Annotation - Chapter 1, Page 2
Charcoal produces the high temperatures needed for smelting iron. The use of reddy is unclear here (some readers see it as "the iron [that is] ready at Widders Dump") but from later context it seems that the iron reddy is a place where iron is both heated red and made ready—i.e. a forge. (RH concurs: "The iron reddy is a smelter where old iron is melted down to make it ready for new uses.")
Widders Dump: See Places.