Jeremiah 6:27-30

27“I have made you a tester of metals and my people the ore, that you may observe and test their ways.

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

29The bellows blow fiercely to burn away the lead with fire, but the refining goes on in vain; the wicked are not purged out. 30They are called rejected silver, because the LORD has rejected them.”