Item from acotar-wings-and-ruin by
Cold iron is the one metal that burns, weakens, and pierces fae flesh, a mortal-made bane that the High Fae fear more than any blade of their own forging.
Cold iron is the mortal world's answer to the immortal—a metal that burns fae skin on contact, severs magic at its source, and can kill what no other weapon can wound. It is mined from deep veins in the mortal lands south of the Wall, where the earth has never known the touch of faerie magic, and shaped by human smiths who work it with salt water and ash. To a faerie, cold iron is a poison and a cage, a reminder that even the most powerful High Lord can be brought low by a simple mortal blade.
Cold iron looks unremarkable at first glance—a dull, greyish metal that does not gleam or catch the light as faerie-forged steel does. It feels cold to the touch, unnaturally so, and leaves a faint, unpleasant chill on the skin even after it is set aside. When worked by mortal hands, it takes on a rough, unfinished quality, as if the metal itself resists the polish and grace that fae smiths prize.
Also known as: Iron, Fae-bane Metal, Mortal Iron, The Cold Metal