Cold Iron

"All elves feel the shadow of iron, and to those who walk our higher paths, it is a bane that breaks the body and twists the mind."

— Etheliel, Battle for Wesnoth, The South Guard, "Into the Depths"

One of the most commonly-seen Depleted Phlebotinum Shells and the traditional bane of The Fair Folk. Other supernatural creatures, such as werewolves and vampires, may also display a weakness to it. On occasion, this may also extend to elves.

Iron may be treated as naturally magic-disrupting or just poisonous for certain creatures. Sometimes it works by sucking the magic out of The Fair Folk (similar to the way it sucks heat out of the body), or it might just be a corrosive substance that damages them on contact, usually accompanied with screams about how "it burns". Sometimes it's got something to do with the physical properties of iron like its ferromagnetism, nuclear stability or resistance to rust, or sometimes there's a more mystical reason such as it being "man's metal", a symbol of civilization and mastery over nature.

Even when it doesn't actually harm anyone, iron may be portrayed as a magically inert substance that blocks, weakens or dampens magic, or that cannot itself be affected by it.

There's little agreement about what "cold" means in this context. Sometimes it just means that the iron, at the moment, isn't hot. Sometimes it's cold-worked iron, as opposed to hot-worked. Sometimes it's more complicated, like iron that has never been smelted, or iron that's been smelted in a magic way that doesn't involve any heat. Or it may also be a reference to the fact that heating magnets to a certain point causes them to lose their magnetism, so "cold" iron is iron that still has its magnetic (magic) power.

Alternatively, it might just be a poetic reference to any iron (much as "cold steel" was used in later times), just because metals at room temperature feel cold thanks to heat conductivity. These instances are generally more faithful to the old folklore behind The Fair Folk, in which this trope comes up as as a particularly old form of "magic vs. technology" symbolism. The logic behind these mythos is that metallic iron, being a man-made substance never found in nature, is anathema to the nature-inclined Fae.

Thunderbolt Iron may or may not be related: meteorite alloys are usually iron-based and can be cold-worked when no fuel is available to make steel. They are good in cold climates because they don't become brittle in cold as easily as carbon steels do (if they're one of those rarities among rarities that isn't brittle at all temperatures because of impurities).

Cold Iron may be a reason why Armor and Magic Don't Mix, as well as a form of Unobtainium in some cases.

Sub-Trope of Supernatural Repellent and Fantasy Metals. See also Silver Bullet, for another metal with anti-supernatural properties.

Not related to Elemental Weapon.

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Examples:

Anime & Manga

• The Ancient Magus' Bride: Fairies are vulnerable to iron, and can be restrained with something as simple as a glove with iron thread woven into it.
• In Princess Mononoke, an iron bullet is what corrupts the boar-god. More generally, Irontown is slowly destroying the forest and the gods therein.
• Radiant: Black Silver and White Silver are some of the few of none magical methods that counter Fantasia, with the Inquisition employing them to hunt Sorcerers.
• Ushio and Tora: Highly implied: the Kouhamei sect's weapons are made of iron and used against youkai, while the Beast Spear itself is made of, possibly, Thunderbolt Iron. Even Big Bad Hakumen no Mono has a tail made of iron (later upgraded to a tail made of steel blades) to specifically kill other youkai.

Card Games

• Munchkin: In Munchkin Bites, Cold Iron is a trap card that only affects Changeling characters.

Comic Books

• Astro City: The series invoked this during the climax of "Things Past". The destruction of the Big Bad's base led to Steeljack accidentally breaking one of the various magical trinkets The Collector had amassed, this one being the prison of seven malevolent spirits known as The Seven Sisters. Unfortunately for them, Steeljack's power comes from being coated with a semi-organic steel alloy, meaning that his entire body is cold iron. In the ensuing battle, Steeljack destroys five of the sisters before the remaining two flee.
• Hellboy: In The Corpse, Hellboy exposes a changeling by touching an iron horseshoe to its forehead. Later he tests the real baby the same way, just to make sure. Conversely, in The Iron Shoes (usually published alongside The Corpse, since the latter is not quite long enough to fill up an issue), some folklorists explain that a few fairy creatures don't mind iron and in fact are rather fond of it, including the title character:
  ''Live or die,
  Win or lose,
  Best beware...
  MY IRON SHOES!"
• Legion of Super-Heroes: In the Elseworlds story Superboys Legion, Ferro Lad is able to destroy the magical constructs of the Emerald Enchantress's magic eye — the second he heard he was up against magic he turned into his iron form and got to business. This doesn't typically apply to other incarnations of Ferro Lad, though.
• Marvel Comics:
  • Marvel demons are often vulnerable to iron. Even Adversary, an Eldritch Abomination aiming to destroy creation and create a new world had to avoid contact with Colossus. Colossus's organic steel body has also caused difficulty to an entity claiming to be Baba Yaga, and the demon N'astirh.
  • Iron Man: Iron Man is not literally iron,^note it's actually a gold-titanium alloy! but just calling himself "Iron Man" is apparently reason enough for Malekith to call down The Wild Hunt on him in Iron Man 2012 - granted, this was mostly a sign of how monumentally petty and casually sadistic he is (one of the Rings of the Mandarin is trying to influence him that way, it finds out he's Eviler than Thou, and he does it anyway). While Tony's usual suits are not iron, Malekith still ends up getting more than he bargained for after he provokes Tony (newly discovered to have been adopted) with stories about what Dark Elves do to Changelings. Tony has his ally send him a custom suit made entirely of iron complete with huge wrist-blades, a harpoon gun and a combination of iron filings and fans, then promptly goes on a rampage so vicious that he scares everyone, from his ally, to ordinary Dark Elves, to Malekith himself, who eventually ends up giving Tony the Mandarin Rings he's collected and a magically binding oath to send him back to Earth just to get Tony out of Svartalfheim... well, and also to save him from the other Mandarin Ringbearers, who are quite unhappy with Malekith at the moment.^note This takes place during the "Rings of the Mandarin" arc in the 2013-2015 run; the Cold Iron Armor first appears at the end of issue #24. Afterwards, the Dark Elves start using him as a bogeyman for their children (which Malekith actually considers a plus), and it gets a Call-Back during War of the Realms when Malekith makes a point of avoiding Tony and manipulating a dragon into going after him.
  • The Mighty Thor: The dark elves of Svartalfheim are vulnerable to iron. This is explained by iron being "the metal of humans", so it kinda fits with the nature-vs-science thing mentioned above. Lampshaded in The Incredible Hercules #132 where the title character asks Balder (actually Malekith disguised) why the Asgardians have so much trouble with the Dark Elves, citing that even their strongest spells can be nullified by the slightest touch of iron and the Asgardians use steel in their weapons and armor. Balder explains that the Dark Elves have powerful allies that don't share their weakness to iron (cue, a large troll that Hercules just knocked into the ground retaliates and beats the crap out of him).
  • Wolverine: Wolverine's adamantium claws count, since adamantium is a steel alloy. In one story he was able to easily dispatch some yokai, but the big bad was instead vulnerable to gold. Prior to that fight Wolverine had dipped one of his claws in gold and kept it retracted until the critical moment.
• The Sandman (1989): In the story Cluracan's Tale, the title character (a faerie) is captured and bound with cold iron chains, in a cell with cold iron bars. He has to call on the Sandman to free himself.
• Top 10: In the spin-off Smax, Gadgeteer Genius Toybox finds herself having to defeat a dragon in a magical realm where her gadgets don't work. Her eventual solution has a big technobabble justification^note Namely, supernova nucleosynthesis, but for the setting it's essentially Cold Iron.

Fan Works

• Avengers of the Ring: As per Marvel Comics canon, Malekith the Accursed, leader of the Dark Elves from Thor: The Dark World, is vulnerable to iron. So Thor decides to let Iron Man tackle Malekith, while he deals with the Balrog he brought to the battlefield. And Tony makes short work of Malekith once he magnetically pulls up a few iron spikes right through the Dark Elf and leaves him Impaled with Extreme Prejudice.
• Ben 10: Guardians: Anodite aliens are strongly associated with fairies here, which comes with a weakness to cold iron.
• Because The Dresden Files is part of its Massive Multiplayer Crossover, Child of the Storm follows its rule that any iron is deadly to the Fae. Although this trope isn't mentioned much, it crops up a few times, such as when Harry Dresden notes that Magneto is pretty much their worst nightmare.
• Codex Equus: Cold Iron, the bane of old-school Fae, is an allotrope of iron whose magically-disruptive properties can also disrupt any magically-fueled powers. It's however difficult to synthesize, especially in the Second Age.
• A Diplomatic Visit: As revealed in chapter 7 of the second sequel, Diplomacy Through Schooling, the mines where Neighsay and his fellows work are lined with this, blocking magic and keeping his amulet from teleporting him out.
• Dungeon Keeper Ami: Iron negatively affecting fairies is referenced, multiple times:
  • In Meet the Locals, when people think Ami is a Fairy because of her blue hair, they dismiss this possibility due to her handling iron cutlery without discomfort.
    "... blue? ... think she's fey?" "... no, touching the iron cutlery..." "... but ... gloves ..." "...rather young..." "... witch looking for trouble..." "... hair's so short... disgraced... ?"
  • In Diplomacy and Gifts, the Fairy Ambassador confirms that iron burns his people's skin.
  • In Cornering The Duke, when Kivith, a Dwarf, is thinking about Fairies, he bases his dislike for them partly in the aversion to what he sees as a perfectly good, respectable and useful metal.
    Oh, yes, the other point against them, in Kivith's opinion. There just had to be something deeply wrong with creatures that couldn't stand the touch of good, solid iron.
• Foxfire: Iron chains are one of the few things that can hurt and bind powerful spirits.
• Iron Kissed: Iron is anathema to the Fae. Its touch burns them and breaks their glamours, and injuries from iron weapons are lethal to them. In this case, it's specified that this extends to iron alloys such as steel.
• The Life and Times of a Winning Pony: Contact with cold iron causes immense physical pain to fey creatures, and as a result the metal is often used as a way to determine if somepony is a fey in disguise. Cold iron also disrupts and impedes Unicorn magic, something that has led to a lot of speculation in-universe about unicorns' exact relationship with the fey.
• Mendacity: Changelings inherit fairies' weakness to iron — Bon Bon tries not to let it in the house and can't wear iron horseshoes. According to the Bugul Noz, the reason why the Fae are so vulnerable to such a common metal is because Discord, who created them, made them this way as a cruel joke.
• My Little Balladeer: Zecora's staff is made of cold-worked iron and ash wood, which gives it some extra oomph against Thorne's minions.
• Phineas and Ferb in Dimmsdale: Cold iron is made from an alchemic formula, repels fairy magic and remains cold even after smelting.
• In Son of the Western Sea the Tuatha de Danann's equivalent of Celestial Bronze is Blessed Iron, which is one of the few things capable of harming them or The Fair Folk. However, the exact art of making it and the fact it's different from regular iron has been lost by mortals. Percy muses that anyone trying to attack the Celtic monsters with plain iron and expecting it do drive them off would have about as much luck as attacking an Empousai with a bronze door knob.
• Vainglorious: Dark Elves are weak to it. It's also a component in Harrow Blades.
• The Weedverse: Demons are vulnerable to iron, which is why in Nom's Mom Bomb Dim supplies Chartreuse with a fireplace poker that he's spent a fair amount of time working on to make it more effective, as well as adding some salt, also established to be useful against the Things That Go "Bump" in the Night. After Chartreuse is offered the job of exorcist, Luna mentions that she'll be fitted with iron horseshoes at some point.
• Weres Harry?: The fae are vulnerable to natural iron, which here means iron that hasn't been created by transfiguration or conjuration.
• In "An Academic Visit" its mentioned that humans initially had trouble fighting the gryphons because they're resistant to lead based bullets, they cause bruises but can't cause any serious damage, making it necessary to use nuclear weapons, after the war it turned out that iron bullets are more effective.

Films—Animated

• Mega Mind Metro City's Superman expy Metro Man was inadvertently defeated by exposure to copper. later subverted when copper proved ineffective against his replacement , Tighten. It was later revealed Metro Man faked his death and copper is ineffective against him as well.

Films — Live-Action

• In Captain Kronos: Vampire Hunter, the vampires' vulnerability is to iron crucifixes (or to a cruciform sword forged from an iron crucifix).
• Ghostbusters (1984): Somewhat of an Inverted Trope, in that a specific metal or alloy used in the construction of Dana's apartment building is used to attract spiritual forces instead—essentially making it a supernatural magnet. Dr Stantz notes that the building's roofing material was built with "cold-riveted girders with cores of pure selenium," used in no other buildings but apparently also used in NASA's pulsar-sensing equipment. As it turns out, the building's architect specifically designed the building that way to summon an Eldritch Abomination and commence The End of the World as We Know It.
• The Hallow: Cold iron burns the Hallow, which won't come anywhere near it.
• In Hellboy (2019), Gruagach is repeatedly shown to be deathly allergic to iron. He is part of The Fair Folk after all, so this shouldn't come as a surprise.
• The Last Witch Hunter invokes this in Axe and Cross' Badass Boast, "By Iron and Fire", although it's never made clear if it's because iron has any magical proprieties or because iron weapons were the cutting edge technology back when the organization begun its operation.
• Leprechaun 2: While the Leprechaun was vulnerable to four-leaved clovers in the first movie, in this one he's vulnerable to wrought iron instead.
• Lifeforce (1985): The space vampires can be killed by staking; with the stake made of leaded iron instead of wood, and stabbed two inches under instead of through the heart.
• Maleficent: Iron burns fairies, but this isn't common knowledge among the humans. Maleficent as a child tells Stefan this after his ring accidentally burns her while shaking his hand. Years later, Stefan — now driven insane by his paranoia regarding Maleficent coming for him—-uses this knowledge to arm his men with iron armor and weapons, as well as setting up an elaborate trap in an attempt to kill his former childhood friend.
• Night of the Demons (2009): The possessed are vulnerable to rusted iron.
• Quatermass: The climax of Quatermass and the Pit (both the film and earlier TV versions) involves the Martian "devil" appearing as a ghostly projection, powering destructive atavistic urges in humans. Professor Quatermass and Ronay realise that "cold iron", in the form of an electrical conductor, can be used to short out the energy responsible.
• In Supergirl, the titular heroine temporarily neutralizes the witch Selena by forming a cage around her out of iron posts.
• Vampyr: An iron stake (really a railroad spike, as There Is No Kill Like Overkill) is shoved into the antagonist's chest.

Literature

• The Adventures of Amina al-Sirafi: For supernatural threats, Amina carries a blade made of pure iron, inscribed with holy verses, and regularly blessed with zamzam water — it's not very sharp, but it doesn't need to be. She later upgrades to an allegedly celestial blade forged from Thunderbolt Iron.
• In The Bartimaeus Trilogy all spirits are harmed by iron, but are harmed even more by silver.
• The Borden Dispatches: The only thing the creatures from the sea are vulnerable to. Lizbeth's axe has an iron head, and she pounds iron nails into every threshold in the house.
• Chrysalis (RinoZ) has "cold iron" that is literally cold; it's found in the second Dungeon strata at freezing temperatures, and is quite brittle. There's no mention of it having special effects on any particular species, but based on the description of "fire iron" from the third strata, there's a good chance that cold iron has an affinity for ice magic, eg making armour that will resist ice spells.
• Dark Lord of Derkholm: Iron is much harder to work magic on than other substances, and untrained wizards can't use magic while in contact with iron.
• Discworld:
  • In Lords and Ladies, the elves' primary sense seems to be based on detecting magnetic fields, which iron messes with. Magnetised iron is even worse, possibly explaining the reputation of Thunderbolt Iron. The horseshoe above the door is explained by saying the shape isn't important, it's simply that horseshoes are usually the closest available source of iron for most people.
  • In The Wee Free Men, Tiffany Aching uses a frying pan to fight the fairies — this shows that she intuitively knew that iron would be dangerous to them.
  • In The Shepherd's Crown, the elves are horrified to realize that huge iron engines now run across the landscape on iron rails, and goblins who work in the new industry are packing iron filings.
  • In The Last Hero, Carrot Ironfoundersson of the Ankh-Morpork City Watch stands up to the Silver Horde, a band of aging barbarian heroes planning to wipe out the Discworld pantheon. At first the Horde are little more than amused by Ironfoundersson's audacity but almost immediately surmise they are outmatched by the internal logic of heroism and fantasy on which they've always relied. The barbarians note that they are all armed with legendary and enchanted swords while Ironfoundersson has only a standard-issue iron sword which any legend recognises would cut through their fancy swords like butter.
• In Doc Sidhe, the people of the fair world find the touch of iron painful (which makes things interesting for construction workers building 1930s-style steel-framed skyscrapers). Doc and his colleagues are surprised to learn that the human protagonist carries a pocketknife with a steel blade, and more surprised when he demonstrates that he can touch the blade with no ill effect.
• Dracula: In the original novel, Count Dracula is slain by a knife through the heart and decapitation by a second knife, drawing on the use of sharp iron and/or steel tools like knives and needles as protection against vampires. It was never stated in the book that iron, specifically, is what's important, though.
• Dragon Keeper Trilogy: Dragons are hurt by the mere presence of iron, and Dragon Keepers have to use bronze or copper tools around them. This sometimes leads to problems, as in ancient China, bronze was more expensive than iron.
• In The Dresden Files Fae are harmed by anything with enough iron, even if it's part of an alloy, such as steel (The "cold" part is explained as being purely poetic, any iron will do). Fae creatures generally have zero tolerance for it in any form, even mere contact with anything containing iron causes pain. When cut with it, the iron sets the Faerie blood on fire. It was noted by one Fae that even if the damage is not fatal, it will leave pain that lingers for a long time. Also, bringing iron into Faerie Territory (to say nothing of leaving it there) is roughly equivalent to carrying around uncontained nuclear waste. Other beings from the Nevernever don't seem to be harmed by iron — except for Fomor, who are distant relatives of the Fae.
  • There is one exception to the Faerie rule — the Queen Mothers are, quite simply, the most powerful Fae in existence. Both of them use a steel or iron cleaver to prepare their meals. Mother Winter can even make the iron rust.
  • In Grave Peril, Harry plans ahead for when he might need a distraction while he, Michael, and Thomas need a distraction while traveling through fae territory. When they are hounded down by Lea as she tries to collect on Harry's old bargains, Michael and Thomas pull out bags of nails from the hardware store and start spreading them around, buying Harry the few seconds he needed. Harry knows that spreading iron in their territory is a good way to anger the fae, which is a good way to get himself killed, so he used aluminum nails instead.
  • The Knights are mortal champions of the Faerie Queens, and must stay away from iron too. They can still touch it and it's not any more harmful than normal to them, it does instantly disable the Fae powers they get for being the Knight. The Winter Knight, at least, gets both super strength a great deal of resistance to pain, so having the powers shut off at the wrong time can be very bad.
  • There are several uses of this in Summer Knight.
    • When Harry suspects the client before him is a fae he pulls a gun on her and a small steel nail. When he rolls the nail at her, she waits for the last microsecond before it touches her to jump back in fear. This intelligence in deducing her nature allows her to move past the near-injury as it means Harry is good enough for her needs. Who is this fae, but Queen Mab herself.
    • Harry seriously injures a faerie-created tree construct via Car Fu with the Blue Beetle. Since it's an older vehicle that Harry uses because wizards are Walking Techbanes, it has a steel body instead of fiberglass.
    • A few minutes later Murphy finishes the "chlorofiend" off with a chainsaw.
• The Elenium and The Tamuli:
  • The Bhellium, a Cosmic Keystone, is a kind of cosmic spirit that makes worlds, and the touch of iron is anathema to it—implicitly because iron is a "red" metal, while the essence of Bhellium is inherently blue. As such, the touch of any iron—even blood—is extremely painful to it, and the merest sword can shatter it easily, though the resulting explosion might well destroy the world.
  • The Styric people absolutely refuse to touch or use iron under any circumstances. The reasons are not given, but the same limitation seems to affect their gods; as a result, the steel-wielding Elene race has been able to completely overrun and dispossess the Styrics despite their use of theurgical magic.
• The Faerie Path: Faeries call it Isenmort, and it's poisonous to them.
• In The Falconer, it is pointed out that contrary to popular belief, iron is useless against the fair folk. The protagonist recalls having tried to use it, and the failure of that attempt.
• Good Omens combines this with Must Be Invited, with regard to an old cottage that has a traditional iron horseshoe hung over the door, which is able to repell Adam's pet Hellhound. When he forces it to enter, it has to leave some of its demonic nature behind, which incidentally heats the horseshoe to red.
• Zig-Zagging Trope in The Girl The Apprentice And The Dogs Of Iron, where it is well known that iron cannot be enchanted by magic- a rule which is subsequently broken by Rhianna and her Wild Magic when she unintentionally brings life to a pair of iron statues which subsequently run amok.
• Heralds of Valdemar: In Redoubt, demons are vulnerable to a combination of Sun and Iron, in the form of an iron chain wielded in the glow produced by a Suncat. The demons are summoned after dark by the Corrupt Church of Karse, which ironically "worships" the sun god Vkandis.
• Discussed in the eponymous short story of Instead of Three Wishes — although iron isn't directly harmful to the Fae, a sufficient quantity of it does repulse or frighten them. The only example actually seen in the story is when the elf Prince Mechemel is trapped in the middle of a crosswalk while swarms of of steel (an alloy of iron) vehicles rush past.
  "Are elves really bothered by iron?" asked Selene.
  "I don't know that it actually hurts them," said Harold, "but it does, you know, give them the willies."
• In Iron Druid Chronicles, Cold Iron refers to meteoric iron. Iron is the opposite of magic and tends to neutralize it. Fairies are magic, so simply touching it makes them disintegrate. This makes Atticus the walking embodiment of death to fairies, since his aura is bound to a Cold Iron amulet.
• The Iron Fey: Worked iron is dangerous to fairies of the Summer and Winter courts. Meghan, fey from her father's side and human from her mother's, is unusual in her ability to handle it. The series takes its name from a new faerie court; the Iron Court. The Iron King is also able to handle iron, despite being fey.
• Kingdoms of Dust: Lead weakens magic when kept around a mage, in contrast to silver and copper.
• In The Last Unicorn Mommy Fortuna uses cold iron bars to trap the unicorn and the harpy. The unicorn is able to endure being closed in by the iron cage, but feels pain if she touches the bars.
• The Last Adventure of Constance Verity: Because of how effective it is against fairies, iron is banned in the Fae Realms and is considered contraband. Of course it doesn't stop Connie from bringing iron knuckledusters for the sake of caution.
• The Laundry Files: The Nightmare Stacks introduces the alfär to the setting, Space Elves whose short-lived colony/outpost in ancient Britain was the origin of all myths about The Fair Folk. The alfär call iron “the oldest countermeasure” because it grounds out magic — the foundation of their society and military — and slaves are forbidden from handling it on pain of death. It doesn’t have any other effect, however, and the Host of Air and Darkness regularly goes about in steel plate mail. Medieval folklore of cold iron being especially harmful to elves are the result of a long game of telephone started by people who misunderstood their aversion to it in the first place.
• Lockwood & Co.: Iron is a common and good deterrent against ghosts.
• The Long Earth: Iron, for reasons unknown, can't be carried when stepping between worlds, preventing people who do so from relying upon iron-based tools and objects. There is mention of the idea that an iron cage could hold a stepper prisoner.
• L. Sprague de Camp:
  • In the novella "The Castle of Iron", co-written by Fletcher Pratt, Harold Shea attempts to use some gold coins conjured out of sand to pay a blacksmith; however, when he rings the coins onto the anvil, they turn back into sand. (He remembers afterward that the Rudyard Kipling poem that he based his incantation on had made iron "the master of them all.")
  • The novella "Land of Unreason", likewise co-written with Fletcher Pratt, has the Fair Folk burned by the metal. Kobolds can handle iron and so they use it to secure their caves from intruders.
  • In the novel The Triton's Ring, the hero is sent on a quest to save his country by recovering "the thing the Gods fear the most", which is the titular ring. It turns out, the ring is made of Thunderbolt Iron from a meteor, and since the setting is still at Bronze Age, Iron is the ultimate Anti-Magic which allows the user to bypass illusion and spells, ignore demons and even the Gods themselves.
• Malediction Trilogy: Cold iron is the only thing that can cause lasting injuries to trolls and limit their magical power. In addition, the human world is full of iron, so trolls who spent too much time on it could not return to their own world and lost their immortality due to iron in their blood.
• In Masques, practitioners of green magic are affected by iron more than silver. Aralorn makes fun of people who think silver is effective against shapeshifters, as she is easily able to escape a silver cage, but would be trapped in an iron one.
• Merlins Godson: The title character has to save a tiny Fae civilization from an iron nail that has accidentally fallen into their realm.
• In Mermaids of Eriana Kwai, iron leaves mermaids with horrible burns that never heal. Lysi still has a gash on her side from when Meela's father shot her with an iron bolt when she was ten.
• Merry Gentry: Any iron (steel will do, too) can disrupt simple enchantments. Merry wears a clip-on steel-handle folding knife inside her bra, so it is in contact with her skin, as a protection from hostile magics (and as a hidden backup weapon, of course).
• Mick Oberon: The classic fae weakness. Its increasingly common use by humanity is one of the two main reasons the fae left Earth.
• The Midnighters series plays with this trope. Any kind of alloyed metal (like steel) hurts darklings, cutting through them like a knife through warm butter. Rex notes that the darklings' real weakness is new ideas (hence the significance of names and math when fighting darklings), which means that simple worked metal worked against darklings centuries ago, worked stone arrowheads and spearheads worked against them millennia ago, and he predicts that in the future they will have to use plastics, carbon fiber, or other exotic alloys against them.
• Modern Faerie Tales: Faeries are burned by contact with iron.
• The Mortal Instruments: This is one of the fairies' weaknesses. Cold iron weakens them, so they cannot fight. If they're exposed to the cold iron longer, it causes them real pain. Later it turns out that half-fairies are weakened much less. It bothers them at most a little.
• The Name of the Game (Elrod): Iron is one of the few things that can kill a demon, though it takes prolonged exposure to kill them. Irving managed to stay alive long enough for Myhr to separate it from him while he was run-through with an iron sword, acting like he had been drugged all the while. It's also proven to be effective on wizards too.
• My Vampire Older Sister and Zombie Little Sister: Iron wards off evil and is particularly useful as a passive talisman against things like fairies — for example, by hanging a horseshoe in the front door.
• In The Name of the Wind, cold iron is known to be effective against "demons", and also causes severe pain and Glamour Failure in the Fae.
• A Net of Dawn and Bones: Iron shorts out magic from both demonic and fay sources, for different reasons. It works against fay magic because it's the work of humans, while it targets infernal magic due to being forged in the heart of stars. Myrrh muses that it's probably the reason that the two get confused.
• Newts Emerald: Early in, the heroine's maidservant is working on her dress and has several pins in her mouth. The narration notes that the pins are copper with tin plating, rather than the expected iron, which is a clue to the knowledgeable that the servant has fay blood. Also mentioned as an identifying sign is the fact that the servant never touches iron keys directly, but instead holds them through her apron whenever she has to open a door.
• The Obsidian Chronicles: Some magical creatures have a weakness for this. Along with other things, it helps Arlian survive in the south. Some of the people who live there put up iron poles around their settlements to prevent them coming in.
• October Daye: Cold iron is any iron. Changelings have a better resistance to it because of their human blood, and the Coblynau, who are the only Fae able to work with iron, are a very ugly race, implied to be due to their affinity with iron.
• In The Once and Future King the young boys Wart and Kay take iron with them as protection when they visit the fairies' castle.
• On Stranger Tides makes a distinction between two kinds of iron. The former, naturally occurring in contexts such as blood and falling stars, helps magic along; long-term magic users can turn anemic because the iron in their own blood gets used up, and have to eat iron-rich foods to recover after a major working. The latter, "cold" iron — basically any worked iron, such as in a knife or a nail — is magically dead, and impedes magic; the increasing use of iron-based technologies is why you don't get magic much any more.
• The Perilous Guard: Zigzagged. The cold iron cross a village woman gives Kate doesn't hurt The Fair Folk, but it does hurt Kate when she cuts her hand with it, preventing her from falling into an enchanted sleep.
• In The Phantom of the Opera (the novel, at least), everyone at the Paris Opera relies on iron for protection against "the ghost." La Sorelli places a horseshoe on a table near an entrance for everyone to touch before entering the building, and Gabriel the chorus master runs to touch an iron doorknob when he sees the ghost walking behind the Persian, whose creepy presence often makes people touch their metal keys for protection.
• Poul Anderson:
  • In The Broken Sword, the main reason for the abduction of a human baby by the elves is the need for a human warrior able to wield the sword Tyrfing.
  • The Operation Chaos series says the iron is anti-magical, but it's set in an alternate history where one of the famous physicists of the early 20th century found a way of suppressing the effect, allowing mankind to have its cake and eat it too.
• A Practical Guide to Evil: Iron causes the fey immense, often debilitating pain.
• In The Princess on the Glass Hill, Boots controlled the Cool Horses by throwing steel over them.
• In The Princess Series iron only protects from the weakest of fairy magic.
• The Pusadian Series: The mere touch of an object made of iron is enough to break any enchantment. Holding an iron object allows one to see through glamour and illusion. Wearing iron on your person can prevent the gods themselves from communicating with that mortal.
• Rose of the Prophet: The main weakness of all Immortals — it can't hurt them, but it can bind them and render them powerless. A common threat used against the djinn is being locked in an iron box and put somewhere nasty where they'll never be found.
• Saga of the Exiles: The alien race that split into the Tanu and Firvulag (inspiration for later legends) dies from a simple scratch from iron or steel, and refers to it as blood-metal (it's noted in text that their blood is apparently iron-based, as it's red, and they're able to interbreed with humans). It's theorized that it interferes with their psychic-power-enabling torcs, but humans who gain powers from a torc are explicitly not rendered vulnerable to it. Also, human/Tanu hybrids are immune, which leads to a sociological analysis that's not too favorable for the pure-blooded Tanu.
• In The Saga of Hervor and Heidrek, King Svafrlami catches two dwarfs by "drawing his graven sword over them", which takes away their power to vanish into the stone.
• The Saga of Recluce features this with regards to Chaos-mages. Iron, both naturally and when transformed into black iron by Order-mages, is a natural repository of Order. Chaos-mages who have a surplus of Chaos in their body will suffer painful burns when the two energies interact. Consequently, Chaos-mages are fond of white bronze. When the Chaos-mage ruling Fairhaven had a fellow mage locked away, her hands were bound with iron manacles, leaving her screaming in agony; the ruler idly noted that with the amount of Chaos in her body she'd likely be dead before the day was done.
• In The Secrets of the Immortal Nicholas Flamel the Elder Race are weakened by iron, as it negates any and all magic. For this reason, anyone with iron in a shadowrealm will usually keep their iron tucked away somewhere so they don't offend an elder.
• Shadow Magic (2016): The cells in Castle Gloom's dungeon are barred with this to keep magic from getting in or out.
• In The Soldier Son iron is disruptive to magic and very harmful to magic users. The invention of the gun, which can rapidly spray iron bullets, has been instrumental in subduing the magic-using Plains People by the Gernians.
• Special Circumstances: One conversation in Princess of Wands suggests that FBI members who aren't part of the Special Circumstances group could also take part in slaying supernatural beasties, with cold iron bayonets fitted to their rifles specifically mentioned.
• In The Spiderwick Chronicles there is a passing reference to this.
  "Steel. It cuts and burns."
• The Spiritwalker Trilogy: Cold steel in the hand of a cold mage can kill just by drawing blood.
• In Stardust Dunstan touches some coins to an iron nail to make sure that they are real and not "fairy gold".
• A Strange and Ancient Name: Faeries are so harmed by iron that even the slightest scratch is a death sentence, usually fast. Being not fully of faerie means being able to survive even an iron arrow wound — a revelation so surprising that the faerie court, believing their prince to be beyond all help, almost lets him die of fever.
• In Steel Magic, by Andre Norton, old iron is defined as being any metal "forged by a mortal in the world of mortals", so the three protagonists end up using their stainless steel picnic cutlery — a spoon, fork and knife — as weapons. Fortunately the cutlery develops unusual properties in the magical world (such as changing size) and is pretty dramatically lethal to any magical being it touches.
• Susan Dexter:
  • In The True Knight, Wren and Galvin can't work magic on iron, and Valadan can be trapped by an iron bit.
  • In The Wind Witch, the protagonist bargains with a captured raider that she'll set him loose if he works her farm for A Year and a Day. Seeing no other option, he accepts the deal — even though he's a shapeshifter and using iron farm tools makes him sick. She doesn't find out there's a problem until he collapses.
• In The SERR Ated Edge by Mercedes Lackey, the Elves get around the cold iron by making their cars out of fiberglass — which has the added benefit of making them lighter and therefore faster. In addition to harming Elves by simple contact, iron also warps Elven magic. The good-guy Elves have learned to predict what running past an iron bar will do to a spell's trajectory, and take advantage of this during at least one fight scene.
• In Tales from Netheredge presence of iron dampens fey magic; a villain prevents Myr from using magic to teleport Runi out of danger by putting an iron collar on Runi. However, a sufficiently powerful fey won't be stopped by a human-made anti-magic item like this.
• In The Treachery of Beautiful Things, iron is dangerous to The Fair Folk. Jack must get an iron sword to fight the nix. Then Wayland also gives him an iron jack — toy though it is, the iron makes it dangerous.
• In User Unfriendly, elves in the game the heroes are playing are injured by the touch of iron. Two of the players, Arvin and Giannine, are playing as elven characters and have this vulnerability.
• Violet Wings: Iron objects are entirely immune to magic. It can also bind fairies and reduce their magic; disobedient fairies are given iron clamps around their wings as punishment.
• The Wardstone Chronicles has witches and other dark creatures being susceptible to iron, silver, salt and some types of wood (such as oak) and as such spooks use these in their weapons (usually making oak staffs with iron or silver spikes and making pits with Iron bars lined with salt or silver chains to bind their foes).
• In Warlock of Gramarye, iron in any metallic form is potentially deadly to the Little People. A handful of nails thrown into the bushes by a villain in one book is answered with cries of pain. And hanging scrap iron around your house also prevents the Wee Folk from entering. It doesn't bother their half-human king, however, and occasionally they'll call him in to get rid of the stuff for them. (The first book's claim that "witchcraft" can't affect iron is RetConned away very early on.)
• We Walk the Night: Iron hurts fairies, and does not occur naturally in their world.
• The Wheel of Time has "Iron to bind" to deal with the Finn, who are selectively insubstantial to any other potentially harmful material. It has to be true iron, though; steel doesn't work. They're also vulnerable to music and fire.
• The Witcher: While common parlance for why witchers carry two swords is "silver for monsters, steel for men" Geralt says in The Last Wish that's not entirely accurate, there are a fair number of monsters as vulnerable to iron as others are to silver. Of course then he goes on about how monstrous humans can be. But mainly just for make think you need two kind of swords so there will be less demon hunters like him.
• The Wizards of Once: Iron is the only thing magic doesn't work on, which is why people are concerned that Wish can perform magic on iron.

Live-Action TV

• Being Human (US): Iron of any form can dissipate a ghost, sending them back to the spot where they originally died. A fireplace poker is enough to do the job most of the time, particularly in the trio's home.
• Doctor Who: In the serial "The Dæmons", the Doctor successfully uses a trowel to fend off a gargoyle that merely thinks it's susceptible to Cold Iron.
• The Librarians: In "The Librarians and the Hidden Sanctuary", Cassie uses iron shavings to slow a fairy down, while staging an accident to summon it. Later on, when it's freed and goes on a rampage, she and the townsfolk lure it into a wrought iron gazebo, rendering it powerless.
• Supernatural: Iron, including that in things like wrenches or fireplace pokers, can be used to temporarily decorporealize a ghost. It also weakens magical beings, and binding someone with steel or iron shackles can prevent them from using magic.

Myths, Folklore & Religion

• Ars Goetia tells that you should craft the demon's seal in specific metals by rank (Kings in Gold, Marquises in Silver, Dukes in Copper, etc.). As for the Counts/Earls, associated with Mars and the Tuesday and, by extension, to Iron, the grimoire asserts you should use Silver and Copper instead. Several occult writters agree it's due this very trope in effect^note  and some go on and say you should spare the iron to, hm, "discipline" uncooperative spirits, like the punishments already ascribed in the Goetia ritual were not enough.
• The Bible's Book of Judges has a fairly famous verse (Judges 1:19) where God is unable to bring the men of Judah victory over an enemy for the stated reason that they had "chariots of iron". However, later in the same book, God defeats a similarly equipped army so thoroughly that the army flies into a full on route. The contradicting passages are reconciled by a passage in between the two where in God explains the tribes had angered him by not fulfilling their part of a covenant.
• In Brazilian Folklore, iron is needed to turn an enchanted snake into a human, as well as to cure the curse on a Headless Mule(specifically an iron needle in the later case). Blades of iron or steel are also said to harm and scare the werewolf and the Caboclo d'água (a river creature who perturbs fishermen).
• in the irish folklore, the fearsome dullahan, a headless horseman-like evil fae, can be repeled with gold.
• Islamic djinn are apparently also vulnerable to iron.
• In Scandinavian folklore, iron was a good deterrent against most supernatural creatures, and putting an iron object (a horseshoe, or a smithed tool) over a door or window was a surefire way to keep them out — or in. Some hypothesise that crafted metal represents civilization and technological advancement, the opposite of the supernatural and the old.
• Putting a horseshoe over the doorway was considered a way to protect the home from intrusion of The Fair Folk — this has allusions to the story of the Exodus and the Passover. Sometimes burying a doornail was used this way too. Although often burying iron was a way to conceal the iron from The Fair Folk, and if you could get them to stand over it they would be trapped and bound until they agreed to your demands.

Podcasts

• In Metamor City "cold iron" refers to cold-worked iron, and Damascus steel is produced at low enough temperatures to qualify.

Radio

• Big Finish Doctor Who: Used against the "marsh weans" (a disembodied intelligence believed to be evil spirits in 1950s Orkney) in the audio drama The Revenants. The Technobabble explanation is that ferrous metal "presumably disrupt[s] the electromagnetic force that keeps it together". (In a Doing In the Wizard twofer, the local streams are heavy with iron ore, which is why they can't cross running water.)

Roleplay

• CDT Adventure:
  • This is the reason why Sindar (a fairy) insists on the barkeep at the restaurant serving his ale in a non-metal glass.
  • One of many tools in Seenarnha's cursebreaking arsenal is a pair of cold iron tongs which she uses for handling magical items (or snakes) that shouldn't be touched with bare hands.
• In Dawn of a New Age: Oldport Blues, the cold steel of a fire extinguisher is shown to be the only thing able to affect the other incorporeal snake apparitions that attack the main characters. The next day, Hyeon stocks up on fire extinguishers just in case they attack again.

Tabletop Games

• 7th Sea: The Sidhe are vulnerable to cold iron. The second edition defines cold iron as iron which has been cold-worked, i.e. hammered without heating to make it stronger, and wrought iron (i.e. smelted worked iron) doesn't work on them. It's commonly used to make everyday tools, but rarely weapons; there's no reason given for the vulnerability.
• Anima: Beyond Fantasy: (Normal) iron as well as its alloys are the bane of the Duk'zarist, the dark elves ^note very likely taken from the Final Fantasy IV dark elf as detailed below, with just touching something made of iron or an iron alloy having the possibility of killing them (oddly enough, the Sylvain — light elves — aren't affected by it that way). Even Duk'zarist nephilim are affected by it, albeit in a much milder way.
• Beyond the Pale: Many creatures, including fey, are vulnerable to this substance. Its effects increase inversely to the degree to which it's worked — raw iron ore is the most potent variant, while steel has almost no effects whatsoever.
• Champions: In the adventure The Coriolis Effect, Ch'andarra and her daughter the Black Enchantress take damage when touched by raw (cold) iron.
• Castle Falkenstein: The Fae are vulnerable to all ferrous alloys, but the purer and less worked they are, the more dangerous they are. Being stabbed with a sword made of modern alloy steel will hurt a fae, but is unlikely to be lethal. On the other side, even being in the same room as an iron meteor (referred to as "starmetal" by the fae) can reduce a fae to a ball of crippling pain.
• Dungeons & Dragons:
  • The "Fool's Gold" spell makes copper coins look like gold, but it fails when the false gold touches iron.
  • Depending on the edition, demons that could normally only be harmed by magical weapons could also be harmed by iron weapons.
  • 3e+ has Cold Iron as a special material (like mithril or adamantine) for metal weapons. The rule of thumb is that you need this to harm (or at least, do full harm) to Fey or chaotic outsiders. The downside? It's one of the flimsier special metals (although just as strong as steel), and there's a static price that must be paid in order to enchant it, doubling the price of the lowliest weapon enhancement (at least in 3e based systems). Still, it's arguably one of the best special materials for weapons. Fluff-wise, the Dungeon Master's Guide for 3E explains it as a special form of iron that is mined deep underground and cold-worked to preserve its properties.
  • Even as early as 2nd Edition, some undead took double damage from cold iron weapons.
• Exalted: Iron weapons likewise deal enhanced damage to The Fair Folk and dispels their glamours. Name "cold iron" in this case references just the burning cold it feels to them, not any specific way of making it — any iron will do (note that most cultures use bronze or steel). Although protagonists rarely bother with such measures and generally just stab them with the same gigantic swords of magical gold they use on everything else.
• Faerys Tale allows you to implement cold iron, though it's optional. Under the game's take, cold iron is simply wrought iron (as opposed to cast iron), and although it can't truly kill faeries (nothing can kill faeries), the merest touch of it will send a faery into a deep sleep for anywhere from hours to weeks.
• GURPS: The 4th Edition version of GURPS Fantasy discusses cold iron, and multiple different ways of implementing it. The default is that it's simply a descriptive term for regular iron.
• Pathfinder: Cold iron is a specific form of iron minded deep underground, which does additional damage to fey and demons. Linnorms, a breed of ancient, primal dragons, are also vulnerable to cold iron weapons, something presumably linked to their close ties with the First World and the fey.
• RuneQuest: Iron is poison to elves and trolls, because the dwarves who invented it — not "found", not "refined", they invented a metal — designed it as a weapon against them. The most ancient dwarves claim that they'd have made it work against humans, too, if they'd known how much trouble they'd become as well.
• Warhammer: Cold iron, defined as iron worked without the use of fire, can create weapons capable of harming spirits and other ethereal creatures.
• White Wolf games:
  • In Changeling: The Dreaming, cold iron wounds do aggravated damage to changelings — and if they're killed with it, their fae soul will never reincarnate, effectively becoming a ghost. The only reason steel doesn't screw up the Kithain is because a changeling pulled a Heroic Sacrifice back in the day to ensure that it wouldn't.
  • In Changeling: The Lost, "cold iron" is anything that has a 95% iron content, and it negates any defense wrought by fae magic. The main book emphasizes that in the modern era, you'll rarely get anything like that unless it's a specialty work or from an earlier era.^note Stainless steel, which makes up a lot of modern consumer goods, generally contains at least 10-15% chromium On top of that, you've got hand-forged iron, which is iron that's never been heated by human hands or means. This means most hand-forged iron weapons are rough and blocky, but they do hideous amounts of damage to the True Fae. There are many given accounts on why this is, but the most common one is that the Gentry once had a Contract with Iron; they got power for it in return for making sure it remained unshaped. Then humans discovered smelting, the Contract broke, and Iron is pissed.
    • In the second edition, the effects are as above but acquiring iron and cold iron is slightly easier. Iron is defined as "what the average person would think of as iron" (so an iron gate or frying-pan would count, but not a steel sword or stainless-steel utensil), while Cold Iron is iron which was hand-forged, not cast or created by machines or magic. It's also mentioned that iron can never be manipulated, blocked, or affected by fae magic, this includes the basic effects of being a Changeling (so, for example, Changelings cannot use their escape artist powers if bound by iron shackles).
    • Unique among fae creatures, the Huntsmen are not affected by iron, and consequently make frequent use of it in their tools and weapons.
  • Werewolf: The Forsaken: The idigam Ansar-zalag cannot harm anyone carrying a piece of meteoric iron.

Video Games

• In Ancient Domains of Mystery, playing as a Mist Elf will make you suffer damage with each turn you are in contact with iron or steel items. Equipping a cursed or autocursing iron item, with no way of uncursing it to get rid of it, is one of the million possible ways to die in the game.
• Battle for Wesnoth: The dialogue in The South Guard reveals that elves have a weakness to cold iron, which gets more severe with age. While the novices find the sensation only mildly uncomfortable, an elven sage would suffer unbearable searing pain. You are told so by Mebrin, who was tortured this way.
• Evolve Idle: The weakness of the Fey-genus races is "Iron Allergy", being described as iron being toxic to them and must be handled with care. This causes Iron as a resource to be mined and refined at a 25% slower rate.
• Final Fantasy IV: The Dark Elf is vulnerable to iron and has enchanted his cave to be heavily magnetic, requiring you to reach him without wielding anything metallic. When you reach him, at first it's a Hopeless Boss Fight, but if you talked to Edward in the castle, he gives you a harp which breaks the spell, allowing you to wield metal. Alternatively, you can go to the one town that sells silver (i.e. non-magnetic) equipment beforehand. It's a bit of a trip, but worth it.
• In Pokémon, Steel-type attacks are super effective against Fairy-type Pokémon, and Steel-type Pokémon resist Fairy-type attacks. Prior to the introduction of the Fairy-type, most Pokémon based on Fairies were Normal-types, which are also resisted by Steel. Of course, that makes sense when thinking how throwing your body against, or simply lashing out at, a piece of metal would indeed be woefully ineffective, but they resist even energy attacks like Swift and Hyper Beam.
• Princess Maker 2: In the adventure section of the game, there is an NPC Elf that can change your daughter's statistics. However, he will run away if your daughter is equipped with iron weapons or armor.
• Tomb Raider Chronicles: During the segment set in Ireland (when Lara was 15 and therefore without weaponry) she is attacked at several points by small imp-like creatures. Throwing a piece of iron at them reduces them to a smoking puddle.
• In Dragon Age: Origins & Dragon Age: Origins – Awakening, "Cold Iron" is a weapon rune that does bonus damage against the undead.

Webcomics

• In Codename Hunter, the Fey are extremely vulnerable to iron, but not so much to iron alloys.
• Dragon Mango: Elves are extremely vulnerable to iron (merely touching it causes pain), but through Training from Hell can learn to resist it. Afterwards they use iron armors as a Power Limiter. Half-Elves are completely immune to it, likely due to their human half's iron-based blood.
• Never Never: Cold iron prevents Pookas from using any of their special abilities, including changing size and increased luck.
• In an early strip of The Order of the Stick, Haley didn't know whether Sabine was a devil or a demon, and thus whether she had a vulnerability to silver or cold iron. When they fought, Haley simply shot her with both types of arrow, though was frustrated by the fact that this didn't tell her which arrow she ultimately needed. In a later conflict, Haley stabbed her with both types of arrow in a flanking manoeuvre, as she still didn't know which she was meant to use. For the record, Sabine is a demon, and so is indeed weak to cold iron.
• Realta: True to myth, the fae are repelled by iron, and Amelia rebukes Elowen for traveling in the woods without some.
• Rogues of Clwyd-Rhan: Iron hurts the Fair Folk, including Kel, who's half-elven. She later uses an iron necklace to keep her elven powers under control.
• In Roommates, cold iron seems to be the default weakness of the fae, because, well, it's believed to be. It's literally one of the two known things to be able to injure the resident one (the other being a magic sword specifically designed to hurt him and his subjects). There is no agreement in the comic what makes anything cold iron, though, but experience showed that steel swords don't count, but iron frying pans do.
• Tales of the Questor makes extensive use of this trope. Although it claims "cold iron" is a mistranslation of "north iron" i.e. lodestone.
• In The Weave, the fairy queen Rhiannon is murdered with iron, which seems to be sacrilegious; the other fairies are outraged, and so is the ghost of Rhiannon herself.
• Whither: The people of Finn's hometown make barriers out of this stuff to keep out The Fair Folk.

Web Original

• In Faeophobia, iron is an irritant to Fae and it also disrupts magic (including magic cast by humans). Since the Fae now live together with humans, this weakness means that iron and steel are either replaced by other metals (such as aluminium) or covered in paint. Iron is used in prison cells for Fae.
• Looming Gaia: All fae races (elves, goblins, gnomes, sirene, cecaelia, and nymphs), magical animals, and some monsters are weak to iron, as it negates their magic abilities. Gaians (satyrs, fauns, centaurs, minotaurs and gorgons) that learn magic also gain a weakness to it.
• Pact has a variation in that any crude, unworked material, not limited to metal, has an effect against fairies.
• In The Saints, Cold Iron is described as an effective tool against faeries.
• The Salvation War: Demons have a deep-rooted fear of iron. It's apparently toxic to them and screws up their regeneration abilities. While it's never really explained why, the Human forces are quick to exploit it.
• Whateley Universe: Fey the Magical Girl is susceptible to cold iron (and synthetics) as soon as she gets her powers and changes into one of the true Sidhe. As she finds out the moment she picks up her mom's iron frying pan. "Cold iron" is cold-forged iron or wrought iron, according to Word of God.

Web Videos

• Tales From My D&D Campaign: Little One wields a Cold Iron sword. Per standard D&D rules, it cuts through the defenses of any sort of Fey creature, which saves the party more than once.

Western Animation

• The Avengers: Earth's Mightiest Heroes: Similarly to the Comic Books example above, Iron Man tries to exploit this against Malekith the Accursed, attempting to use his armor to hold the dark elf back. It's subverted as the suit's alloy is primarily composed of titanium, and while there is iron in it there's not nearly enough to affect Malekith beyond mild discomfort - though it does serve as a useful distraction.
• Batman: The Brave and the Bold: In "Trials of the Demon!", Jason Blood is burned by iron twice, and later, Jason Blood/Etrigan throws James Craddock's iron cane down Asteroth's throat, destroying Asteroth.
• In Gargoyles, Oberon's Children are all weak to cold iron, up to and including Oberon himself. This is utilized in a number of ways — iron chains to bind Puck and the Weird Sisters, an iron robot named Coyote to catch the mythical Coyote, and ringing an iron bell to take down Oberon when he agreed to use only as much power as one of his children for a contest (though when he was at his full power an iron harpoon to the chest only slightly injured him).
• A Mesoamerican take in Onyx Equinox. Obsidian, the main metal equivalent to these cultures, can kill any supernatural entity, even gods.

Real Life

• In the life cycle of larger stars, when they run out of hydrogen in their core to produce energy, stars start fusing other elements in order to maintain itself. The star keeps on building layer after layer within the core fusing heavier and heavier elements, and getting less and less return. Fusing iron will give no energy return. A few nanoseconds after it starts to make iron in its core, it will go supernova. So iron is the star killing metal.
• In real life, iron is typically found in ores. Methods to extract the iron from them almost always involve very high temperatures, sometimes even higher than iron's melting point. What is almost never found in nature is "native iron", also called "telluric iron". The only known large deposit is in Greenland. Being bona fide iron, not ore, it does not have to be reduced first — you can forge it right away. One other source of iron exists, and that is Thunderbolt Iron. Metallic meteors of mostly iron can exist in space, and if they fall without being completely destroyed then they can serve as a source of workable metal. These non-ore sources are sometimes called "cold iron" because they hadn't been heated — by human action.
• One theory about the origin of the trope relates to the original way that iron was made. The process is called direct reduction. Essentially the ore was exposed to carbon or carbon monoxide at very high temperatures, causing a chemical reaction with products of pure iron and carbon dioxide. Direct reduction was actually the first way that iron was extracted from ore (as it requires lower heat which kept it in use up to the 16th century), contrary to popular belief, which holds that smelting was the first method (which involves melting the metal). Both direct reduction which creates "sponge iron" and smelting iron which creates "pig iron" or were not very useful alone; they either had to be hammered into "wrought iron" or remelted into "cast iron". Because of differences between solid and liquid iron, pig iron contains more carbon than the solid solubility limit of 2.2% and so the carbon precipitates as graphite flakes that make the metal easier to re-melt (for casting) but promote rust. Steel was first created by using a type of furnace called a bloomery to purify the iron without melting it. Before the Industrial Revolution (and the rise of misleading trade names like "Maraging Steel") steel was essentially any malleable iron that had enough carbon to be fully hardenable (more than 0.45%). If the bloomery was too cold to produce steel, the iron wouldn't absorb much carbon and much of the slag from the ore wouldn't be burned out. The slag actually helped to protect the iron from rust. Since fairies were blamed for sour milk and misbehaving babies, they might have been blamed for rust, too. Thus the cold-refined iron could have been seen as repelling rust-fairies.
• On a more microscopic level, hereditary hemochromatosis is an iron storage disorder that causes the body to absorb too much iron, leading to organ damage and possibly death if left untreated.
• An euhemeristical explanation about this weakness is that in the first conflicts between the first members of the Homo sapiens species and less evolved species of hominids (whom could had inspired the myths of trolls and orcs) the forging of metals gave our species a key advantage against the wood and bone weapons of these hominids. Though this claim is extremely dubious given that Homo sapiens didn't start making metal tools until well after it had spread through Eurasia and all other species of human had gone extinct.

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