The subject matter, meaning and purpose of this work and the transformation brought about by restoration are discussed. A close examination of the picture coupled with information gained by x-radiography, infra-red photography and the study of cross-sections, suggested flake losses in the sky and that the bottom of the reliefs, paving stones around Christ's legs and some darker stones were covered by re-touching. During the cleaning, remnants of four small billowing clouds appeared hovering behind the figure of Christ. It was thought that at one time they would have incorporated the heads of cherubim and seraphim. A section is devoted to the materials, technique and condition of the picture. Comments on the presence of an unusual globular green copper carbonate, which the authors first detected in the green paint of the panels of Sassetta's <i>Sansepolcro Altarpiece.