How did ancient civilizations make furnaces hot enough to melt metals like copper or iron with just charcoal, wood, coal, clay, dirt and stone?

Question

How did ancient civilizations make furnaces hot enough to melt metals like copper or iron with just charcoal, wood, coal, clay, dirt and stone?

In: Engineering

Answer 1

A simple clay brick furnace with a bellows attached to a tuyere can get hot enough to melt, or at least soften, iron to be shaped or poured into a mould.

Primitive Technology on Youtube has a few experiments with iron bacteria.