This is a method of removing the black tarnish from your silver items (if they are small enough to put in the pot!), that my father, the Industrial Chemist, taught me. He said that instead of rubbing your silver away by removing the black coating, this method will add the silver back onto the item!
This is the way we did it:
- Something silver (my daughter's earrings)
- An aluminium saucepan (or perhaps an enamel or stainless one, with aluminium foil on the bottom)
- A few bits of aluminium foil
- Hot water
- Sodium Bicarbonate (also called Baking soda)
Bring the water to the boil to speed up the reaction.
What is happening:
The black tarnish on silver is a sulfide.
The silver sulphide, will be reduced (gain electrons) to form pure silver and the aluminum will be oxidized (lose electrons) to form aluminum oxide.
The water acts as the electrolyte that allows the electrons to flow from the cathode (silver) to the anode (aluminum).
Chemistry:
Here are the chemical reactions (I got them from All Experts)
(Primary reaction)
silver sulfide + aluminum <-> silver + aluminum sulfide
3 Ag2S + 2 Al <-> 6 Ag + Al2S3
(Half reactions and secondary reactions)
Ag2S + 2 e- <-> S2- + 2Ag
Al <-> Al3+ + 3 e-
Al3+ + S2- <-> Al2S3
2H+ + S2- <-> H2S