Near Eastern ancient bronze objects from Tell Beydar (NE-Syria): insights into their corrosion

T site of Tell Beydar is located in north-eastern Syria, somewhat 30 km north of the modern city of Hasake, along the river Khabur (Figure 1) [1]. The history of Tell Beydar starts with the foundation of Nabada, its ancient name, around 2800 BC. Semitic nomad tribes were most probably the founders of this city. A palace was built around 2500 BC and the city passed through a period of great prosperity. At the end of the 25th century BC Tell Beydar was placed under the reign of the kingdom of Nagar (Tell Brak), whose king was visiting Nabada at regular periods in order to participate in certain religious and political events. The city was dominated by Akkadian oppressors during the Akkadian period (2350-2200 BC) and was finally abandoned. The lower parts of the city were again inhabited in 1500 BC by the Mitanni. In the 7th century BC Assyrians built their homes at Tell Beydar. Again Tell Beydar was departed until the Seleucidians and Parthians started to inhabit the upper town in the 4 century ad [2]. Excavations at Tell Beydar have been conducted by a European-Syrian mission under the direction of the European Centre for Upper Mesopotamian Studies in Brussels [3]. All of the bronzes discussed in this work (twenty in total) were excavated during the 1994, 1998 and 1999 field seasons. The samples date to the Early Dynastic II-III period (2700-2300 BC). In a preceding study, chemical analysis and metallographic examination of a set of copper alloy objects were performed [4]. The objective here was to identify the metals used at Tell Beydar during different periods of occupation. Drawings of the objects are shown in Figure 2. Results showed that four different compositional groups could be distinguished based on their arsenic and tin content: a low arsenic group (As 2 w%),an intermediate tin group (Sn between 3 w% and 6 w%) and a high Sn group (Sn> 7 w%). Moreover a clear chronological sequence in the use of copper alloys at Tell Beydar could be observed. Throughout the EDII period (2700-2600 BC) low and high arsenical bronzes were in use simultaneously, while there is clearly no evidence of the presence of tin bronzes. Later, during the EDIII period (2600-2300 BC), tin bronzes come into use and the presence of high arsenical bronzes ceases. Finally during the Akkadian (2300-2200 BC) period results show that both tin bronzes and high arsenical bronzes are no longer present. The fact that Tell Beydar was part of another kingdom during this Akkadian period is a possible explanation for the disappearance of the tin bronzes. Later on, during the Seleucid and Parthian occupation (400 BC – 200 AD), tin bronzes appear again in the metal repertoire of Tell Beydar. Apart from these conclusions the results also indicated that the studies of Tell Beydar bronzes have possibly a different provenance. The study of the microstructure revealed that, in general, the same basic working techniques were used during the period studied. Basically the rough shape of the object was formed by casting the liquid metal into a mould. The object was hammered into shape, both cold and hot, after cooling down. Although it is clear that the same basic methods were used throughout the various periods, the evolution of the microstructure shows that metal smiths were achieving better control over the process of cold and hot working the metal. At the end of the development period the metal smith knew how to create objects having the same composition but with different properties, especially hardness.