I cleaned my silver teapot with the aluminum foil-baking soda-hot water method. Usually this works well on my silver plated flatware.

However, this time it left a hard yellowish coating. I was only able to remove it by very strenuous manual polishing with a silver polish paste and when desperate, I even used toothpaste. The trade off was that it could scratch very finely, but that was preferable to the yellow.

Now I'm afraid to use this method on unusual pieces.

--> How can I prevent this from happening again? Are there kinds of silver and metal combinations that produce this reaction? Is there an easier way to remove it? Thanks!

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    $\begingroup$ Usually that happens when the metal is not 100% pure silver. Alloys don't clean very well with this Al foil method. Contact the manufacturer to find out if is 100% pure. If you also add a picture that would be useful. $\endgroup$ – M. Farooq Jul 15 '20 at 21:41
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    $\begingroup$ It might help if you edit your question to state the exact steps in your silver cleaning method and also check your silverware: Sterling silver is 92.5% silver and 7.5% copper. But if the flatware is not that, then maybe it is silver filled or silver plated. If it is Sterling, there should be a “925” on it somewhere. $\endgroup$ – Ed V Jul 15 '20 at 21:49
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    $\begingroup$ If the teapot has value to you, I suggest taking it to a professional jeweler and having them tell you exactly what it is and how much it will cost to restore its beauty. People here like to help, but nothing beats having an experienced professional examine the teapot and tell it like it is. All the best with this! $\endgroup$ – Ed V Jul 16 '20 at 3:18

The source of the "hard yellowish coating" may be Silver carbonate (Ag2CO3), as per Wikipedia:

Silver carbonate is yellow but typical samples are grayish due to the presence of elemental silver.

I suspect the teapot in question is "electroplated Britannia metal" per Wikipedia with a nickel alloy as the base metal, as to quote:

After the development of electroplating with silver in 1846, Britannia metal was widely used as the base metal for silver-plated household goods and cutlery.[5] The abbreviation EPBM on such items denotes "electroplated Britannia metal". Britannia metal was generally used as a cheaper alternative to electroplated nickel silver (EPNS) which is more durable.

The Baking Soda will interact with any soluble Ag ions to form the unstable Silver bicarbonate which breaks down to Ag2CO3 on warming.

The question is what is the source of Ag+?

My speculation is that the Al foil was completely coated given the surface area of the teapot, and the nickel-based alloy is notoriously cathodic (hence, the use of Nickel alloys in coins). So now, the Silver itself can be subject to an anodic attack in the presence of H+ (from amphoteric NaHCO3) and O2 (from air exposure), resulting in Silver ions.

This was a somewhat unique situation, hence the successful use of the Al/NaHCO3 process on the Silver-plated flatware.

  • $\begingroup$ (+1) Thought provoking answer: it will be interesting if EPBM appears on any of the items! I suppose the 6% Sb in the Britannia metal is no health issue. ;) $\endgroup$ – Ed V Jul 15 '20 at 23:40
  • $\begingroup$ Thanks Ed V, yes thought provoking, but I also have an alternate path, perhaps less consumable for the general population, presented here, at a link you supplied: chemistry.stackexchange.com/questions/35213/… which may actually be more accurate. $\endgroup$ – AJKOER Jul 16 '20 at 3:25
  • $\begingroup$ I deleted that link (though you have it in your comment) because I am now thinking that the OP should simply take the teapot to a jeweler and get a professional, hands on opinion. Ultimately, I think only that will be satisfying, even if it turns out the teapot has little intrinsic value. But it was a nice little puzzle and thanks for the Britannia metal information! By the way, there are already two close votes and I did not downvote or vote to close. $\endgroup$ – Ed V Jul 16 '20 at 3:42

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