Finding The Culprit For Van Gogh’s Darkening Yellows

The Sunflower still-life series is possibly Vincent van Gogh’s most famous work. Unfortunately the warm yellow hues that make the paintings memorable come from pigments that don’t have a long life-expectancy. During the 19th century, chrome yellow pigments came in to fashion among painters and then quickly went out again, as artists realized that the vibrant yellow color was unstable and would lose its vibrancy when exposed to light. For example, Claude Monet and Pierre-Auguste Renoir both steered clear of the chrome yellow pigments. But van Gogh threw caution to the wind and continued to use chrome yellow until his suicide in 1890—a tragic hint, perhaps, of his own instability and imminent breakdown. This week, conservation scientists at the Van Gogh Museum in Amsterdam have been taking a closer look at chrome yellow pigments in Vase with Sunflower, and a few other paintings, to learn more about the degradation problem. The museum’s staff has recruited a group of traveling conservation scientists from Perugia, Italy, called MOLAB to come help out. (MOLAB has a sophisticated collection of analytical equipment that can study artwork without harming it.) It’s not the first time MOLAB has worked on the chrome yellow issue. Last year, they worked with almost the same team of van Gogh experts to discover why chrome yellow turns from bright yellow to a dingy brown in the presence of sunlight. Here’s why: Chrome yellow pigment is primarily lead chromate (which, incidentally, is the pigment for yellow school buses and was also briefly used to color candy in the 1800s—yikes!). Different yellow hues can be made by mixing in lead chromate oxide and lead chromate sulfate. The darkening of the yellow paint occurs because the chromium in the pigment is reduced from a hexavalent (Cr6+) to a tetravalent (Cr3+) state. The team also reported that sulfur compounds in the paint seem to exacerbate the process. The sulfur is probably present from lead chromate sulfate added to modulate the yellow hue. MOLAB has been back in Amsterdam this week to study more van Gogh paintings, says Costanza Miliani, a lead researcher with MOLAB. The plan is to see if sulfur is indeed a culprit in chrome yellow degradation. Hopefully the team will eventually find a way to thwart and reverse this breakdown so that van Gogh’s vibrant yellows aren’t lost...

Read More

Rare Aztec Document Gets A Check-Up

In 1521, the Aztec capital of Tenochtitlan fell to the Spanish invaders, who burned libraries and destroyed most of the manuscripts pertaining to Aztec history, religious rituals and economy. The Codex Fejérváry-Mayer is one of just two dozen or so Aztec texts to survive the Spanish invasion. It’s also just one of just six screenfold books that were penned before Cortez started his conquest of Mexico’s indigenous people. So suffice to say that it’s a pretty exceptional record of the pre-Spanish Mesoamerican world. This codex is called a screenfold book because Aztec scholars would literally twist and fold the 22-page, double-sided document to cross-reference a particular date to two calendar cycles: the yearly cycle of 365 days and the sacred cycle of 260 days (called tonalpohualli). Joanna Ostapkowicz, a curator at the World Museum in Liverpool, which hosts Codex Fejérváry-Mayer, explains it in this way: “In the hands of ritual practitioners and other high-ranking individuals, the codex became a guide for people’s actions. The screenfold’s internal reading structure is right to left and is determined by the number-and-sign sets of the calendar: how the images and symbols cross-referenced each other was then interpreted by the reader, who was well versed in the significance of the various icons. Although an object of great respect, the codex was also a tactile, malleable reference tool: a user could consult both sides simultaneously by folding parts of the codex onto itself. Reading it offered guidance on appropriate days to travel, to celebrate a deity’s beneficence with sacrifices, to plant crops or to name a child.” These days the codex is not twisted and folded as it once was. In fact, it doesn’t get handled much at all due to the animal-skin document’s fragility and worth. When Mesoamerican experts want to study the codex, they typically have to rely on photographs, Ostapkowicz notes. A very rare exception was made a few weeks ago when MOLAB, a nomadic team of conservation scientists from Italy, drove up to Liverpool to help museum staff study the pigments, dyes and binders used to make the codex. The MOLAB team has a battery of snazzy equipment that can study fragile artwork without taking a sample of it—in the same way that an X-ray, ultrasound or MRI can give doctors insight about what’s going on inside a patient without invasive surgery or removal of a blood sample. In the case of the codex, the analytical equipment used by the scientists relies on X-rays and infrared light to diagnose the document’s inner make-up. I’m really looking forward to what the researchers find, once all the data is analyzed. As Ostapkowicz puts it,...

Read More

Think You Can Identify A Van Eyck?

Many art historians have eyed Three Maries At The Tomb and agreed that it’s a Van Eyck. What’s debated is whether Jan painted the artwork or whether it was his older brother Hubert. Or more likely, whether the painting was a sibling collaboration. For example, the brothers both worked on the famous Ghent Altarpiece: An inscription on the back says it was started by Hubert and finished by Jan, six years after Hubert’s death. However, art historians debate which brother had a greater influence on the paintings in the Ghent Altarpiece. Did Jan humbly follow his older brother’s stylistic lead or did Jan turn the artwork into a masterpiece with his own artistic flair? These sorts of questions also arise with Three Maries At The Tomb. There’s a good chance it was also a brotherly collaboration: Art historians note that Three Maries At The Tomb is stylistically similar to a painting in the Ghent Altarpiece called Adoration of the Mystic Lamb. Furthermore, experiments to date Three Maries At The Tomb’s wood backing suggest the artwork was made sometime after 1419, which is before Hubert died in 1426. This week, science will weigh in further on the sibling teamwork. Conservators at the Museum Boijmans Van Beuningen in Rotterdam are currently preparing Three Maries At The Tomb for an exhibit later this year. During this process, they requested the services of MOLAB, the traveling group of conservation scientists from Perugia, Italy. (MOLAB is funded by the European Union to help museums do scientific research on art, with equipment they might not otherwise be able to afford. Before Rotterdam, MOLAB was just in Gdańsk, Poland, where they were working on some Memling paintings at the National Museum.) MOLAB scientists will use all sorts of snazzy, non-invasive equipment to image the artwork’s surface and interior in 3D. They will also use X-rays and infrared light to study the painting’s pigment chemistry. Museum researchers will then compare this data with previous results from experiments on the Ghent Altarpiece paintings. These investigations may help museum researchers eventually figure out who did what on the collaborative paintings—not just Jan or Hubert, but also other artists and conservators who retouched the painting over its several centuries of life. If you want to do your own (visual) examinations of Three Maries At The Tomb, check out the Road To Van Eyck exhibit in Rotterdam later this...

Read More

Vincent Van Gogh’s Last Months

In the last year of Vincent van Gogh’s life, as his mental illness escalated and before his suicide in 1890, the Dutch impressionist painter voluntarily committed himself in to two French hospitals. The isolation didn’t thwart van Gogh’s productivity–he painted some 200 paintings during the 15 months he spent in treatment. Nor did the isolation prevent him from experimenting with trendy new pigments bequeathed by the industrial revolution, such as chrome yellow, which he used to paint his famous sunflower series. This pigment fell out of favor by the 1950s when its lead and chromate make-up was found to be toxic. Unfortunately, chrome yellow and other then-trendy pigments degrade if they are exposed to light. For example, the degradation turns the bright yellow pigment into a rather sad looking green color. Earlier this year Koen Janssens, at the University of Antwerp, in Belgium, explained the chemistry behind this degradation, by using X-ray spectroscopy to show that when the chromium in the yellow paint was subjected to too much light, it went from a hexavalent state to a trivalent state. Many media outlets reported on the discovery, including C&EN and Newscientist. Now Janssens has turned his attention to the so-called red lake pigments that van Gogh used in paintings during the 15 months of his life. Janssens recruited the help of MOLAB, a group of roaming scientists who travel around Europe with high tech, portable equipment. Their gear can help him study light degradation of the valuable art without harming it. Last week, the MOLAB team, aka CHARISMA, drove 1500km from Perugia, Italy, to the Kröller-Müller Museum, in Otterlo, in the Netherlands. The Kröller-Müller has 22 paintings from van Gogh’s last months of life, and with the help of the mobile lab, the researchers can study the red pigment degradation without moving or harming the artwork. Hopefully the new research will clarify the chemistry of the paint breakdown so that further degradation of van Gogh’s work can be avoided. I can’t help thinking about the tragic irony of it all… that as van Gogh’s mental health was rapidly deteriorating, he was expressing himself using paint that was itself...

Read More

Up Some Scaffolding, En Route To Heaven

During most of my visits to Italy, I end up with neck cramps after craning my head backward for hours to look at faraway ceiling frescoes in churches across the country. But last week, I found myself peering directly into the eyes of fresco angels at the top of the Capella Maggiore in Florence’s famous Santa Croce Basilica. These frescoes have been under restoration since 2005 and for the next few months small groups of people can climb the scaffolding to view the artwork up close. The frescoes were painted in the 1380s by Agnolo Gaddi, a disciple of Giotto, one of the architects of the Italian Renaissance. I climbed up the scaffolding with Mariarosa Lanfranchi, a restorer from the Opificio delle Pietre Dure, Italy’s foremost restoration laboratory. She’s been leading the fresco restoration project. One of the first questions she asked me is whether I suffer from vertigo, because we would be going up about 30 meters to reach the very top of the cathedral. Assured that I wouldn’t suffer a panic attack, she began her awesome tour by telling me that the last restoration of part of the church’s frescoes was in the 1930 or 40s. Since then, air pollution has coated the art with a layer of brownish grime. Meanwhile, construction around the city has covered the artwork with little chunks of gypsum dust. The frescoes are porous, and with the city’s high humidity, the gypsum penetrated into the frescoes, giving the artwork a rather speckled look, Lanfranchi explained. To remove the grime and gypsum, the restorers used the “Florentine method,” a combination treatment of ammonium carbonate, followed by a treatment of barium hydroxide, Lanfranchi said. The first step of adding the ammonium carbonate dissolves the unwelcome dust and gypsum (calcium sulfate dihydrate) so that both can be removed from the surface and inside the fresco’s pores. But this first step of the cleaning process also has a downside. It produces some ammonium sulfate, a salt that could be problematic to the frescoes in the future. So the second step of the Florentine method is to add barium hydroxide which turns the problematic ammonium sulfate salt into barium sulfate, which is benign to the artwork. The second step also produces some barium carbonate, which acts as a stabilizing agent (called a consolidant) to the sensitive frescoes. With more than 800 meters squared of fresco surface to restore, Lanfranchi said the scaffolding became like “a second home” to her over the past years. As we walked around the scaffolding she pointed out small details in the frescoes–a bird or an angel or a crack–with the same familiarity...

Read More