Charles Ellicott Commentary Jeremiah 6:28

"They are all grievous revolters, going about with slanders; they are brass and iron: they all of them deal corruptly." — Jeremiah 6:28 (ASV)

Grievous revolters ... —Literally, rebels of rebels, as a Hebraism for the worst type of rebellion.

Walking with slanders. —The phrase was a common one (Leviticus 19:16; Proverbs 11:13; Proverbs 20:19), and pointed to the restless eagerness of the tale-bearer to spread his falsehoods. (Compare to 1 Timothy 5:13, wandering about ... idle tattlers.)

Brass and iron. —Base metals serving for vile uses, no gold or silver in them. The imagery, which carries on the thought of the previous verse, had been made familiar by Isaiah (Isaiah 1:22; Isaiah 1:25), and was reproduced afterwards by Ezekiel (Ezekiel 22:18–22) and Malachi (Malachi 3:3).

Corrupters. —Better, workers of destruction.