1)
What is the significance of dross silver plated over earthenware?
1.
Rashi: It is stuck to Cheres used to refine. It shines as if it is silver, but it has no use.
2.
Malbim: It appears to be silver, but it is really Cheres. One whose lips burn with (he passionately expresses) love, but the heart is evil, he is worse than a Nirgan.
2)
What are "Sefasayim Dolekim v'Lev Ra"?
1.
Rashi: [Also this looks nice, but has no benefit.] They pursue people to entice them with smooth talk. They speak with the mouth unlike the heart. They appear like lovers, and they are enemies. Dolekim is [pursuing], like "Dalakta Acharai" (Bereishis 31:36).
2.
Malbim: Refer to 26:23:1:2.