Why casting weapons like they do in the movies doesn't really work
It's one of the coolest moments in medieval fantasy films. A blacksmith sweats over the forge, slowly pouring bright-orange, molten iron into an open-topped stone mold of a mighty sword while the audience watches a cool shot of the weapon taking shape.
Go ahead and toss in a shot of the warrior looking on with joy, let the audience watch as they quench the hot blade in snow, a person, or whatever, and presto, our hero has a neat toy for the next scene.
It's too bad that this isn't how any of it's done in real life — and if it were, it'd be a sign of terrible craftsmanship.
First, it should be stated that there's a huge difference between casting a weapon and forging one. Back in the Bronze Age, before blacksmiths knew any better, they would take molten bronze and pour it into a stone cast to create a battle-ready weapon. This is casting.
Bronze was made from mixing copper and tin. For blacksmiths in 1200 BCE, this wasn't a problem as both were abundant enough. Mankind had known about iron for hundreds of years at this point, but using it required a tremendous effort to create a product that was on par with bronze alternatives. When it was discovered that just a bit of carbon could turn the Earth's most abundant metal into steel, they embraced the challenge.
Steel makes for stronger, more durable weapons, so blacksmiths began using this metal instead, but the process required was much different. To create something, smiths needed to forge it, starting from a blank (or piece of metal) that was the relative size of the weapon they intended to make, heating it, and painstakingly hammering it into shape.
The switch to iron and steel meant that they could make weapons longer without sacrificing durability. Which is important when you're trying to stab someone without getting stabbed.
(Picture by J.J. Luder)
It's not impossible to cast iron weapons — but the process will yield a cheap, crude weapon. This works for the Uruk-hai Orcs of The Lord of the Rings, but it's just not practical for anyone else. This is also how most cheapo swords that medieval fans have on their walls are made. For decorative weaponry, that's fine, but the blade would probably snap in half given just a bit of pressure.
When you pour the metal into the cast, it's going to take shape of the mold. Which means that it's only going to be half made when it's done with an open-top cast. The other half of the sword will be flat when the metal hardens. If they were to rework the metal into a complete shape after that, it'd defeat the purpose of the mold all together.
No matter how cool of an opening scene this is, it's still kinda of wrong.
If you want a durable weapon made out of anything but bronze and looks beautiful, you're going to need to forge it. This process can take days — even just to get a standard-looking sword. You're looking at weeks of master craftsmanship to get the caliber of weapons used by main characters.
Most films opt to go with the more cinematic approach. Bright-red liquid (fun side note: Molten iron heated to the point where it can be cast is actually more of a pale yellow. They're using aluminum) looks cool when it takes form, but the actual process of making real weapons is far more impressive — even if it takes a lot longer than a montage.
To see how it's done, check out the video below!
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