'Rust' in the Bible

‘Therefore, thus says the Lord God,“Woe to the bloody city,To the pot in which there is rustAnd whose rust has not gone out of it!Take out of it piece after piece,Without making a choice.

“Then set it empty on its coalsSo that it may be hotAnd its bronze may glowAnd its filthiness may be melted in it,Its rust consumed.

“She has wearied Me with toil,Yet her great rust has not gone from her;Let her rust be in the fire!