Investigation on the Bronze Metallurgy of Tepe Marlik, Gilan

The emergence of copper production on Iranian Plateau goes back to about 7th Millennium B.C. This technology was continued till late 4th/early 3rd millennium B.C. when the bronze (copper-tin alloy) was raised as a new product to make different objects and was developed during the Bronze Age. The bronze production was the main archaeo-metallurgical activity even in the Iron Age of Iranian Plateau. Many bronze objects were discovered during different archaeological excavations from various Iron Age sites of Iran. Archaeological excavations at Marlik graveyard, Northern Iran was carried out by late E.O. Negahban in 1961-62 lead to reveal some important archaeological remains from Iron Age I and II. The metal collection of Marlik including various gold, silver and bronze artefacts is consisting of one of the significant metal finds from prehistoric Iran. Many of these objects are produced by tin bronze alloy and study on bronze technology of Marlik metal collection may lead to identify bronze technology during the Iron Age. This paper constitutes an analytical investigation on some bronze alloy from Marlik which are preserved in the National Museum of Iran now. Chemical composition of 25 artefacts is determined to reveal the metallurgical processes in Northern Iran by the 2nd/1st millennium BC. Analytical studies were carried out using ICP-MS quantitative method; The results proved that the samples have been manufactured with a binary copper-tin alloy with a variable tin content from 4 to 11 percents in weight. Other elements such as, As, Ni, Pb, Zn and Sb are detected as minor/trace amounts. Variable tin content which may relate to application of an uncontrolled procedure of bronze alloy production (i.e. co-smelting or cementation). On the other hand, the results were compared with the results of previously performed analytical studies on other bronze objects from Marlik. Based on the comparative studies, the variable tin amount was observed in all analysed samples; further, Arsenic has detected as a major element in some previously analysed samples while the recent results showed that Arsenic is a minor/trace element in the composition of bronze objects. Also, the composition on the previous and new analysed objects was compared on the basis of some trace element contents and some differences which were observed in the composition of objects especially because of their arsenic content. These differences may be due to using different metal resources to produce some objects of Marlik or these objects may be manufactured in another place with a partially different technology and imported to Marlik as votive objects.