[whswhs]

There's a belief held by some fantasy readers that "cold iron" is some special form of iron with extraordinary magical properties (I have the impression the qualities of meteoric iron in Dungeon Fantasy may allude to this, for example). I don't think this is well founded in the sources. Kipling's ballad "Cold Iron," for example, describes the nails used on Jesus at the Crucifixion as "cold iron"—and I don't think Kipling was suggesting that the Romans used some rare magical alloy to nail up a common felon. Poetically, the adjective "cold" is used to fit the meter of a line, and as an intensifier that evokes a striking property of the thing described, the feeling of coolness that comes from its thermal conductivity, the way "red gold" evokes the vivid color of gold.

But I just thought of a couple of interesting possible implications of this:

1. The specific nails used at the Crucifixion took on magical (or anti-magical) powers from contact with Jesus's blood, and are now potent relics.

2. That contact granted special powers not just to those particular pieces of iron, but to the metaphysical essence of iron. Since then, iron has had that potency—but if you lived in or travelled to the past, before then, iron had no special magic. Nor would it have such magic in an alternate timeline where Jesus never lived, or wasn't put to death, or was put to death in some other way, assuming such timelines are possible.