do they oil it? nickel plate it? do nothing?

if they do nothing - why do they do nothing?

thanks.

They do nothing. After several hundred years it might get to be a problem but during the expected working life of a sword I doubt it would be. Someone correct me if I'm wrong here but isn't authentication of Japanese swords even based on the rust on the tang to some extent?

Patina is often used to at least get a guess at age and authenticity. It would take many years to worry in the normal life of a sword about rusting of the tang. However, I would guess that ancient adhesives were probably used as sealers much like they are by makers today. (I've been using epoxy to try to get an air tight seal on the tang. Whether it will work for years or not, is anybody's guess. I do feel better for doing it, though...)

Interesting... who uses sealers Scott? Al Massey and Jacob Powning come to mind upon reflection. However, to my knowledge Arms and Armor, Del Tin, Angus Trim and Albion don't do much of anything... Perhaps folks from those outfits can correct me if I'm wrong?

I personally don't worry about a little oxidation on the tang. 5160 picks up a patina easily, but normally doesn't pit. The oxidation doesn't hurt anything and may add some extra protection.

very interesting! Thanks all. I guess it makes sense. The steel in leaf springs for car shocks show rust, and yet they seem to last quite a number of years in wet, salty and muddy conditions.

FWIW the Japanese sword world doesn't worry about it. As Russ already mentioned it is sometimes an appraisal point (determining age, composition, etc.). And frankly it isn't much of a problem if you're thinking evil red rust. The nakago (tang) of a Japanese sword is either in a friction fit wood tsuka (handle) or mounting in a similarly friction fit wood shirasaya (storage scabbard). And when you handle or inspect a well polished blade outside of the mounts the tang is the only part of the blade you handle. Skin oils get on, air gets on, etc. But since it's stored in a relatively air free environment in a steel friendly wood (non acidic) the steel tends to develop a very stable, slow forming patina. In other words active red, fast growing rust never forms only a slow forming and very stable patine. This protects the nakago over time. I've held a number of blades now over 800 years old with nakago that are still in fantastic shape. They were of course meticulously cared for, but that really means stored properly.

Just fwiw.

800 years old? That is simply amazing. Thanks.

Most makers, though, don't do anything. My understanding is that at a certain point, oxidization can form a protective layer against further oxidization. I believe some forms of blueing, blackening, and browning (russeting) are controlled oxidizations.

That's exactly right... just think about all the people with rusty swords out there... :)