Rothko painting vandalised in Tate Modern The website declares that it is a "Manifesto of Yellowism," saying: "Yellowism is not art or anti-art. Examples of Yellowism can look like works of art but are not works of art. One of the witnesses to the attack, Tim Wright, posted a picture of the defaced painting on Twitter. He said: "This guy calmly walked up, took out a marker pen and tagged it. Surreal. We gave a description to the gallery. Very bizarre, he sat there for a while then just went for it and made a quick exit. Tate Modern is the world's most-visited art gallery and was packed with visitors yesterday afternoon when the vandal struck in the "Rothko Room." The gallery is covered by CCTV and police are studying the footage. A Scotland Yard spokesman said: "We were alerted at 3.35pm to a report of criminal damage at Tate Modern. The suspect was a white male, believed to be in his late 20s. No arrest has been made at this time. The Tate said a visitor had defaced one of the Seagram murals "by applying a small area of black paint with a brush to the painting." Questions will be asked about security at the gallery, where the Rothkos are not protected by glass and are separated from visitors only be a low-level barrier that can easily be stepped over. Typically, each room is monitored by a single gallery attendant. It was Rothko himself who stipulated how his work should be displayed at the Tate. The defaced painting was one of a series commissioned from Rothko in 1958 for the Four Seasons restaurant in New York's Seagram Building, but never installed. In 1969, the artist donated nine of the paintings to the Tate on the proviso that they be displayed "as an immersive environment." He died the following year. Last year, the National Gallery also fell victim to vandalism when two 17th century masterpieces were defaced. A man sprayed red paint from an aerosol can over Nicolas Poussin's The Adoration of the Golden Calf and The Adoration of the Shepherds. On that occasion, the culprit was swiftly arrested.