Paint layers on a stretched canvas or solid support present complicated behavior and failure patterns. The cracks, cups, blisters, and sagging commonly found in paintings give ample evidence of the detrimental effects of environmental changes on a composite of mechanically dissimilar materials. Under variations in stress caused by environmental conditions, the materials are inelastic and non-linear individually and collectively are anisotropic. The authors have conducted extensive biaxial tests on dozens of painting samples under variable stress, strain, relative humidity, and temperature [1,2,3,4].