Cleaning an old BSA knife

[Makri770]

I found an old BSA knife that I was wondering what the best way to clean and maintain it is.
https://m.imgur.com/eyOqKb2,wqHe4PD

Specifically the black on the blade and how to make it open and close smoother.

 

[Bill DeShivs]

You can scrub the blade with 0000 steel wool to remove some of the rust/discoloration.
I would give the knife a bath in hot water/detergent with a tooth brush. Dry with paper towels, and immediately flush with WD 40-liberally.
Dry with paper towels until no more WD 40 comes off. Then, use a quality oil on the joints if necessary.