It’s acid with no good usage in engraving (7)

I believe the answer is:

vinegar

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'it's acid' is the definition.
(vinegar is a kind of acid)

I cannot understand how the rest of the clue works.

(Other definitions for vinegar that I've seen before include "Pickling fluid" , "Pickling agent" , "Pickling medium" , "Condiment - bad temper" , "Acidic condiment" .)

I've seen this clue in the Evening Standard.

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