When I burn insulation off wire.
If its a big lot (5Kg +), I do it outside & let it cool down before returning home to recheck it.
Its normally black & has charcol & ash in it along with a greasy liquid, I wash it with water & find the water & ash is very acidic & stings the multitude of cuts on my hands.
Going from that experience, I expect that washing it with a acid containing product (water & vinegar etc etc) isn't going to do much. Its allready acidic anyway.....
So once thats cleaned off I am now washing it with water & some (small amount) dishwashing powder.
Its Caustic ( alkaline) & dissolves the oily stuff & rips the 'black' off the copper wire.
Sometimes the copper goes a 'pinkish' colour & the black stuff, which I think is a Copper oxide of sorts drops to the bottom of the water filled bucket quickly.
The coppers soft & will break up a bit, I save that stuff anyway, in a pinch I can rewash it & drop it into a copper pipe & close each end. I tell the scrappers what I have done there too. They are OK with it once its explained its still 100% Copper
I have been saving it up so that one day I can electroplate the copper back out & sell it.
The percentage weight isn't high but by saving it up I expect to get a bonus $ one day.
Its all about the recycing. 30Kg +..
When I do it at home.
With 1 Lb bunchs of coated wire, I burn it off in my incinerator (Inside fireplace with 'wetback' (yeah I know that words funny to Americans....) that heats up the water cylinder too).
I just poke it in, let it burn off with as less smoke as possible, then pull it out a bit, bash the ash off & dump it directly into a pail of cold water.
Theres no oily layer on it too.
The black just drops off, heat shock I expect, & the copper turns a real nice Gold/Copper colour.
Its nice & stiff too, crushes up nice & dosn't break up at all.
So, cleaning copper? Try caustic stuff like dishwashing powder, you only need a spoon full.
Or burn it in small amounts & 'quickshock' it in cold water.
Save the polluting black discarded ash, its still worth $ at sometime.