Energy · c. 6,000 BCE

Charcoal making

Slow-burning wood without air yields a clean, hot fuel for metalworking.

Charring wood in low-oxygen pits or mounds drives off water and volatiles, leaving nearly pure carbon that burns above 1,000 C. Charcoal made copper smelting and later iron smelting practical, and it remained the metallurgical fuel of choice until coke replaced it in the 18th century.

See it in the living treeWikipedia