pass a sponge over the slate

In reference to a wet sponge being used to wipe a writing slate clean.

pass a sponge over the slate (third-person singular simple present passes a sponge over the slate, present participle passing a sponge over the slate, simple past and past participle passed a sponge over the slate)

1. (obsolete) Synonym of wipe the slate clean. [19th century]

   Synonym: draw a sponge over the slate