A scientific investigation of five polymeric materials used in the conservation of murals in Dunhuang Mogao Grottoes

Mogao Grottoes in Dunhuang is one of the World Cultural Heritage sites with splendid ancient murals and sculptures. Since 1950s, polymeric materials, such as polyvinyl acetate, polyvinyl alcohol, polyacrylates, silicone-acrylate copolymers and gelatin have been used as adhesion and consolidation agents for repairing the damages of flaking, powdering, disruption and paint loss on the murals. However, the scientific investigation of physicochemical properties and conservation efficiencies of these polymeric materials, which are quite crucial for the on-site evaluation of the previous conservation treatments and the long-term preventive preservation and monitoring of the works of art in the future, has not been fully performed yet. In this paper, we report the results of fully scientific investigation of these polymeric materials, using Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry, Gel Permeation Chromatography, Scanning Electron Microscopy analyses, and viscosity, strength, pH, nonvolatile matter tests, as well as water vapor permeability and surface wettability evaluation. The results show that polyacrylates, silicone-acrylate copolymers and gelatin, compared with polyvinyl acetate and polyvinyl alcohol exhibit better physicochemical and conservative properties, less affecting or changing the nature of murals. The data obtained will be helpful for the formal documentation of conservation materials used in Mogao Grottoes.