Characterization of ancient coloured paintings on the mortars from the ‘Teatro Marittimo’ of Roman Hadrian's Villa (Rome, Italy)

The research aims to study some rare original coloured painting samples (still present) from the ‘Teatro Marittimo’ at Villa Adriana (Tivoli territory, Rome). The Villa was designed by the Emperor Hadrian in the years between 118 A.D. and 135 A.D. and belongs to the Cultural Heritage of UNESCO since 1999. The structure of this ancient building is characterized by a circular body with an axial entrance that leads into the circular portico supported by Ionic columns topped by a barrel vault. A circular channel delimits an artificial central island in which there are a domus, a secondary residence in the Imperial Villa. The main objective of the research is the study of the original coloured-painting finds, applied on the mortar substrate substantially lime-based that coat the internal walls of the circular perimeter of the ‘Teatro Marittimo’ mainly using the LIBS technique. LIBS is an already tested laser spectroscopy technique that lends itself well to be used for measurements in a sensitive sector such as the Cultural Heritage. In fact, it is a fast technique (only a few seconds are required for the acquisition of a spectrum) and, especially, minimally destructive (the crater produced by the laser beam is generally of the order of a few microns). The analysis allowed a detailed mapping of the chemical composition of the coloured surfaces and to hypothesize the raw materials used in the mixtures. Moreover, through physical, petrographic (OM), XRD, SEM and thermo-gravimetric (TG-DSC) analysis, it was possible to identify: i) the composition of the mortar binder; ii) the physical features of the mortar (i.e. porosity, density, aggregate particle size, etc.); iii) the microstratigraphy of samples from the adhesion-surface of the mortar substrate to the bricks of the wall, to the overlapping colour levels of the original painting