We just learned about Coal.
Another fuel used for metalworking is called Coke.
Coke is made by taking coal and heating it up very very hot, sometimes over 2,000 degrees F!
It is baked and heated for a long time, sometimes for days.
When it is done, the coke is removed and then can be used as fuel for smelting, that will burn even hotter and faster than a wood fire or charcoal fire.
(from: wikipedia - coke (fuel))
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