I have expertise in coin collection, history, identification, and care.
What's the Best Way to Clean the Coins You Find While Metal Detecting?
People using metal detectors often find themselves with loads of coins that can’t be spent in the shops nor exchanged at banks. The corrosion that has occurred over the years while these coins were hidden from underground or in the sea often renders them unusable. Out of all the methods for cleaning up coins, one of the best and easiest has got to be processing them in a metal barrelling or rock tumbling machine.
While you can buy brand-new rotary tumbling machines at reasonable prices, it is also possible to pick them up at secondhand markets. Barrelling machines have pretty simple set-ups and tend to last for years, as there is not much that can go wrong with them. They all do tend to overheat and become quite hot to touch, however, so if this happens to yours, don’t worry about it. Here are some hints and tips for coin cleaning using a rotary rock tumbling machine.
Tips for Using a Rotary Rock Tumbler
- If your machine is normally used for tumbling stones or rocks, consider purchasing a new barrel to use with metals only. Otherwise, make sure the barrel is thoroughly washed. Deposits left behind from rock tumbling can damage metals and coins.
- Do not tumble different coloured coins together. You will only end up with copper-stained silver coins or silver-stained copper coins, and this is almost impossible to fix.
- While you have a whole range of different mediums to use to tumble with your coins, from walnut shells to ceramic shapes, coin cleaning works best with stainless steel media. Half a kilo (1 lb) of stainless steel shot is more than sufficient to use in a 3 lb barrelling machine.
- Stainless steel shot should be saved and re-used. It does not rust.
- Stop the machine from tumbling now and again to release air from the barrel. Simply lift up the edge of the lid while pushing down on the centre. You should hear a hiss as air is released.
- Make sure your tumbling machine is on a level surface. Use a spirit level to check if you are in doubt.
- Make sure there is a good air-flow around the base. This will help disperse the heat generated by the tumbler.
- Do not overload your barrel. A 3 lb tumbling machine can take a maximum load of 6 to 7 lbs, including barrel, medium, coins and liquid.
- Do not put valuable or potentially valuable coins in a tumbler. Collectors prefer those coins to be "as found," or with only the minimal cleaning offered by soap and water. This method is best for cleaning newer coins so that you can deposit them for face value.
- You can use just one coin or as many as 300, depending on weight and size. Just make sure they are all the same colour on the outside.
- Do not exceed the weight limit specified by your tumbler's manufacturer. For coin cleaning, the best results are obtained when the barrel is only one-third filled with coins.
Instructions for Cleaning Coins in a Rotary Tumbler
- Add a burnishing soap to clean off oxidization on the surface of the coins. This can be a proprietary compound sold by the company that manufactures the tumbler, or you can use normal household soap, cut into shavings. You can also use soap powder designed for washing clothes or even washing up liquid. You only need a small amount. If using a powder, 1 heaped teaspoonful is sufficient. If using a liquid, put less than a teaspoonful in.
- Add warm water. You can use cold water, but warm water will help dissolve the detergent quicker. You do not have to fill the container to the brim with water. The more water you add, the gentler the tumbling action will be.
- Put the lid on, making sure it is securely home so that there is no leakage, and place it on the rollers. Switch the power on and leave to tumble for about 10 minutes.
- Take the lid off and release any gas build-up inside. You can see if gas is building up at any stage. The lid will depress inwards. Simply stop the machine and release the gas.
- Leave to tumble in the rotary rock tumbler for about two hours, checking after one hour. If the water is really dirty, consider changing it. Coin cleaning in really dirty water will not work.
- As you drain the liquid off, some of your stainless steel shot may escape. In order to collect it up again, always strain the water off through a sieve. As some of the ball-bearing shaped shot is tiny and can escape through the mesh in a sieve, add a lining of kitchen paper.
- Do not pour really dirty water down the drain in your sink in case it clogs up your pipework. Instead, drain off the liquid into a bucket or other container for disposal elsewhere.
- After about two hours in a stainless steel media, your coins should be pretty well clean. They might not look shiny and new, but they will be clean enough to put in your purse for spending. Remove coins that are sufficiently clean, leaving dirty coins to tumble for longer.
How to Make Your Coins Sparkle Like New
- Remove your coins and media from the machine and rinse under running water until the media is clean. Replace in barrel.
- Add a compound called Barrelbrite (if you are in the UK—I have no idea what chemical is in it, as the makers seem to have left that information off the product label). I have read that it cannot be disposed of down the drains, but no-one has said whether the user needs protective wear while using it. If anyone knows exactly what is in Barrelbrite, please let me know.
- 10g or a dessertspoonful is the recommended amount to place in the barrel. Use less in soft water areas. The water is very soft where I am, so I use a heaped teaspoonful.
- Fill up the barrel with warm water, replace the lid, and tumble for another two hours or so. The end result leaves your coins looking like new. They will be all sparkly and glittery like shiny gold and silver.
All of the photos on this page belong to me, but they may be freely used by anyone in return for a link back to this article. Happy hunting!
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
ADC on August 26, 2017:
Great article, thank you. Can you recommend any suppliers of tumblers, stainless steel shot and Barrelbright?
Blackspaniel1 on October 14, 2014:
I am glad your are not cleaning collectible coins but those to be spent. Cleaning collectible coins like this would devalue them, but cleaning for face value is fine.