Albert Barnes Commentary Proverbs 26:23

"Fervent lips and a wicked heart Are [like] an earthen vessel overlaid with silver dross." — Proverbs 26:23 (ASV)

Burning lips - i. e., “Lips glowing with, affection, uttering warm words of love,” joined with a malignant heart, are like a piece of broken earthenware from the furnace, which glitters with the silver drops at stick to it, but is itself worthless.