Jeremiah 6:28-30 New International Version (NIV)

28. They are all hardened rebels, going about to slander. They are bronze and iron; they all act corruptly.

29. The bellows blow fiercely to burn away the lead with fire, but the refining goes on in vain; the wicked are not purged out.

30. They are called rejected silver, because the Lord has rejected them.”

Jeremiah 6