Clean silver with aluminum foil and *

Question

I already have two questions touching on this subject and there is a third question as well.

The thing is that all the other question talk about cleaning silver with aluminum foil and carbonated water. The recipe I use though is to soak the silverware and the aluminium foil in salt water (simply mix table salt and cold water). I got the idea many years ago watching a commercial for a product called "SilverStar" or something like that on TV-Shop which was essentially a 0.5 cm thick aluminium plats which you were supposed to but in a bowl with saltwater and all your jewellery and it would magically become polished.

The explanations for the "recipes" using carbonated water are all along the lines that the acid dissolves part of the aluminum and then the aluminum ions in solution somehow react with the silveroxide.

The question then is if I only use table salt and (still) water will the chemistry be more or less the same but only much slower (relying on CO₂ dissolving in the water from the air) or is there something else going on?

My understanding of what was happening with the salt water was that the salt water acted as a "wire" and the aluminium acted as the "sacrificial metal" in a Cathodic Protection. I always thought that you could essentially put the aluminium in one bowl and the silver in another and connect them with a copper wire.

So the question is twofold

• What is the purpose of the table salt in my recipe?
• Is there any (chemical) difference between "my" recipe with table salt and the more mainstream one with different flavours of carbonated water?

Answer 1

Since you want to remove the tarnished silver ($\ce {Ag2O}$), you would convert it into silver metal (or reduce it). Therefore, you would oxidize the aluminum ($\ce {Al -> Al^3+}$). The silver and aluminum need to be in physical contact and the sodium chloride or the carbonated water is just providing the medium to transfer the ions; the aluminum does not dissolve first.