I have heard that boiling the strings in vinegar will take off the tarnish and oils and make them like new. Wound stirngs should be clamped into a vice at the ball end, and the winding clampet at the head end in a vicegrip and would tighter. I saw this on a web site from an old friend and former teacher. Its said to renew the strings and get more life out of them. Probly works best on acoustic strings, I have never tried it myself.