Sometimes we do our best work in the dark.  This scene from the Retablo of Saint Peter is entitled Simon the Magician Carried through the Air.  The panel is lying flat on the table while losses to the paint and gilding are being filled with bright white conservation putty.  A strong spotlight rakes across the surface of the painting from the top of the composition.  The raking light helps the paintings conservator sculpt each fill to match the level and texture of the surrounding original surface.  (Note on the right that the raking light has also captured the geometric incisions that the artist inscribed in the gesso layer of the panel to compose the wooden tower in the scene.)  Matching level and texture is critically important when filling; inpainting alone cannot wholly conceal an area of loss if the fill does not match.  For that reason, filling is often the stage of a paintings conservation treatment that takes the longest time. 

Detail: Lorenzo Zaragoza (Spanish, active 1363-1406), Retablo of Saint Peter, c. 1400, tempera and gold on wood. The Edwin and Virginia Irwin Memorial fund 1960.473