Assessing the Deterioration Risk of Polychrome Clay Sculptures Based on the Hygrothermal Environment: A Case Study of Baosheng Temple, China

The polychrome clay sculptures of the Buddha at Baosheng Temple in Suzhou, China are important and famous cultural heritage with a history of more than 1000 years. Currently, they are tarnished by cracking, peeling, and fading. To evaluate the current conservation environment and deterioration risk to the sculptures, the hygrothermal environment of Luohan Hall and the temperature and moisture content of the surfaces of the Buddhas were analyzed by field environmental monitoring and a heat and moisture transfer model. The results show that the air temperatures near the sculptures have different fluctuation patterns in different orientations and that the relative humidity of the air near the sculptures fluctuates sharply, with the daily fluctuation exceeding set limits most of the time. The fluctuations of the air temperatures and relative humidities in Luohan Hall are mainly due to air exchange with the outdoors. The surface layer of the sculpture is in a dynamic state of absorption and evaporation depending on the humidity of the surrounding air, and evaporation from the sculptures' surfaces is more significant in autumn and winter. The air tightness and insulation performance of Luohan Hall should be improved, and dehumidification during periods of high humidity might be needed to reduce the evaporation of the surface layer of the sculpture.