Production technology of early-hellenistic lime-based mortars originating from a punic-Roman residential area in palermo (sicily)

Abstract

The topic of this study is the mineralogical and petrographic characterization of lime-based mortars of Hellenistic-Roman age (3rd century BCE), collected from a residential area located in the present historical centre of Palermo, near the remains of the Punic-Roman walls. The collected mortars have been analyzed by optical microscopy, X-ray powder diffraction analysis and scanning electron microscopy, coupled with energy-dispersive spectrometry. The aim of the study was the characterization of the mortars as pertaining to their aggregate and binder composition, aggregate size distribution and aggregate/binder ratio, so as to establish the provenance of raw materials and acquire information useful in terms of formulating suitable restoration mortars. The mineralogical and petrographic investigations allowed to recognize four different recipes used for the formulation of the studied mortars. The aggregate is made up of different proportions of alluvial calcareous and siliceous sands or, in some cases, by 'cocciopesto' - opus signinum. Aerial lime-based mortars have been attested for the majority of the wall coatings and decorations subject to analysis. Furthermore, an unusual mosaic flooring, manufactured with tesserae obtained from overfired, locally produced limestone scraps, was attested. The sandy aggregate was quarried from the coastal alluvial deposits of the river Oreto, whose estuary is situated in the vicinity of the ancient city walls. The binder was primarily produced by the calcination of locally available limestones, lacking in magnesium carbonate. It presents a satisfactory technological similarity with two roughly coeval manufactures, located in western Sicily and relating to the aggregate, as well as the mortars manufactured for the purpose of decorating the historical palaces of Palermo. This in turn indicates a remarkable continuity regarding the selection of locally available raw materials, an aspect mainly dictated by their qualitative characteristics.