An Easy Way to Clean Tarnished Silverby Jonathan DuHamel on Jun. 16, 2009, under Miscellaneous Stories
Many people have old silver tea sets or silver commemorative bowls that tarnish over time. The usual method of restoring the shine is to buy silver polish and rub it on the object. That method is messy and sometimes hard work. There is a much easier way to clean silver using things you already have around the house.
Place aluminum foil (shiny side up) in the bottom of a non-metallic container big enough to hold the piece to be cleaned. Add a few teaspoons of salt and baking soda, then fill with hot water – the hotter, the better. Make sure the salt and baking soda are dissolved.
Place the object to be cleaned in the container so that it touches the aluminum foil. Most tarnish will disappear in a few seconds. Leave the piece in the solution for one or two minutes for stubborn tarnish. No rubbing required.
Why it works (I think):
Tarnish on silver is principally silver sulfide or silver sulfate. The sulfur comes from the atmosphere and slowly combines with the silver. This method of removing tarnish relies on the fact that silver and aluminum have different standard electron potentials. When the two metals are in an electrolytic solution (salt water) and are connected electrically (touching), electrons can travel between the two. The silver will be reduced (gain electrons) to form pure silver (which plates out on the silver piece) and the aluminum will be oxidized (lose electrons). This causes the sulfur in the tarnish to transfer to the aluminum. In this situation salty water acts as the electrolyte that allows the electrons to flow and the baking soda forms a weak acid which also aids electron flow. The reaction is: silver sulfide + aluminum > silver + aluminum sulfide or 3Ag2S + 2Al > 6Ag + Al2S3. (If the piece is very heavily tarnished the baking soda may take up some sulfur to form H2S, rotten egg gas.)
If any chemists read this post and can offer a better explanation of why it works, please reply.
Also I would be interested in a similar method, if any, to clean copper.