'Bow' type fibula brooch, c 700-500 BC.
© Science Museum / Science & Society Picture Library
Found at Hallstatt in Austria, this Celtic brooch is made of bronze and deeply ribbed with a light green patina. 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.