Siderite is the most perfect Iron that ever existed, this is true. However, Cold Iron specifically states that in order for it to be banal against the Fae that it cannot; be forged in bulk nor forged by magic.
- You can summon it, wholly formed if it existed in the form it was summoned as, and still count as the bane.
- You can use magic to find Naturally occurring Siderite and forge it mundanely to have it still count as the bane.
- You cannot use the Matter spell that allows you to turn base Iron into Siderite and have it count as the bane.
- You cannot use the Matter Spell Shaping to turn a hunk of Siderite into a usable form, and have it still count as the Bane.
- You cannot simply Will Siderite into Existence, and have it count as the Bane.
- Magically Manifested Siderite will still count as Iron for things like its immunity to Fae Magic, and cutting through defenses related to Fae magics.
CtL pg 102
PGttCC pg 14
This will be added to this page sometime today: Contagion Chronicles Rules