Analytical study of a newly excavated fine painted ceiling at the Archaeological Park of Pompeii

This work concerns an in situ and laboratory study of a fragmented painted ceiling found during the excavations in the Regio IX insula 10 of the Archaeological Park of Pompeii (Naples, Italy). This artwork was painted in the Fourth Pompeian style of a unique artistic quality that still maintains a remarkable chromatic vividness. The diagnostic study of the painted fragments aimed to determine whether the quality of the raw materials and execution technique aligned with the artwork's stylistic quality, and to assess the conservation state of the newly excavated wall paintings. The results of the in situ spectroscopic techniques (X-ray fluorescence, Raman and Fourier-transform infrared spectroscopy techniques) showed the presence of a variety of pigments. Among them, the use of cinnabar, considered one of the most expensive pigments used by the Romans, further highlights the superior quality of the retrieved mural painting. Additionally, an unusual execution technique, involving the application of pigment grains on the surface, has been identified in some areas where Egyptian blue and malachite were found. The study of two micro samples by means of Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) has made possible to investigate the execution techniques. In addition, the observation of the cross sections and the detection of traces of organic material suggested that the wall paintings were realized with secco technique. Fragments from the three preparatory layers (support of the mural painting, arriccio and intonachino) were sampled to perform X-Ray diffraction analysis and extraction of soluble salts followed by ion chromatography analysis. The results obtained with this last technique showed a low content of soluble salts, suggesting that a preventive salt extraction intervention does not need to be performed by restorers.