IRON is one of the four symbolic metals, standing north in a quaternary with Gold (south), Silver (east), and Brass (west). It is the metal with which Los works. His forge and furnace and all his instruments are of iron; he has an iron mace; and Urthona’s bow is of iron.
However, Blake also associates Iron with all forms of cruelty: war (which comes from the North), with its weapons, armor, and the captains’ whips (J 65:35) ; also Urizen’s Book of Iron (Ahan 3:64), and his Plow of the Nations (FZ ii:70), and Vala’s spindle of destruction (J 66:10) ; and imprisonment, with its chains and fetters, including the bonds of selfish love. Fuzon’s chariot (Ahan 2:1), Los’s Chain of Jealousy (Ur 20:19, 24), the vessels of the Shadowy Female (Am 1:3) and of Urizen’s daughters (FZ vii:96), and the trumpet of the Last Judgment (Eur 13:2) are all of iron. “Some Sons of Los surround the Passions with porches of iron & silver” (Mil 28:1) ; that is, in the writing of comedy, the poets use Iron (wit-combat) and Silver (love).