'Insincere' in the Bible

Like a [common] clay vessel covered with the silver dross [making it appear silver when it has no real value]Are burning lips [murmuring manipulative words] and a wicked heart.

The refining pot is for silver and the furnace for gold [to separate the impurities of the metal],And each is tested by the praise given to him [and his response to it, whether humble or proud].