This is an old trick using household products to remove the tarnish from silver or silver plate chemically without polishing off or in any way removing any of the good silver.
I'm sure this sight will be familiar if you've left anything silver or silver plated in a cupboard for a length of time - a layer of blue-black heavy tarnish.
You can buy an aluminium plates for this purpose which you can use again and again but it's the aluminium that's important, and household aluminium foil will work just as well.
You will need:
I don't know the optimum proportions needed, but I use a small amount of salt and a larger amount of bicarb. In this example I'm using a teaspoon of salt and a tablespoon of bicarbonate of soda. I suppose that the best amount of bicarb is enough to dissolve to saturation. I may have used too much here as it remains very cloudy.
When it's ready it'll look a bit scummy but much brighter. A rub with a clean cloth will clean off the dull scum and hopefully leave the item looking like new. If any tarnish remains, repeat the process.