Analytical Investigation of Two Syrian-Style Bronze Sphinx Plaques from the Iron Age of West Asia (First Millennium BCE)

Two plaques in the form of sphinxes in the collection of the Metropolitan Museum of Art, Syrian in style and attributed to the early first millennium BCE, were subjected to scientific studies to identify their production and manufacturing technologies and to address material questions regarding their authenticity. The plaques were investigated with µ-XRF spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and optical microscopy techniques to identify their alloy composition and microstructure as well as to characterize their patina. Results revealed that they are made of a leaded tin bronze alloy with ca. 15 wt.% of tin and <2 wt.% of lead. The microstructure shows an α-solid solution of bronze with numerous α + δ eutectoid structure, lead globules and sulfidic inclusions. Although the plaques were subjected to thermo-mechanical treatment during their original shaping, eutectoid islands remained due to the high tin content of the alloy. The patina consists of the tin-rich layer accompanied by some intergranular attack below the limit of the original surface resulting from decuprification. Based on their similar microstructural features and tin-rich patinas, it appears likely that both plaques were produced in a same workshop and were subjected to the same burial environment for a considerable period.