More Than Meets the Eye: X-rays of the Painting
Like a medical X-ray, an X-ray of a painting shows the subject's underlying structure. X-radiography is a noninvasive technique for examining a painting in order to assess its condition. It can reveal tears, fills, or losses in the original paint layer and changes to the dimensions of the canvas that cannot be seen with the naked eye. It may also provide important information about the artist's techniques and materials and useful data on earlier restorations. Changes made in a painting's composition can frequently be detected on an X-ray. The most dramatic, if not unusual, X-rays reveal a complete second painting beneath the top composition.
Reading an X-ray of a painting is similar to reading a medical X-ray. The densest areas of the subject absorb the most rays and show up as the lightest details on the film. Thus, human bones appear bright white. In a painting, the lightest areas tend to be those containing lead white, a very dense pigment.