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.

Burning lips and a wicked heart - Splendid, shining, smooth lips; that is, lips which make great professions of friendship are like a vessel plated over with base metal to make it resemble silver; but it is only a vile pot, and even the outside is not pure.

Burning lips and (k) a wicked heart [are like] a potsherd covered with silver dross.
(k) They will soon break out and utter themselves.

Burning lips, and a wicked heart,.... Either burning with wrath and malice; breathing out threatenings and slaughter; pursuing men with reproaches and slanders, arising from a wicked heart: or rather, burning with profession of love to God, and affection to good men; with great pretensions of kindness, and promises of good things, when their hearts are wicked, and they design noticing less; say one thing with their lips, with the greatest show of affection and sincerity, and mean another in their hearts. These
are like a potsherd covered with silver dross: which at a distance, or to less discerning persons, looks like silver, and is taken for it; when the covering is only dross, and what is within is only a potsherd, Or a piece of an earthen vessel, good for nothing: such are the specious professions and deceitful words, which flow from a wicked heart.

A wicked heart disguising itself, is like a potsherd covered with the dross of silver.

Warm professions can no more give value to insincerity than silver coating to rude earthenware.

The proverbs next following treat of a cognate theme, hypocrisy (the art of dissembling), which, under a shining [gleissen] exterior,
(Note: Vid., regarding gleisen (to give a deceitful appearance) and gleissen (to throw a dazzling appearance), Schmitthenner-Weigand's Deutsches Wrterbuch.)
conceals hatred and destruction:
23 Dross of silver spread over an earthen vessel -
Lips glowing with love and a base heart.
Dross of silver is the so-called gltte (French, litharge), a combination of lead and oxygen, which, in the old process of producing silver, was separated (Luther: silberschaum, i.e., the silver litharge; Lat. spuma argenti, having the appearance of foam). It is still used to glaze over potter's ware, which here (Greek, κέραμος) is briefly called חרשׂ for כּלי חרשׂ; for the vessel is better in appearance than the mere potsherd. The glossing of the earthenware is called צפּה על־חרשׂ, which is applicable to any kind of covering (צפּה, R. צף, to spread or lay out broad) of a less costly material with that which is more precious. 23a contains the figure, and 23b its subscription: שׂפתים דּלקים ולב רע. Thus, with the taking away of the Makkeph after Codd., to be punctuated: burning lips, and therewith a base heart; burning, that is, with the fire of love (Meri, אשׁ החשׁק), while yet the assurances of friendship, sealed by ardent kisses, serve only to mask a far different heart. The lxx translate דלקים [burning] by λεῖα, and thus have read חלקים [smooth], which Hitzig without reason prefers; burning lips (Jerome, incorrectly: tumentia; Luther, after Deuteronomy 32:33, חמת: Gifftiger mund = a poisonous mouth) are just flattering, and at the same time hypocritical
(Note: Schultens explains the labia flagrantia by volubiliter prompta et diserta. But one sees from the Arab. dhaluḳa, to be loose, lightly and easily moved (vid., in Fleischer's Beitrgen zur arab. Sprachkunde the explanation of the designation of the liquid expressed with the point of the tongue by dhalḳiytt, at Proverbs 1:26-27; cf. de Sacy's Grammar), and dalḳ, to draw out (of the sword from its scabbard), to rinse (of water), that the meaning of the Hebrews. דלק, to burn, from R. דל, refers to the idea of the flickering, tongue-like movement of the flame.)
lips. Regarding שׂפתים as masc., vid., p. 85; לב רע means, at Proverbs 25:20, animus maestus; here, inimicus. The figure is excellent: one may regard a vessel with the silver gloss as silver, and it is still earthen; and that also which gives forth the silver glance is not silver, but only the refuse of silver. Both are suitable to the comparison: the lips only glitter, the heart is false (Heidenheim).

Burning - With malice or hatred: A slanderous or evil tongue. Dross - Such a tongue and heart are of no real worth, although sometimes they make a shew of it, as dross does of silver.