Baking soda, when it contacts aluminum, such as aluminum foil, creates a chemical reaction that removes the tarnish from silver. This can be done by dissolving one cup of baking soda in one gallon of hot water, pouring it into a pan lined with aluminum foil, and immersing the silver in the pan.
For tarnish removal to occur, the silver and aluminum must be in contact with each other. Light tarnish will be removed in a few minutes. Heavily tarnished silver may need several treatments.
Unlike abrasive cleaners that remove small amounts of silver with the tarnish, this method doesn't harm the silver. Instead, an electrochemical reaction carries the tarnish from the silver to the aluminum.