prehistoric period (the Copper Age was originally defined as a transition between the Neolithic and the Bronze Age)
In the Bronze Age, people added tin to copper to make bronze, an alloy which is much harder than either tin or copper. During the Copper Age, this fact became known, but was not much used because tin was scarce.
- Trigger, Bruce C. 1996. A history of archaeological thought. 2nd ed, Cambridge University Press. p226
- Miljana Radivojević et al.: On the origins of extractive metallurgy: new evidence from Europe. In: Journal of Archaeological Science, Vol 37, Issue 11, 2010, pp 2775-2787 doi:10.1016/j.jas.2010.06.012