This paper investigates the sensitivity of modern commercially produced artists’ oil paints to the use of aqueous and other solvents for cleaning. Water sensitivity has been observed in oil paintings where the paint has been used to create a great range of surface effects. It was reported in paint that exhibits efflorescence where fluctuations in environmental conditions or former treatments may have accelerated migration of degraded components to the surface of the paint film. The colored passages most frequently cited as problematic included ultramarine, cadmium yellows, chromium oxide green, and cobalt violet. Oil paint films, based on twentieth-century manufactured paints, with known proportions of pigments, stearates, aluminum hydroxide, hydrolyzed linseed oil, and hydrogenated castor oil in linseed oil were prepared and cured. After artificial aging, the paints were tested for water sensitivity. Ultramarine paints were the most sensitive to water applied by swab, followed by chromium oxide, whereas raw sienna was the least sensitive. The inclusion of linseed fatty acids and aluminum hydroxide increased the sensitivity of the paints to water. Aluminum stearate-containing paints swabbed with aqueous solvents exhibited localized stearic acid efflorescence. Ultramarine stearate-containing paints formed a paint-medium skin that was initially resistant to swabbing with water but contained water-sensitive paint beneath.