Help with a Discoloration

[Rick Bowles]

I'm selling some knives for the family of a good friend that passed. One of his sons who had custody of the gun and knife collection suffered a fire in the garage where the gun safes are. Now most of the folding knives show a gray "shadow" on the part of the blade that was exposed outside the handle. Has anyone experienced this and is there a way to clean it without buffing?