I had a couple nicks in the blueing on my old Chief, didn't mind the appearance so much but they tended to rust when IWB carrying so I touched them up with Oxpho Blue. Well, they don't rust any more but they look kinda blotchy. I have had better results with touching up holster-wear than with these nicks.
I had 2 different old Chiefs with bad looking cylinders-- one had some big spots where the blueing was flat-*** gone (I was told it was blood damage), the other was rust-freckled pretty bad. I bead-blasted the blood-damaged one, warmed it up, and re-blued the whole thing with Oxpho. It came out pretty good, so I went ahead & did the other cylinder about a month later. Both had a greenish tint to them at first which went away after a while.
The bead-blasting not only removed the old blueing so the re-blue would look even, it also (purposely) gave the finished product a matte black finish which I like a lot.