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Bit of a niche question here, but I’ve been mulling this over in my head for a while now. I’ve only ever seen or heard of people using lump charcoal to smelt iron in a bloomery furnace. What if, for example, you have a culture in a desert or plains environment where wood is too valuable to burn in large quantities, but they have relatively easy access to coal mines and are experienced in stone-working and mining.

Could they use coal to operate a bloomery furnace? Would you still use 1:1 by weight of coal to ore as with charcoal, or would you have to change it? Would these answers be different if it’s anthracite coal vs bituminous? And finally, if bituminous coal isn’t workable, what if they made it into coke first?

Are there impurities in the coal that would be absorbed into the iron that would affect its quality? Would the coal make the furnace too hot or too cold to properly smelt the ore into a bloom?

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They used char coal because that was the only form of coal they had, not because of magic properties. Yes, decent quality stone coal works just as well; it just was simply not available before late medieval times, because of how poorly developed transportation networks were.

Coke is basically char coal made from stone coal. Anything you can do with one you can do with the other.

As for impurities, bloomery furnaces actually produce a spongy mass of iron mixed with slag. It needs to be purified anyway, by heating it up and beating the slag out with big hammers.

Note: Char coal is spelled like this intentionally, to indicate that char coal and stone coal are both forms of coal.

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    $\begingroup$ This summer I have been to a museum enacting a prehistoric village, the furnace section explained that 10 kg of wood were needed to make 1 kg of charcoal, which would then be put in the furnace with 1 kg of ore to get the spongy mass of pig iron. $\endgroup$
    – L.Dutch
    Sep 19, 2022 at 12:22
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    $\begingroup$ Not really applicable to an arid environment, but peat can also be made into charcoal/coke. If you need it badly enough. $\endgroup$
    – Zeiss Ikon
    Sep 19, 2022 at 12:43
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    $\begingroup$ @L.Dutch Pretty sure the minimum quantity for the bloom process is a lot more than 1 kg -- and you need more charcoal/coke than ore. $\endgroup$
    – Zeiss Ikon
    Sep 19, 2022 at 15:52
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    $\begingroup$ @ZeissIkon, it was just the proportion, to make visitors figure out how much effort was needed to make a small amount of iron, because of course that wood had to be chopped $\endgroup$
    – L.Dutch
    Sep 19, 2022 at 16:49

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