'Brass' in the Bible

'I go before thee, and crooked places make straight, Two-leaved doors of brass I shiver, And bars of iron I cut asunder,

From my knowing that thou art obstinate, And a sinew of iron thy neck, And thy forehead brass,

Instead of the brass I bring in gold, And instead of the iron I bring in silver, And instead of the wood brass, And instead of the stone iron, And I have made thy inspection peace, And thy exactors righteousness.