Ore to iron: Smelting in the Highlands

Back before I started my pottery, I studied Experimental Archaeology and happily fell into a project researching how early Scandinavian settlers in Iceland smelted iron, and I got to 'reconstruct' the process. This started off 8 years and counting of building ceramic furnaces and then chucking loads of iron ore and charcoal into it, pumping bellows to get it HOT and (hopefully... usually...) making iron out of earth!


Furnace in action

The process is called bloomery iron smelting. It was used in northern Europe at least from the start of the iron age until around the 15th century. It's tricky to reproduce archaeologically accurate smelting since furnaces almost never survive aside from a base pit, but we think they built shaft furnaces which create a reducing atmosphere where the charcoal and iron ore is burning without much oxygen. This atmosphere converts the ore into metallic iron and also melts out the excess rock parts of the ore which turns to a waste product called slag. Slag is often found in archaeology, sometimes the raw iron called 'blooms' survive too as a rough block. The weird thing about bloomery smelting is that the iron never melts, it forms as a solid roughly stuck-together block that needs loads of forge welding and processing to make into a bar and then tools, blades etc. It's a super intensive involved process to make iron, make a bar and then make a thing. That metal was so precious!


The roasted ore

Our lovely Scottish birch charcoal from Big Tree Charcoal.

Building the ceramic furnace

Now, I'm making it sound simple.... There's a ridiculous amount of variables involved and even with a pretty reliable and repeatable system to make metal, sometimes the metal god's just feel like causing mischief and throwing in a weird smelt here and there. We just had one of those!


I came together with some friends to try and smelt iron in the hills around Loch Tay, starting with ore (maybe limonite?) that had been hand dug up only a few miles away. We spent our first day setting up camp and roasting the ore. Day two in true Scottish fashion pissed it down so we worked to build a furnace whilst it was squishing and slumping in the rain... An interesting experience! And day 3 we tried our smelt, even adding an offering to the furnace as seems to be done in many cultures to try and ensure our efforts paid off. We know almost nothing of any beliefs tied into ancient Scottish smelting but who knows, maybe they made offerings, added faces or painted designs. Metalwork, especially smelting, is alchemy after all!




The smelt was interesting from the start. We had slag bubbling and blocking the tuyere almost from the word go. The slag didn'twant to come out when we coaxed it so we had to interfere andpull it out. The bellows decided to malfunction. The furnace had to be emergency opened since the air wasn't getting in. And after all that we had almost only slag with only little bitty prills of iron instead of several kilos that we'd hoped for. Oh well, we learn and sometimes that's just how it goes, seems like this time too many thing just went a bit awry. Would've been devestating if that happened to craftsmen in the past relying on the product though!


Pulling out molten slag


Until next time my furnace friend!

Thanks to Peter from the Woodland Tannery for the ore, and Andrew for the charcoal from Big Tree Charcoal.

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