There are two rules to cleaning coins:
1. Never clean your coins.
2. Refer back to rule 1.
Before reading any further, don’t send me an email about how you damaged your coins cleaning them from a method you learned about on Metal Detecting In The USA. If you do, I will refer you to the above rules. With that out of the way, lets discuss a few methods to clean old coins found in the ground and make those “dug” coins more presentable.
How to clean dug up coins
To clean old coins found in the ground while metal detecting, you first need to identify the coin, its collector value, and type of metal before considering cleaning methods such as baking soda, vinegar, soaps, tumbling, or anything else.
Check the date and mintmark on the coins you want to clean. Be absolutely certain that they are not key collector coins but common coins that are worth face value or silver (or gold) value. If you do have a key collector coin, take it to an expert and let them decide the best course of action. There are two categories that we need to discuss and they are copper coins and silver coins. Nickel coins can be cleaned the same way as copper. I will link you to some of the coins that have been cleaned using the various methods. Some are worthwhile and some are, well, I’ll let you be the judge. Remember, cleaning a coin de-values it considerably. I clean my coins to make them more presentable and with the foresight of knowing that I am not going to sell them.
When you are out metal detecting and find a nice coin like a silver half, quarter, dime, or copper wheat penny NEVER rub the dirt off to check the date or to identify the coin. Doing so will risk devaluing them. Why? Because dirt is like sandpaper and will put tiny scratches on the coin when rubbed. I can guarantee you that if you try to sell a rubbed coin to a dealer he will tell you about the scratches and it’s reduced value.
Related: Buyer’s guide to coin detectors
How to clean corroded coins
More often than not, the coins that are most corroded with be clad. Clad coins are the easiest to clean and if you goof up and they look bad, so what. They are still spendable. While some people use things like baking soda, hydrogen peroxide, soda, vinegar, I prefer to tumble all of my dirty clad coins in bulk with pretty good results. It is an effortless job. I fill the tumbler between half and 3/4’s full of coins and aquarium gravel, add white vinegar and a tablespoon of salt and let the tumbler do it’s job. Always tumble like coins such as quarters, dimes and nickels. If you put copper pennies in with the clads they are going to turn a copper color. Clean your memorial pennies the same way but by themselves. This method will clean most of the dirt off of them. It will not remove tough stains though. To remove tough stains from coins, soak them in CLR. Let them sit as long as needed, even overnight. Changing the solution in between soaks can help a lot with stubborn stains. After soaking them, put them back in the tumbler and then they should be ready to spend. You can also tumble your coins with CLR and aquarium gravel.
Do not tumble your clad coins with those new “gold” dollars. They will turn all of your clad coins a nasty gold color.
I have heard of people putting the clads in a tumbler (after using the methods above) with sawdust or wood shavings. I personally have not tried this but I think it would work great at “polishing” them. This is all I do on clad coins. Anything more in my opinion is too time consuming, especially for clad coins.
Related: how to clean clad coins.
How to clean old copper coins
The most common copper coin found metal detecting is the wheat penny. I tumble wheat pennies. I always check the date and mintmark and if it is a common wheat, it goes in the tumbler. The way I look at it is, out of the ground it is worth a penny, cleaned up it is still worth a penny, only now it looks better. I also clean wheat pennies with a brass brush. The same type of brush used for cleaning suede shoes or your BBQ grill. That’s right! Brass is softer than copper. Sure, you can put scratches on a penny if you scrub it too hard. Be gentle, use a circular motion, back and forth and sideways. Whatever it takes to clean it up. Check out these examples of cleaned wheat pennies using a brass brush: Example One, Two, and Three. In example three you can see that it doesn’t always work. These wheat pennies are so encrusted that they will never be cleaned to the point that they have eye appeal. You lose some, you win some.
Other methods I have tried on wheat pennies (but no longer recommend) are soaking them in the vinegar solution. Oh yes, it works great. They come out a dull copper color, similar to a new penny only dull looking. Years ago after doing this I rubbed sulfur on the surface of the dull coin and they toned up nice. It actually worked very well. Environmental reasons prevent me from using this method plus health and safety would also be a concern. Try using Dellar’s Darkener to tone cleaned copper. It is sold in most coin shops. Also, don’t soak them in bleach. It doesn’t work at all.
Don’t use Ajax cleanser (or similar products) on copper coins, else you’ll risk damaging them. I did back in 1975 and almost ruined my most favorite coin…the 1796 Liberty Cap large cent. Twenty-five years of natural toning has helped it look pretty good now. When I first cleaned it, shiny copper areas could be seen everywhere. I sent it into a grading service and it came back as a Good 6 with environmental damage. However, they did not slab it. It is better that you learn what not to do from Metal Detecting In The USA than experimenting on your own. Learn from my mistakes, that is the purpose of this article.
DO NOT USE AJAX CLEANSER ON COINS!
Also, if you use electrolysis (but potentially the most disastrous to your coin) to clean copper coins they come out the same way as using the vinegar method. Soaking them in vinegar or using electrolysis lifts dirt out of holes on the coins that you didn’t know were there. Don’t use it on coins that you want to give eye appeal to. I have tried the “olive oil” method of soaking copper coins. It takes too long and doesn’t work very well (my opinion). It will also stain your coin a dark color. An alternative to olive oil is “mineral oil”. It will not stain your coins and will actually preserve them. Another method is to use tape, like duct tape to “pull” the dirt off of the coin. It will pull some of the dirt off, but they still look stained. Copper coins found in my area (Pennsylvania) take a beating while in the ground and in other parts of the country they look like they came out of pocket change.
There are several ways to make silver coins look very presentable. Occasionally you can dig a silver coin out of the ground that looks great. Well, more than on occasion because silver actually fares very well in the soil compared to copper. I use a soft toothbrush with warm water and soap. That is usually all they need. The examples above also have silver coins included in the picture. They were all cleaned with just a toothbrush. This is the best example.
Sometimes silver does get stained or so encrusted that you have to use other methods. You can use electrolysis or the vinegar solution. This will turn the coin a dull silver color. Now you have another problem that has to be addressed…the dull color on a nice silver coin. Well, I use a product called Wrights Silver Cream (Google it). It will take the dull away, I guarantee it! It can be purchased at your local grocery store or jewelry shop. I have also used it on silver coins without soaking them in vinegar and they still come out very presentable. There is one problem with using the silver cream. They will be shiny-looking when you are finished with them. An example can be found here. See how shiny it is. It actually caused the light on the scanner to reflect causing a bad scan. It actually looks better visually looking at it. The 1874 dime that I recovered last June had to be cleaned with the silver cream. It had a bad black stain on it but now it looks pretty good. Sure, it hurt the value somewhat, but it is not for sale and I don’t have to look at that black stain anymore. You have to decide for yourself whether or not to clean an old silver coin. The 1878 dime was cleaned up with just a toothbrush and it looks just fine.
That is about it for cleaning silver coins. Anything more than what is described above and I think you would run the risk of ruining your coin. The bottom line on silver is, try cleaning it with a toothbrush in warm soapy water. Next try the vinegar solution soak or use electrolysis and the silver cream as a last resort.
Silver rings can be cleaned up nice on a buffing wheel with Wrights Silver Cream. I have gotten incredible results using this method on silver rings. One last note on the silver cream. That black stuff you see when cleaning the coin or ring…that is silver being taken off of the surface! You be the judge.
I received this method of cleaning silver coins from a treasure hunter down under. I have not tried this method so cannot attest to how well it cleans silver coins.
How Not to Clean Coins
Do not use muratic acid to clean your coins. It is a mild solution of hydrochloric acid (HCL). Yes, I have used it on coins and ruined a good Flying Eagle cent and two shield nickels. It only takes seconds to reduce the coin to nothing more than a slug. I also tried it on an aluminum token. It dissolved it completely.
The same goes for sulfuric and nitric acid. Unless you are trying to make slugs, avoid using them. Acid is very dangerous and should be used outdoors with plenty of ventilation. Don’t use gasoline, bleach, Clorox, ammonia or any combination of common household cleaners. They won’t clean coins as good as what I have described above. Learn from my mistakes. I worked in a laboratory back in the 70’s and tried the various acid’s using a hood to vent the vapors. The results were awful to put it mildly. DON’T USE ACID TO CLEAN YOUR COINS!!! It is not worth it.
Do not use stainless steel as an anode during electrolysis. Why? Because it will produce chromates in your electrolyte solution. If your solution turns yellow, that is a sign of chromates. Stainless steel contains chromium and the solution can cause burns and even cancer. It is illegal to dispose of this solution onto the ground or down the drain. It needs to be dried and the residue place in sealed containers and disposed at a hazardous collection site.
If you are using salt and vinegar in a bowl, use it in a well ventilated area. The salt will break down into sodium (harmless) and chloride gas which is very harmful.
One last note. Refer back to rule number one!