I do ship and yacht electronics for a living and as you would imagine corrosion is one of the biggest problems for electronics.  One of the very common problems is corroded connectors that need to be replaced.  It is quite common to cut from several inches to several feet off of the ends of a wire and to still have corrosion all around every strand of the wire.  It is typically black and I guess is more of a lead or tin oxide of the tinning instead of the green copper oxide you see on copper wires.

Sometimes you can replace the whole wire or cut enough back that you get a clean enough wire to solder to and sometimes you don't have enough wire an it would require removing a sailboat mast or some other extreme thing to replace the cable and you just need to get it working until the wire can be replaced.

I have fanned out all of the strands and used sandpaper to get some clean copper to solder to, but was wondering if there is some kind of chemical method to take off all of the oxides down to bare copper? 
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