[Philip]

....for instance, in the kitchen. Just tonight I made this wonderful little appetizer of sliced Japanese "momotaro" tomatoes sprinkled with chopped fresh basil and some crumbled chevre, and drizzled-over with some Greek olive oil. Oink!

For de-rusting and stabilizing corroded surfaces without compromising the patina, I like to use a brand of penetrating oil called "Break-Free" which is popular with firearms enthusiasts since it loosens superficial rust and does a great job of lubricating and preserving without harming finishes such as bluing, parkerizing, or browning (the latter being a form of oxydation which is a cousin to the natural patina on old iron and steel surfaces such as your rapier).

I tend to eschew the use of sandpaper of all kinds when preservation of a dark patina is an issue, in favor of
1. Small brushes with fine brass and stainless-steel bristles, these are about the size of the ones you brush your teeth with.
2. Steel wool in various grades in the medium-to-fine range (2 to 00)
3. Picks and scrapers made of hard non-metallic materials (in Japan, deer antler is the traditional material for the tools used on corroded iron tsubas and sword-tangs. The reason that antler is so favored is that it's hard enough to flake rust away yet won't expose bare metal which is a no-no for tsubas and tangs.
4. Stainless steel dental picks -- use only in the deepest pits or otherwise inaccessible areas such as between blade and guard.
These are listed in "mild to aggressive" order. The first two are the mainstays, with the oil they will take off most of the surface rust one normally encounters and yet when used gently and judiciously, the hard patina underneath will be preserved. The second two work best in "lunar-landscape" areas. Gentle but persistent prodding with the tools does the trick, until the active rust is flaked off the affected area.

When the surface is where you want it to be, you can clean all the accumulated oil and residue off with something like WD-40 and a succession of clean rags until the cloth is more or less unsullied with gunk and rust, and then follow up with a non-greasy preservative like Renaissance Wax. The beauty of the Break-Free is that repeated applications during the time you've been working on the piece will enable the molecules of the oil to really sink in to the pores of the metal (that's why it's such a good lube for things like semi-auto firearms whose working parts are subject to lots of friction). The Renaissance Wax is an effective surface protector that won't get your hands all dirty when you're playing with your toys, and more importantly, won't stain the wallpaper or the backing of your display cabinet if you like to hang them up for all to admire...