I think that very few if any stains on edged weapons are actually caused by blood. As Justin said "Collecters get far too caught up in these things,Im content with believeing that most of the older swords/knives/daggers that I own were used in battle,people have never had a problem finding reasons to kill,and it was much easier to get away with prior to modern forensics". I totaly agree with Justin on this. But what sounds better and more exciting when showing to or telling someone about one of your favorite weapons, that the stains were caused by it being bloodied in battle or that it was poorly taken care of. Most people I think would like to believe the first.
