It doesn't look like anything was done to the gun to obtain the finish, that is, other than neglect. The finish looks like every other 150 year old English gun I have owned where the original finish has faded to the point of being almost unrecognizable. The lock would have originally been color cased, and I would bet you a Coke, much of the original color is still present on the inside of the plate. I don't believe someone intentionally steel wooled the finish off, because you can still see a VERY faint remnant of the original case colors still present on the standing breech, just forward of the hammer. If someone removed the original color, they didn't do a very good job. Unfortunately, the only ones you can blame (or thank, depending on your taste) for it's current state, is Father Time, and neglect.