The relationship between the microclimate and efflorescence of revealed mural paintings and the later protection strategy

Throughout history, there were many fine mural paintings concealed within ancient buildings, hidden beneath layers of plaster, wall or other structure. In recent decades, research and practical efforts had primarily focused on nondestructive diagnosis of these hidden murals and the removal of their surface coverings. However, limited attention had been given to the consequences of overlay removal on mural preservation. This study aims to address this gap by examining the revealed mural paintings in the Prince Shi's Palace as a case study, employing an analysis of mural ontology, investigation into the preservation environment, and simulation experiments to comprehensively analyze the factors contributing to the rapid deterioration of these revealed murals. The findings indicated that certain carbonated lime particles adhered to the mural surface, and in a humid environment, these particles absorbed sulfur dioxide from the atmosphere and converted into calcium sulfate. The strong hygroscopic property of calcium sulfate enhanced the humidity on the surface of murals, thereby increasing their susceptibility to sulfur dioxide absorption. Over time, the murals suffered more sulphate and moisture damage. Additionally, historically inaccurate interventions such as non-breathable shading curtains installation and organic coatings reinforcement exacerbated this deterioration process. Therefore, safeguarding the integrity of these exposed concealed murals necessitated prioritizing the preservation of environmental humidity and acid gas levels.