Research of a complex fire-induced pollution on the marble relief from the Pushkin state museum of fine arts collection

Abstract Background Fundamental restoration of sculptures must include the research of pollution composition and exhibit surface condition as well as accurate identification of the materials of sculptures, bas-reliefs and coatings. In the recent years, studies of marble objects aimed at identification of contamination nature and composition have been developed. It should be noted that some exhibits have individual features as objects of restoration due to complex exposure to the environment, e.g. to fire. Results The article describes the results of surface contamination study on two exhibits from the Pushkin State Museum of Fine Arts collection. Marble relief sculpture “The Flagellation of Christ” was the main object of the study. Glazed terracotta (majolica) “Madonna Friedrichshain” was studied as a control sample with the same type of contaminations but with less sensitive surface. According to the results of different gas chromatography and X-ray fluorescence analyses, pollution compounds were identified as fatty alcohols, fatty acids and esters, part of which being residues of pyrolysis gasification, including those containing iron and lead. In order to gently clean the exhibits, several variants of chemical compounds were proposed based on various chelating agent mixtures, and, after studying their comparative effectiveness, the optimal scheme was chosen for removing existing contamination. For verification of marble exhibits safety, selected cleaning mixtures were tested on polished Carrara marble sample. Conclusion The most suitable scheme of organic contaminations removal including those containing iron and lead was suggested as part of restoration process. There is a number of working schemes of cleaning the surface of exhibits, however our proposed scheme interacts with the marble surface more gently because the target cleaning mixture composition was formulated taking into account the nature of pollutants and the least possible impact on the sample surface.