I notice that Shiloh Sharps Rifle Company offers three lock-action finishes for their 1863 cap lock rifles and their 1874s. Pedersoli offers a chemical color case and some sort of polished silver finish on their Kodiak double rifles' locks.
What finishes were regularly used by British gunmakers, such as Alexander Henry, Purdey, Rigby, etc., with bar action percussion sidelocks - when the locks were used for Express rifles and African or Indian game hunting, circa 1850-1875?
Were lock plate's exterior finish some sort of case or pack hardening, would that finish also have been applied to interior lock parts? To hammer? Other?