Cleaning Metal Detecting Finds with Ultrasonic Cleaners (and Other Methods)


Metal detecting finds can be quite dirty or corroded when brought out of the ground or water. Can ultrasonic cleaners help bring back the beauty to some degree? Let’s find out.

Ultrasonic cleaners are good for some things and not so good for other things. For metal detecting, “it depends” is the answer. They are certainly recognized as useful for cleaning jewelry, watches, coins, badges, and medals. However, other methods may be a better choice.

The items listed above are in the sweet spot for valuable finds. To get the best and safest results when you clean your finds, there are important caveats to know. We’ll dig into those as we go.

NOTE: MetalDetectorUniverse.com is not liable for any damages, losses, liabilities, costs, and expenses to the extent they arise from attempting any of these cleaning methods. This post is merely an informational discussion of ultrasonic cleaners as a method hobby detectorists are using to clean what they discover.

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Ultrasonic Cleaners

Home Ultrasonic Cleaners

Home ultrasonic cleaners have an engine and a cleaning tray. The motor creates the ultrasonic vibration that enables the cleaning. The cleaning itself is done by very small bubbles that knock against the surface of the item being cleaned. This action is what knocks the dirt off. Scientists call this process cavitation. The beauty of this method is that it cleans difficult-to-reach places.

Ultrasonic cleaners can use plain tap water or a chemical solution, depending on the materials that need to be cleaned. Most home ultrasonic cleaners just use tap water or a non-abrasive cleaning solution. Some units have a heater element as well, which is intended to speed up the process.

The instructions in the model you select should indicate if something more, like detergent or ammonia, can be used. The manual should also guide you on things not to use so you don’t destroy the item. For example, bleach or acid are typically not recommended.

Use caution, as once damage is done, it’s done.

Cost of Ultrasonic Cleaners

Looking at typical 4-star prices on Amazon (searching “ultrasonic cleaner”), I see home units range in price from $40 $230 and typically contain the keywords we’d be looking for, such as jewelry, rings, and coins.

You can find more information on my Recommended Gear page.

Why Ultrasonic Cleaners Can Damage Coins

Here’s a great review of the dangers of leaving coins in the ultrasonic cleaner for too long. It’s worth watching all the way through. You can see how cleaning coins is part art and part science.

Also, this shows how coins may or may not look better after ultrasonic cleaning. One other interesting point made is to do the cleaning in small time increments. At some point, you’ll see things are going in the wrong direction and you’ll have time to stop before too much goes wrong.

Note – there are a few places where the audio drops a bit because of the machine’s noise, but it doesn’t hurt the value you’ll get out of this video.

Ultrasonic Cleaners – “Street Knowledge”

Some of the best info I’ve come across on ultrasonic cleaners comes from listening to those who’ve done it a lot. Here are a few nuggets of wisdom that are worth passing on (free advice, worth what you pay for)

  • Get the best unit you can
  • Something like Dawn dish detergent (a surfactant) helps keep the tank clean and allows the water to better remove dirt and grease
  • Be cautious (refer to the video above)
  • Try a toothbrush, toothpick, wooden matchstick, or a set of Andre’s pencils first (see Recommended Gear page.) You may like the result you get and not need to do ultrasonic cleaning.
  • There are many methods of cleaning the coins and jewelry we dig up. Ultrasonic cleaning is just one. You typically will hear of electrolysis and tumblers. Do some research and talk to fellow detectorists to see where they’ve had success or failure. As with most things, everyone has an opinion, though… look for trends in what you hear.
  • Experiment. If you are happy with an old toothbrush, soap, and water then stick with it.
  • Jewelry is probably the best use of an ultrasonic cleaner. Jewelry can have a lot of detail that gets filled over time with dirt and even skin cells. Most jewelers include an ultrasonic cleaner in their arsenal for a reason.  
  • Ultrasonic cleaners may fog up gemstones or possibly cause them to shatter.  
  • One consistent school of thought is to never clean a coin as it undoubtedly reduces value. That’s debatable, but most likely the safest thing you can do is just rinse the dirt off in water (maybe a mild little soap) so you can see what you found. Ultimately it’s your choice. Refer to the Mohs Scale of Hardness graphic below.
  • Use the basket provided so your items don’t sit on the metal pan. The vibrations in direct contact with the pan may cause damage to your item. You want the water and cavitation to do the work.

Safety and Cautions

Generally recognized safety considerations for ultrasonic cleaning include:

  • Avoid using flammable cleaning solutions. Ultrasonic cleaners raise the liquid’s temperature, possibly causing discomfort or burns if you reach into the fluid.
  • Some people recommend you use distilled water in the ultrasonic cleaner. This is because cavitation produces heat. Salts or chemicals in the water may produce harmful vapors.
  • Obviously, we don’t dig up professionally graded coins, but once you get your ultrasonic cleaner, you may be tempted to. Don’t. Cleaning a graded coin can easily and greatly reduce its value.
  • If you have any doubts about the worth of a coin that you dig up, consult a professional for advice before you destroy it. If you’re cleaning for sentimental value only, cleaning is certainly worth a try.
  • Too much cleaning can damage coins. Keep an eye on the process and look for wear or pitting. 

I find these Andre’s Pencils quite interesting. Here’s a good video, and check in at about 10:15 to specifically see Andre’s Pencils in action. Check my Recommended Gear page for more details and a link to get them.

How to clean old coins found in the ground (identifying those old, crusty, rusty coins)

Those rusty/crusty old coins should clean up nicely in something that vibrates bullet casings. I’ve seen people discuss this in a forum and have had success using a mix of aquarium gravel, a little dish soap, plus a couple of tablespoons of water. You’ll need to run it for quite a while – some have said all night but I’d prefer daytime so you can keep an eye on it.

This method should help you identify the coins better. One caution I’ve read is not to use this method on silver coins … not sure why, but if that was the recommendation, I’d follow it.

What about cleaning copper coins?

Some people recommend letting copper coins dry completely before doing any cleaning. If you lightly use a toothpick and don’t dig on the surface you can loosen surface dirt.

Liquids that have been tried with degrees of success include peroxide or olive oil. Warming the peroxide is said to help as well as gently rubbing the coin with a soft bristle brush.

You also can use a water bottle or spray bottle to rinse dirt off in the field or at home since water is a sort of universal cleaner.

For a more detailed, recipe-like strategy, check out this post on how to clean copper coins.

Cleaning pennies can be done in a number of ways, including

  • ketchup
  • eraser
  • vinegar and salt
  • lemon and salt
  • a wide range of cleaning products

BONUS Tip – More methods to clean metal objects

Vinegar for Encrusted Rust

Some detectorists have had good success cleaning encrusted metal objects with a process using vinegar and something called EvapoRust. An example of this was a gentleman who unearthed an old metal toy gun, heavily encrusted with rust and other corrosion. He gave me permission to post this before and after picture. Note the words at the top:

before and after toy encrustation

Cleaning Old Coins

Other methods can be used to clean old coins. Some of the common treatments for cleaning old coins you’ve uncovered include:

  • Electrolysis
  • Soaking in apple cider vinegar mixed with distilled water
  • Simply let the coins dry and gently clean them with a toothpick
  • Soak in distilled water and gently use a soft toothbrush

How to Avoid Scratching Metal Detecting Finds (Mohs Hardness Scale)

One of the biggest mistakes you can make is scratching the coins, jewelry, or other metal objects you’ve found and ruining them. This is why cleaning recommendations tend to be on the “soft side” to start with. Water and soft toothbrushes are good examples of the first steps in cleaning.

Sometimes you need to be a bit more aggressive, and this is where Mohs Scale of Hardness can help you make decisions.

This graphic is from the National Park Service and shows the relative hardness of objects. You can see that a copper coin is far down the list and only a few items are softer. This helps guide you in what or what not to use to rub against the coin or jewelry during cleaning.

mohs hardness scale

Cleaning Coins with Vinegar, Coke, Baking Soda, Ketchup, Hydrogen Peroxide, or Lemon Juice:

There are a lot of other techniques to use. Each has a purpose and a result, so please research a bit before cleaning anything potentially valuable. Cleaning is somewhere between a no-brainer and “danger, danger” depending on the item being cleaned.

Do your research and ask other detectorists in person or on social media, then go at it.

Here’s an interesting collection of ideas using various cleaning agents.

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