“Like a coating of silver dross on earthenware are fervent lips with an evil heart.”Proverbs 26:23 NIV
There is an ancient Japanese art of repairing old pottery by infusing it with liquid gold. It’s called kintsugi. What is described here in proverbs 26:23 sounds like the opposite. Instead of the pure metal being added to the pottery (earthenware) it’s the impurities that were removed from the liquid precious metal, silver.
The Septuagint translates it “smooth” instead of “fervent” tongue. Either way, that plus an evil heart does not add to anything. It’s waste product. It can’t even be repurposed. It will drive down the value of anything you affix it to.
It’s likely that earthenware is a metaphor for people.