This might seem like a strange question... It doesn't matter what brand of strings or type of instrument (electric guitar, acoustic, bass), but my fingers always have a black substance on them after I finish playing, even for a short session. It looks like I've just handled graphite powder. It doesn't matter if I've just restrung with fresh strings, wiped them down with a string cleaner, or haven't done any string maintenance for months. It seems that this occurs more severely with my acoustic guitar than with my electric or bass, but it does happen with all three, and with different brands of strings and material types. It doesn't seem to make a mess on the actual guitar necks as far as I have noticed; rather, whatever the substance is seems to be transferred directly from the strings to my hands. I've been playing for about 15 years, but I never really knew where I could ask about this. Are strings typically coated with something that should be expected have this result, or is my skin just reacting in a peculiar way? At one time I thought it might be build up of skin oils from my hands, but since I see the same thing with brand new strings that shouldn't have a build up of anything on them, that doesn't seem likely. I'm just wondering if this is common or if there is something I can do to keep this black substance off of my hands.