Here's some of my thoughts.

I've learned these things making muzzle loading firearms, as well as other places.

Steel or iron can be both blued and browned -- I've done both. Browning is the oldest technique. The metal can also be left "in the white" or, more properly, "in the silver" -- you polish it and leave it alone. Naturally, you do have to oil it! Blueing and browning were done to create rust on the surface, controlled rusting, and rusting of a a small, small grain.

Knives were also both blued and browned, and I see no reason why swords wouldn't be. Fighting against someone with a darkened blade would be disconcerting, especially during periods of low light. Even at bright noon it would be difficult.

I have also experimented with coloring metal using ammonium chloride (sal ammoniac), but with little success.

One thing I'd like to try someday is coloring metal by boiling it with logwood. I understand that some of the 19th C. revolvers were done that way.

Parkerizing is another, but 20th C., way to darken metal.

I have a sheath knife my brother made which has a damascus blade. My other brother sharpened it. It will shave the hair on the hair on the back of my hand off.

Ted now starts knives on a diamond hone and finishes on hard Arkansas stone, but in the past he's used straight Arkansas, moving from coarse to black. After he finishes on the stones he uses a strop, one with a canvas side and a leather side, to remove the "wire edge" the stones leave. He has done this for scalpels, winning a bet with a local surgeon that he could sharpen a scalpel by hand at least as sharp as a disposable one came from the manufacturer.

Ted has done the "paper on the edge of the knife" trick, but admits that it is just that -- any weapon so sharpened and used in a fight would quickly be rendered dull.