Archaeometric Investigation of Artificial Stone Materials from the Theatrum Marcelli (Rome, Italy)

This study illustrates the results of minero-petrographic and microchemical investigations of artificial stone materials (mortars, plasters, and bricks) taken from the Theatrum Marcelli (Rome, Italy). To achieve this objective, the artificial building materials were analysed using Polarized Optical Microscopy (POM) and a Scanning Electron Microscope (SEM) used in backscattered electron (BSE) mode and coupled with an Energy-Dispersive Spectrometer (EDS) after a sampling campaign. The POM was aimed at collecting information on the textural and mineralogical characteristics of the samples (identification of the main minerals constituting the aggregate, grain size and shape, and the evaluation of the binder/aggregate ratio). The data also supported technological assessments through the characterization of the raw materials used for the manufacture of the mortars/plasters. Furthermore, the SEM-EDS investigations revealed the chemical composition of both the aggregate and the binder, which was useful for estimating their hydraulicity index (HI). The diagnostic campaign allowed us to obtain interesting information on the plasters/mortars used in the Theatrum Marcelli, together with their probable production technology. In particular, the raw materials were quite homogeneous, thus confirming the traditional methodology used in Roman times to create natural hydraulic mortars by the addition of pozzolanic volcanic material to aerial lime. The volcanic component of the aggregate seems to be compatible with the ultrapotassic products of the Roman Magmatic Province-likely with the Pozzolane Rosse pyroclastic deposit of the Alban Hills district.