The science of making swords

We visited a blacksmith's forge to explore the science of sword making
19 March 2019

Interview with 

Magnus Sigurdsson, Blacksmith


Sword sitting in a forge's embers


One of blacksmiths' roles in days gone by was making weapons and armour from steel. And although the blacksmiths didn’t realise it, when they were beating a piece of metal, they were driving atoms of carbon from their forges into the crystal structure of the iron, turning it into a hard steel. Jack Tavener went to speak with Magnus Sigurdsson, who still makes swords and other historic implements the way that traditional metal workers have been doing for centuries...

Jack - Swords and armour were our best friend for thousands of years, both weapons of war and means to protect families and possessions. And though we may not use swords any longer modern armour and blades are still very relevant and they were all made with steel, a metal that can be shaped into almost anything.

Now safe to say, it’s pretty hard to find a local blacksmith these days, but Magnus Sigurdsson is one of only a few people in the UK who can make traditional swords, daggers, armour - you name it. I went to meet him at his forge and he showed me the traditional method of making a blade. To start we simply needed the all-important piece of steel...

Magnus - Iron is incredibly difficult to harden. If you turn it into steel, which is just actually iron and carbon, and yet you can vary the amount carbon and the different types of heat process, it can be used for most things from making cooking pots to decent blades to suits of armour. The other thing is, of course, iron ore’s a lot more common than copper and tin so it easier, it's more available, it’s more out there.

Jack - A lot of positives to using steel then. But it's reliant on the carbon content within the iron to make it hard. To understand how carbon does this, imagine a cup of tea and adding a sugar cube, creating a solution where the sugar particles are evenly dissolved throughout. The carbon in the steel is just like the sugar in the tea, the carbon fits in the gaps of the iron's crystal structure preventing the crystals from moving and increasing the hardness of the whole material.

Magnus - It’s difficult in that time because of the smelting process to get good quality steel that's high carbon content all the way through a homogenous piece of steel with good quality carbon all the way through - evenly dispersed. So you can control it to a limited extent on a charcoal powered forge by just heating it through and stacking it. You get to a temperature before the carbon is burnt out but that it will absorb carbon. If it's in basically a stack with almost no oxygen, at the right temperature it will absorb the carbon before it burns it out.

Jack - So that's the point, you bury it in all this charcoal?

Magnus - Yep. You heat it up nice and slowly.

Jack - All the carbon transfers and then that's what gives you that hardness that you're looking for?

Magnus - Yeah. I mean this is the way that they would have done it, you know, through the Medieval period.

Jack - The  forge was already lit, so we stoked up the heat using bellows that filled an entire room next door to blow air through the fire and crank up the flames until they glowed a bright bluey purple colour. Magnus buried our bar of steel into the ferocious charcoal fire at 1,300 degrees celsius. Temperatures this high cause the steel to glow bright orange and become soft so that it can be worked into the shape of our blade. He pulled it out of the fire and started beating it with a hammer over his anvil - that's right, that large chunk of metal often dropped from the sky in the cartoons, and this continuous bashing has a lot of benefits.

Magnus - It’s moving it into a different shape. It's also refining the structure of the steel as you work it, so it's making the structure finer so you're actually improving the quality of the steel. What you're doing here is making the crystals smaller and finer so you've got a small and finer grained structure. You're also working by the feel of the metal and the sound. If I hit where it's colder it rings more, if I hit where it's hotter -  a duller sound. So you can actually feel by how it's responding, how it's working. Everybody thinks it's actually the hammer that's doing a lot of the work but you're actually using the anvil to keep the surface smooth and get rid of the hammer marks. As you can see now it's really lost colour very very quickly. If the steel got a fair amount of carbon in you don't want to work it cold, it will crack the steel.

Jack - And so, it was back into the flames of the forge, then reheat the steel, bash it some more and essentially repeat the process until you've got a sharp edge.

Magnus -  We prefer to refine most of it on the forge, and in the forge on the anvil and not grind it because again, I'm not wasting steel, which they wouldn't have done years and years ago because steel was way too expensive to just grind most of it off. And I feel we get a better quality product; as I said you refining the structure of the steel all the way through so why just grind most of it away.

Jack - how do they know how to make all these different materials?

Magnus - Trial, error, inspired guesswork. At the time they weren't sticking all this under an electron microscope and looking at the structure and things like that, and what they found worked they stuck with. And there were rituals that each blacksmith; he'd have water or his brine at a certain temperature because that worked for him and everything else. I mean if he had an amazing day and did everything perfectly well and he tripped over the step coming into the forge that morning, he would then try and make that part of the ritual. We know in a lot of cases, they carried on using processes where only one bit of the process gave them what they wanted, but because they discovered it by using the other processes, they kept the other processes in. I mean how was iron, bronze first produced? It wasn't a bunch of people sitting by a campfire and noticing that they'd melted metal. So you start off with a copper period; copper's mined very closely to arsenic. If you've got any arsenic in the smelt with the copper, you get bronze. The first bronzes were not copper and tin, they were copper and arsenic which was really good for everybody!

Jack - Hmm, maybe not! Poison aside, it was then time to dunk our blade into some water, otherwise known as quenching.

Magnus - What this has done is suddenly caused all the vibrating particles to actually lock solid. You're trying to get hard and tough. You get hard it snaps, tough is slightly softer so you actually run through several heat cycles to actually get the effect you want. And it's called tempering where you heat it up, quench it, and let heat back into the blade. And different heats and tempering processes give you different qualities in different types of steel.

Jack - Okay. So you trying to make, I guess, a hard edge on the blade but not so that it snaps like a ruler or something? Very easy if you bend it to much it breaks, you wouldn't want that on the battlefield?

Magnus - No, it's a fine line. You've got to work out what you need for what we’d call a working edge. You know, what is this tool or weapon going to be used for and use a heat process that will give you, if not exactly what you want, as close as physically possible can the achieved with the materials you've got.


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