What a difference a cleaning can make,” Guardian art critic Jonathan Jones writes in his latest column, describing The Virgin of the Rocks, a recently restored painting that the National Gallery in London has long attributed to Leonardos students. The museum said in a statement that, post-cleanup, “it now seems possible that Leonardo painted all the picture himself,” and Jones, who is perhaps the hardest-working scribe in the British Empire, concurs.

According to Larry Keith, the museum’s director of conservation, varnish that was applied to the painting in the middle of the 20th century dulled its color and obscured its brushstrokes, leading scholars to doubt whether it was the work of Leonardo. With that material freshly removed from the painting, the museum’s curator of Italian Renaissance painting, Luke Syson, tells Jones, “We now have a picture which I believe is entirely by Leonardo.”

“It’s a painting that has haunted me since my first visit to the National Gallery,” Jones tells his readers, arguing that the work represents “the passionate play of a genius at work: ceaselessly experimental, provocative, brave.” Debate, Syson notes in the article, will continue. (And, as David Grann points out in the New Yorker this week, even the most definitive methods of connoisseurship are never certain.) But for now, Jones declares, “A treasure is reborn.”