etymology - What is the origin of "eyewash"?

The two meanings included in the Oxford English Dictionary for eyewash are:

1. A wash or lotion for the eye.




2. colloq. Something that is intended to obscure or conceal actual facts or motives; humbug, blarney; nonsense; something said or done merely for appearance or effect; spec. in Mil. slang = bull n.4 4.

The colloquial sense has written use dating from the 1800s:

1884 C. T. Buckland Sketch Social Life India ii. 45 Most officers of any tact understand the meaning of eye~wash.

The Wordsworth Dictionary of Phrase gives some explanation of why eyewash also means to "obscure something", writing:

So this "fulsome adulation" is figuratively putting a wash over someone's eyes. There are no clear references on where this "wash" came from. It could be from the first meaning of eyewash--if you are flattering someone, you are figuratively putting some type of wash in their eyes that prevents them from seeing your true intentions. It could also be from a meaning of "wash" as in a coat of paint (a wash of watercolor), so you are again obscuring someone's vision. I would guess that the slang sense was actually a figurative application of the first sense, however.