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Rasouli A, Hejebri-Nobari A, Khamseh H. (2021). Microscopic and Structural Studies of Bronze Jewelry Obtained from Iron Age Sites in Northwestern Iran. Parseh J Archaeol Stud. 5(16), 69-79. doi:10.30699/PJAS.5.16.69
URL: http://journal.richt.ir/mbp/article-1-368-en.html

Abstract
In explaining Iron Age archeology, the study of metal artifacts is of particular importance because of the hidden technical values. The study of metalworking methods enhances our understanding of the industrial centers of metallurgy, stylistics, and available mines. The purpose of this study is to identify the methods of construction and elemental analysis of “ornaments” discovered from “Iron Age” sites in northwestern Iran, using metallographic experiments and an SEM-EDS elemental analysis device. In the Iron Age, the making of metal objects, especially those with many ornaments, flourished. Therefore, knowing the manufacturing methods and the type of alloy used in them is one of the essentials of this research. This research responds to the question, what methods used to make the discovered ornaments from the Iron Age sites in the northwest? Or what were the most used elements in the construction of these objects? In these areas, the current research hypothesis is that most of the “ornaments” made by hot hammering and casting methods and have a large amount of tin in their structure, which uses for greater strength and flexibility of copper and tin (bronze) alloys. In this study, several samples of ornaments discovered from Iron Age sites in northwestern Iran, which were geographically very close to each other, were tested by metallography and elemental analysis. In this experiment, using a scanning electron microscope equipped with an SEM-EDS element analyzer, making these metal objects and their constituent elements were determined. This study shows that the main methods of making these metal objects have been hot hammering, but those objects that had a large volume made using the casting method. Also, the most used element to increase the strength and flexibility of objects is the element of tin. 
Keywords: Iron Age, Northwest of Iran, Bronze Objects, Metallography, SEM-EDS.

Introduction
In the Iron Age areas of the northwest, metalworking was done at an advanced level. The expansion of the tradition of metalworking in the northwest can be seen in other Iron Age areas of Iran. (Talaei, 2001:77-83) One of the reasons for the development of metalworking in the Iron Age areas of northwestern Iran has been the abundance of copper and iron ore mines in this region. During the excavations of the Hasanlu area in the south of Lake Urmia, founded a large number of iron and bronze objects. The large volume of metal objects discovered in the Hasanlu area indicates the prevalence of metalwork in this region of the Iranian plateau. (Pigott, 1989: 67-79) According to the studies, the residents of Hasanlu have supplied their required copper ore and iron ore from the mines that probably existed around this area. The development of metalworking art in this region, in addition to the existence of metal mines and fuel reserves, has been the development of furnaces and metal smelting molds, which in some Iron Age sites such as Hasanlu, obtained a large number of these metal smelting molds. The main reasons for the development of technology and style of metal products in northwestern Iran in the Iron Age could have been powerful governments such as Urartians and Manas. (Aliun and Sadraei, 2011) They were skilled metalworkers in the vicinity of Iron Age sites. One of the signs of this effect is discovering a bronze bracelet discovered in the Toul Talesh cemetery in northern Iran, which shows the expansion of Urartian territory in this region. There is a Urartian cuneiform inscription on it. This inscription shows that Argishti II, King of Urartu, gave this bracelet to Khaledi God. This person could have been a prince or a military person. (Tahmasebi and Masoudi Nia, 2015) The main issue of this research is to know the construction methods and the constituent elements of the jewelry discovered from the northwestern region of Iran. In the Iron Age, especially the Seldouz valley, these sites are primarily located in the Seldoz Valley and are geographically very close to each other, which can help understand the methods of construction and elemental analysis of the metal samples tested. The present research has been done by analytical-experimental method and based on scientific and laboratory studies. The purpose of this study is to identify the methods of construction and elemental analysis of “ornaments” discovered from “Iron Age” sites in northwestern Iran, using metallographic experiments and an SEM-EDS elemental analysis device. This research responds to the question, what methods used to make the discovered ornaments from the Iron Age sites in the northwest? Or what were the most used elements in the construction of these objects? In these areas, the current research hypothesis is that most of the “ornaments” made by hot hammering and casting methods and have a large amount of tin in their structure, which uses for greater strength and flexibility of copper and tin (bronze) alloys.

Materials and Methods 
In this research, the first eight metal samples from different Iron Age sites in northwestern Iran were collected through the reservoir of the National Museum of Tehran and sampled in the same place, and then sent to the Materials and Metallurgy Laboratory of the Sharif University of Technology for metallographic testing.

Discussion
Laboratory analysis and elemental analysis of metal samples using the SEM-EDS method show that a small amount of arsenic was founded in the alloy composition of the samples Because most copper metal ores before extraction and smelting contain amounts of arsenic. Therefore, there is a possibility of the unintentional existence of arsenic in the composition of these metals. Another element that a large percentage obtained in the composition of these metal samples is tin. Metallographic images of the ML-98-7 and ML-98-8 specimens show that these two specimens have a branched or dendritic structure in their body and are made by casting. Also, tiny cracks on the metallographic images of ML-98-2-ML-98-3 and ML-98-6 samples formed due to stress and fatigue caused by continuous hammering work on these metal works. The dark spots seen in most of these microscopic images indicate oxygen, carbon, and a lack of copper and tin, which have caused corrosion and sulfidation of these metal objects.

Conclusion
The results from the images obtained by scanning electron microscopy equipped with an SEM-EDS device found that the metal samples have a relatively large amount of tin. A small percentage of arsenic found in the metal samples tested. Considering the amount of arsenic in these samples can be concluded that metalworkers of this period may not have noticed the harms of using arsenic at that time and therefore used this element to improve the properties of bronze alloy. Ancient metalworkers used tin, arsenic, and antimony elements in the composition of bronze alloys to increase the hardness of the work. The items in the category of jewelry need to pay more to get the right shape. Another possibility is the unintentional presence of arsenic. The presence of large amounts of tin in these samples indicates that arsenic may have been naturally present in copper ores and Ancient metalworkers used tin to lower the melting point of copper and increase its strength and flexibility. Microscopic studies of bronze objects show that many copper sulfide compounds are present in metal samples. The presence of copper sulfide inclusions dispersed on the surface of the metal matrix and stretched in the longitudinal direction of the microstructure of ancient copper alloys may indicate the use of oxide ores along with some copper sulfide ores for extraction. Most of the ornaments found in the northwestern Iron Age sites, such as bracelets and collars, were made by hot hammering, subsequent hammering or forging, and objects with larger volumes and decorations molded by casting. In general, the objects discovered from the Iron Age sites in the northwest, especially the Hassanlou site, are more complex in terms of technique and construction style than the Iron Age sites in other parts of Iran, where existed local and indigenous governments. This issue has been due to the proximity of northwestern Iran to powerful governments such as Urartu and Manna.