.
They are, however, related to the whole problem of climate change and the sustainable development goals (SDGs) of the United Nations. I think it’s interesting to see how you are coping with them.
We could hold an entire discussion on SDGs and cultural heritage. There is one SDG that is addressing the field of cultural heritage. Section 11.4 lays out more efforts for preserving the world’s cultural and natural heritage.
We are very pleased that our field is named within the SDGs. That means we can go to the politicians and say: Look here, according to the SDGs, we are tasked with doing more about this.
The SDGs, for example, say you should use your materials for as long as possible and in the best way possible. This is what we are doing in cultural heritage. The materials have been there for hundreds of years, not just for 30 years. We use the materials in the best way, too, because we avoid waste by preserving our buildings. We do not need raw materials to build new locations. We need fewer materials for restoration or maintenance.
We are not good in saving energy, though. We have a problem there. Many of the older building exteriors are not built for energy efficiency.
Yes, and if you need air conditioning or something, then this energy problem you just mentioned arises again. But, coming back to climate change, I guess its effects on the outside of the building must be an even worse problem than inside?
It depends on the materials. The more sensitive materials, the hygroscopic ones, are more often found inside. If you have a stone wall, for example, that is not so problematic if you have higher temperatures and more rain. Of course, it does have some influence, but if you have a thick stone wall there isn’t as much influence as if you have a wooden exterior or if you have a painting on a wall within a church or an altarpiece. In that case, you might have very thin wood pieces with a painting on them, and you might have a layer of paint and maybe a second layer of paint. If you were to have any movement among these elements, it would influence the painting on the surface. This means these problems are more important inside than outside. Naturally, you will have problems outside, but the damage happens more quickly on the inside.
Another thing is evident if you look at the structure of a building. You have the basement and the foundation. Normally you have a certain water level within your soil. If this changes, such as getting drier, it’s possible that problems will develop in the structure of the building. Or if you have some wooden piles in the ground and the building is situated on them, this is normally done with a constant level of water so you have a stable system. But if it gets drier, the system may become unstable. This is a problem not just for the exterior but for the whole structure.
Data on climate change and cultural heritage in Germany in relation to the last three dry and very warm years is currently being evaluated. It is still too early to say anything more precise on its effects.
So would you say that these additional problems because of climate change are becoming increasingly important compared to other issues you had to deal with in previous years?
The problems are changing. In the past we had mainly to deal with huge amounts of SO2 that were emitted into the air and that had an effect on the exterior surfaces of buildings. Some examples are chips and crusts on historical glass windows.
Today it has changed to other pollutants. We are aware of NOx and things like that, but as far as we know these pollutants are not affecting our cultural heritage objects as much as those in the past. There is an influence, but we don’t know it in detail because there no research has been done on it so far. But the problems due to climate change will probably be greater in the future.
Are you able to learn from other countries where the climate might have been different but perhaps buildings were built around the same time and with the same construction methods?
There are hardly any research projects on climate change and cultural heritage. There was an EU project with German participation, and we do learn from our partners, but there is still too little exchange. Recently a larger project has been started by Fraunhofer.
Let us come back to chemistry. You said that there is only a limited number of analytical methods you can use. Can you say more about your methods?
For us most of the time the question is: What are the materials for a paint layer? There are two parts, a pigment that provides the color and a binding material. We have to deal with these two components. So in most cases we have an inorganic part and an organic part in a mixture in a very tiny sample, and the location owner wants to avoid giving samples to the lab. They really like to have non-invasive testing systems on location so that they don’t have to give out samples.
Of course, we have techniques with which we can analyze the object directly, such as portable Raman and portable Fourier transform infrared (FTIR) spectrometers. The problem with all these techniques is that we only analyze the surface. There are currently some tests with laser ablation in a mobile version where you burn a hole in the surface to get below the surface. For us, this means that if you really want to analyze the different layers of paint you have to take a sample and then you have to take it to the laboratory.
The first step is to understand the sample: which side is outside, which is inside, or which is the newest area and which is the oldest one. For this purpose, we examine the sample by means of light microscopy either with normal light or with UV light. Once we understand our sample, we go to the scanning electron microscope with EDX energy-dispersion spectroscopy and perform an elemental analysis on the sample. To investigate the organic part, we perform an FTIR spectroscopy examination.
For the binding media, we use a combination of thermogravimetric analysis (TGA), IR spectroscopy, and GC-MS. We started this for analyzing the binding materials. These are natural products, often a mixture of different natural products, and if you’re analyzing them using normal infrared spectroscopy you get a combination of curves you can’t separate easily. So we use TGA to separate the samples and analyze the different parts of the sample.
If we have other questions, we have to go to other labs to do X-ray diffraction (XRD), for example, if you want information about a corrosion product.
Are these the same labs that analyze, for example, paintings for museums?
Yes, we normally go to a laboratory that also deals with cultural heritage analyses because they have the relevant libraries. It doesn’t make sense to go to a 24/7 laboratory because they usually don’t have the databases and the information about the specific corrosion products that we deal with.
What is the biggest challenge in the analyses?
The biggest challenge for us is always the organic compounds because, for example, in Germany in the field of cultural heritage, we don’t have many laboratories that deal with the organic part. Nobody wants to deal with it because organic compounds are so complex. So we are very happy that we will have a new professorship to study the organic materials here in Bamberg.
And what is the most exciting part of your job?
The most exciting part for me is working with cultural heritage objects. Really, the difference between studying materials science and the heritage science I studied after that is working with objects that have a history. For me, I wasn’t interested in whether this piece of metal is able to cut a kilometer of wood or two kilometers of wood. For me, the story of the wood itself is much more interesting. We have objects with a history, and we need a detective, as we said earlier, to gather all the information and combine it with that from the humanities and the other disciplines to form the big picture of our history and how an object has changed.
How long does one of these investigations normally take?
It depends on the investigation. When we do a research project, we have up to several years to do the research and to go into more and more detail. We also have requests from the affiliated institutes, where archaeologists come and ask if we can analyze a few samples or if we can contribute some information. For those queries, the time is shorter.
When there is a restoration campaign or a conservation campaign on a wall painting and we are asked to provide information during the process, it takes maybe a week or two to get the information for the restorers.
It is important to understand that we work as a team. We are chemists, material scientists, and geologists with a special curiosity for the minute details. And for us, it is really a problem that there are too few young scientists who are interested in chemistry and history.
Maybe they exist but don’t realize that they could go into that field or that it offers possibilities for chemists!
Thank you for the interview and the exciting insights into your field.
Paul Bellendorf studied materials science at Friedrich-Alexander University in Erlangen-Nuremberg, Germany, and subsequently “Denkmalpflege – Heritage Conservation” (Monument Conservation – Heritage Conservation) at Otto-Friedrich University in Bamberg, Germany. In 2007, he received his Ph.D. there for an interdisciplinary study on the heritage of monuments and their endangerment by environmental influences on metal tombstones from Franconia and Thuringia from the 15th to the 18th centuries. From 2006 to 2009, he was a research associate at Otto-Friedrich-University Bamberg. From 2009 to 2012, he was head of the Environmental Monitoring and Cultural Property Protection department at the Fraunhofer-Institute for Silicate Research in Würzburg, branch office Bronnbach, Germany. And from 2012 to 2018, he was head of the Environment and Cultural Property department at Deutschen Bundesstiftung Umwelt (German Federal Foundation for the Environment).
Since 2018, he has been professor of building preservation science at Otto-Friedrich-University in Bamberg.