A 26-year-old man has been jailed for two years for defacing a Mark Rothko painting at London's Tate Modern gallery.
Wlodzimierz Umaniec, also known as Vladimir Umanets, vandalised the mural, worth between £5m and £9m, at the gallery on October 7 this year.
The Polish national, who co-founded the artistic movement Yellowism, stepped over a barrier and daubed his name and the words "12 a potential piece of Yellowism" before fleeing.
He admitted criminal damage in excess of £5,000 - but estimates suggest the restoration of the painting, called Black On Maroon, will cost around £200,000.
Inner London Crown Court Judge Roger Chapple described his actions as "entirely deliberate, planned and intentional".
The court heard Umaniec, who lives in Worthing, West Sussex, went to the gallery intending to put his "signature" on a picture, but decided to damage the Rothko painting only at the time he saw it on display.
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 added that 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.
Gregor McKinley, prosecuting, said it would take about 20 months to restore the painting as part of a "complex" process.
He said: "Complications to this work include the unique painting technique used by the artist and the fact the ink used by Umaniec has permeated the paint layers and the canvas itself."
Paintings by Russian-born artist Rothko often fetch 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.
The defaced painting was donated to the Tate in 1969 by Rothko himself.
Outside court before the sentencing, Yellowist Ben Smith attempted to explain the concept of the movement. "Everything is equal. Everything is art. Everything is a potential piece of Yellowism," he said.