Roman wall paintings from the Roman Forum district of Carthago Nova: Characterisation of mortars and pigments

Abstract

This paper aims to study the construction technique and characterisation of original mortars and wall paintings at the Roman Forum district of Carthago Nova (Spain). A multi-analytical approach was conducted on original fragments using Optical Microscopy (OM), Field Emission Scanning Electron Microscopy (FESEM), colour tests (CIE L*a*b*) and contact angle measurements. Besides, the chemical composition was studied by X-fluorescence (XRF), Thermogravimetry (TG), X-ray diffraction (XRD) and Infrared spectroscopy using attenuated total reflectance (ATR-FTIR). The mortars showed a multi-layered pattern consisting of three distinguishable layers that were decorated with low-thickness coatings. The top layer composition was eminently calcitic, while the central and bottom layers were probably elaborated with pozzolanic materials. It is worth noting that unusual minerals as cerussite (PbCO3) were identified in some layers, and probably associated to subsequent activities carried out in the site after Roman times. The top coating was made of hematite (Fe2O3) for red decoration, whereas graphite (C) and hydroxyapatite (Ca5(PO4)3(OH)) were identified in black coatings, which suggests the use of animal bones in the production of black pigments. In addition, the outer surface of some fragments was most likely coated with organic substances to enhance colour and durability. Finally, SEM examination and EDX analyses also confirmed some of the above findings and the existence of NaCl surface crusts due to natural weathering.