I have just been stripping the bark off a piece of willow I cut recently and it has left a nasty sticky residue on my mirror finish carbon steel blade. Eventually I managed to clean it off with hand sanitiser gel. The question is whether the willow residue is corrosive? A bit of patina is ok of course and there are a few blemishes on my blade through use, but I really would not want to risk leaving anything on that is going gradually etch it's way into the blade.