Two weeks ago I polished the silver again and applied a new treatment whenever I have a load of silver to wash:
Line plastic rectangular container (like a dishpan) with foil (the thin, cheap kind)
Fill the container with silver or silverplate
Sprinkle liberally with baking soda
Pour boiling water over the silver and let cool
Wash silver with a liquid detergent
Dry
Silver will be shiny and tarnish free -- especially after a couple of applications