Archaeometric research on decorated bricks of Tol-e Ajori monumental gate (6th century BC), Fars, Iran: New insight into the glazes

The archaeological excavations ongoing since 2011 at Tol-e Ajori – located 3.5 km NW of the Persepolis Terrace – discovered an Achaemenid monumental gate dating back to the second half of the 6th century BC. Thousands of glazed clay bricks, flat or in relief with decorative and figurative motifs, which are very similar to the bricks of Babylon’s Ishtar Gate, were unearthed from Tol-e Ajori. As the glazed surfaces of the bricks were seriously degraded, due to the long period of burial, a set of non-invasive investigations was first carried out to identify the original hues, also in situ, using digital microscopy, portable energy dispersive X-ray fluorescence (ED-XRF) and visible reflectance spectrometry (Vis-RS). Minute samples were also investigated by micro-X-ray fluorescence (μ-XRF), polarised light microscopy (PLM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (ESEM-EDS), and micro-Raman spec-troscopy. The occurrence of brizziite (sodium antimonate, NaSbO 3) and calcium antimonate (CaSb 2 O 6) as white opacifiers embedded in the lime-alkali glaze was evinced. Lead antimonate was also shown to be a yellow opacifier while cobalt and copper occur as colouring agents in the blue glazes. The greenish hues were obtained by mixing Cu 2+ with the yellow opacifier. These results are coherent with the general knowledge available on the Iron Age glaze production in the ancient Near East. Moreover, the iconographical and archaeological features suggested close ties between the glazed bricks from Tol-e Ajori monumental gate and the Ishtar Gate. We also considered the similarities and differences between glaze technology evidenced in Tol-e Ajori and important archaeological sites in Iran and Iraq. In addition, the source of Co in the glazes from Tol-e Ajori bricks and other Achaemenid glazed bricks from Susa and the Persepolis Terrace is discussed.