I clean mine down completely, all the string & insulation, whats left is what I can't get to with a genuine effort.

I sometimes even wash the oil off fridge compressor copper wire...
Once they had a second look at the microwave transformer coils & tried to pick the most obvious paper bit & gave up after 3 attempts.

Now they look at me with awe when they check my copper, they even noticed the lack of oil the first time I did it.

Thats what they get for being a great honest scrapmetal buyer (I even snip off the soldered ends on the wire..)