IRA FLATOW: This is Science Friday. I’m Ira Flatow. In 1888, Vincent van Gogh– or “Van Go,” depending on how you like to pronounce it– in either case, he dashed off a letter to his brother Theo. He described a painting he was working on. His tiny bedroom in France was the subject. “Looking at the painting should rest the mind, or rather the imagination,” he told Theo.

Arguably, that painting might be the most famous bedroom in art, with its sky-blue walls, its yellow chairs and red blanket. Van Gogh’s bedroom is beloved by art fans. In fact, van Gogh himself loved the first bedroom painting so much, he painted it two more times. Since his death, van Gogh’s three bedrooms have been scattered in museums across the globe. But last month, they were reunited in a show at Chicago’s Art Institute.

It’s a big moment for van Gogh fans and for science, because by bringing van Gogh’s bedrooms together, museum scientists made a startling discovery. Those blue walls are not so blue after all. My next guest helped solve this art history mystery. Francesca Casadio is the Andrew W. Mellon senior conservation scientist at the Art Institute in Chicago. Welcome back to Science Friday.

FRANCESCA CASADIO: Thank you, Ira. It’s a pleasure to be here.

IRA FLATOW: And we’re going to be tweeting out paintings as we’re talking. So if you want to follow along and see some pictures– you can’t see them on the radio, but we’re going to tweet them at SciFri and you can get an idea. How can a painting change after it’s gone up on the wall like that?

FRANCESCA CASADIO: Well, we hardly put art and science together. But there’s actually a lot of chemistry happening as soon as the paint leaves the brush. And so there’s constant change, like there is change and shifting in own bodies as we age. And some pigments in particular, we are finding, are changing colors more quickly than other, especially due to the effect of light and humidity.

And this is because when you enter into a museum, we keep temperature and humidity and light very controlled, because we know those are factors that can accelerate that shifting.

IRA FLATOW: Let’s get a sense of what the bedroom looks like a little bit more. We’re tweeting this painting out right now, and it’s on our website so people can follow along. Unless you’re driving– we don’t want you to do that. If you were to visit van Gogh’s bedroom painting today, what would you see, Francesca?

FRANCESCA CASADIO: Well, first of all, people visiting Chicago can actually try to snatch one stay in Airbnb because we have recreated this painting in an apartment in the Chicago neighborhood. But in any case, what I would see is a very small room, but with very, as you described in van Gogh’s own words, very brightly painted furniture. The yellow chairs and the bedstands and the floors are pink and green hues.

And the window frame is a bright green, as was very typical both in France and in my home country, Italy. And there are paintings on the wall because of course, van Gogh also feverishly decorated this room for himself and for the community of artists that he was hoping to attract to the south of France. There’s a lot of excitement in his description of the bedroom and this sentiment is transpiring also in the depiction of the bedroom itself.

IRA FLATOW: So what was your first clue that these bedroom walls weren’t always so blue?

FRANCESCA CASADIO: Well, the first clue was actually given to us not only by our curator, of Gloria Groom, who curated the exhibition, but by van Gogh self, because you read the description as you have, Ira, and it says the bedspread is red, the window green. The walls are lilac. The doors are purple. And you’re like, wait a minute. The walls and doors are no longer lilac and purple. And the floor doesn’t look the broken, faded, red tiles that he’s describing.

And because science and technology have evolved so much these days, and in the past 10 years, we’ve become more attuned to the fact that these pigments can change and we now can measure the change and we can identify those fading pigments, we immediately set out to try to answer these questions– were the walls of the Chicago painting painted in a different color and it’s no longer purple, or is there something going on here? So it was a wonderful detective-type work that we were allowed to do on this iconic masterpiece.

IRA FLATOW: Let’s talk about some of that detective work. I know that one of these tools you use looks sort of like a blaster gun from Star Trek.

FRANCESCA CASADIO: Absolutely. Well, we use a gun-like instrument that emits x-rays. And it’s a way of getting information about the pigments without having to touch the surface or remove even the smallest amount of material. And actually, this technology was developed to go on the Mars Rover originally, to do exploration in space.

And we can use it for our art because it basically allows us to identify the atoms that make these pigments, if they are derived from minerals, from what we call inorganic sources. And so this gave us a little bit of a time machine to go back and understand what colors van Gogh put on his palette, but yet didn’t answer completely the question about what made the purple.

And this is because in general, these purples and pinks were made from natural sources like insects and plants or from the booming chemical industries of the 19th century that produced so many new pigments. And the Impressionists and those artists of the times embraced them. And so that required some extra efforts beyond using x-ray fluorescence, this kind of elemental fingerprinting using x-rays.

IRA FLATOW: You did take a tiny paint chip from the painting, right? And that was sort of the smoking gun?

FRANCESCA CASADIO: Absolutely. We used scalpels, like surgical scalpels, and under a microscope with a very steady hand. You don’t want to have had too much caffeine that day. We removed a sample that is no bigger area than a dot on a printed page. And my colleague Inga Fiedler, who’s been a research microscopist with the museum for the longest time, called us up. She mounted this fragment on a microscope slide.

And then we were all huddling around the microscope, because when you looked at the surface of the sample, it was light blue. But when she flipped it over, exposing the bottom part of this paint layer which had not been exposed to light, it was purple. And you could see all of these pink particles that had been preserved because they had not been directly exposed to light.

IRA FLATOW: We asked our audience on Twitter which version of the painting they liked better. We got 2,600 votes. And 55% of the people liked the re-colored purple version. Does that surprise you?

FRANCESCA CASADIO: That’s good news. Well, I think that we’re excited that we are able, through science and the letters and conservation and art history to propose this new visualization of what the painting looked like. And this, people should realize is really an expression of van Gogh’s emotional state. Because we know from art historical research that our colleagues have done that the walls of the bedroom where whitewashed.

So he very deliberately picks these colors also because he was interested in the effects of putting together a purple with a yellow, these complementary colors that make then enhance the strength of the image. I can quote him saying, “I want to make simplicity with bright colors.” And so it’s exciting that today with chemistry and science and conservation, we can propose this visualization.

But we also only have to understand that we’re part of a continuum of the history of this painting. And so we don’t want to say one version is better than the other. It’s just getting closer to the E.T. moment of connection, of human connection with something that resonates with so many of us. So it’s great that you got so many responses.

IRA FLATOW: Well, I should’ve mentioned that we made a digital version of the van Gogh– you made it– of a van Gogh’s bedroom painting and showing what it might it looked like when he painted it. And we put that up on our website and it’s still there at ScienceFriday.com/vangogh. And that’s where people can actually see the difference.

And we also tweeted out the paint chip and you can see it as it flashes back and forth. It looks blue on one side and it looks purple on the other side. Why did the purple fade? Did van Gogh– did he know that the paints– were they cheap paints because he couldn’t afford better, or was that just the state of the art of the day?

FRANCESCA CASADIO: Well, this is a myth that we’re very happy as museum scientists to be able to dispel. Because some of these pink colors, we can go back to 19th century catalogs of color makers. And they were as expensive as other colors. But certainly, at the time when van Gogh painted. He was aware that some of these colors would lose their strength. And in fact he says, paintings fade like flowers.

And but still, he thought that if he painted them boldly, they would maybe be toned down. And this was a sentiment shared by many of his peers– Renoir, also we have quotes from him. I don’t think that they were aware that, especially when mixed with other pigments and if exposed to regular, unfiltered light, these pinks and purples could completely vanish.

IRA FLATOW: And this is really interesting, because this is going to be on exhibit. And you’re in Chicago. And you can see the paintings, van Gogh’s bedroom paintings in the flesh. They’re on view at the Art Institute in Chicago through May 10th. I wish I was in Chicago to see this. You see these three paintings, all together in one place.

FRANCESCA CASADIO: It’s really the opportunity of a lifetime, Ira. I don’t think that for the next two centuries, this will be possible. And what is exciting really of this presentation that Gloria Groom has done that we want to share with the public who comes to Chicago and will come to Chicago, is to be able to see the three bedroom paintings altogether.

And then you turn your head slightly and you can see an immersive digital experience that will give you a sense of the physicality of van Gogh’s brush strokes. And then we have a very comprehensive video that explains this behind the scene exploration. So it’s really a very, very exciting.

IRA FLATOW: I wish I were there. Thank you for taking time to talk to us about it, Francesca. Have a good weekend.

FRANCESCA CASADIO: Thanks to you, Ira.

IRA FLATOW: And good luck with that exhibit. Francesca Casadio is a senior conservation scientist at the Art Institute of Chicago. And you can see the bedroom paintings, what they might have looked like in 1889 at ScienceFriday.com/vangogh if you can’t make it to the museum.

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