A Multianalytical Approach for the Study on Manufacturing Process in Ancient Bronze Coffin From Luristan, Western Iran

Abstract

In this study, a recently discovered metallic coffin from the Chubtarash village, near Khorramabad, Luristan area, western Iran is investigated to identify alloy composition and manufacturing process. It is a large metallic bathtub-like coffin in which a skeleton is found with two gold strips covering its eyes and mouth. The coffin has four metallic handles that are joined to the bathtub body with pins. The coffin has been made in one piece but has been broken into some pieces during burial time. For this study, two samples from different parts of the coffin were selected. They have been analyzed with inductively coupled plasma-mass spectroscopy (ICP-MS), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), and metallography methods to identify alloy composition and manufacturing process. Results of chemical analysis showed that the coffin is made of binary copper-tin alloy. Other elements such as Zn, Pb, and As are detected as minor components. In fact, these elements cannot be considered as the alloying constituent in the composition. The microstructure of bronze in scanning electron microscopy-backscattered electron (SEM-BSE) micrographs shows that the thick edge of the coffin has a two-phase microstructure including alpha matrix and eutectoid mixture, while thin body includes a single phase alpha solid solution. Further, it is visible that the bronze in the coffin is corroded heavily at the thin body area. Etched microstructure of the coffin includes equi-axed grains with twin lines and strain bands indicating application of a cycle of cold working and annealing to shape this large bronze coffin into one piece.