It is a simple chemistry experiment that you can use to clean the silver. I do ask you to get permission before doing this. While it may seem a nice surprise, some silver is not to be cleaned, so be sure to ask before you do this experiment. It starts all bright and shiny and soon turns dark and dull. The tarnish is a chemical change which takes place when sulfur compounds in the air combine with the silver to make silver sulfide.
Silver sulfide is black.
Some silver polishes actually grind away the silver sulfide. This makes the silver nice and shiny, but it also removes a bit of the silver. This is especially serious for silver plated items, as years of polishing will wear away the silver, revealing the metal underneath. With this experiment, we will change the silver sulfide back into silver, leaving in place instead of removing it. To do that, we need to remove the sulfur.