Cleaning Coins? Is It A Good Idea?

Collectors don't like cleaned coins because cleaned coins "look wrong". A heavily-worn coin that looks all slick and polished is like an ageing past-their-prime movie star with slathered-on makeup - they are trying, but failing, to disguise their true age.

Cleaned coins are also "damaged". Once a coin is cleaned, it cannot become "dis-cleaned" again, the process is irreversible.

This is why cleaned coins have lower value - nobody wants them, thus demand is reduced; lower demand means lower price.


Litteton Coin Company's modus operandi has been the subject of much debate; just do a forum search for "Littleton" and you'll find all the discussion you could want on the subject. Suffice to say, they are not very popular with most collectors, as they effectively are "forcing" you to purchase coins that they decide you should be buying. Sure, you aren't actually "forced" to buy, you can return it if you wish - but LIttleton's target market are the people who are too shy and timid to try to return or cancel anything.

Are Littleton coins "cleaned"? Perhaps. It's not a complaint I've heard about Littleton before. It might depend on exactly which product stream you're hooked up with. Littleton would certainly end up with its fair share of cleaned coins that it purchases, and they've got to dump those cleaned coins onto somebody.


An ultrasonic bath is not really suitable for cleaning coins. In theory it should work nicely, but the problem in practice is how to suspend the coin in the middle of the bath, without it touching anything. Coins don't levitate, and a coin in a sonic bath is going to vibrate back and forth rapidly, rubbing against anything it touches - other coins, the walls of the bath, a plastic rack the coin is sitting in, even a piece of string tied around the coin, can all cause "rub". And rubbing a coin is "bad".


It might be bright green or bright blue, but it's not "copper sulfide crystals". Copper sulfide is black. If it's green or greenish-blue, then it's likely to be some combination of copper hydroxide, copper chloride, copper carbonate and copper bicarbonate. Copper coins turn green if they've been buried in the ground for centuries; green is therefore the "natural" colour for ancient and mediaeval copper coins. Modern coins aren't supposed to have had enough time to naturally turn green yet, so any that have turned green have done so because of environmental damage. Feel free to clean such coins, if you wish. Whether you prefer a "cleaned, formerly corroded coin" or a "green, corroded coin" in your collection is entirely a matter of personal preference (though most collectors would insist that neither of those options are desirable).

What to use to remove green corrosion products is entirely up to you. Acidic cleaning agents will tend to attack the raw copper metal as well, doing further unnecessary damage to the coin. Lye (sodium hydroxide) is often used, as this attacks just the corrosion and leaves the raw copper metal alone. Ammonia is the same, and I have had some success with it myself, though ammonia tends to turn the coin a particularly unpleasant shade of pinkish-orange.

If we're talking cleaning coins with chemicals, the tiny amounts of hydrogen sulfide given off by the cleaning process, are going to be the least of your worries.

To the Forum.

Wow! a lot of great advice here. I don't think I can add anything to the above advice, except for: don't clean your coins, please, cleaning just ruins the Value natural luster and patina of the coins.

For a type collection... Clean or not?

#2, #4 and #5 all have the pale-green, dusty appearance of active verdigris. These should be treated.

#1 looks like fire damage. Not sure there's anything to be done that might actually help or improve this coin. I'd leave it as-is.

#3 appears to have "stable" corrosion - if left alone, it shouldn't get worse all by itself. Treating it is an aesthetic decision, rather than one of necessity. It is a cupronickel coin, so I'm not quite sure how it got into that state, but would probably clean up fairly nicely, as opposed to a bronze/copper coin which is much more likely to become a weirdly-coloured, pitted mess.

I'm going to continue the numbering system from my previous post; the three at the top of this page are numbers 6, 7 and 8.

#6 has something odd going down; the way it' s been scoured away across the shield make me think some kind of blob of glue or some such got stuck there, then broke away again. Perhaps even a soldering job that didn't stick, or even a blob of green paint. So I'm not entirely sure the green stuff is "natural". As with number 3, it's cupronickel, so should clean up reasonably well.

#7: I don't think it's true verdigris. I have seen, and treated, this kind of greenish-brown corrosion before, with mixed success. It's probably stable, so leaving it alone might be best. I don't think "corrosion cameo" is a true collector term, but that's what I'm kind of seeing here.

#8: pale green and powdery, this looks more like classic verdigris. Treat immediate.

A note on verdigris: this pale green powdery form is active and "contagious", also known as "bronze disease", so called because the way it spreads, people in olden times thought it actually was something biological in origin, some kind of metal-eating lichen or something. Not only will it continue to spread across the surface of a coin, but if bits of the powder fall off and land on other coins, those other coins can start to corrode too. Coins with untreated verdigris should not be stored together with un-corroded coins. I have seen buckets of loose coins where a single coin with verdigris on it has caused dozens of otherwise nice coins in the bucket to become ruined.

#1, #5 and #7 surprise me; all the others turned up about as well as I'd expect.

Watch #8: I'm seeing a few residual flecks of green, in the crevices. To prevent bronze disease recurring, either continue treatment or give the coin a good baking in an oven over 100 deg C for half an hour. (This is another reason why people thought bronze disease was biological in origin: heat "kills" it.)

Sap, I want to thank you for your participation and contributions. I'm very impressed with your Florin. That is what "Conservation" is all about.

But I'm even more impressed with your patience. These last few weeks I've not been able to get to my computer to make a timely response. That is not my usual nature, but a temporary health problem. One wrong move and I yelp like a puppy that has had his tail stepped on. But I can laugh because it is only temporary, and not life threatening.

Thank you again.