After describing the visual effects of surface dirt accumulation on paintings - desaturation of hue, reduction of the luminosity of the light tones, the paper examines ways of removing surface dirt from paint layers that are invarnished; especially works that are too large for protective glazing. The testing procedures and treatment were applied to a large work by Stanley Spencer, Resurrection Port Glasgow , painted between 1945-50. The use of saliva cleaning, detergents, distilled water, and other materials is outlined.