As with so many other issues, Runequest had the elegant solution and D&D ham-fisted it. In a medieval, iron-using society, there's nothing special about the metal itself. Thus the peculiarity, in the AD&D Monster Manual, of seeing iron as the bane of demons and other evil creatures. And the backpedaling, in a couple of entries, to insist that only "cold iron" bans a ghast or harms a quasit.
|Adding injury to St. Dunstan's insult.|
"Cold iron" is near-meaningless, more a poetic epithet than a technical term. Iron can't be extracted from ore without heat, and "cold forging" is a modern industrial term which assumes you can die-stamp a sheet of rolled iron (which passed through heat in the smelting and rolling processes). One obvious way to get iron "cold" is to chip it off a meteorite, but with what tools exactly?
Over the years, the D&D rules got cleaned up to the point where only this "cold iron" can harm some immune monsters, and the 3rd edition SRD lists it as a special material: "This iron, mined deep underground, known for its effectiveness against fey creatures, is forged at a lower temperature to preserve its delicate properties ."
Well, but there's something too game-y balance-y about this solution, full of vague and passive rules-speak. "Stuff that harms the Weird is super expensive because it comes from a Place of Rareness." It makes sense but lacks resonance. The same goes for meteorite iron. I suppose if only dwarves or lost human races had the technology to whittle blades from meteorites that would sound a bit cooler. But ...
Why not have iron (as opposed to steel) just show up the ability of non-carbon-forged tools and household implements to resist the supernatural? After all, the silver that devils and werewolves fear is dirt-common in the D&D world. Silver pieces are crappy coins that make slightly more expensive sling bullets than lead. A party in my campaign once bought a silver teapot, filled it with sand, and swung it as a flail against the equivalent of wights. So why not have desperate halfling housewives fending off a quasit with a skillet? Or adventurers chucking their iron door spikes at ghasts?
As a bonus, if elves can't stand iron spikes, it throws a little game balance into elven PC's who (at least in AD&D) are far superior to poor old humans.