- It's because what you are trying to clean is not silver.
- It's because you need to put the silver in the boiling water, on top of the aluminum foil, with the baking soda. The silver will only turn where it makes contact with the aluminum
- it's because you can't use this method to remove dirt... just oxidation.
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When I used to work in a restaurant, they collected the dirty cutlery in a large bin filled with a vinegar/water solution with a sheet of aluminum foil on the bottom. Maybe just another variation of the method you're using, but may help. Good luck.
I am a chef and I know first hand about this subject. We have cleaned 10s of thousands of pieces of silver over the years. If it is silver plated, it is possible that the silver has been removed from either hand polishing w/ an abrasive paste or the silver has been cleaned with the aluminum and sodium bicarbonate process so many times, it has removed the silver as well as the tarnish. We used this process for a couple of years and the silver plated flatware started looking darker and darker until i finally took a piece to a silversmith and he told me that the process actually is "reversing the electroplating process" and said it would all have to be replated, which was far too expensive. This is why I am so adamant about telling people about this.
I was told to look online for a product called Silvermate liquid silver cleaner because it is 96% water and only takes 30 seconds to clean a piece of silver and it polishes it as well. www.silvermatecompany.com
Hmm.., it's a little hard to say what might be going wrong -
I get good results on heavily tarnished pieces using warm water with plenty of baking soda and a drop or two of dish of soap, and molding the aluminum foil around the silver piece to provide as much good electrical contact as possible. I know it's working when the dishpan starts stinking - only mildly, thank goodness - of rotten eggs.
It also helps to scrub the silver piece with a paste of baking soda, dish soap and water from time to time while it's soaking. A couple of scrubs and an overnight soak usually turns a piece that looked like it had been shellaced a metallic black into one that looks like lightly tarnished silver.
But for the only lightly tarnished pieces, this method doesn't work so well for me. I have to resort to a commercial silver polish to get those last bits of tarnish off.
So I'm guessing that maybe you didn't have enough of your silver piece in good close contact with the aluminum? ....Or maybe it just wasn't tarnished enough to drive the reaction?
(Or maybe you have the one tarnished-looking silver piece that really has been shellaced a metallic black? (jk))
The surface of foil is not terribly active, chemically. Try a piece of scrap aluminum that has been cleaned with sandpaper. Be sure that the baking soda solution is hot when you bring the silver in contact with the aluminum. Do not use salt; silver chloride is about as insoluble as silver sulfide.
Why is it that you're trying - point us to the method you're working from?
http://www.darylscience.com/Demos/Silver.htmlhttp://chemistry.about.com/cs/howtos/ht/silverdip.htmIt's essentially an electrochemical transfer of sulfur from the silver (silver sulfide tarnish) to the aluminum. The baking soda (not "washing soda"!) dissolved in water acts as an electrolyte. Some of the recipes Google pointed me to suggested adding salt as well.
So this is specifically for sulphur-tarnished silver? A bit suprised aluminium is good for this - what about Fe?
I suspect it's a question of rate. A quick check of electronegativity (Pauling scale) has Al = 1.63, Ag = 1.93, and Fe = 1.83. So yes, you could transfer the sulfur from silver to iron, but it would take about 3 times as long, assuming a linear dependence of rate. That assumption may not be valid.
Aluminum is very-aggressively reactive in theory, but all your regular schooling, (and advanced) says it doesn't corrode to dust in minutes because-
Iron likes sulphur and then again so does mercury, it's down to the d-orbital overlap.
Good points. As we both know, aluminum doesn't corrode through because the oxide is both inert and mechanically stable. Thus, once the aluminum surface layer oxidizes, the bulk is isolated from further corrosion.
That's not the case with iron oxides, for example, which are porous and crumbly. As iron rusts, the oxide flakes off, exposing a new, clean layer of the bulk to corrosion.
What I don't know (as I'm not a chemist by trade) is whether aluminum sulfide is also mechanically stable.
Neither do I. It's interesting, but while I have eggs, I don't have any silver to test it.