Huh... Well, I guess it can be stained then.
I thought it was near to impossible just from my own experience with it.
I had an old knife called an Air Assault made by Newt Livesay. It was my rough-and-tumble knock around knife for quite a while.
I'd use it for anything and everything and needless to say it got heavily gunked up. The blade had almost no parkerization left on it, edge was rusty and dinged up, handle was absolutely filthy dirty.
I took a blue scotchbrite pad and dawn dish soap to the handle and it looked like the day the guy made it. I sharpened most of the dings out of the edge, sprayed it with WD40 and it was ready to go again.