How To Clean Old Coins Dug Up

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The Best Ways to Clean Metal-Detecting Finds

udit saptarshi

Coins and jewelry that have been underground or in salt seawater for any length of time are usually badly tarnished/corroded. The aim of this article is to help you learn the best ways to clean them.

Gold is such a stable metal that it seldom, if ever, oxidizes; it usually stays shiny and new. But many lesser metals blacken or get covered in verdigris, which turns them a dark shade of green. Yet other metals suffer from a buildup of rust, making it hard to make out the features, especially on coins (known as the patina). If you can make out any part of the coin at all, try to determine what denomination it is, the identity of the head on the back, and most importantly, the date. This will help you determine if your find is valuable or not.

Metal detecting finds that include artifacts, whether coins, jewelry, or other historically important objects, should NOT be cleaned. Leave that to the professionals. Everyday (non-historical) rings, bracelets, coins, and other precious and useful items among your metal detecting finds can be cleaned up using one or all of the methods outlined below.

Mild acids: Soak the metal objects and coins in an undiluted solution of brown sauce, white vinegar, or Coca-Cola. This will remove the blackened areas, revealing the details on coins. Be aware that this method is also damaging to most metals, and while you can then read any markings, copper or cupro-nickel items take on an unnaturally orange hue.
Baking or washing soda: For silver, clean the object with a toothbrush soaked in bicarbonate of soda (baking soda). This will remove any blackened/tarnished areas while preserving all the precious metal. Silver coins clean especially well in a bath of washing soda, hot water and aluminium foil.
Ammonia or white vinegar: Soak the cleaned silver, or gold, overnight in vinegar or ammonia. This will bring back the shine.
Distilled water: Soak your coins or jewelry in plain distilled water for several days, before removing and scrubbing with a water/washing up liquid solution. Use a nail-brush to get into corners and hard to reach spaces.
Olive oil: Soak your finds in olive oil. This is considered to be one of the safest way to clean up valuable coins, as the oil is so gentle it does no harm to the patina. It can take many months for the olive oil to completely clean coins.
Wax: Experts use a product called Renaissance Micro Crystalline Wax to treat cleaned coins. Once treated, coins are ready for display and protected against further deterioration. Only use this on valuable finds; it is more expensive than the other methods.

Other Cleaning Methods

Tumbling: You can buy a tumbler especially designed for cleaning coins and jewelry. There is no difference between a rock tumbler, used for polishing stones, and a barrelling machine used for metals. While one machine can do both, it is highly recommended you purchase two separate barrels as the grit left behind in rock tumblers can irreversibly damage metals.
Electrolysis: This involves passing an electric current through a conductive solution in which a coin or other choice metal object is attached to the negative pole, while an earth metal like carbon is attached to the positive pole. Using this method, many metals can be cleaned up almost instantly within a few minutes.

I have found that one of the very best ways to clean metal detecting finds is in a stone or rock tumbling machine. Coins found by a metal detectorist that are still in currency are difficult to use unless they are properly cleaned up first. Many banks will not even accept coins that are just blackened messes (as you can see from the coins on the top row of the photo). These coins were cleaned in a metal barreller/rock tumbler, with the middle row showing you the difference after 2 hours in a rock tumbler. The final row shows the coins after being through the polishing process.

It is important to separate the coins to be tumbled into similar groups. Those affected by salt corrosion should be cleaned with other coins also suffering from salt corrosion, those with a lead-coating with others that are lead-coated, and so forth. This is to prevent cross-contamination of the various deposits which will ruin the coins and prevent further clean-up efforts. As you can see from the photo, salt corroded and lead-coated coins clean up quite well, but copper-coated coins less so.

Which Rock Tumbler Is Best for Cleaning Coins?

Barrelling machines are very low wattage and barely use more power than that of a light-bulb, which is one of the things that makes them a good choice for cleaning your finds.

Many people will tell you to avoid plastic barrelled rock tumbling machines because they are very noisy. The cheaper ones designed for children are usually made of plastic, not like those with rubber drums. Noise can be an issue if you are tumbling rocks, as it can take 2 weeks or more of constant grinding to break down rocks into smooth pebbles. But what's a bit of noise between friends?

When tumbling metals, however, the whole job can be completed in a single afternoon. It takes about two hours to clean metal detecting finds, and a further two hours to polish them, after changing the medium in which they are tumbling.

Cleaning Coins in a Tumbler

The Best Ways to Clean Valuable Copper or Brass Coins

When you first pull a blackened coin out of the ground or the sea, it is quite possible it is so encrusted with dirt that it becomes impossible to see what type of coin it is or make out its year of mint. It could be valuable, but you won't know until it is cleaned up a bit.

The best thing to do is to place it in a saucer containing plain water with a little bit of lemon juice added. After a few minutes, the worst of the encrustation should be loosened. It is better to soak it in a lemon/water mix too briefly than too long because the acetic acid can damage the coin face if left on too long. Take the coin and gently rub it with a soft toothbrush under running water, then set aside. Next, treat it to a finish of Renaissance Micro-Crystalline Wax, and make no further changes to it.

If it is in good condition, all the features of the coin will be clear, and the date will be easily read. The color may be wrong, but that doesn't deter collectors.

I hope you have found something useful in this article. Some people are quite happy to leave finds as they are, but most of us like to see that shine brought back to metals that once looked really good, and can again.

You can even clean metal detecting finds for the scrap metal market, and make yourself some money from finds you would otherwise have thrown away. Scrap metal recycling is big business, and the value of old stainless steel, aluminium, brass and copper now far surpasses that of many old coins. One of the demands of scrap metal recycling plants is that your old metal objects are thoroughly cleaned before they will accept them. I would strongly suggest putting small metallic objects in a stone tumbler as this cleans them up beautifully.

Resource

GoMetalDetecting.com

This article is accurate and true to the best of the author's knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Ralph on July 22, 2019:

Found chunks of what looks like silver that's been melted down. Tried the ice test and that works the way it so posed to, it melts right away, but pieces are heavily corroded. What do I do to clean them. A lot of twisted metal in these pieces.

Jim Burr on November 04, 2018:

Surprised you did't mention crushed walnut shells as a medium in your rock tumbler, it's not abrasive, can be found in sporting goods store or a shop that sells reloading supply's as they tumble brass casings. It may take two days and The tumbler is in the basement. I then dump the contents in my handheld sand scoop to sift things out. Thanks for the article.

Ruby from United States on March 15, 2016:

a lot of times i just scrape, scrape, and scrape some more with my fingers lol :p Or I will use a little water with possibly a toothbrush. The dirt gives it an authentic look lol.

Metal Detectorist (author) on October 18, 2012:

I'd be out there in a flash, with the most expensive metal detector I could afford - the top of the range ones can find anything! Good luck if you do go!

Lela from Somewhere near the heart of Texas on October 18, 2012:

I just read that one. It makes me want to fire up my old basic metal detector again. Some say that the outlaw Sam Bass left a hoarde of $20 gold pieces around these parts. They were stolen from a stagecoach robbery. I would sure like to find those!

Metal Detectorist (author) on October 18, 2012:

I love this story - http://www.dailymail.co.uk/news/article-1225271/Da... - it's very motivational!

Lela from Somewhere near the heart of Texas on October 18, 2012:

Some shooters take a squirt bottle of distilled water to rinse off dirt. They also say to handle all coins by their edges only. I guess they also take soft jewelers cloths to wrap any good finds in?

I would love to find some buried treasure someday. It's the perfect hobby.

Metal Detectorist (author) on October 18, 2012:

Absolutely. Good advice, Austinstar. Even rubbing the dirt off valuable finds with your fingers can cause irreparable damage.

Lela from Somewhere near the heart of Texas on October 17, 2012:

If you suspect for a moment that the coin may be valuable, do not clean it at all! Only an expert should touch it unless you are planning to never sell it. If you want to keep it, then clean with the wax or the olive oil only!

Metal Detectorist (author) on October 17, 2012:

Or the fellow in Scotland who found an ancient gold hoard worth well over £1M on his very first day out with a metal detector!

It's great fun, and gets you out in the open air too. I never knew there were so many ring pulls and old Coke cans under the ground! lol Cleaning the coins without damaging them is trickier, but well worth doing.

CMHypno from Other Side of the Sun on October 17, 2012:

Interesting hub, as I would never have known how to clean old coins and jewelry. Sounds like it could be a really interesting hobby, and after all the Staffordshire Hoard was found by a guy with a metal detector