Bronze: the alloy of two metals that gave a whole age its name

The Olympic Games award a bronze medal for third place. But few people know that the metal does not occur in nature in this form. It is an alloy made by humans. Its discovery was so important that historians named a whole period of human history after it: the Bronze Age.

What is bronze?

Bronze is essentially a mixture of copper and tin. According to the Royal Society of Chemistry in Britain, when about 5 per cent tin was added to copper, the result was a metal that melted at a lower temperature and was therefore easier to work. It was also much harder than pure copper. It proved the best material for tools and weapons.

Researchers Omid Oudbashi and colleagues, who reviewed ancient metalworking on the Iranian plateau, say that adding about 10 per cent tin makes the metal harder and stronger still. This quality gave bronze the edge over copper.

First arsenic, then tin

The path to bronze was not straight. According to Oudbashi and his colleagues, early craftsmen first used ores that naturally contained arsenic. This produced “arsenical copper”. They say this alloy was an important stage in the journey from copper to tin bronze. They say it became common in the Near East in the second half of the fourth millennium BCE, and probably began with the accidental use of arsenic-rich ore. The Louvre Museum in Paris holds a double axe of this kind from Susa in Iran, dating to the middle of the fourth millennium.

According to the same review, true tin bronze appeared in Mesopotamia and western Iran in the late fourth and early third millennium. Its extensive use began in the middle of the third millennium. Researchers generally date the Bronze Age in south-west Asia from 3300 to 1500 BCE. According to the Royal Society of Chemistry, the peoples of Egypt, Mesopotamia and the Indus valley were using bronze by about 3000 BC.

A surprising foil from Serbia

In 2013, Miljana Radivojević and colleagues published an unexpected discovery in the journal Antiquity. At Pločnik in Serbia, a thin foil of tin bronze was found in the floor of a house near a copper workshop. It dates to about 4650 BC. The researchers say it is the earliest securely dated example of tin bronze known so far. It pushed back the history of bronze making by about 1,500 years.

They say this bronze was not made by deliberately mixing two metals. It was made by smelting an ore that naturally contained both copper and tin. In the researchers’ view, the find challenges the common belief that bronze was first made in the Near East.

The search for tin

Obtaining tin to make bronze was not easy. According to a Royal Society of Chemistry programme, tin was so important that the secrets of its trade were closely guarded. According to Radivojević and colleagues, several tin sources used in the Bronze Age have been identified in present-day Iran, Afghanistan, Uzbekistan and Tajikistan. The same programme says the Greeks spoke of “Tin Islands” that were never found. Their tin probably came from northern Spain and Cornwall in Britain. All the Greeks knew was that tin came by sea from the north-west.

Bronze of the Indus valley

In our own region, the craftsmen of the Indus valley were skilled in bronze. According to the World History Encyclopedia, the people of Harappa made knives, fish hooks, arrowheads, saws, chisels, sickles, pins and bangles from copper and bronze. They also cast vessels and statuettes from it.

Their most famous work is a small bronze statuette known as the “Dancing Girl”. It is about 10 centimetres high and was found at Mohenjo-daro in 1926.

Bronze today

Bronze is still part of our lives. According to the Royal Society of Chemistry, most tin is now used in alloys, including bronze, phosphor bronze and solder. Tin is added to bell metal because it is the most resonant of all metals.

The experiment a craftsman made five thousand years ago by combining two metals gave humans tools far stronger than those of stone and copper. The search for tin also linked distant regions to one another.