Knowledge checks for special materials

[O11O1]

Which knowledge skill do you use, and what would the DC be?

The example that I'm worried about right now is cold iron in unexpected locations, like the cold iron spigots on a public fountain. (The local government really hates fey.)

My first thought was Arcana, but it seems like craft skills would be more suitable.

[Happler]

To recognize the material, Knowledge: Dungeoneering would work (per the table in the PRD: Knowledge Skill DCs.

Quote:

Identify mineral, stone, or metal Dungeoneering 10

But to know what that would effect, you would need Knowledge: Nature to know that it would effect fey, Knowledge: Planes to know that it would effect demons, etc.