How to darken Bess steel area where scraped?

[QM 8687]

I have a brown bess 3rd pattern that has nice rustic colour on barrel. But there is a spot about half an inch square where it might have been banged or scraped against something, leaving a bright white metal mark that stands out. Even the original Tower lock has a tiny ding that shows up a glowing.
Is there a way to rust brown a small area that can closely match 200 years of oxydation?

 

[Fultron]

A small amount of mustard or vinegar placed on the offending spots will bring back a dark patina on old carbon steels. It likely will not match the plum/rust coloured 200 year old patina but it will be a dark blue/black and much less noticeable.

 

[Win 38-55]

For small shiny scratches, I have used Birchwood Casey Plum Brown. You heat up the scratch with a propane torch untill the metal boils water. You then take a Q-tip, dip it in the Plum Brown, and apply it to the scratch until the metal cools enough such that the liquid does not boil off. You then take a wet cloth and clean off the residue. If it is just a shiny scratch, it will become almost invisible.

 

[QM 8687]

Left area soaking in vinigar for a few hrs. White metal darkened about a fifth of the way there, unfortunately an area of rusted barrel that also got wet lost that much patina.
I'll try a few more speed up tricks.
I did leave a hammer for the bess in the outside elements for a year, hammer, a replacement original, was buffed and remainder of lock rust brown. After a year they were pretty closely matched. Might go that route here.