How Do You Tell a Vandal From a Visitor? Art Museums Are Struggling.

LONDON — For Hans-Peter Wipplinger, the director of Vienna’s Leopold Museum, the last few weeks have been challenging. As climate protesters across Europe stepped up their attacks against art, Wipplinger took measures to protect his storied collection, which includes famous paintings by Gustav Klimt and Egon Schiele. Bags were banned; coats, too. The museum hired extra guards to patrol its five floors.

It didn’t work. Last week, members of a group called Last Generation walked into the museum and threw black liquid at one of Klimt’s major works, “Death and Life.” A protester had sneaked the liquid into the museum in a hot water bottle strapped to his chest, Wipplinger said.

The Klimt, protected by glass, was unharmed. But Wipplinger said his security team could only have stopped the attack by subjecting visitors to invasive body searches, “like at the airport.” He didn’t want to even consider that prospect, he added.

“If we start such procedures, the whole idea of what a museum is dies,” Wipplinger said. “A museum is a place that should always be open to the public,” adding: “We can’t stop being that.”

With the attacks showing no sign of abating, museum directors across Europe are settling into a nervous new equilibrium, fearful for the works in their care but unwilling to compromise on making visitors feel welcome. So far, nothing has been permanently damaged. But many fear that an accident, or an escalation in the protesters’ tactics, could result in a masterpiece being destroyed.

The actions, which began in Britain in June, are already increasing in frequency and daring. At first protesters glued themselves to the frames of famous paintings, but since footage of activists splattering Van Gogh’s “Sunflowers” with tomato soup spread rapidly on social media last month, masterpieces have been doused in pea soup, mashed potatoes and flour.

Those works were all protected by glass, and the protesters’ projectiles never touched an artist’s brush stroke. Yet last Friday, protesters in Paris poured orange paint directly onto a silver Charles Ray sculpture outside the Bourse de Commerce contemporary art space. (A Bourse de Commerce spokesman said the sculpture was cleaned within a few hours.)

In a statement earlier this month signed by the leaders of over 90 of the world’s largest art institutions — including Daniel H. Weiss, the chief executive of the Metropolitan Museum of Art, and Glenn D. Lowry of the Museum of Modern Art in New York — museum administrators said they were “deeply shaken” by the protesters’ “risky endangerment” of artworks. The activists “severely underestimate the fragility of these irreplaceable objects,” the statement added.

Yet few museums appear to have taken bold steps to protect their collections. Norway’s National Museum and the Barberini Museum in Potsdam, Germany, have, like the Leopold Museum, banned visitors from taking bags or jackets into their exhibition halls. Others have made no changes. In London, visitors may still carry bags around museums including the National Gallery, Tate Britain, Tate Modern and the British Museum. All four inspect bags at their entrances, but the checks are often cursory. At Tate Britain last Friday, security guards waved through several visitors without looking inside their backpacks.

Wipplinger, of the Leopold Museum, said there was little that a bag check could achieve, anyway, since items like tubes of glue were easy to conceal. “If a person wants to attack an art piece, they will find a way,” he said.

With museums reticent to act, politicians are beginning to weigh in. On Sunday, Gennaro Sangiuliano, Italy’s culture minister, said in a news release that his department was considering the actions it could take, including a requirement to cover all paintings in Italy’s museums with glass. Such a program would be expensive and museum entrance fees would rise as a result, Sangiuliano added.

Wipplinger said his teams had been protectively glazing works in its collection for decades, but couldn’t do that quickly for every remaining piece. Nonreflective glass was costly, he said: Work on a painting of moderate size — a square yard, say — could come in at around $1,000.

Robert Read, the head of art at the insurance company Hiscox, said that he was advising museum clients to put more works in their collections behind glass, but Hiscox’s policies did not require it. A contemporary art installation, for instance, simply couldn’t be glazed, he said.

And sometimes a barrier between a painting and its audience is contrary to the work’s spirit. Mabel Tapia, the deputy artistic director of the Reina Sofia museum in Madrid, said she would never allow that collection’s highlight, Picasso’s 1937 antiwar masterpiece “Guernica,” to be displayed behind glass. It was “a symbol of freedom, and of the fight against fascism,” she added.

Tapia said she had recently redeployed security guards so they could focus on high-profile works — something she commonly does at times of protest — but she felt there was little more she could do. “The only measure that would actually do something is if we closed the museum,” Tapia said, “and we’re not going to do that.” Museums are meant to be places where people meet to think about important issues, she added. “We need to keep them open.”

There was “no silver bullet” for dealing with the protests, Read, the insurer, said. Museum administrators just had to hope the protesters reminded “genteel, middle-class liberals” who took steps to avoid permanent damage, he added.

Florian Wagner, 30, the member of Last Generation who threw the black mixture at the Klimt painting in the Leopold Museum, said by phone that he knew before the protest that the work was protected by glass. He practiced the stunt five times at home, he said, and was convinced it would not disfigure the painting. “We are not trying to destroy beautiful pieces of art,” Wagner said, but to “shock people” into acting on climate change.

He wouldn’t be staging any more protests, he said, adding, “I think I’ve made my point.” But he said he was sure others in Austria and across Europe would continue. The actions would only stop, he added, once governments “act on this crisis.”

Elisabetta Povoledo contributed reporting from Rome.