The magic of sorcerers, wizards, and necromancers is Of Chaos. Chaos has a high affinity for black iron, the less refined, the better. Raw ore is the easiest to enchant, followed by wrought iron, forged iron, and steel. Cultists refer to iron as “the teeth of Tiamat”, although that is not accepted Church doctrine.
The divine miracles of clerics is Of Law. Law has a high affinity for brass, and (for the spectacularly miraculous) adamant.
The nature magic of druids and elves is Of Balance (which may, or may not, be a refinement of chaos magic). Nature magic has an affinity for wood, stone, and if need requires metal: bronze or aurichalcum (an alloy known to the dwarves which they know as mithril).