Bronze mirror with light patina, Roman, 100 BC-100 AD.
© Science Museum / Science & Society Picture Library
Bronze is an alloy of copper and tin, yellow or brown in colour. It is harder than pure copper, more suitable for casting and also resists corrosion. Bronze may contain as much as 25% tin, together with small amounts of other metals, mainly lead. It is one of the earliest metal alloys known, and was used widely by early people in the period known as the Bronze Age (about 5000-1200 BC in the Middle East and about 2000-500 BC in Europe). Knowledge of bronze was slow to spread, and depended on the availability of tin, a scarce metal. The Aztecs did not discover the alloy until the 15th century, and in sub-Saharan Africa, Australasia and much of America there was never a Bronze Age at all.