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[personal profile] mordwen
Doug and I went to the markets today and discovered an awesome company called Rewine. Like Swords, you bring your bottle back and get a discount. Unlike Swords, who take the bottle and commercially wash it, refill it and reseal it, Rewine just fills up our clean, empty bottle from enormous wooden barrels of wine in front of your eyes in the market. Everything is on taste, so you can sample before you buy. They have at least one organic red and one organic white on tap at any one time. We bought a (non-organic) tokay and a red.

That's not the science bit though. My lovely second cousin Jo bought us gorgeous silver port goblets as a wedding present. They've tarnished somewhat and we wanted to bring them out to sample the tokay. We don't have any silver polish. Doug used his mad google skillz and found a recipe on the interwebs for removing silver tarnish. Take equal parts bicarb soda (I believe you Americans call this baking soda) and salt, and pour into steaming hot water. Lie one sheet of aluminium foil in the basin and set the silver items onto the foil. Leave for up to five minutes. The tarnish will simply slough off. We lifted the goblets out and wiped them with a soft cloth and they're as shiny as new. There's a slighty odd-smelling gas that's given off as you do it.

We chatted about what the chemical reaction is for a while but we really don't remember enough to work out what's going on here.

ETA: Found it!
"A very popular technique for removing tarnish ( silver sulfide ), involves
an electrochemical cell that utilises the electrochemical series. In an
electrochemical cell, oxidation occurs at one electrode, whilst reduction
occurs at the other. Electrical contact between the two metals provides the
pathway for electron migration to occur from the anode to the cathode, and
when immersed in an electrolyte, charge will be balanced by transfer of
the sulfide ions.

The standard electrode potential at 25C of Ag+ + e- -> Ag is +0.799V, and if
the other metal is anodic relative to silver, the silver in the sulfide at
the cathode will gain electrons and revert to metallic silver. The metal
at the anode will be oxidized by the removal of electrons. The sulfide ions
can travel to the anode via the electrolyte. The electrochemical series
indicates metals that will work, and some readily-available and cheap metals
are iron, zinc, aluminium and magnesium. The standard electrode potential at
25C of Al3+ + 3e- -> Al is -1.66V, and aluminium foil is cheap.

When aluminium is the anode, and water is the electrolyte, the aluminium
surface will eventually be coated with an insulating film of aluminium
sulfide - which will gradually decrease the cleaning speed. Adding sodium
bicarbonate ( baking soda ) or sodium carbonate ( washing soda ) to the
electrolyte will assist in the evolution of hydrogen as the silver is
converted, and the hydrogen will combine with the sulfide ions to produce
some hydrogen sulfide gas ( rotten eggs smell ). The aluminium at the anode
will be converted to aluminium oxide. " (from How do I remove silver tarnish?)


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January 2011

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