So I recently had need to clean some silver, and this technique was shown to me.
Basically you put hot water, baking soda and foil in a bowl. Add the silver and tarnish disappears in under a minute.
Can anyone explain to me what, chemically speaking, is happening here? Otherwise I’m going with witchcraft.
Did it produce a smelling gas? I think you should get hydrogen sulphide from this reaction.
Baking soda is NaHCO3, Aluminum AL Silver Ag
My chemistry is too rusty to do the equation for you.
Electrolysis. The silver, aluminum, and bicarbonate solution act as a battery, with the aluminum donating electrons to the silver. Aluminum is highly electronegative, and silver is highly electropositive, so the reaction occurs quite readily.
Hmm… I don’t see any sulfur in there.
the tarnish is silver sulfide
sulfur comes from the tarnish
clean the silver when you want it shiny for use or looks. the tarnish is not destructive to the metal.
Wouldn’t the tarnish be silver oxide?
There’s a theory that silver didn’t tarnish as badly in the pre-industrial age. There’s more sulfur in the air and causes more tarnishing.
Cecil disagrees about the extra sulfur in the air.
So the tarnish is either silver sulfide or silver oxide? Does the tarnish de-oxidise somehow returning it to normal silver? (Yes there was a nasty smell). So this method is actually better than polishing which removes a layer of silver?
Thanks for the answers.
both silver sulfide and silver oxide are black. tarnish is silver sulfide. this method changes the silver sulfide back to silver. this method is easier and better than polishing which removes some of the material (which could be turned back to silver).
In my experience with using this method I’ve found that removing the tarnish is not the same as polishing. The object may not be shiny, but won’t be tarnished.
In my experience, this method leaves the silver bright, but not shiny. The surface is rendered slightly rough or matt. I strongly disadvise doing this to any piece you care about.
We both have slver wedding rings, as we don’t like the colour of gold. Mrs G’s ring was looking a little tarnished, so, following my mothers advice, we mixed up a cup of biological soap powder and some water, and left the ring over night.
Big mistake.
Very big mistake.
Next morning the ring was completely black. In thinking about mums advice, she only had gold jewellery, so it’s never going to tarnish, and the gunk in the powder didn’t have an effect.
After a small panic, we bought a jewellery bath from a local jewellers, and with the help of a polishing cloth, the ring came up very nice. The ingredient in the bath was a urea compound.
Listen to your mother, but be selective which advice you follow.
chemical reversal of the tarnish has the advantage of not loosing any metal, happens quickly and without physical effort. if you has something with lots of crevices then it would take a long time to remove thetarnish and you risk damaging the object physically trying to scrape in those areas.
you don’t get a mirror finish.
chemical methods and physical methods each have their advantages.
Basically, silver is less reactive than aluminum. I am not sure of the valences involved, but the primary reaction is that silver sulfide + aluminum —> silver + aluminum sulfide. I see no reason why it wouldn’t also reduce silver oxide. I would assume (but I might be wrong about this) that the main function of the bicarbonate is to increase electrical conductivity, but I guess there is some reaction with it as there is some hydrogen sulfide being given off.
Yes, it does produce a matte finish. But you don’t lose the silver. For solid silver, this might not matter too much, but if you keep polishing silver plate you will eventually wear it down to the base metal.
You could probably also use some combination of polishing and electrolyzing to get a good compromise between losing material and matting.
Can someone provide a citation on the claim that none of the metal is lost in this process? I accept that the chemical reaction of tarnishing is being reversed in this process, but is it guaranteed that the restored silver is remaining on the piece? (rather than, say, remaining in suspension in the bath) Is the matt surface the result of replating?
Hmmm. The way I understand it, the oxidation of the silver means the single molecule layer on the surface of the silver is already GONE, removed from the metallic silver. Cleaning the silver, either by this chemical reaction or by polishing, is simply removing the oxidized layer.
Think of rust on the surface of iron. The part of the iron which has reacted and turned into rust is GONE from the metallic iron. No matter how you clean the rusted part off, you cannot salvage any of the iron which has been transformed into rust by oxidation.
~VOW
Sure you can - oxidation is (in general) a reversible chemical reaction. I’m just not certain that the products of that reverse reaction truly do end up back on the item being cleaned.
chemical reactions like this are reversible. sulfides and oxides that remain attached to the bulk metal can become the metal again through a chemical reaction.