A man has been jailed for two years for defacing a Mark Rothko painting at London's Tate Modern gallery.
Wlodzimierz Umaniec, 26, of Worthing, West Sussex, had previously pleaded guilty to criminal damage to property valued at more than £5,000.
Witnesses saw a man daub the mural, Black on Maroon, on 7 October before fleeing the gallery.
Tate Modern has said the damage was much worse than originally feared and could take up to 20 months to repair.
Polish national Umaniec, who co-founded the artistic movement "yellowism", stepped over a barrier in the gallery and daubed his name and the words "12, a potential piece of yellowism" before running off.
The court heard that he went to the gallery intending to put his "signature" on a picture, but decided to damage the painting only at the time he saw it on display.
Judge Roger Chapple, at Inner London Crown Court, told Umaniec: "Your actions on the 7 October of this year were entirely deliberate, planned and intentional."
Speaking about "yellowism", Judge Chapple said it was "wholly and utterly unacceptable to promote it by damaging a work of art" which he called a "gift to the nation".
He said it was "abundantly clear" that Umaniec was "plainly an intelligent man" and told the court he had described Rothko as a "great painter" in a letter he had written to him.
The judge also said the incident had led to galleries reviewing security arrangements at a cost to themselves and the taxpayer.
"The effects of such security reviews is to distance the public from the works of art they come to enjoy," he said.
'Everything is art'
Gregor McKinley, prosecuting, said Sotheby's had given Tate Modern a verbal estimate of pre-damage value of between £5m to just over £9m.
He added work to restore the painting would take about 20 months and cost about £200,000.
Paintings by Russian-born artist Rothko often sell for tens of millions of pounds.
Earlier this year, his Orange, Red, Yellow sold for £53.8m - the highest price paid for a piece of post-War art at auction.
Black On Maroon, was donated to the Tate in 1969 by Rothko himself.
Outside court before the sentencing, Ben Smith, who called himself a "yellowist", attempted to explain the concept: "Everything is equal. Everything is art.
"Everything is a potential piece of yellowism."
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