Bras is an alloy of copper and zinc. Bras which contains a proportion of les than 36 per cent zinc is ductile when cold and can be easily worked into complex shapes. A proportion of zinc greater than 36 per cent makes a harder and stronger alloy. The earliest bras was made by the Ancient Greeks, probably around 330 BC, but the Romans were the first to produce the alloy in any quantity. This early coin is from a collection formed by Dr John Percy (1817-1889) FRS, between 1842 and 1889, illustrative of his treatise on metallurgy. The collection comprises examples of fuels, ores, metals and their alloys, with specimens illustrating the adaptability of various metals to industrial purposes.
© Science Museum / Science & Society Picture Library