Judge Roger Chapple, at Inner London Crown Court, told Umaniec: "Your actions on the 7th of October of this year were entirely deliberate, planned and intentional."
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.
More top news
Britain's highest court will rule on whether the government requires parliament's approval to get Brexit under way.
New sentencing rules mean serious speeding offences will be met with a 'clear increase in penalty'.
Donald Trump has wasted no time making his mark on international matters as well as domestic. So how will his presidency affect the world?