Unveiling the craftsmanship and knowledge behind Iranian stuccoes (11th–14th centuries): New insights from an archaeometric perspective

Gypsum-based stucco decorations of 47 monuments in Iran, from the Seljuq to the Ilkhanid period (11th-14th centuries), were studied by multimodal analytical methods, including X-ray diffraction, X-ray fluorescence, scanning electron microscopy and image analysis to evaluate their composition properties. The assessment of results shows that stucco masters in those periods exerted control over the setting process of the gypsum-paste and its microstructure by adjusting water-to-plaster ratio, fine-clay addition, and by means of mechanical processing. Furthermore, the presence of anhydrite in the composition of stucco decorations located in the hot-desert climate of Iran provides evidence for the probability of gypsum-anhydrite transition, which has technical and preservation consequences for this less-investigated type of cultural materials. • Multimodal analyses , (XRD, XRF, SEM) studied gypsum-based stucco in 47 monuments from 11th-14th century Iran. • Stucco masters controlled gypsum paste by adjusting the water-to-plaster ratio, incorporating fine clay, and mechanical processing. • Anhydrite in stuccoes from hot-desert climates suggests a possible gypsum-anhydrite transition affecting their properties and preservation.