Once you've removed the strings, chuck them into a pot. It's best to have a dedicated pot for this job, just a cheap one will do fine. After all, no-one wants beans on toast with added teflon flakes do they? That's to say nothing of rusty chicken soup, or Hollandaise sauce with a hint of nickel... Cover them with water, add a couple of tablespoons of vinegar, and a couple of teaspoons of Bicarbonate of Soda. Even before it boils, you should get a nice fizzy reaction. Boil them for at least 15 minutes, but don't let the pot boil dry. While they're boiling away, get the grill (or better still the oven) up to a moderate temperature. If you're feeling peckish, now's the time for toast. Speaking of which; back in a mo'... ...that's better. Now where was I? Yes! Drain the strings, and lay them in the grill, still coiled up. Turn them over every 5 minutes or so, until they're completely dry. At no point in this process should they be any hotter than they were when they'd been boiled. If you can be arsed, turn the heat down a little each time you turn them, it'll help bring the grain structure of the metal back into line nice and gently. Which is nice. See? Millenia of good science debased in the name of the wanton hussy that is cheapskate-ism! Wonderful... Now we freeze them. Put them in something dry with a lid on. This will set the all important grain structure properly. An ordinary freezer will do, although I did once take advantage of my driving to put them in a freezer trailer with 20-odd tons of chicken at -25C. It's the next best thing to a pot of liquid oxygen. Except for the missing -248 degrees, and the faint aroma of poultry. So not really, then. Freeze them for at least 6 hours, overnight preferably. When you take them out, let them come back up to room temperature for a bit (half an hour usually does the trick), and just check there's no frost on there. If there is, just wipe it off. Restring, and tune up. You won't find them stretching quite as much as new strings, but they ought to be more-or-less as bright. Not a bad result for the outlay of a few bob, and a bit of bronze-age sciencing, I think you'll find. For the record, I find that D'Addario and DR strings boil up well; Ernie Ball aren't too bad - a bit hit and miss to be honest. Nickel Rotosounds don't fare well at all, but then they always felt to me like they'd already been boiled... Merry Christmas and a Happy New Year!