How To Preserve Artworks In A Microbial World

11:44 minutes

“Incoronazione della Vergine” by Carlo Bononi, which has experienced biodegradation. Credit: Wikimedia Commons

When you go to the museum to see a popular exhibit, sometimes you have fight through the crowds to get up front to see all the details. But there’s another group also trying to get a closer look at these pieces of art.

Fungi, bacteria and lichens can grow on paintings, monuments, and other types of artwork. They feed on different pigments, oils, and canvas. In a study out this week in the journal PLOS ONE, researchers analyzed a 17th century painting and found microbes that could degrade and others that could protect the painting.

Robert Koestler, the Director of the Smithsonian’s Museum Conservation Institute (who was not a part of that study), discusses why microbes like to munch on paintings and what can be done to protect these works of art.

Further Reading

Read the study in PLOS ONE.

Segment Guests

Robert Koestler

Robert Koestler is director of the Museum Conservation Institute at the Smithsonian Institution in Suitland, Maryland.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Coming up, our picks for best science books of the year. Looking for that special gift for someone who likes to read books? Well, we want to hear what you have to suggest also. And you can tell us by calling us. You can make the call but only if you make the call, 844-724-8255. That’s 844-SCI-TALK, or tweet us @scifri. 

First, when you go to the museum to see a popular exhibit, sometimes you have to fight through the crowds, right, to get up front to see all the details. But there’s another group also scurrying around trying to get a closer look at these pieces of art. The microbes, fungi, bacteria, even lichens like to grow on paintings and monuments. And they can do damage to these artworks. 

So how do you protect a painting from these microbes? Well, you call in a biologist. And that’s my next guest. Robert Koestler is a cell biologist, director of the Smithsonian’s Museum Conservation Institute in Suitland, Maryland. Welcome to Science Friday. 

ROBERT KOESTLER: Thank you, Ira. It’s a pleasure to be here. 

IRA FLATOW: Oh, it’s nice to have you. There are microbes crawling around everywhere. Why is a painting a good habitat for these microbes? 

ROBERT KOESTLER: Well, a painting, any painting, or any surface is a great habitat. Microbes are around us all the time in spore form. And when they land on a surface, if there’s moisture there, they’ll start growing. So it sometimes happens that our paintings are too close to an outside wall, and they get condensate forming on the back of it. And the microbes land, that have already landed there, will start growing in the water. And within three or four days, you’ll get a nice little growth of a particular fungi growing on these things if you don’t, yeah– 

IRA FLATOW: No, just saying, is there a list of usual suspects that grow on the paintings and the walls? 

ROBERT KOESTLER: Oh, well, almost any fungus will grow on them. They’re so good at eating anything that you just put them on the surface, if they can– if there’s enough moisture there, they’ll start trying to figure out a way to eat it. 

IRA FLATOW: Mhm. And what shows up on the paintings in particular? 

ROBERT KOESTLER: Well, what shows up there, we had a case once of a Chumley painting that was called Autumn. It was an egg tempera on Masonite. And what happened, this was a rolling hill scene with a nice little stream in front. And from a distance, it looked like there was snow, with a light coating of snow on the hills. 

And when you got closer, it looked like a fog had rolled in on the hills. And when you got really close, you could see the fungal hyphae standing up with the fruiting bodies like little trees. It was absolutely beautiful from a biological point of view. 

IRA FLATOW: So you loved it as a biologist, but as a conservation person, you didn’t want to see that. 

ROBERT KOESTLER: Well, I was thrilled. And when the curators see me being thrilled about something, they know there’s a problem. 

IRA FLATOW: So when you say a problem, what kind of damage can these microbes due to a piece of artwork? 

ROBERT KOESTLER: Well, if you leave them long enough, they’ll start eroding some of the pigments, or some of the ground, or the gesso, or even getting onto the cotton substrate. It’ll start weakening the surface. And if you let it go long enough, years sometimes, depending on how wet it is, you’ll get the paint flaking off the surface. 

IRA FLATOW: Oh, is there special paint they like more than others? 

ROBERT KOESTLER: Well, they don’t like paints that have heavy metals in them, things like lead, copper, zinc, mercury. That tends to slow them down or stop them completely. The acrylic paints they’ll like. Egg tempera, they like because it has so much protein in it. So they’re looking for certain nutrients to keep them going, nitrogen particularly. 

IRA FLATOW: If it’s an older– the older the painting, is it more edible, delicious to the microbes because they don’t have the modern stuff in them? 

ROBERT KOESTLER: Well, the older ones tend to have the lead ground in them, so they tend to be a little bit more poisonous. But also the ones of the Old Masters that we see have been around a long time, and they’ve survived all kinds of things, usually the climate, poor climate control in churches or museums. So they’re survivors of a horrible environment and attack by microbes. 

IRA FLATOW: Are certain areas on the painting that are more susceptible? 

ROBERT KOESTLER: It all depends. Perhaps the edges would be more likely to be attacked first because moisture might get onto those first, and then it would spread from there coming in. But it all depends on where the moisture is coming from. If it’s coming through the whole back, well, the whole front surface is liable to be attacked. 

IRA FLATOW: Let me ask you more about that John Chumley painting that looked so beautiful. What was the outcome? What did you wind up doing with that painting? 

ROBERT KOESTLER: Well, what we wound up doing was that we could not put anything on the surface to kill it. There are some tricks in our tool chest, biocides, that we sometimes use. But anything we were going to put on the surface to kill the fungus would also have interacted with the paint and damaged it. 

So what we ended up doing was a technique that I developed in the museum world which was called suffocation process using argon gas. So we basically wrapped the object up in a bag, replaced the oxygen-rich air with argon, almost pure argon, and let it sit like that. And eventually, it dried out a bit. 

We put it in around 50% relative humidity so we could bring the humidity down. But the argon, the lack of oxygen stopped any growth immediately. And then we could dry the piece out over time. And that would take the moisture out and stop any future problem. So all the fungal tissue stopped growing, and some of the fungi dies under argon. And then the conservator could go in and just remove it with a Q-tip very easily– well, laboriously, but easily. 

IRA FLATOW: Wow, cheap tool. Isn’t that sort of the same thing you see at the– when you go into Washington, and you look at the preservation for the great documents of the United States, they’re all under argon– the Declaration of Independence, the Constitution, things like that. 

ROBERT KOESTLER: Right. And that’s because it’s so totally inert that we won’t get any oxidation going on there. That was the main reason for doing not so much insect or fungal control, but more for the iron gall ink wouldn’t react from– it wouldn’t oxidize in air. So it’s very nicely preserved. 

IRA FLATOW: So that’s the green glow you see. 

ROBERT KOESTLER: Well, you have to put a little charge through it. I think they have, might have [INAUDIBLE]. 

If you put a current through argon, it’ll turn out a little bit blue. 

IRA FLATOW: It turns like neon. 


IRA FLATOW: It’s glowing. Was argon always used as a preservative? Or were other gases used? 

ROBERT KOESTLER: Well, sometimes nitrogen is used. It’s cheaper, and that’s been fairly common. The reason we use argon is that it will kill fungal tissue whereas nitrogen just keeps them alive. So whenever we think we’ve got fungi there, we want to use argon. 

IRA FLATOW: What about helium or something like that? 

ROBERT KOESTLER: I’ve tried helium, but it’s very difficult to keep that into a bag. And it doesn’t– it has such a small molecule, it won’t push the oxygen out of the way. So we’ve got to get that oxygen out, and the argon does a very nice job of doing that. When you have it in a bag, the argon sinks to the bottom, and the oxygen will rise to the top when you just let it sit. 

IRA FLATOW: Oh, that’s a trick of the trade. 

ROBERT KOESTLER: And nitrogen does the opposite. Nitrogen will rise to the top, and oxygen will sink to the bottom. 

IRA FLATOW: Don’t want to do that, no. 

ROBERT KOESTLER: Right. But usually, your object’s on the bottom. 

IRA FLATOW: Details, details. I know you worked to stop an infestation of booklice in a monastery. Tell us about that. 

ROBERT KOESTLER: Oh, that was quite a fascinating one. This was the Great Lavra Monastery in the Halkidiki Peninsula in Greece, closest to the Bosphorus. And it was somebody sent me some insects to identify. When I was at the Metropolitan Museum of Art, I not only did fungi, but I did insect control. So I looked at these and said, well, these are booklice, OK. But booklice, what are they doing on a book that’s in a library? They’re supposed to be eating fungi. So why do they have them on their books? 

So they brought me over to take a look at this. And it was a fascinating experience because it took about 24 hours to get there in different forms of transportation, the last being a boat, to the– they call it an island, but it’s a peninsula, and then a Jeep driven by a monk over these rough roads, until the middle of the night I arrived at this monastery. 

And I was expecting the Western kind of monastery, something from Umberto Eco, The Name of the Rose. I had this vision in my head about Western medieval kind of structures. And this was so different. It was Byzantine. The courtyard was a rough stone with grass between it. And most of the structures had a rounded dome on it. It was very, very pretty, very different than what I expected. 

And there were about a dozen or two dozen monks in is very giant structure. The Great Lavra Monastery was built and it started in the 10th century. It’s the oldest monastery on the peninsula, right under the Mount Athos mountain. And when I got there, I found these about 2,000 rare books they had in a 19th-century building. And the building was sort of a U-shaped structure. One side had a rare book. The other side had their pieces of very– books [INAUDIBLE] that they had when they first started at the monastery. 

But at any rate, as I looked at this, there were some– the books had all been put into cloth covers, and the Greek conservators had written on the outside in Greek– Greek to me, and Greek to them– what the condition of the manuscripts were, whether they needed conservation, and so on. And then they put them on shelves against a wall. 

And I realized the walls were the outside walls of the building. And as I looked at the outside of the building, there were no gutters and leaders on the building. So the water was running, from rain, would run down the side of the building, wick up the wall, seep into the inside, and get onto these cotton cloth covers, soak into the books, and then stain the edges of the books with water, and fungus would start growing on the books. 


ROBERT KOESTLER: So we’d open them up and take a look, and you’d have maybe 2- or 3-inch section all around the books covered with fungi. And that’s what the book lice were eating. So the whole problem was water. When you look at what causes– why were these book lice here? You go back to, well, if we just put gutters and leaders on this building and get the water away from the building, we’ll solve our complete problem. 

IRA FLATOW: And did they? 

ROBERT KOESTLER: And it did, yeah, yeah. I ended up treating a few of these with argon again, a favorite thing, just to show them how to do it just to stop the fungal growth immediately. 

IRA FLATOW: So you’re like a detective then. You have to figure– 

ROBERT KOESTLER: Well, we do. It is. We always want to know the cause when we see a problem. We’ve got to look at, well, it’s not enough just to treat the symptom, like a physician. We look at the same thing. They want to know why. They see the symptoms. They wonder what the real cause is. And once we know the cause, we can say, well, how– we have to change that cause because if we solve the immediate problem, we put it back in the same environment, we’ll get the same problem again. 

IRA FLATOW: Wow. It sounds like you have an interesting job there. 

ROBERT KOESTLER: It’s been very fascinating. Yeah, it led me to go around the world a few times. 

IRA FLATOW: And we need more people like you because things are getting old all the time, aren’t they? 



IRA FLATOW: Abso– I can vouch for that. Thank you, Dr. Koestler. 

ROBERT KOESTLER: Yeah, you’re welcome. 

IRA FLATOW: Robert Koestler is director of the Smithsonian’s Museum Conservation Institute in Suitland, Maryland, right over the border from DC.

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