Jeremiah 6:27-30 NIV

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