Tin is an essential metal in the creation of tin-bronzes, and its acquisition was an important part of ancient cultures from the Bronze Age onward. Its use began in the Middle East and the Balkans around 3000 BC. Tin is a relatively rare element in the Earth's crust, with about two parts per million (ppm), compared to iron with 50,000 ppm, copper with 70 ppm, lead with 16 ppm, arsenic with 5 ppm, silver with 0.1 ppm, and gold with 0.005 ppm. Ancient sources of tin were therefore rare, and the metal usually had to be traded over very long distances to meet demand in areas that lacked tin deposits. Known sources of tin in ancient times include the southeastern tin belt that runs from Yunnan in China to the Malay Peninsula; Afghanistan; Cornwall and Devon in Britain; Brittany in France; the border between Germany and the Czech Republic; Spain; Portugal; Italy; and central and South Africa. Syria and Egypt have been suggested as minor sources of tin, but the archaeological evidence is inconclusive.
Early use
Tin extraction and use can be dated to the beginning of the Bronze Age around 3000 BC, during which copper objects were formed from polymetallic ores which had different physical properties. The earliest bronze objects had tin or arsenic content of less than 2% and are therefore believed to be the result of unintentional alloying due to trace metal content in copper ores such as tennantite, which contains arsenic. The addition of a second metal to copper increases its hardness, lowers the melting temperature, and improves the casting process by producing a more fluid melt that cools to a denser, less spongy metal. This was an important innovation that allowed for the much more complex shapes cast in closed molds of the Bronze Age. Arsenical bronze objects appear first in the Middle East where arsenic is commonly found in association with copper ore, but the health risks were quickly realized and the quest for sources of the much less hazardous tin ores began early in the Bronze Age. This created the demand for rare tin metal and formed a trade network that linked the distant sources of tin to the markets of Bronze Age cultures. Cassiterite (SnO2), oxidized tin, most likely was the original source of tin in ancient times. Other forms of tin ores are less abundant sulfides such as stannite that require a more involved smelting process. Cassiterite often accumulates in alluvial channels as placer deposits due to the fact that it is harder, heavier, and more chemically resistant than the granite in which it typically forms. These deposits can be easily seen in river banks, because cassiterite is usually black or purple or otherwise dark, a feature exploited by early Bronze Age prospectors. It is likely that the earliest deposits were alluvial and perhaps exploited by the same methods used for panning gold in placer deposits.
Archaeological importance The importance of tin to the success of Bronze Age cultures and the scarcity of the resource offers a glimpse into that time period's trade and cultural interactions, and has therefore been the focus of intense archaeological studies. However, a number of problems have plagued the study of ancient tin such as the limited archaeological remains of placer mining, the destruction of ancient mines by modern mining operations, and the poor preservation of pure tin objects due to tin disease or tin pest. These problems are compounded by the difficulty in provenancing tin objects and ores to their geological deposits using isotopic or trace element analyses. Current archaeological debate is concerned with the origins of tin in the earliest Bronze Age cultures of the Near East.
Ancient sources
Europe
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