A combined use of optical microscopy, X-ray powder diffraction and micro-Raman spectroscopy for the characterization of ancient ceramic from Ebla (Syria)

Ancient ceramics from the archaeological site of Ebla (Syria), dating back between 2250 and 1800 B.C., have been characterized by a combined use of optical microscopy (OM), X-ray powder diffraction (XRPD) and micro-Raman spectroscopy (micro-RS). Petrographic observations indicate that different fabrics are present, in terms of microstructure, groundmass and inclusions. XRPD allowed the identification and quantification of mineral phases of both unheated and heated samples at 950 °C, by means of Rietveld refinements. In particular, XRPD of heated samples highlights significant differences among the mineralogical assemblages of the analyzed samples, suggesting that the relative amount of carbonate and silicate minerals plays a key role, driving the reactions during the firing process. Furthermore, the mineralogical composition of unheated samples suggests a firing temperature in the 800–850 °C range, excluding a sample fired at lower temperatures (400–500 °C). Concerning the redox state of the firing atmosphere, the occurrence of hematite in some samples indicates that they were fired in oxidizing conditions, whereas other ceramic artifacts containing magnetite were fired in reducing conditions. Micro-RS results highlight that the mineralogical components of the decorated surfaces are hematite in the red areas and magnetite in the black ones.