This journal article, translated from French, discusses ethical considerations and technical problems of restoring the Pieta , a panel painting by Sebastiano del Piombo. Damage to the ground layer had occurred from humidity, yet important drawings, possibly attributed to Michelangelo, on back of the painting, precluded transfer to a more stable support. Surface blisters were consolidated and the painting maintained at a constant relative humidity (RH). An earlier restoration by Montessuis and Camuccini resulted in further damage to the surface and a darker varnish was applied. Cleaning of the overlaying, dark layer of oxidized varnish was dismissed by Pigazzini, a later restorer, as careful examination revealed several layers of tinted glazes and varnishes which were used by numerous European masters (eg. Correggio) for shading, modelling and dull reduce glaring colors. Each artist had his own formulas and techniques. Therefore, before cleaning is undertaken, each painting must be carefully examined and solvents tested to prevent deterioration or removal of original glazes and varnish. This is a reference for materials and techniques of European master painters, and early conservation treatments of oil paintings. -- CCI