I recently acquired a face mill that has a glossy black oxide surface finish. The mill is in excellent condition except that the previous owner allowed it to develop some surface rust (mostly on the upper surfaces; probably from sitting around uncovered on a shelf). The surface rust is like freckles, with most very small, but some spots of 2-3mm dia. Naturally, the black oxide finish on these upper surfaces (between the rust spots) is also dull.
I was wondering if there is a way to remove the rust (or majority of rust) without significantly damaging the black oxide. In the past, when I has some surface rust on some black oxide impact sockets, I tried the following:
- Green scotchbrite and kerosene.
- Phosphoric acid.
- Salt & vinegar bath.
All three methods removed the black oxide as well as the rust.
How about polishing? That will also remove the black oxide, but perhaps not as much. Or is there an easy (and inexpensive) way to renew the finish?
Any advice would be greatly appreciated.