TRACING THE TRAJECTORIES OF EGYPTIAN BLUE PRODUCTION TECHNOLOGY: XRD, SXRF AND SXANES ANALYSIS OF HELLENISTIC AND ROMAN SAMPLES

TRACING THE TRAJECTORIES OF EGYPTIAN BLUE PRODUCTION TECHNOLOGY: XRD, SXRF AND SXANES ANALYSIS OF HELLENISTIC AND ROMAN SAMPLES Ariadne Kostomitsopoulou Marketou1, Fani Pinakidou2, Eva Luna Ravan3,4, Francesco Paolo Romano3, Hariclia Brecoulaki5, Alexandra Rodler-Rørbo6, Andreas Germanos Karydas7 1 MF Norwegian School of Theology, Religion and Society, Oslo, Norway 2 Deptartment of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece 3 Istituto di Scienze del Patrimonio Culturale, CNR, Catania, Italy 4 Sapienza University of Rome, Rome, Italy 5 Institute of Historical Research, National Hellenic Research Foundation, Athens, Greece 6 Austrian Archaeological Institute, Austrian Academy of Sciences, Vienna, Austria 7 Institute of Nuclear and Particle Physics, NCSR “Demokritos”, Athens, Greece Corresponding author's e-mail: [email protected] Egyptian blue (EB) is the artificial blue pigment that dominated ancient Mediterranean art. It is produced through a complex pyrotechnological process, during which a copper compound is heated with silica- and calcium-rich sand and an alkali flux, in temperatures ranging from 850 to 1050 °C. The outcome of this process is a multicomponent material, which includes a newly synthesized copper calcium tetrasilicate (CaCuSi4O10) crystalline phase, responsible for the pigment’s impressive blue colour. Despite the wide diffusion and use of Egyptian blue (EB) across the Graeco-Roman world, there is little information regarding the pigment’s manufacturing loci and trade. Variations in the choice of starting materials used and/or the operational sequence followed for the production of EB could result in products of varying chemical and mineralogical compositions. The present contribution discusses the XRF and XANES (Cu-K edge) analysis of EB samples carried out at the Elettra Synchrotron (Trieste, Italy). In addition, we have performed at the lab XRD analysis of the same samples. The analysed samples derive from a range of well-documented archaeological sites, including wall paintings from Macedonian tombs and pellets from Kos (Greece), Noricum (Austria), and Ostia (Italy). The analysis sheds light on the choice of starting materials and the specifics of the production process, such as firing conditions, through the characterisation of the chemical state (XRD, and XANES) and environment of Cu-species (XANES). The obtained results contribute to EB provenance research and illustrate technological adaptations and developments. Keywords polychromy, pigments, synchrotron radiation, pyrotechnology, archaeometry, provenance studies