The study of metal works of Bam citadel (Arg-e-Bam) is underway to study the pathology of metalworks in Iran.The aim of this project is to study and investigate the corrosion mechanisms of metal objects. Various metallic works including iron, silver and copper alloys have been gained from the area of Arg-e-Bam. The research is focused on a number of bronze works of this historical site.The studies have been done using Microscopic and Macroscopic methods including metallography, wet chemistry, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). According to dendritic structure of these objects, the results show that most of them have been made in casting method and corrosion products are including Cuprite (Cu2O), Azurite (Cu3(CO3)2(OH)2), Brochantite (Cu4(OH)6SO4), Cassiterite (SnO) and the chloride compounds like Atacamite (Cu2Cl(OH)3), Paratacamite (Cu2Cl(OH)3, Nantokite (CuCl) and Melanothallite (Cu2OCl2). The noticeable point is that there are inclusions containing iron and sulfur in all specimens that represent the using of sulfide ore in copper extraction process.
With the advent of Islam, bronze temporarily replaced gold and silver in the production of metal vessels. Among the bronze artifacts used during this period, high-tin bronze (white bronze) objects, valued for their silver-like appearance, gained significant attention. One such artifact is a vessel discovered during debris removal operations following the 2003 Bam earthquake, located in the southern part of the Bam Citadel, specifically the southern section of the house known as Mir Akbar. Similar decorative patterns are found in artifacts from the Seljuk and Timurid periods. In this study, the artifact was examined using X-ray imaging, and microstructural analysis of a sample from the vessel’s base was conducted using reflected light optical microscopy after preparation. To further the technical investigation, Scanning Electron Microscopy (SEM) equipped with Energy-Dispersive X-ray Spectroscopy (EDX) was employed to analyze the alloy composition and metallic and non-metallic phases. The results indicate that the vessel was produced through casting, with directional mechanical work causing elongation of non-metallic sulfide phases within the metal matrix. The microstructure of the vessel consists of single copper-rich grains dispersed in a needle-like beta phase rich in tin, characteristic of high-tin bronze (white bronze). After cooling, the alloy underwent heat treatment at approximately 650°C followed by rapid quenching, leading to the formation of the needle-like phase and resulting in the vessel’s hardness and brittleness.
