Mechanisms of preservation damage: restoration materials affecting salt distribution and soil expansion in wall paintings of Dunhuang

Relics are precious, but the use of improper restoration materials may intensify their deterioration and result in preservation damage. Five restoration materials, including polyvinyl acetate (PVAc), polyacrylic acid (PAA), silicone-modified acrylic (SMPA), gelatin, and Paroloid B72, were used to restore simulated samples of the Dunhuang grotto murals. Simulated samples were ranked by their durability in response to cyclic weathering experiments. Experimental results revealed two mechanisms in sample deterioration processes. First, preservation materials affect salt migration, which have caused considerable damage to relics. It is found that more hydrophilicity synthetic polymers showed better performance. Second, interlayer expansion discrepancies may cause diseases such as flaking, and for this reason, gelatin should not be applied to plaster layers.