Fig. 6

A 4 h cycle of wall temperature, with an average value below ambient. The painting, without back protection, was mounted with a 10 mm gap between the frame and the wall. The difference between the RH measured at the sensor 1.5 mm from the back of the canvas and the RH calculated at the nearby surface temperature is shown by a tinted band. The calculated value is named RH-c in the key. The sensor temperature and the canvas surface temperature are also linked by a tinted band. The RH in the room was the same for all experiments and is therefore not included in other figures with stable room temperature