Behind the facades of Ctesiphon: an archaeometric study of stucco architectural decoration from the Sasanian and Early Islamic periods

Ctesiphon, the capital of the Sasanian Empire (ca. 224–651 CE), was a major center of political power and artistic production in Mesopotamia. Excavations conducted in the 1920s–30s by the Staatliche Museen zu Berlin and the Metropolitan Museum of Art revealed an extensive corpus of stucco decorations from Sasanian and Early Islamic contexts. Their varied forms, decorative patterns, architectural contexts, and dates of production make these stuccos particularly valuable for comparative study. Despite their significance, however, the technology of stucco production at Ctesiphon has remained poorly understood. This study employs an integrated archaeometric approach combining optical microscopy, petrographic thin-section analysis, micro–X-ray diffraction (µXRD), and scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS) to characterize sixteen stucco objects at the Metropolitan Museum of Art. The results indicate that most Sasanian stuccos were mainly produced using prefabricated molds followed by limited hand finishing, whereas Early Islamic examples from Selman Pak exhibit wider technological variability. These results may evidence a less centralized production at Ctesiphon during the Early Islamic period compared to the Sasanian period. Chemical compositions show no correlation with decorative motifs but reflect the use of locally sourced evaporitic raw materials. The presence of bassanite, anhydrite, amorphous aluminosilicate phases, and combustion residues indicates heterogeneous firing conditions associated with traditional gypsum kilns, providing valuable markers for reconstructing production practices and assessing authenticity.