X-rays show that Degas worked and reworked a painting over the course of 40 years as his ideas changed. “The x-ray shows flurries of reworking, as figures become more and less distinct, the teenagers turn towards one another and then look away, the detailed background landscape is softened into a blur. At one point, Degas scrubbed out their classically handsome faces, and replaced them with Parisian urchins.”