A stress tester for stretched canvas was developed by the authors and placed in an environmental chamber for testing of canvas paintings. Test samples were prepared and the reactions of a typical canvas to controlled environmental changes were investigated in its raw state, then after sizing, after priming, after painting and after aging. Electronic equipment was installed to collect the data and record them day and night, without interruption. The tests showed that even large environmental changes are dissipated if they occur slowly and in a continuous form. In contrast, small but rapid changes showed disproportionately large stress changes. The deformations that accompany stresses are not fully recoverable, due to the plasticity of the materials. Under cycling conditions, the non-recoverable deformations are accumulated with each cycle and cause tensile failure (cracking) within the materials and separation between the layers (blisters). Stress concentrations caused by the initial failure create progressively more extensive failures such as cupping and bulging. Thus, the findings of these tests have further confirmed the hazards of cycling environmental devices. -- AATA