Ruth Hoppe, the modern art conservator for the museum, noticed that the painting had been retouched to cover up tiny holes in it. On closer inspection, she found that there were shards of glass wedged into the canvas. Ms. Hoppe decided to do a more extensive investigation. She X-rayed the work, and discovered something extraordinary: Underneath the “Wisteria” was another painting — of water lilies. – The New York Times