G’day.
There is no secret in this process of tarnish removal. The tarnish on
silver items is nearly always due to sulphur combining with the
surface of the silver, whether from atmosphere, body oils, or
patinating compounds like the polysulphides.
Aluminium foil is attacked by alkalies, like sodium carbonate or
bicarbonate, with the result that pure ‘nascent’ hydrogen gas is
given off. Normally hydrogen nearly always goes around intimately
associated with another hydrogen atom, and is written H2. But when
freshly prepared by this reaction, the hydrogen is just single atoms,
though it quickly pairs with another H atom. So the fresh highly
reactive hydrogen reacts with the sulphide molecule of the tarnish to
produce minute quantities of hydrogen sulphide gas, which bubbles
off, leaving pure silver. Thus the surface will look slightly rough,
but can easily be burnished to a bright finish. You will see that no
silver is removed in this treatment.
Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ