Gentle chemistry method for cleaning low value silver coins

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Jamesey1981
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Hi everyone, I have posted this elsewhere before so apologies if you have seen it but I thought I would share it here while you're doing your cleaning series.

I started with two George 5th sixpences, one 1916 so sterling silver, and one 1920 which is 50% silver, this one is pretty worn and with the tarnish it's hard to see any detail.

I have seen a lot of different methods for cleaning these, and most work, but most work by removing metal or dissolving the tarnish, this method works by using an electrochemical reaction to convert some of the tarnish back to silver.

This is essentially what is happening when you use the spit and tin foil method, but it acts on the entire coin.

Take a bowl and line it with aluminium foil, place your coins into it, they need to be in good contact with the foil. Cover them with a teaspoon or two of dry bicarbonate of soda (baking soda) then cover them with boiling water.

It will initially bubble a lot as the bicarb dissolves, but when that subsides you will see small bubbles rising from the coins, this is the reaction taking place.

When the water is cool enough to put your fingers into (wear gloves if you want, but not rubber ones, plastic is OK but rubber damages silver) you should be able to remove the coins and the remaining tarnish will just wipe off with your fingers. If you need to you can give the coin a second bath. Give them a good rinse and dry with a soft cloth and you're good.

The 50% silver coin got clean much faster than the 92.5% one so bear that in mind if you have a mixed batch.

The way this works is as follows, tarnish on silver is in large part silver sulphide, by immersing it in an electrolyte in contact with aluminium it causes the two metals to generate an electric current, this causes the sulphides to detach as they would much rather react with the aluminium, so they form aluminium sulphide, which is yellow and will precipitate into your reaction container, as a by product the reaction forms hydrogen gas, (this is most of the bubbles you will see) and hydrogen sulphide gas in small amounts as the aluminium sulphide reacts with the water.

The reaction is as follows:
3Ag2S + 2Al --> 6Ag + Al2S3,
this doesn't take into account the side reaction of the Al2S3 + H2O.

The only thing you lose is the Ag2O, this is the remaining part that wipes off as it is mixed with the 3Ag2S and when that breaks down it loosens it from the surface.

I wouldn't suggest doing this with a valuable coin, but for those everyday ones that we would just like to pretty up for the collection this works great and doesn't use any nasty or expensive chemicals.

Any coin with natural toning that has developed over time is best left with the toning as that adds to the value, but coins that have been buried a long time can develop an undesirable tarnish due to the chemicals in the soil so don't use it for collector's coins, just metal detecting finds, and then only ones that are low enough value that they don't warrant specialist attention.

Before and after photos below. The 1916 could probably do with another bath, it looks a little pitted in the photo but that's just a few spots of left over tarnish.
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Pete E
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Thanks for that, and the detailed chemistry behind it...

It's not a method I have come across before but I will file it away for future use...
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Jamesey1981
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Pete E wrote: Sat Dec 05, 2020 10:33 pm Thanks for that, and the detailed chemistry behind it...

It's not a method I have come across before but I will file it away for future use...
It's one I had seen used on big silver tableware, I nicked it to use on coins, wouldn't use it on a hammy but for lateish milled silver it works really nicely, it works a bit too well for hammies and leaves them flat and horrible.
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Very interesting stuff Jamesie
Thank you for taking the time to post it, it will be usefull :thumbsup:
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Easylife
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Jamesey1981 wrote: Sat Dec 05, 2020 10:44 pm It works a bit too well for hammies and leaves them flat and horrible.
I guess there must be a way of changing that back? I have one that is flat dull and looks awful.
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Jamesey1981
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Easylife wrote: Sat Dec 05, 2020 11:18 pm I guess there must be a way of changing that back? I have one that is flat dull and looks awful.
In that case you need to check out the latest video on the forum YouTube channel, the method John uses produces a dark colour but not from silver sulphide, it produces silver chloride which darkens when exposed to light or heated, but it looks the same, then you can just gently pick out the highlights, it is a method I have used before as well, does a pretty good job if you have overcleaned a coin.
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Thanks for that Jamesey :thumbsup:
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Thanks for the excellent info with a lot of detail put across very simply, Jamesey :thumbsup:

Another valuable nugget of knowledge to stash away and all I have to do now is find a suitable victim to try it on. Don't find many milled, for some reason.

Thanks again, chap :thumbsup:
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Some years ago I was confronted with a 16th cent silver piece which was in very nice condition apart from the fact that (i) someone had stabbed it with a sharp implement and (ii) the resulting hole had filled up with some very unpleasant green crud. The hole in itself did not detract much from the coin's overall appearance but the hardened muck in it certainly did.

I have not much chemcial knowledge myself but, when asking someone about the odds of being able to clean it up, my companion answered me in just four words: "Shove it in a lemon". I tried it, or rather immersing the piece in juice, which is the same thing, and it did the job perfectly. I understand that the critical component is citric acid.

That may be fine for high grade silver, and it doesn't take many minutes, but don't ever do it with copper, it wrecks the surface of the piece. As for billon, i.e. inferior grade silver alloy, well.... I don't know, I haven't risked it yet. By all means try it out if you have some appropriate low-grade grot, but not on anything you really care you for. However, I do still use the method with silver occasionally, although with careful selection; remember that it will take any decent patina off as well.
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Jamesey1981
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leadtokendavid wrote: Tue Dec 08, 2020 9:57 pm Some years ago I was confronted with a 16th cent silver piece which was in very nice condition apart from the fact that (i) someone had stabbed it with a sharp implement and (ii) the resulting hole had filled up with some very unpleasant green crud. The hole in itself did not detract much from the coin's overall appearance but the hardened muck in it certainly did.

I have not much chemcial knowledge myself but, when asking someone about the odds of being able to clean it up, my companion answered me in just four words: "Shove it in a lemon". I tried it, or rather immersing the piece in juice, which is the same thing, and it did the job perfectly. I understand that the critical component is citric acid.

That may be fine for high grade silver, and it doesn't take many minutes, but don't ever do it with copper, it wrecks the surface of the piece. As for billon, i.e. inferior grade silver alloy, well.... I don't know, I haven't risked it yet. By all means try it out if you have some appropriate low-grade grot, but not on anything you really care you for. However, I do still use the method with silver occasionally, although with careful selection; remember that it will take any decent patina off as well.
Lemon juice will work, but if you use lemon juice you lose all the silver that has turned into silver sulphide, it will dissolve and you'll pour it away, that's why I like this method as the silver sulphide is converted back to silver, and the only think you lose is the silver oxide, which is a much smaller part of the overall tarnish, as an example take a look at how worn the 1920 coin is, you really wouldn't want to lose anything more off that coin as there's very shallow detail left, so acid for long enough might result in a coin of nothingness.

For greenish grot acid might be your only option short of picking it off as this won't get rid of that as it isn't silver sulphide.

If you want a horribly brutal method that will even sort out PVC damage then you can dip it in acetone, but although this will get rid of pretty much anything the coin will be pretty much bullion value afterwards, but then that applies to pretty much any cleaning method really, if it's valuable then get it cleaned by a specialist, but for coins like mine that I used it on here that are worth less than a fiver even on a good day it's fine just to clean them up so they look how you want them to look.
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Any tips for cleaning up the Cupronickel coins? My current method involves Lemon juice and very fine wire wool, followed by a polish with a Dremel type tool and some jewellers compound. It's not really worth the effort, so if there's a quick and easy method, I'm all ears. :thumbsup:
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Jamesey1981
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TerraEnglandia wrote: Wed Dec 09, 2020 4:39 pm Any tips for cleaning up the Cupronickel coins? My current method involves Lemon juice and very fine wire wool, followed by a polish with a Dremel type tool and some jewellers compound. It's not really worth the effort, so if there's a quick and easy method, I'm all ears. :thumbsup:
That's about all I have come up with for cupronickel, that or white vinegar and salt for beach spendables, they never look 100% normal though so i tend to use them in machines.
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