What bronze is
Bronze is an alloy, a mixture of metals, made mainly of copper with tin added. A typical ancient tin bronze contained somewhere around one tenth tin, though recipes varied widely by place and purpose. Later bronzes used other additions, such as lead, which made casting easier, and in some regions the term is applied to copper alloyed with other elements.
The “Bronze Age” is a modern label used by archaeologists for the period in which bronze was the main metal for tools and weapons. It did not begin or end at the same time everywhere. In parts of the Near East bronze use is often dated from roughly the late fourth millennium BCE, in Europe somewhat later, and in many regions it gave way to iron near the end of the second millennium BCE or later.
Before tin: copper and arsenic
Pure copper is soft. Hammered copper tools dull quickly, and cast copper can be full of gas bubbles. Early smiths in several regions improved it by smelting copper ores that naturally contained arsenic, producing arsenical copper, which is harder and casts better. The fumes were hazardous to the smiths, and the arsenic content was hard to control, since it depended on the ore.
Why tin bronze won
Adding tin made a dependable improvement. Compared with pure copper, tin bronze:
- is noticeably harder, and can be hardened further by hammering
- melts at a somewhat lower temperature, so it is easier to melt in a simple furnace
- flows better into a mold, producing sharper detail and fewer flaws
- can be remelted, so broken tools and scrap are recycled into new ones
Bronze was never as strong as good steel would later be, but it gave an edge that held better than copper and could be cast into a wide range of shapes.
How it was made
Smiths smelted copper ore with charcoal in a small furnace, and either added tin metal or tin ore (cassiterite) directly. The molten alloy was poured into molds. Early molds were open, carved from stone, and later two-piece closed molds of stone or clay were used to make socketed axe heads, spearheads and swords. For complex objects such as figurines or bells, craftspeople used lost-wax casting, covering a wax model in clay and melting the wax out. The finished casting was then hammered, ground and polished. Some bronzes were also sheet metal, hammered thin and joined by rivets.
The tin problem
Copper ore is found in many places, but tin deposits are fewer and more scattered. That meant tin often had to be moved far from where it was mined. Sources likely used in antiquity include parts of Central Asia and the Iranian plateau, Cornwall and Devon in Britain, Brittany, the Iberian Peninsula and Central Europe’s Ore Mountains. Exactly which sources supplied which regions at what time is a lively research topic, and the evidence is not always conclusive.
Some physical evidence is clear. A shipwreck found off Uluburun on the southern coast of present-day Turkey, dated to roughly the fourteenth century BCE, carried a large cargo that included copper ingots and tin. Written records from Mesopotamian trading communities also mention tin shipments. Together these show that tin moved by overland caravan and sea over long distances.
Trade, power and disruption
Because tin was scarce, control of its supply could mean influence, and trade networks carried not only metal but also ideas, styles and techniques. Some scholars have linked disruptions to trade around 1200 BCE, a time of upheaval in the eastern Mediterranean, to growing interest in iron, which was available from widely distributed ores. This connection is debated, and iron’s rise probably had several causes, including the long-term development of the bloomery furnace.
Legacy
Bronze never disappeared. It continued to be used for statues, bells, coins, mirrors, weapons and later ship fittings, gears and bearings. Modern bronzes still show up in sculptures and machine parts, where their wear resistance and corrosion resistance are valued. The Bronze Age is a useful reminder that alloying, mixing metals on purpose to get new properties, is one of metalworking’s oldest ideas.