The deformation of paintings on wood with slow or rapid changes in relative humidity was investigated using samples of pine (20X6X1.3 cm) sealed in a 19th century frame with a backing of fiberboard or waterproofed plywood. The sealed samples were protected against rapid changes in relative humidity, with waterproofed plywood being a more effective backing material. Wood samples not encased in frames showed cyclic deformations with changes in relative humidity. A glazed tight frame does not secure pictures against long-lasting changes in relative humidity, but reduces the speed of attaining equilibrium moisture content. -- AATA