LONDON—British authorities are searching for a man who took responsibility for defacing a valuable Mark Rothko canvas with black paint at the Tate Modern museum on Sunday afternoon.

The man walked up to one of Rothko's murals—an untitled 1958 painting often referred to as "Black on Maroon"—and tagged it with the words: "Vladimir Umanets '12, a potential piece of yellowism." The vandal then quickly left the building.

The incident was witnessed by Tim Wright, a 23-year-old marketing executive from Bristol, England, who said he "turned around and heard this scratching sound," only to see a young man finishing his letters on the Rothko painting.

"It was all very surreal," Mr. Wright said. "One minute he was sat down, and the next he had climbed over a little barrier and was knelt down doing his tag." Mr. Wright snapped a picture of the defaced painting—marked with the black letters in the bottom corner— and uploaded it to Twitter.

Vladimir Umanets, an artist working in London who has published a "Manifesto of Yellowism," claimed in several British media outlets on Monday, including ITV and the Guardian and Evening Standard newspapers, that he had defaced the painting, describing his act as art. Mr. Umanets told the Guardian that the incident would increase the value of the Rothko canvas.

"I don't want to spend a few months, even a few weeks, in jail." Mr. Umanets told ITV News. "But I do strongly believe in what I am doing, I have dedicated my life to this."

Mr. Umanets declined to comment to The Wall Street Journal.

A spokesman for the Metropolitan Police said authorities are looking for a suspect described as a white man in his 20s and have taken note of reports in the British media naming the alleged suspect.

Rothko, a Russian-American painter known for his abstract color fields, painted the murals in the late 1950s for the Four Seasons restaurant in New York's Seagram Building. The artist's decision to accept the commission was subversive, according to a Harper's Magazine piece by the late editor John Fischer, who famously recounted Rothko's hope that the art would "ruin the appetite of every son of a b— who ever eats in that room."

The paintings were never exhibited in the New York restaurant because Rothko decided to keep them. He gave a set of the now-famous murals to the Tate in 1969, just before he committed suicide.

The murals are an important part of Rothko's oeuvre because they mark the first time he created multiple paintings designed to surround the viewer, according to David Anfam, a Rothko expert and commissioning editor of fine art at British publisher Phaidon. Mr. Anfam says he thinks conservators will be able to repair the Tate's damaged canvas, which he says is likely worth tens of millions of dollars. In May, Rothko's 1961 painting "Orange Red Yellow" was sold at Christie's in New York for $86.9 million, becoming the most expensive Rothko work ever sold.

The Tate declined to comment on potential restoration.

"With the Seagram Murals, this was Rothko's first and seminal bid to create an entire environment—which is absolutely key—rather than just isolated individual works on canvas," Mr. Anfam said.

The incident Sunday served as a reminder of how vulnerable prized paintings can be when on display in high-traffic museums.

At the Tate on Sunday, two staffers who had been manning the room ran to summon security, but the vandal had left by time the guards arrived, Mr. Wright said. He said the museum soon evacuated the entire building, located across the Thames River from St. Paul's Cathedral.

The Tate confirmed in a statement that a visitor defaced one of Rothko's Seagram murals "by applying a small area of black paint with a brush to the painting." The museum declined to comment further.

Rothko's children, Kate Rothko Prizel and Christopher Rothko, also issued a statement, saying: "The Rothko family is greatly troubled by yesterday's occurrence but has full confidence that the Tate Gallery will do all in its power to remedy the situation."

The Rothko mural isn't the first work of art to be attacked in the name of art. In 2000, also at the Tate Modern, two performance artists urinated on Marcel Duchamp's sculpture "Fountain," itself a urinal. Four years earlier, Canadian artist Jubal Brown ate blue foods and purposefully vomited on a Piet Mondrian painting at the Museum of Modern Art in New York. A few months before, he had vomited in red hues on a different painting in Toronto.

-By Paul Sonne

Hirshhorn Museum and Sculpture Garden

Ai Weiwei will probably be regarded as the most important artist of the past decade. He is certainly its most newsworthy and arguably its most inspiring. Over the repressions of Chinese authorities, he has used a wide range of resources to broadcast a message of freedom.

Through his art, he has spoken with a voice that also includes those who have been silenced. A dissident under a capricious regime, he has endured trials that have captivated world attention while galvanizing an underground culture at home.

The arrival this week of Mr. Ai's first North American retrospective, "Ai Weiwei: According to What?"—which begins at the Hirshhorn Museum in Washington and travels to three other cities, concluding at the Brooklyn Museum in 2014—is itself newsworthy. That this exhibition largely fails to inspire not only speaks to Mr. Ai's own limitations but also to the challenges and missteps in exhibiting this increasingly multifaceted artist.

It bears remembering that following his youth in a Chinese labor camp and his punk bohemian immersion in 1980s New York, for several years Mr. Ai, now 55, was a member of Beijing's cultural elite. A sly thinker and adept designer, he emerged in the late 1990s along with the booming market for contemporary Chinese art to become a sanctioned and profitable ambassador of the modernized socialist state. In 2008, he even served as the artistic consultant on National Stadium, the "Bird's Nest" centerpiece of the Beijing summer Olympics.

It was the Sichuan earthquake in May of that year that turned Mr. Ai from cultural purveyor to iconoclast. He rightly believed that the tragedy of this event, a thousand miles from Beijing in the heart of rural China, was magnified by the state's refusal to investigate its particularly tragic circumstances: the death of more than 5,000 children due to shoddy school construction.

In the years that followed, Mr. Ai put this belief into action. He visited the devastation, documenting the sites in photos and videos, and organized what he called a "citizens' investigation" to identify and memorialize each child killed in this disaster.

As he pursued this project, Mr. Ai increasingly faced off with the Communist state. He came under surveillance and sustained a beating at the hands of local police, a life-threatening brain injury, the destruction of his studio in Shanghai, 81 days of imprisonment and psychological torture, a state-driven campaign of intimidation, multimillion-dollar charges and fines, and the stripping of his freedom to leave the country—including his plans to attend this North American retrospective.

The Hirshhorn show is an update of the one at Tokyo's Mori Art Museum in 2009, which was organized largely before Mr. Ai's dissident chapter. While the current exhibition brings in some important new pieces, it still feels weighted toward the state-sanctioned years. Even the recent selection largely follows the earlier formula.

Much of this work falls under what I call the Salon style of contemporary Chinese art: Oriental idioms, passed through Pop-art sensibilities, processed into large works with a factorylike finish. Mr. Ai can be particularly taken with Western art's historical references. Several examples here are minimalist-inspired sculptures with flourishes of Chinoiserie. "Cube in Ebony" (2009), carved with a traditional rusticated surface, recalls Tony Smith's "Die." "Moon Chest" (2008), created through traditional cabinet-making techniques, riffs off Donald Judd's "specific objects." "Cube Light" (2008), which is a recent acquisition by the Hirshhorn and also the most oversized, underwhelming piece in the show, is minimalism transformed into a kitschy chandelier.

Too much real estate gets taken up by these large works. The Mori's Mami Kataoka, who also curated this show, calls the art a "warm" minimalism for existing "between formalist and contextual methodologies"—in other words, Western work with an Eastern twist.

It is true that Mr. Ai includes personal, social and political references in his sculptures. At times they can seem like the coded messages of a prisoner tapping on his cell wall. "Surveillance Camera" (2010), a marble sculpture that turns an object of oppression into a work of art, is ominous and poignant. But often the sculpture, outsourced to inexpensive Chinese artisans, is a lot of effort for not much return. Sculptures that require lengthy explanations—that one was inspired by a small wooden box left by the artist's dissident poet father, Ai Qing, or that one was inspired by the shaking of the chandelier in Sergei Eisenstein's 1928 film "October"—are not so much "warm" as warmed over. One exception is "Straight" (2008-2012), a new floor installation made up of 38 tons of rebar recovered from Sichuan after the earthquake that is a rough and powerful work regardless of what else we know about it.

Mr. Ai has always been a conceptual artist. The challenge of a conventional museum exhibition is that his output has become more and more immaterial. It could be that Mr. Ai is now best reflected in other ways—for example in Alison Klayman's inspiring documentary "Ai Weiwei: Never Sorry." Blogging, Twitter and the Internet itself, to which Mr. Ai devotes eight hours a day, have become his genuine new media and his most consequential work. Unfortunately, this traditionally mounted show tells us little about that. Walls of photographs—with both wonderful snapshots from his New York years and thousands of digital images from his Internet feed—could offer extra context, but they are so poorly labeled and hung so high that they serve as little more than decoration.

For a retrospective, there is also regrettably little about his involvement in the Beijing avant-garde of the late 1970s—he was part of the "Stars" group during a brief thaw known as the "Beijing Spring." Nor are there examples of his underground books published in the mid-1990s.

A deep humanity runs through Mr. Ai's best work. "I've experienced dramatic changes in my living and working conditions over the past few years," he says in an interview with Hirshhorn curator Kerry Brougher reproduced in the exhibition catalog. But he resists being taken in by his own politics. "Maybe I'm just an undercover artist in the disguise of a dissident," he says. Believing in "freedom of speech, free expression, the value of life, and individual rights," he tempers his politics with empathy.

That's why his work on the "citizens' investigation" is so affecting and stands apart from the more ornamental aspects of this show. Alongside a wall-size spreadsheet listing all the child victims of the Sichuan quake, including their birthdays and schools, he presents a recording that reads off their names. In this stripped-down piece, we sense the full extent of the loss, a tragedy that is magnified for the victims' parents by China's one-child policy: "These people have cried a lifetime's worth of tears," says Mr. Ai. "In their hearts, they know that the precious lives they gave everything to protect are no longer." Beyond politics, the work strikes at the heart of death and remembrance. It also shows us how present this artist can be even in his absence—and just what is missing in so much else of this exhibition.

-By James Panero

The National YoungArts Foundation has purchased the famous Bacardi complex in Miami, with plans to create — with Frank Gehry’s help — a new center of arts activity.

A pair of historic, glittering buildings sat empty beside a busy Miami thoroughfare. An arts foundation with a nomadic background was looking for a place to plant permanent roots and expand.

That is how the National YoungArts Foundation, founded 31 years ago by Ted and Lin Arison, came to find its new home: the iconic Bacardi Tower and Museum complex along Biscayne Boulevard. The campus will get a Frank Gehry-designed master plan and year-round programming to link downtown’s burgeoning arts scene with the hip Wynwood and Design District neighborhoods.

Officials with the organization and company will announce the news Wednesday.

“This was really, I believe, a match made in heaven,” said Paul T. Lehr, executive director of YoungArts. “There was no better place for us to go and there was no better purchaser for this campus than us and what we were going to do.”

Lehr said Bacardi U.S.A. sold the 3.3-acre site at 2100 Biscayne Blvd. to the foundation for $10 million, though the market value was over $20 million. The blue and white tiled tower, by architect Enrique Gutiérrez, was completed in 1963. The mosaic square known as the “jewel box,” designed by Ignacio Carrera-Justiz, was added in 1975.

They were designated as historic in 2009 by Miami’s historic preservation board.

Facundo L. Bacardi, chairman of the board of spirits producer Bacardi Limited, said the sale wasn’t about making money. The privately held company moved its Americas headquarters to Coral Gables in 2009 and has maintained the Biscayne Boulevard site but used it only rarely.

When Lehr approached him with the idea about nine months ago and discussions started within the company, “it was kind of like a light bulb went off,” Bacardi said.

“We were looking for somebody to extend the legacy of the property and how much it means to us,” he said. “I don’t think we could’ve come up with a better partner.”

While closely guarded, the news had been shared with some YoungArts supporters in recent days. Reactions were enthusiastic.

“It’s not only a milestone in Miami’s evolution as a cultural community, I think it’ll be a powerful magnet for talent for decades to come,” said Alberto Ibargüen, president and CEO of the John S. and James L. Knight Foundation, which has supported the organization. “The whole thing just strikes me as perfect for a cultural center for this town.”

Despite working with more than 16,000 students over the last 31 years — including alumni like Vanessa Williams and Nicki Minaj, who have become household names — YoungArts has kept a relatively low profile. The organization finds and nurtures artists 15 and older, bringing in 150 a year for a week of intensive classes with masters in their field.

Even with its new home, the foundation is also planning a huge expansion of activities beyond Miami, including year-round events in New York, a Los Angeles version of Miami’s YoungArts Week and continued presence in Washington as the only nominating agency for the Presidential Scholars in the Arts.

“It’s all coming together at once,” Lin Arison said. “That’s because it’s meant to be. We’ve been doing our quiet work for 31 years, and now it is going to become visible.”

As the foundation expands nationally, it has added Gehry, singer Plácido Domingo and dancer, choreographer and director Bill T. Jones as artistic advisors. And it has added a 10th discipline, architecture and design, to a lineup that includes cinematic arts, dance, jazz, music, photography, theater, visual arts, voice and writing.

And its YoungArts MasterClass television program, which has appeared on HBO, is being used in public schools in Miami, New York and Los Angeles with a teachers guide so educators can use lessons from mentors in their classes.

Arison, who said she sold paintings by Claude Monet and Amedeo Modigliani to support the move, envisions the new campus as a place where visual arts by alumni will be displayed year-round, popular art walks in the nearby Wynwood district will spill over and outside projections like the well-known wallcasts at the New World Center will take place. Gehry designed the new Miami Beach home for the New World Symphony, which the Arisons co-founded.

“Once people get in here, they’re going to own it,” Arison said. “The kids are going to own it, the mentors are going to own it and hopefully the community is going to own it.”

While YoungArts will move its administrative headquarters into the new building by mid-October, the timeline for the rest of the project was not yet known. Mentors in the program will be asked for input on how the space should be used, and Gehry will involve students in the overall design of the campus.

“Whatever she wants me to do, I’ll do,” Gehry said of Arison.

An office area next to the tower building will be transformed into a performance space, and a parking lot will become a park that will attach to the existing plaza and green space, Lehr said.

“It’s nice that they’re taking over a building that’s a symbol in Miami but has been underused in the last years,” said Meaghan Lloyd, a partner in Gehry’s firm. “We’re very happy to be part of that story, which is a big part of the history of Miami.”

Yara Travieso, 26, remembers the complex from her days growing up in Miami-Dade with an architect father; they would drive around admiring buildings in the area, and the Bacardi structures were a favorite.

Now a New York-based director and choreographer who attended The Juilliard School on a full scholarship thanks to her involvement in YoungArts as a student, Travieso said she is overjoyed about the organization’s new permanent home.

“I think it’s perfect timing, it’s the perfect location,” she said. “This new generation needs that.”

Michael Kaiser, president of the John F. Kennedy Center for the Performing Arts and a consultant who has worked with YoungArts for more than a year, said young people are involved in much of Miami’s artistic momentum.

“This is about vibrancy and youth, which seems so fitting for this city to make this the calling card,” he said. “Arts organizations all over America are trying to find ways to engage younger people, and Miami’s going to be truly the center of activity for younger people and serious engagement for young people with the arts.”

-By Hannah Sampson

In June 2010, Apsara DiQuinzio, then a curator at the San Francisco Museum of Modern Art (now at the Berkeley Art Museum), received a grant from the Andy Warhol Foundation to travel around the world and find six relatively off-the-chart cities where significant new art institutions, movements and activity had taken root and flourished in the past 10 or 20 years. The cities she ended up with were Beirut, Lebanon; Cali, Colombia; Cluj, Romania (the Communist government added “Napoca” to its name in 1974, but no one ever uses it); Saigon, Vietnam (the Communist powers have renamed it Ho Chi Minh City, but no one except bureaucrats ever uses that name, either); Tangier, Morocco; and San Francisco.

The result is the eye-opening “Six Lines of Flight: Shifting Geography in Contemporary Art,” which fills the top floor of SFMOMA. It contains 60 works in many media by 19 artists or art collectives from these cities, separated geographically by gallery.

San Francisco doesn’t belong on the list. As an art city, it’s not “marginal,” or “peripheral,” as the catalog authors define the other locales, and its significance as a creative center has long been acknowledged. Ms. DiQuinzio’s justification was that “this exhibition was about the importance of the local, and I had to include my own locality.” But what if she lived in New York?

Moreover, the San Francisco contribution, by an environmentalist, anticorporate group called Futurefarmers, is the weakest of the six: 10 audio recordings about the future, by experts (on ecology, planning, astronomy, physics, biology, etc.) from Berkeley, Harvard and other universities, that could have been PBS broadcasts.

The only other disappointing contribution from Ms. DiQuinzio’s six chosen cities is the sole one from Tangier. There is no question that Morocco’s colonialist past, and the two decades of repressive national government that came after independence, provide plenty of material. But in her photographs, posters and videos, Yto Barrada (director of the Cinémathèque de Tanger) focuses on the uglification of her native city since masses of impoverished new immigrants and wealthy tourists have led to the destruction of old quarters and the erection of banal hotels and apartment blocks. A good story, yielding grim, banal photographs.

Unlike the U.S. and Morocco, the other four countries have been through hell in the past 20 to 50 years. This goes a long way to explain why their suddenly released artistic energies—as they try to remember, rediscover and rewrite their tragic pasts—are so much more moving.

Lebanon has a 3,000-year-old history, perpetually cloven by religious and cultural divisions and invasions. Akram Zaatari tries to reconstruct this messy history through the archives of hundreds of thousands of photographs he discovered, all taken by a popular Beirut portrait photographer Hashem el Maadani since the 1940s; the exhibit includes a reconstruction of this photographer’s studio. Joana Hadjithomas has taken dozens of colorful “Welcome to Beirut” postcards of the good old days—the beaches, grand hotels, quasi-Parisian night life—and burned or smudged each one. (Museum visitors are invited to take copies home.) Lamia Joreige has composed a wall-filling “time line” of the history of Beirut, from 1200 B.C. to A.D. 2100—made up of 29 photos, drawings, reproduced paintings, maps, texts and video monitors—that would take a day or more to absorb.

Cluj, in Romania, is a city that not one museum visitor in a thousand is likely to have heard of. Yet it is that country’s second city, arguably its most active in terms of new art and intellectual activity, looked down on (like Saigon by Hanoi, Cali by Bogotá) by the more powerful capital city, Bucharest.

After serving as dictator of the country since 1967 (and after 1971, as the most repressive, neo-Stalinist dictator in Eastern Europe), Nicolae Ceaușescu and his wife, Elena, were seized by the army (which had joined forces with the revolutionaries, after four days of national mass demonstrations), given a brief show-trial, and almost instantly shot by a firing squad on Christmas Day 1989. The assassination was shown on national television and the Communist Party dissolved.

Cluj painter Adrian Ghenie’s large 2010 oil called “The Trial” depicts a blurred, freely painted image of the Ceaușescus sitting before an L-shaped judgment table—an image shown on TV—shortly before they were killed. Another, “Dada is Dead” (2009), shows a spot-lit, frightened and frightening gray wolf in a dark cellar. A third (“The Collector,” 2008) is a large, blood-red painting of Hermann Göring at his desk, surrounded by paintings he had looted from all over Europe. All three are museum worthy; “The Trial” belongs to SFMOMA.

Also from Cluj is Ciprian Muresan’s video of a gang of animated dog-puppets shouting out the oppressive evils of the world, tormenting a female member of the Eternal Republic of Dogmania with every kind of insulting accusation, and then torturing to death one of their members for being insufficiently dedicated to the ruling regime.

Particularly impressive are the contributions of new Cali artists, after 21 years of rule by a brutal drug cartel often in collusion with a corrupt government. Wilson Diaz’s video of a Colombian pop group (in military fatigues and bearing rifles) singing and playing jauntily about the recent atrocities of life in Cali is no joke. Oscar Muñoz’s gradually fading images of his own face and of significant moments in recent Colombian history remind us of how quickly the present disappears into the past. Most powerful of all is Luis Ospina’s 28-minute mockumentary (“The Vampires of Poverty”) about the poor people of Cali, with paid actors, written lines and a borrowed set. Just before the end, the gaunt, dreadlocked, gap-toothed owner of the shack breaks in, curses the film crew as exploiters (what Latin Americans call purveyors of “pornomiseria” for the middle class), chases them out, and ruins their film.

We know something of Vietnam’s historical horror story, because we had something to do with it, during what the Vietnamese now call “the American War” of 1965-75. It is against this background that the art on display from Saigon—the former capital of the U.S.-allied South, still regarded with suspicion and disdain by Hanoi—must be seen.

The Propellor group—two returned Vietnamese and one American—made a slow-motion video of an underground North Vietnamese tunnel near Hanoi (one of the thousands that were a major weapon in the Communist victory) that has been excavated and converted into a shooting gallery for tourists, mainly Americans, who pay to aim at a target with AK-47s. The ironies involved are almost stifling. Dinh Q. Lê’s video contrasts a stiff, perfunctory daily assembly of Vietnamese soldiers in front of the huge white mausoleum of Ho Chi Minh in Hanoi with exuberant scenes of hundreds of gleaming motorcycles racing at night (sometimes upside-down) through the jovial chaos of still-Westernized Saigon.

Tiffany Chung’s exquisitely drawn, colored and embroidered maps of each of the six cities (commissioned by SFMOMA) turn cartography into art overlaid with social commentary. Her precise, beautiful maps depict cities expanding through increased population growth (Cali, Cluj); past earthquakes and predicted floods (San Francisco, Saigon); major political events (Tangier); and total social chaos (Beirut).

I can’t say that “Six Lines of Flight” totally won me over to its premise: that the relatively new, “peripheral” art cities of the world may now have as much to offer the “center” (New York, London, Paris, Berlin, Los Angeles) as they once drew from these art-world capitals. But, thanks to Ms. DiQuinzio and SFMOMA, I feel a slightly better-informed citizen of the world.

-By David Littlejohn