You will need:
One bowl big enough to hold whatever you are cleaning
And of course, dirty silver jewelry
Place your jewelry pieces on the foil and lightly dust with baking soda and salt (start with about 1 tsp of each depending on how much jewelry you have in the bowl).
Carefully pour the boiling water into the bowl so that all the jewelry is covered. Almost immediately, the tarnish will begin to disappear. If the silver is only lightly tarnished, all of the tarnish will disappear within several minutes. If the silver is badly tarnished, you may need to reheat the baking soda and water mixture, and give the silver several treatments to remove all of the tarnish. Let the jewelry sit in the dish until all the tarnish is removed and the water has cooled. You may need to turn the jewelry pieces a few times to make contact with the aluminum.
Remove pieces from the bowl, rinse in cool water, and dry with a soft cloth.
And that's it! So simple. The solution is safe to pour down the drain and you can throw the used foil in the recycling bin.
When silver tarnishes, it combines with sulfur in the air and forms silver sulfide (Ag2S). This is the dark gook that we see on the surface of the metal. To remove the silver sulfide and restore the original lustrous finish, we can either polish the silver by rubbing, which removes a small portion of silver, or we can reverse the chemical reaction by reducing the silver sulfide back into silver. In the reaction, silver sulfide reacts with the aluminum metal. The aluminum is oxidized to aluminum oxide (Al2O3) and the silver sulfide is reduced back to silver. Hydrogen sulfide is also produced in this reaction. The chemical reaction is listed below.
OXIDATION: 2 Al(s) + 6 OH– (aq) –––> Al2O3(s) + 3 H2O (l) + 6 e–
REDUCTION: Ag2S(s) + 2 H2O (l) + 2 e– –––> 2 Ag(s) + H2S (aq) + 2 OH– (aq)
3 Ag2S(s) + 2 Al(s) + 3 H2O (l) –––> 6 Ag(s) + 3 H2S (aq) + Al2O3(s)
The silver and aluminum must be in contact with each other, because a small electric current flows between them during the reaction. This type of reaction, which involves an electric current, is called an electrochemical reaction. Reactions of this type are used in batteries to produce electricity. How's that for a little throw back to high school chemistry!!
Sources: SciFun Website; UMASS Amherst Chemistry Dept.