The cleaning of an unvarnished oil sketch by J.M.W. Turner is discussed. The surface layer responded little to conventional cleaning agents, and various chelating agents and others were assessed with respect to effectiveness of dirt removal and possible damage to the paint surface. A 2.5% solution of tri-ammonium citrate, cleared with water, was the most effective and safest, and gave comparable cleaning effects to a plastic eraser with debutyl phathalate plasticizer. The surface of the painting was analyzed by optical, fluorescence, and chemical microscopy, scanning electron microscopy/energy dispersive x-ray spectrometry, and Auger electron microscopy, and proved to be richer in lipids and lead, most likely as a result of a diffusion process during drying and aging of the paint.