Step 1. Take piece of aluminium foil, or aluminium pot.
Step 2. Place tarnished silver in pot or foil in direct contact.
Step 3. Add baking soda or baking powder (sodium bicarb)
Step 4. Add boiling water or bring to the boil.
Step 5. Wait about 10-30 minutes (keep checking the object)
Step 6. Voila. Clean.
How does it work? The sulphur in the air reacts with the silver, tarnishing it. When you use bicarb and hot water, it forms an electrochemical cell (like in a car battery) and transfers the sulphur to the aluminium. After the reaction you will notice a sulphur smell if you sniff the aluminium foil.
1. Tarnish: 2 Ag(s) + H2S(g) → Ag2S(s) + H2(g)
2. Polishing: 3 Ag2S(s) + 2 Al(s) → 6 Ag(s) + Al2S3(s)