what is the blue junk on old strings?
you know what i mean. after a week or two, if you brush off the strings before you play them, a bunch of blue dirt falls off. is that a copper oxide or something?
that doesnt happen with mine.
if anything it is more black.
but yes, it is oxidation, finger grease, sweatlets, dead skin flakes, you name it
strings get full of gunk.
that is why it is important to wipe them with a soft cloth after playing.
AND changing them after twenty to forty hours of playing is a good idea. because they sound dull and tend to break with all that stuff on em.
yes, I said it, twenty to forty hours.
It's copper carbonate. Usually it's green (malachite), but can be blue (azurite.)
Nickel will make a green crust when it corrodes, too.
"A cheerful heart is good medicine."
I'd go with copper as well. Are the strings that do this bronze? Bronze is a copper alloy, so it's in there in decent quantities. You remember copper sulphate from school? Is it that kind of blue?