Chemical and Metallurgical Investigation of Bronze Vessels from the Archaeological and Anthropological Museum of Rasht, Guilan (Iran)

In this research, 18 bronze vessels belonging to the Rasht Museum's treasure were studied. The aim of this study was to obtain more details about the metallurgy of the bronze vessels, including their manufacturing process, chemical composition, and microstructures. To this end, a comprehensive investigation by optical microscope (OM), scanning electron microscope equipped with an energy-dispersive spectrometer (SEM-EDS), and micro x-ray fluorescence (mu XRF) was used. Chemical analysis of the samples confirmed a binary alloy composition of high-tin bronze (Cu-Sn), also known as beta bronze. Metallographic examinations indicated that all bronze vessels exhibit quenched beta needles and islands of alpha phase. Additionally, some of the grains are clearly twinned with straight twin lines, suggesting that all samples have been subjected to hot working. Furthermore, the vessels have been quenched from high enough temperatures (586-798 degrees C), effectively preventing the formation of delta phase. Overall, the microstructural investigation of the vessels clearly demonstrated that variation exist not only with the extent of hot forging but also with the speed and the temperature from which they were quenched.