How To Tell If Coins Have Been Cleaned

Hi, welcome!
I had a lot of trouble telling cleaned coins for a long time myself and might even get fooled today.
I am not sure how much you mean when you say "high dollar" mercury, but if you are talking high enough dollar, then you could always consider buying them already professionally graded and then you are not taking any chances.

Best advice yet! Don't buy "raw" coins until you Learn Lesson #1.

Look for anything that looks polished but has a similar amount of details as a worn coin. Those are the most common cleaned ones. The more you see the more you will instantly spot them. Shiny can be super bad. Learn the difference between original luster and a altered surface. Again this is easier to spot on low grade coins. Also look for unusually darker toned areas in the coin surface of crevices in the design like the insides of letters like o or a. I would hold off buying higher grades for now unless they are graded by a reputable company.

Great question. As you will see here many times a day, collectors will display photographs of their coins asking for grading and/or condition appraisals. There are a lot of folks who frequent these type of threads are masterful at giving concise and precise information about why they think a coin grades at a particular numerical point. If the coin has been cleaned, that will also be discussed, and the reasons for why someone thinks a coin has been cleaned will often be detailed, too.

You can learn a great deal by watching for those requests for grade/condition and how individuals decide on what is or may not be a cleaned coin.

A point to keep in mind, however, is that it is virtually impossible to assure that a coin has NOT been cleaned from photographs alone, even if the photographs are very well done. It is difficult to capture the play of light on a coins surface with single point photographs. The exception to this, which has been mentioned above, is if you see a number of small scratches (commonly called hairline scratches) that are all parallel to one another. That will almost certainly indicate a coin has been "mechanically" cleaned, by means of rubbing the coin to remove toning or corrosion.

Coins can also be "dipped" in a number of solutions for a number of problems and not all of those are considered "cleaning". For example, a coin that has PVC "green slime" may look considerably better if placed in an acetone bath for a period of time. This is actually helping to save that coin from more corrosion on the surfaces because of those left over chemicals that adhered to the surface of the coin.

However, the single best way to learn if a coin has been cleaned is to look at as many coins that are "slabbed" by NGC or PCGS (or ANACS) as the vast majority of those will not have had harmful cleaning if they are certified by those companies. They are not perfect, but they are a heck of a lot better than almost anyone else for catching problems.

Once you know what a MINT coin looks like, especially on a series like Mercury dimes, you will have a much better idea when you buy coins yourself. But remember, ANYONE can be fooled by photographs only. In person is always best.

Last, if you intend to purchase Mercury dimes, or any series, at what you consider a higher price, it is best to simply buy them in a TPG holder to begin with. You have to decide where your comfort level is, for yourself. I, for example, very rarely (if ever) buy a coin over $200 unless it is certified by NGC or PCGS. You just need to establish your own 'comfort line'.

I'll confess that unless there are marks on a coin as described above, I have an very hard time telling if a coin has been cleaned. I recently had a bunch of coins graded that I had had for a while, and most of them came back with the designation 'cleaned'. I did some looking into detecting cleaned coins, and I found a couple of useful tips...

1. Obviously of the coin is worn, yet it shines, then it was cleaned (and maybe polished, buffed, etc) - those are easy to detect.
2. I'll call it 'uneven grime'...take a look at some old quarters. Lots of times there will be grime in the crevices around Washington's bust, but the other surfaces of it will not be as discolored. That's supposed to be a sign of cleaning, but I must confess that most of the older raw silver coins I see have this trait...and one of the coins that wasn't designated as 'cleaned' has a little bit of this as well.
3. Supposedly you can also tell if a coin has been cleaned by tilting it in the light looking for light reflection. I was told that non-cleaned coins will reflect more luster than those that have been cleaned. I COMPLETELY buy this explanation, but I guess my eye isn't trained enough to look at some older silver coins and use this method to tell if a coin's been cleaned.

I'd love to learn more to where I could spot cleaned coins aith more accuracy!

moxking - Just a little post script here. Your reply above is EXCELLENT! You convey both expertise, as well as patience. I just wanted to say thanks for the kind reply to the OP. Often times people post less considerate answers, even to legitimate questions. Justinwd is obviously new to the hobby and looking for help. Your answer was exactly right. Jack

Good quality liquid metal polishes are not abrasive, and do not leave micro scratches on coins.
However, the mint luster on a coin is highly sensitive to polish, and is obviously affected by metal polishing of any type.
A coin thus treated is shiny, in quite an obvious unnatural way.

For heavily patinated coins in MS condition, the patination can mask the mint luster. The salient point here is that the coin should be graded strictly on wear, even if the mint luster is hard to find. The usual things like nicks and scratches are still taken into account when grading.

Sometimes blast white silver coins in high MS condition with luster, may have otherwise very unsightly stains on them. The collector is tempted to clean them to remove the stains. Usually, the stains consist of either silver sulfide or chloride. A silver dip solution will remove them the stains, but will still affect the surface of the coin anyway, and the luster will be affected.

Heavily patinated coins should be left as they are. If the patination is removed, the shiny white appearance will be very obvious.

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With ancient coins, the situation can be very different.
It is common for a genuine ancient to be recovered from ground burial. The freshly dug up coin may be completely unrecognisable until it is cleaned.
In these sorts of cases, such coins are best cleaned by museum trained professionals, who are supposed to know what they are doing.
Ancient coins are not up in the Americas or Australia anyway, and so come onto the market already cleaned.