Archaeological Research of Iran

Archaeological Research of Iran

Manufacturing Technology and Corrosion Mechanisms of Ancient Metal Artifacts from Qalaichi Tepe

Authors
Hamidreza Bakhshandefard 1
,Zahra Rahimi Kelishadi 2
Farshid Iravan Ghadim 3
1 Department of Conservation and Restoration of Cultural and Historical Objects, Faculty of Conservation and Restoration Art University of Isfahan, Isfahan, Iran (Corresponding Author).
2 Department of Conservation and Restoration of Cultural and Historical Objects, Faculty of Conservation and Restoration Art University of Isfahan, Isfahan, Iran.
3 Department of Archaeology, Faculty of Cultural Materials Conservation, Tabriz Islamic Art University, Tabriz, Iran.
10.22084/nb.2025.9515.2664
Abstract
The Mannaean Kingdom was one of the major Iron Age polities that flourished in northwestern Iran during the first millennium BCE. Qalaichi Tepe, identified as the Mannaean capital Izirtu, represents one of the most significant archaeological sites of this period. This study investigates nine copper-based artifacts recovered from systematic excavations conducted at Qalaichi between 2002 and 2004 under the direction of Bahman Karegar. The assemblage comprises a complete bracelet, one fragmented object, and seven additional metal fragments dating to the first millennium BCE. The research aims to reconstruct manufacturing technology, characterize microstructural features, identify corrosion products, and assess the corrosion mechanisms affecting these artifacts. To achieve these objectives, optical microscopy, metallography, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), and X-ray diffraction (XRD) were employed. Microstructural observations indicate that the artifacts were manufactured through combinations of casting, cold working, hot working, and repeated annealing, reflecting advanced metallurgical knowledge. SEM–EDS analyses showed that seven artifacts were made of tin bronze, whereas two specimens consisted of nearly pure copper. Elongated sulfide inclusions preserved within the metallic matrix indicate incomplete smelting of sulfidic copper ores and provide evidence for the nature of raw materials and extraction technology. XRD identified the principal corrosion products as cuprite (Cu₂O), nantokite (CuCl), malachite (Cu₂CO₃(OH)₂), and brochantite (Cu₄SO₄(OH)₆), reflecting complex burial-induced corrosion processes. Microstructural evidence further demonstrates selective corrosion characterized by preferential dissolution of the copper-rich phase, secondary tin enrichment, intergranular corrosion, microcracking, and localized porosity. Despite variations in corrosion intensity, the artifacts exhibit notably similar manufacturing characteristics, suggesting standardized metallurgical practices within Mannaean workshops. These findings provide new insights into Iron Age copper-alloy production technology in northwestern Iran while contributing valuable archaeometallurgical data for understanding Mannaean metallurgy and informing the conservation of archaeological copper-based cultural heritage.
Keywords
Qalaichi Tepe, Mannaean Culture, Manufacturing Technology, Corrosion Mechanisms, SEM&‌‌‌ndash
EDS
Subjects
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Archaeological Research of Iran
Volume 16, Issue 49
2026
Pages 147-181