An abstract painting worth an estimated $1.5m (£850,000) is in need of repair after a 12-year-old boy stuck a piece of chewing gum on the canvas.
The Bay has hung in Detroit since 1965. Photo: Detroit Institute of Arts
The gum left a small stain in a corner of The Bay, a 1963 painting by American artist Helen Frankenthaler.
The boy, who visited the Detroit Institute of Arts with a school group, has now been suspended by teachers.
Curators at the museum said they were researching how to remove the stain, but expected no permanent damage.
Frankenthaler is regarded as one of the most influential second generation US abstract expressionist painters.
The Bay, one of her most celebrated works, is thought to be one of the most valuable paintings in the museum's collection.
Rock, rap and art
The director of the Holly Academy, where the boy goes to school, confirmed that the pupil had been suspended for his actions.
"Even though we give very strict guidelines on proper behaviour and we hold students to high standards, he is only 12," Julie Kildee said.
Abstract work concerned with nature
Influenced by Jackson Pollock
Most famous work is Mountains and Sea (1952)
The Bay completed 1963
Bought by Detroit Institute of Arts 1965
"I don't think he understood the ramifications of what he did before it happened, but he certainly understands the severity of it now."
His parents had also taken disciplinary action, Ms Kildee said.
A security guard spotted the gum on the corner of the painting after the group of schoolchildren had left the display room.
Staff moved quickly to remove the gum, which had not stuck firmly to the canvas. It did leave a small stain, which curators expect to remove in the near future.
Becky Hart, assistant curator of contemporary art at the museum, said she had tried to explain to the boy how the museum helped preserve works of art.
"I knew that probably wouldn't make any sense to him, so I asked him what kind of music he liked," Ms Hart told the Detroit Free Press.
"He said he liked rap, so I said: 'Well, you know what rock and roll is,' and he did.
"So I said: 'Can you imagine if somebody had messed up the beat in rock and roll so you didn't have any rhythm in rap.' And he looked at me, and he got it immediately."
The painting will be kept on display while repairs are carried out, but the museum is to review its display policies.