There isn’t an intrinsic method of dating metal as there is for wooden objects such as radiocarbon-dating or tree-ring dating. Much depends on the assessment of the object. For instance, an axehead made of bronze is likely to date from the Bronze Age, before knowledge of how to make iron. The date of the discovery of metal-working is going to vary in different parts of the world, but in Britain it will be towards the end of the third millennium BCE – roughly 2300-2000 BCE. The method of working the metal is also a crucial factor for ageing. Casting of iron only became possible during the Industrial Revolution in north-west Europe, for example.
Answered by Bryan Sitch, Manchester Museum.