'Dross' in the Bible

Son of man, the house of Israel is to me become dross: all they are brass, and tin, and iron, and lead, in the midst of the furnace; they are even the dross of silver.

Therefore thus saith the Lord GOD; Because ye are all become dross, behold, therefore I will gather you into the midst of Jerusalem.

Make the pot stand empty on the coals until its bronze glows red, its rust can be scoured off, and its dross completely removed.