The next proverbs are concerned with hypocrisy. The Hebrew denotes the comparison simply by position (see on Proverbs 25:11), thus: An earthen vessel (or, potsherd) overlaid with silver dross—growing lips and a wicked heart.
So called "silver dross" is litharge, an oxide of lead used to this day to put a glaze on pottery (comp. Ecclesiasticus 38:30). The comparatively worthless article is thus made to assume a fine appearance.
Thus lips that seem to burn with affection, and give the kiss of glowing, love, may mask a heart filled with envy and hatred Judas kisses and words of friendship hide the bad feelings that lurk within.
Septuagint, "Silver given with guile is to be considered as a potsherd; smooth ( λεῖα) lips hide a grievous heart" (comp. Matthew 23:27).