Though painting today employs many techniques and a lot of collage, the Old Masters painted methodically. They started with priming and underdrawing, then brought on color and brushwork, following up with corrections and finishes. Over the years, technology has been developed to trace each step, and x-rays, specialized microscopes, can now uncover the particularities of painters. In this exhibition—the first of its kind—works from the Middle Ages to the Symbolists are examined. The show is structured in the same way a canvas moves from preparation to finished work of art, and reveals 700 years of painting techniques. —E.C.