The “Restoration of the Restoration”: Investigation of a Complex Surface and Interface Pattern in the Roman Wall Paintings of Volsinii Novi (Bolsena, Central Italy)

(1) Background: The present paper reports the results of the analyses performed on the wall paintings of Room E of the Domus delle Pitture (Room of the Paintings) in the Roman archaeological site of Volsinii Novi (Bolsena, Viterbo, Central Italy) aimed at supporting the recently concluded restoration. (2) Methods: ultraviolet fluorescence photography was conducted to evaluate the conservation state. Painting materials were investigated via portable X-ray fluorescence spectrometer (p-XRF), µ-Raman spectroscopy, cross-section analysis under polarizing microscope, scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), and Fourier transform infrared (FTIR) spectroscopy. (3) Results: This analysis revealed the presence of traditional pigments used in Roman wall paintings, such as ochres, earths, and Egyptian blue. Additionally, it identified pigments from previous restoration containing titanium and chromium, along with other materials present in the surface and interface of the wall painting containing arsenic, copper, lead, and vanadium, where a bluish alteration was observed. In these samples, µ-Raman spectroscopy detected calcium oxalates but also copper arsenates, likely conichalcite and/or duftite. (4) Conclusions: This result is highly relevant from an analytical point of view and in relation to the restoration decisions. Addressing the irregular bluish stains on the wall paintings poses challenges in understanding, requiring a decision on whether to remove or retain them.