Before the Iron Age
The history of iron can be identified from the eyes of ancient blacksmiths. For example: many questions are raised regarding why Iron Age could not have begun at about the same time as the early Bronze Age as it clear that blacksmiths of that time had enough information of their forging work. They could easily observe the color change during scratch tests and heating. The blacksmiths’ greatest artistic accomplishments were the Damascus and Japanese steel swords. The results achieved to do useful work that enhances the high temperature processing of carbon steels and that improves the low and intermediate temperature mechanical properties.
Copper and bronze were not being hardened by heat-treatment. There was only one way to harden them by work-hardening. To make this happen, a joint of bronze was lightly hammered for a long period of time. The localized repetitions caused the essential changes. The hardened bronze can then be ground to sharpen it to make edged tools.