Folk beliefs speak of something called "cold iron" that is supposedly a bane to fairies. As metal tools are normally cold, many people assume this means any metal at all. Others think it means items made of pure iron, rather than the more technologically advanced steel, in which iron is mixed with other metals.

It seems likely however, that "cold iron" probably means "wrought" iron, as opposed to "cast" iron. (More durable than cast iron but less so than steel.)