"But Iron — Cold Iron — is master of them all."One of the most mundane Depleted Phlebotinum Shells and the traditional bane of The Fair Folk. Iron may be treated as naturally magic-disrupting or just poisonous for certain creatures. Sometimes it's supposed to suck the magic out of The Fair Folk (similar to the way it sucks heat out of the body), usually accompanied with screams about how "it burns". Sometimes it's got something to do with ferromagnetism, or related to iron's nuclear stability, or its resistance to rust. There's little agreement about what "cold" means in this context. Sometimes it just mean 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. It might just be a poetic reference to any iron (much as "cold steel" was used in later times), just because metals that aren't hot feel cold thanks to heat conductivity. It may be pulled as "magic vs. technology" symbolism. 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. 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 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. It is a subtrope of Fantasy Metals.
— Rudyard Kipling, "Cold Iron"
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- In Munchkin Bites, Cold Iron is a trap card that only affects Changeling characters.
- In The Sandman 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.
- Marvel Comics
- In 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).
- Marvel demons are also 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 is not literally iron note , but just calling himself "Iron Man" is apparently reason enough for Malekith to call down The Wild Hunt on him. When Tony decides he's had enough, he 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, he starts hunting the elves with such viciousness and ferocity that he scares everyone, from his ally, to ordinary Dark Elves, to Malekith himself.
- Wolverine's adamantium claws also 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.
- In the Top 10 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 justificationnote , but for the setting it's essentially Cold Iron.
- In the Hellboy story 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,
MY IRON SHOES!"
- In the Elseworlds story Superboy's Legion, Ferro Lad of the Legion of Super-Heroes 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.
- The possessed in the Night of the Demons (2009) remake are vulnerable to rusted iron.
- An iron stake (really a railroad spike, as There Is No Kill Like Overkill) is shoved into the chest of the antagonist in the 1930s German classic Vampyr.
- In Captain Kronos Vampire Hunter, the vampires' vulnerability is to iron crucifixes (or to a cruciform sword forged from an iron crucifix).
- 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.
- Somewhat of an Inverted Trope in Ghostbusters, 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.
- 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.
- Andre Norton's novel Steel Magic. Cold 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 as weapons; respectively a spoon, fork and knife. 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.
- In Lords and Ladies, elves' primary sense is 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 horsehoes are the closest available source of iron.
- 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 against them.
- 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.
- 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 signifigance 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.
- Poul Anderson's 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.
- Still Poul Anderson: in The Broken Sword, the main reason of the abduction of a human baby by the elves is the need for a human warrior able to wield the sword Tyrfing .
- In The Princess on the Glass Hill, Boots controlled the Cool Horses by throwing steel over them.
- Cold iron is any iron in the October Daye series. 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 Tim Powers's On Stranger Tides, it's said that the presence of iron disrupts magic, and the increasing use of iron-based technologies is why you don't get magic much any more.
- In The Dresden Files, "cold iron" is any iron, even if it's been smelted into steel. Fae creatures generally have zero tolerance for it in any form — injured by mere contact with anything containing iron. 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. "Cold Iron" is explained as being descriptive text, kind of like "hot lead".
- 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.
- The Knights are mortal champions of the Faerie Queens must stay away from iron too. While not as poisonous to one as to a fae, it is an instant, total off-switch to his Knight powers. That's a very bad thing in battle, or if the extra power is keeping injuries from affecting him.
- One of the more spectacular uses of this happens in Summer Knight. 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 Murph finishes the "chlorofiend" off with a chainsaw.
- In Fletcher Pratt and L. Sprague de Camp's novella "The Castle of Iron" 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 Wheel of Time has "Iron to bind" to deal with the Finn. It has to be true iron, though; steel doesn't work. They're also vulnerable to music and fire.
- In The SERRAted 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 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 the book Merlin's Godson the title character has to save a tiny Fae civilization from an iron nail that has accidentally fallen into their realm.
- In The Once and Future King the young boys Wart and Kay take iron with them as protection when they visit the fairies' castle.
- In Stardust Dunstan touches some coins to an iron nail to make sure that they are real and not "fairy gold".
- 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.
- In The Spiderwick Chronicles there is a passing reference to this.
"Steel. It cuts and burns."
- 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 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.
- Rudyard Kipling's "Cold Iron", quoted at the page top, uses the reference solely as a metaphor for armed combat (as opposed to gold, silver, and copper, for trade, jewelry and metalcraft). Then it gets overtly Christian.
- 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 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 Bartimaeus Trilogy all spirits are harmed by iron, but are harmed even more by silver.
- In Kate Elliott's Cold Magic trilogy, cold steel in the hand of a cold mage can kill just by drawing blood.
- 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.
- Count Dracula is slain in the original novel 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 was important, though.
- 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.
- In Josepha Sherman's 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.
- The Ward Stone 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 Ruth Frances Long's 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 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.
- In Julie Kagawa's The Iron King, all the fairies. Meghan's ability to handle it is significant. And then there's the iron king.
- In Susan Dexter's 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 True Knight, Wren and Galvin can't work magic on iron, and Valadan can be trapped by an iron bit.
- In the Warlock of Gramarye series, 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.)
- In the Heralds of Valdemar book 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.
- 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.
- Like in The Bartimaeus Trilogy, iron is a common and good deterrent against ghosts in Lockwood & Co..
- In The Princess Series iron only protects from the weakest of fairy magic.
- The Bhellium, Cosmic Keystone of The Elenium and Tamuli, 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.
- Additionally, the Styric people absolutely refuse to touch or use iron under any circumstances. The reasons are not given, but the same limitation seems to effect 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.
- In The Name of the Wind, cold iron is known to be super effective vs "demons".
- In Julian May's Saga of the Exiles, the alien race which is split into the Tanu and Firvulag (inspiration for later legends) die from a simple scratch from iron or steel, and refer to it as blood-metal (it's noted in text that their blood is apparently iron-based, as it's red, and they are 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 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.
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Mythology and Religion
- 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". In a later chapter of the same book He does defeat an army so equipped, but by setting their soldiers against each other as opposed to direct power. It should be noted that in this period iron chariots would be ludicrously advanced military technology (as in "M1 Abrams tanks in the American Revolution" advanced), and many historians consider it an anachronism by the author writing centuries later.
- Used against the "marsh weans" (a disembodied intelligence believed to be evil spirits in 1950s Orkney) in the Big Finish Doctor Who 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.)
- Dungeons & Dragons
- 'Fool's Gold' spell made copper coins look like gold, but it fails when 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 payed in order to enchant it, doubling the price of the 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.
- 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 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.
- Likewise, in the predecessor game 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 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.
- 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.
- Faery's 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.
- Champions adventure The Coriolis Effect. Ch'andarra and her daughter the Black Enchantress both take damage when touched by raw (cold) iron.
- (Normal) iron as well as its alloys are the bane of the Duk'zarist, the dark elves of Anima: Beyond Fantasynote , 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.
- In 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 is 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.
- Or 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 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.
- In Pokémon, Steel-type attacks are super effective against Fairy-type Pokémon, and Steel-type Pokémon resist Fairy-type attacks.
- 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.
- 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 weapon or armor.
- Elves in Dragon Mango are extremely vulnerable to iron, 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.
- Cold iron in Never Never prevents Pookas from using any of their special abilities, including changing size and increased luck.
- Tales of the Questor makes extensive use of this trope. Although it claims "cold iron" is a mistranslation of "north iron" ie lodestone.
- 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.
- In Codename Hunter, the Fey are extremely vulnerable to iron, but not so much to iron alloys.
- Demons in The Salvation War have a deep rooted fear of Iron. It apparently is toxic and screws up their regeneration abilities. While it's never really explained why, the Human forces are quick to exploit it.
- In the Whateley Universe, magical girl Fey 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.
- Little One in Tales From My D&D Campaign 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.
- Cold Iron is described as an effective tool against faeries in The Saints.
- In Gargoyles, Oberon's Children were 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).
- 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 days 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 Cold Iron trope relates to the original way that iron was made. 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. Contrary to popular belief, it wasn't usually smelted (which involves melting the metal). Smelting iron creates "pig iron" or "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.