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

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

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How hot a fire can be is determined by the vessel you’re starting it in. The type of fuel you’re using. And how that fire is getting fresh air to use for the burn.

Early civilizations found ways to improve from just making simple fires on open ground to making specifically shaped furnaces with special fuel and forced air delivery to make a fire burn hotter and for longer.

Furnaces with thick walls of clay, mud, and stones insulate the fire so heat isn’t lost to open air or make it difficult to be near such a hot fire. Better shapes allowed air to flow more effectively into the fire and make it burn hotter.

Better ways to deliver air got more oxygen into the fire for a hotter burn. Tuyeres (clay tubes to focus airflow), bellows, etc.

But one of the biggest changes was fuel. Charcoal, and how to reliably produce it, was a huge game changer for early societies working on the foundational metallurgy we’ve built on over the course of centuries and millennia. Charcoal burns hotter, longer, and cleaner than wood.

These things all contributed to tools like bloom furnaces. Which were able to reach temperatures to not just soften metals to make them able to be pounded into useful shapes… But also could make them so hot they melted entirely and could be poured into molds to make jewelry, hand tools, weapons, and armor.

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