Actually, to be honest, I have never heard of this happening before. We used to use "Blue Magic" to get tarnish, dirt and all that good stuff off and make the knives look good as new. You just wipe in on, rub it around and buff it off, but be sure not to wipe it from one material surface to the other, because it will carry over. The other thing that we had was some kind of citrus orange stuff that worked pretty good for "newing" up the knives. Something else that I would try myself just to get stain out, but I've never seen it used in the factory, is a smooth white toothpaste. That stuff works great for all kinds of stains. Just be sure not to use ANYTHING abrasive, and don't soak it for ANY length of time, because that will definitely ruin your knife.