I have some Cold Black solution ( like cold blue) I got years ago somewhere, gives a nice black finish, Have not seen it for yrs.
I have some Outers cold blue I picked up at Canadian tire while back that is darker than the benchwood casey paste I find, it is liquid, so use a bit on a q tip, degrease I use brake cleaner spray ( on a cloth), works good for me for stuff like this. after, lightly buff with coarse cloth or 0000 steel wool, oil.
If it is blackened stainless , will not work.