It occurs to me that someone here may have a use for aging brass fittings in a manner that looks like 100 year old untouched brass.
I have stored cages of oysters in a salt pond which has brackish salt water. The cages were connected underwater by lines with brass snaps on the ends from September to the following May. All brass snaps including the new ones looked like the old brass on my Mississippi Rifle when brought out in May. The aging in the brackish water produced that old dull satin finish looking surface and markedly accentuated the 'grain' in the metal structure.
Just thought this might be useful in some way to someone.
Samchap

I can age the brass in 2 minutes. Just wipe the brass down with the cleaning patches you just used on the bore. The sulphur residue will darken the brass, and after a few applications, you will have a genuine "aged" look.

Cold bluing will darken brass, but you might need to rub off a laquer finish first.