Cleaning silver bullion coins

[zxtm99]

Firstly, I am fully aware that numismatic coins should never be cleaned under any circumstances. My question here though is purely regarding bullion coins, bought mainly for pleasure – mass produced 21^st or late 20^th century Brits, QBs, Maples etc.

I sometimee see on eBay coins that someone has clearly left on a windowsill or covered in thumbprints. They can often sell at quite a discount, maybe £25/ozt for coins that would usually go for £30+. The coins usually look toned (but not in a nice way), often a pale brown colour, and/or have obvious fingerprint marks. They would not look nice in your collection.

If the coin will never be graded, or considered of much more than bullion value (just collected), does it make sense to grab these ‘bargains’ and can their shine be restored without completely ruining them? That is, to the naked eye (not a loupe or scope), can they be restored to their former glory? If so, which is the best way to restore their shine and remove the prints? I have searched and read the forum, and aluminium and soda seems popular and in theory at least is pretty harmless to bullion coins, but this technique also has its doubters.

Or is it impossible to ‘add value’ for collecting purposes only, by carefully cleaning?

 

This is a possible example (not one I have my eye on). Not sure if it is toned, or just badly lit, to be honest, but I bet it'll go at a decent discount to normal eBay prices for a sinle 1 ozt bullion coin.

 

Here are some really bad ones - are they completely FUBAR, to borrow an American phrase, or could they be restored to a point where they would at least look nice to the naked eye?

Edited August 8, 2021 by zxtm99
typo

[Pete]

Provided the silver is only toned - and that can mean "deep black in the worst case" the only way I know of restoring to factory finish silver is to use an acid dip with e-Zest being one that I know and have used. It works a treat and you need to be careful with the timing in solution often only a few seconds.

If your coin is grubby with fingermarks you can try washing in hot soapy liquid using a cotton-wool ball to wipe.
Only start wiping after the coin has been soaked a little or agitated to remove any surface grit that will scratch the coin.
I use an ultrasonic cleaner and sometimes add a drop of ammonia.

Occasionally the fossilised fingerprints will still be obvious so sometimes washing in acetone can remove these.
Again use a soft cotton wool ball to wipe the surface then rinse in clean water and immediately pat dry.
Leaving water on the surface can most likely leave droplet rings.

Your very last resort to restoring some degree of a nice finish is to use metal polish.
However most commercial polishes add a noticeable finish that is obvious.
Perhaps you don't care but the coin definitely looks a lot better that the tatty one you just worked on.

I have experimented using a Dremel and jeweller's rouge.
You can buff out fine lines and blemishes as you are re-polishing the surface by removing the top layer.
Done carefully you can obtain great results BUT may coins have a semi-matt finish created by sand blasting.
Re-polishing will totally destroy this duller finish and your coin will definitely look different and I would say ruined but you are only valuing your second grade bullion by weight so it doesn't matter really.

 

[Chorlton]

If you are going to try best to find a very low value coin to experiment with that way you will lose very little if things don’t go well. For most people any form of cleaning that involves anything above soaking rarely gives a good result due to scratching. Especially on older or proof coins it mainly reduces value.

[zxtm99]

Thanks Pete, that is a nice list in order of riskiness! Thanks Chorlton, in general, I clean nothing (and I'm not just talking silver coins here 😚). I'm a fan of 'nice' patina, and hate 'up-cycling' in general. My question is purely about whether I can occasionally plug gaps in colllections on the cheap by buying discounted coins that have been badly cared for and look a bit nasty. Strictly 21st century mass-produced bullion I want to loook shiny.

The scientist in me likes the sound of the baking soda plus aluminium foil technique. "In theory" this should be harmless - just the silver sulphide toning should be broken back down to pure silver and aluminum sulphide(phate?). Have many tried this?

Another thing I have actually tried is silver jewelers cloth. It's basically a bit like a polish, but apparently gentler. I did have a cheap bullion bar with a little brown patch, and the cloth brought back the clean silver shine. No damage was visible to the naked eye (which was all I cared about on this 'bog-standard' bar), but I suspect an expert could detect it.

Those horrible looking Eagles I linked would be ideal to try things out on, but knowing eBay, they'll go at a big premium regardless....

[KevinFlynn]

I am using soaking methods as well, just soaking, not rubbing. Soapy water followed by hot water followed by alcohol. It removes most smudges (many of those old trade coins are not patinaed, just dirty). That is for gold mainly, I don't believe in patina on gold.

For tarnished silver I have been using aluminum-soda-hot water on bullion. It works very well, the only thing that can happen - and has happened with me - is it can lead to some more matte areas, like a light whiff.

[KevinFlynn]

Incidentally, we have a little Silver sulfide reduction session set up for the weekend...

I will try to write a photo tutorial using this lovely piece:

 

[zxtm99]

Hi Kevin - I would be very interested to see the results. Those tarnished Eagles went for too high a price, and another toned looking QB I bought for a reasonable discount turned out to be nice and shiny - it was just a bad photos (by discount, I mean relative to usual price, not to spot). As such, I've yet to try this. The coin you show above looks like an ideal piece to test on. I do not have any German - is the green packet above bicarbonate of soda?

[KevinFlynn]

Yes, it is Sodium bicarbonate. Behind is a fresh roll of standard household aluminum foil.

We are going to clean the Silver Eagles of my compagnon, and see what we can do with my Maria Theresia Taler restrikes. The Eagles were neglected, the Talers are what I have lying around to play with.

The 10 Deutsche Mark coin was found on a bookshelf, it is a low value (20 Million mintage) silvery coin from the 1970s. It is only 625 silver (9.6g fine). There is definitely more than silver tarnishing going on, so I will soak it in soapy water first, to remove some of the sticky grime.

 

[KevinFlynn]

I started a new thread for the tutorial.