Here's a link to the inventor of the soda aluminum tarnish remover idea. He's now a prof at Johns Hopkins. He explains what happens chemiclally; the combination removes the sulpher that causes the tarnish.
http://www.jhu.edu/news_info/news/ho...ec98/foil.html
Everyone says boiling wter. I haven't tried that. I'm still researching what it does to pearls before I start experimenting with them. I do not want to put pearls in boiling water.