Arsenical bronze

The use of arsenic with copper, either as the secondary constituent or with another component such as tin, results in a stronger final product and better casting behavior.

[2] Although arsenical bronze occurs in the archaeological record across the globe, the earliest artifacts so far known, dating from the 5th millennium BC, have been found on the Iranian plateau.

The method of manufacture involved heating the metal in crucibles, and casting it into moulds made of stone or clay.

After solidifying, it would be polished or, in the case of axes and other tools, work-hardened by beating the working edge with a hammer, thinning out the metal and increasing its strength.

Firstly, the Iranian plateau, followed by the adjacent Mesopotamian area, together covering modern Iran, Iraq and Syria, has the earliest arsenical bronze metallurgy in the world, as previously mentioned.

There was a great deal of variation in arsenic content of artifacts throughout this period, making it impossible to say exactly how much was added deliberately and how much came about by accident.

The two relevant ancient sites in eastern Turkey (Malatya Province) are Norşuntepe and Değirmentepe, where arsenical bronze production was taking place before 4000 BC.

According to Boscher (2016), at Değirmentepe, arsenical copper objects were clearly manufactured around 4200 BC, yet the technological aspects of this production remain unclear.

[10] In contrast, the related Norşuntepe site provides a better context of production, and demonstrates that some form of arsenic alloying was indeed taking place by the 4th millennium BC.

It was in this period that the use of copper became widespread throughout the Levant, attesting to considerable technological developments that parallel major social advances in the region.

[14] Arsenical copper was also processed in the workshop uncovered at Giza's Heit el-Ghurab, "lost city of pyramid builders" from the reign of Menkaure.

[18] One of the largest studies of such material was the research of the Egyptian and Nubian axe blades in the British Museum, and it provided comparable results.

The use of arsenical bronze spread along trade routes into northwestern China, to the Gansu–Qinghai region, with the Siba, Qijia and Tianshanbeilu cultures.

By contrast, the south and central Andes, southern Peru, Bolivia and parts of Argentina, were rich in the tin ore cassiterite and thus did not use arsenical bronze.

[26] A well-preserved mummy of a man who lived around 3,200 BC[27] found in the Ötztal Alps, popularly known as Ötzi, showed high levels of both copper particles and arsenic in his hair.