In-situ non-invasive analysis of conservation materials on mural paintings: a systematic approach in Dahuting Han Dynasty Tomb

In this study, the in-situ non-invasive analysis of the conservation materials on the mural paintings in the Dahuting Han Dynasty Tomb was performed. The analytical process of non-invasive measurement for mural conservation materials has been designed, including digital microscopy, external reflectance Fourier transform infrared spectroscopy, and optical coherence tomography. By using these methods, effective analytical results have been acquired. The microscopic morphologies of the murals were observed and recorded via a portable digital microscope, thereby the effects of the conservation materials on the surface of the murals and the structural characteristics of the coatings were clarified. Through external reflectance Fourier transform infrared spectroscopy analysis, it was found that both the painting ground layer and the edge reinforcement material are calcium carbonate, and there are cellulose nitrate and poly(methyl methacrylate) as conservation materials on the surfaces of the murals in different areas. The spatial location and distribution of these conservation materials were determined by principal component analysis of infrared spectra. The thicknesses of cellulose nitrate and poly(methyl methacrylate) coatings were measured by optical coherence tomography. The above work laid a solid foundation for the subsequent conservation and restoration of the murals. It is proved that the in-situ non-invasive analytical methods applied in this work have broad prospects for the measurement of conservation materials on murals.