In having experience in touching up 2 guns with Oxpho Blue, I wouldn't recommend it. Although it will blue the metal, I wasn't satisfied on how it looked and how the bluing matched. What I eventually did was have the entire gun reblued professionally. I'm not much of one to consider "collector value" whatever that is. My guns are for me to use and shoot, and so if I want them to look good, I have them refinished. You have to decide what is right for you. But to me, a gun missing bluing and having rust just doesn't appeal to me no matter how old it is.