Effectively removing animal glue coated on the surface of ancient mural via dissolution of PVA hydrogel induced by thermal treatment

During the transfer of ancient murals, animal glue is employed as a sealing protective agent. To further restore the murals, the glue needs to be removed after the murals are transferred to museum. However, animal glue is difficult to remove. Here, we propose a method to remove animal glue coated on the surface of murals via polyvinyl alcohol (PVA) hydrogel dissolution induced by thermal treatment. We find that the PVA content significantly affects the mechanical properties of PVA hydrogels, and PVA hydrogels with concentrations of 8% ∼ 11% have usable toughness and flexibility. More importantly, upon heating, these hydrogels placed on top of animal glue coated on murals can be effectively removed without leaving hydrogel residues on mural surface. The efficient removal of animal glue is due to the controllable release of hot water by the partial dissolution of PVA hydrogel induced by heating. During heating, hot water containing PVA gradually dissolves the animal glue, endowing its high viscosity. Therefore, the dissolved animal glue and PVA hydrogel adhere to the surface of the undissolved part of PVA hydrogel, allowing controllable removal of animal glue after removing the undissolved part. Our work opens a new road to clean animal glue coated on the surface of ancient murals and is beneficial to the preservation of cultural heritage.