Copper Sheet Forged from Cast Copper

Copper is soft and can be hammered thin cold, but every blow hardens it until it cracks. Heating it to a dull red anneals it soft again; unlike steel, copper can be quenched straight away without hardening. Hammer, anneal, repeat: that is how sheet was made before rolling mills. It starts from a cast piece of smelted copper. A rolling mill does the same job faster; the hammer needs nothing but an anvil.