Cleaning a coin you've just found while metal detecting can be surprisingly easy to get wrong.
After hundreds or even thousands of years in the ground, soil, corrosion products and mineral deposits can become attached to the surface. It's tempting to start scrubbing until the detail appears, but with older coins especially, over-cleaning can permanently remove the very surface you're trying to reveal.
There's also no single cleaning method that works for every coin. A medieval hammered silver penny needs a very different approach to a heavily encrusted Roman bronze, while a gold coin may need virtually no cleaning at all.
In this guide, we'll look at how to approach different metals, how to preserve the original surface of a coin, what you should avoid and, perhaps most importantly, when it's better to leave a find alone.
Before Cleaning an Old Coin
Before reaching for anything, take a good look at the coin.
If possible, establish the likely metal and age first. Even if you can't identify the exact coin, knowing whether you're dealing with silver, copper alloy, gold or a more modern metal will help determine what happens next.
And remember:
Don't assume everything covering the coin is dirt.
Old coins can develop a patina through long-term reactions between the metal and their surrounding environment. This is particularly important with copper and bronze coins.
A good, stable patina can form part of the surviving surface of an old coin and may contain much of its visible detail.
Removing it in an attempt to expose shiny metal underneath can leave you with a coin that looks considerably worse than when you started.
Start With the Least Aggressive Method
A useful rule for cleaning metal detecting finds is:
You can always clean a coin a little more. You can't put its original surface back.
Start gently and only progress to more involved cleaning when it's genuinely necessary.
If you suspect you've found something particularly rare, valuable or historically important, consider getting it identified before attempting to clean it further.
Cleaning Coins in the Field
Most coins don't need to be completely cleaned while you're still detecting.
Often, you simply want to remove enough loose soil to establish what you've found.
One of the easiest mistakes to make is vigorously rubbing a freshly dug coin with your thumb or against your clothing. Soil can contain tiny particles of sand, stone and grit, which can act as an abrasive against the coin's surface.
If the coin appears reasonably solid, a gentle spray or rinse with clean water can help loosen surface soil without scrubbing it.
A small refillable bottle such as the Searcher Spray Bottle can be useful for carrying water specifically for this purpose while you're detecting.
Shop the Searcher Spray Bottle HERE
For detectorists who like having a few cleaning tools with them, the Composite Field Cleaning Kit provides a portable set of tools in a carabiner pouch for carefully revealing detail in the field.
Shop the Composite Field Cleaning Kit HERE
But don't feel that you need to completely identify and clean every coin beside the hole.
If something looks old, fragile or unusual, safely store it and take a closer look when you get home.
How to Clean Silver Coins
Silver generally survives in the ground differently to copper alloys, although condition can vary enormously depending on the purity of the silver, surrounding soil and length of time underground.
Medieval hammered silver, for example, can sometimes emerge requiring surprisingly little cleaning.
Start Gently
If the coin is simply covered with loose soil, clean water may be enough.
Allowing compacted soil to soften before gently removing it is preferable to immediately scrubbing the surface.
Don't assume that an old silver coin needs to become bright silver again either.
Historic silver can develop grey, dark or toned surfaces that are perfectly normal. The objective isn't to make a centuries-old coin look as though it has just left the mint.
Heavier Deposits on Silver Coins
Some silver finds emerge with much harder deposits or encrustation.
If these are obscuring detail, gradual softening is preferable to immediately scraping them away.
Regularly inspect the coin as you work. You need to be able to distinguish between material sitting on the coin and the original surface underneath.
For more stubborn cases, Composite Cleaning Pencil Silver Coin Cleaning Solution is specifically designed to help ease encrustation from the patinated surface of silver coins and artefacts and is particularly suited to medieval silver coinage.
Simply add the coin and periodically monitor its progress rather than leaving it unattended indefinitely.
Shop Silver Coin Cleaning Solution HERE
If you're dealing with a particularly unusual or potentially valuable silver coin, identification should come before aggressive cleaning.
How to Clean Copper and Bronze Coins
Copper and copper-alloy coins — including bronze — require a particularly cautious approach.
Roman bronzes, Georgian copper coins and other copper-alloy finds can develop substantial patinas and corrosion products during their time underground.
And here's an important point:
Green doesn't automatically mean it needs to come off.
A smooth, hard and stable green, brown or even almost black patina can be part of the surviving surface of the coin.
On some ancient coins, removing that layer can remove detail with it.
Cleaning a Stable Copper or Bronze Coin
If the coin has a solid surface beneath loose soil, begin with gentle cleaning.
Avoid immediately reaching for anything abrasive.
If harder deposits remain, soaking and softening can make them easier to remove gradually rather than attempting to scrape through them.
If you progress to mechanical cleaning, work slowly and ideally under magnification.
You're trying to remove material sitting on top of the original surface, not cut through the original surface itself.
Stable Patina vs Active Corrosion
It's also important to distinguish between a stable patina and a surface that is actively deteriorating.
A hard, smooth green patina isn't the same thing as loose, powdery, cracking or flaking corrosion.
If the surface looks unstable, repeatedly cleaning or brushing it can potentially make things worse.
If you're uncertain about the condition of an important coin, this is a good point to stop and seek more specialist conservation advice.
Cleaning Heavily Encrusted Coins
Some detecting finds emerge from the ground looking like little more than featureless discs.
You know there might be detail hiding beneath the encrustation, which makes it incredibly tempting to start digging into it.
This is where patience really matters.
First consider whether the deposits can be softened rather than immediately scraped away.
The Composite Cleaning Pencil Coin Cleaning Solution uses an active softening formulation designed to aid the removal of encrustations, oxides and hard or soft soils while preserving the object's original patina when used as directed.
It's suitable for objects made from gold, silver, bronze, brass, copper and nickel and can also be used in ultrasonic baths.
Shop Coin Cleaning Solution HERE
Once deposits have softened, more precise mechanical cleaning may be possible.
Using a Cleaning Pencil on Coins
A cleaning pencil isn't something every coin needs.
Its main advantage comes when hard surface encrustation is hiding detail and you need much greater control over exactly what you're removing.
The Composite Cleaning Pencil is designed for precision cleaning around very small details and removing hard surface encrustation to reveal detail underneath.
Shop the Composite Cleaning Pencil HERE
Good lighting and magnification make a huge difference when carrying out this sort of work.
Work on a tiny area at a time and regularly inspect your progress.
As soon as you appear to have reached the original surface, stop working that area.
There's no reason a heavily encrusted coin needs to be completely cleaned in one sitting. Coming back to it several times is far preferable to removing too much because you rushed.
How to Clean Gold Coins
Gold behaves very differently to copper and bronze because it is highly resistant to corrosion.
As a result, gold coins can sometimes survive remarkably well underground.
A freshly discovered gold coin may therefore require little more than the removal of loose soil.
If the coin is sound, a gentle rinse with clean water may be sufficient. Avoid rubbing grit across the surface and don't polish an old gold coin simply because you want it to shine.
Historic gold doesn't need to look brand new.
The general Composite Coin Cleaning Solution is suitable for gold objects if deposits genuinely require softening, but minimal intervention should always be the starting point with a gold coin.
And if you've been lucky enough to uncover an unusual or potentially important gold coin, we'd recommend getting it properly identified before doing anything beyond very gentle cleaning.
What Should You Never Use to Clean Old Coins?
You'll find countless coin-cleaning tricks and home remedies online.
The problem is that being capable of removing dirt doesn't necessarily make something safe for an old coin.
As a general rule, be extremely cautious with:
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Wire brushes or harsh brushes
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Scouring pads
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Abrasive metal polishes
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Sandpaper
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Aggressive household cleaning products
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Bleach
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Power tools
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Hard scraping without sufficient control
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Vigorous rubbing of a dirty coin
You'll also see various methods involving acids and other household ingredients.
Again, the question isn't simply "Will this remove the dirt?"
It's:
"What else might it remove at the same time?"
Something capable of rapidly stripping corrosion or tarnish may also alter the coin's original surface, colour and patina.
If the objective becomes making an ancient coin shiny, you've probably gone too far.
Drying Coins After Cleaning
Drying is an important part of the cleaning process that's easily overlooked.
If you've cleaned a coin using water or another appropriate solution, make sure it's properly dry before putting it into storage.
Pay particular attention to heavily pitted or encrusted finds where moisture may remain trapped within the surface.
Don't immediately seal a damp coin inside an airtight container.
Once the coin is dry, inspect it again.
Cleaning often exposes areas that weren't visible beforehand, and this is a good opportunity to decide whether the coin genuinely requires any more work.
Quite often, it doesn't.
Should You Wax Old Coins?
Microcrystalline wax can be used as a protective coating on suitable metal finds, but it shouldn't automatically be applied to every coin you find.
The object should first be appropriately cleaned, stable and completely dry.
Preserve IT is a blend of high-quality microcrystalline waxes designed to provide a protective finish to artefacts commonly found while metal detecting. Its formulation is based on the same type of technology used in museum and archival products.
It's applied with a cloth before being buffed in a similar way to a conventional wax polish.
Shop Preserve IT Microcrystalline Wax HERE
Again, use some judgement.
With potentially valuable or historically important coins and artefacts, we'd favour getting appropriate advice before applying any conservation treatment.
Photograph Your Coin Before and After Cleaning
Here's a simple habit that's worth getting into:
Photograph your coin before you clean it.
It gives you a permanent record of its original condition and can be extremely useful if you subsequently need help identifying it.
Then photograph it again once you've finished.
For useful records, try to photograph both the obverse and reverse, use consistent lighting and include a scale so the dimensions of the coin can be seen.
Where appropriate, recording its weight can also be useful.
The Searcher Finds Scale Mat has a non-absorbent, wipe-clean surface with a low-reflective finish, providing an easy way to show scale when photographing coins and other finds.
Shop the Searcher Finds Scale Mat HERE
It's also worth recording the findspot and circumstances of discovery where appropriate rather than relying on yourself to remember the details months or years later.
When Should You Leave a Coin Alone?
Knowing when not to clean something is every bit as important as knowing how to clean it.
Consider stopping before further cleaning if:
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You don't know what the coin is
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It could be rare or particularly valuable
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The surface is cracking, flaking or powdery
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You're unsure whether you're looking at dirt or patina
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Detail appears to exist within the patinated surface
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The coin may require professional examination
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Cleaning appears to be making the surface worse rather than clearer
Sometimes a coin simply isn't going to reveal the portrait, legend or date you were hoping for.
Continuing to remove material won't bring detail back if that detail no longer survives.
Knowing when to put the cleaning tools down is part of cleaning coins properly.
Want to Learn More About Cleaning and Preserving Finds?
Coin and artefact cleaning is a huge subject, and we've only covered the fundamentals here.
Different metals, soil conditions, corrosion and states of preservation can all affect the best approach to a find.
For detectorists who want to take their knowledge further, Cleaning Coins & Artefacts by David Villanueva is a handy guide dedicated to safely cleaning and preserving metal detecting finds.
The book goes considerably further into subjects including assessing finds, cleaning in the field, safe storage, mechanical cleaning, chemical cleaning and conservation. Importantly, it also recognises that finds of significant historical or monetary value are often better left to experts.
Shop Cleaning Coins & Artefacts HERE
Coin Cleaning & Preservation Products
You don't need a specialist cleaning product for every coin you find.
Plenty of detecting finds need little more than careful handling, patience and, where appropriate, a little clean water.
For finds that do need some extra help, these are some of the cleaning and preservation products available from LP Metal Detecting:
Searcher Spray Bottle — handy for gently rinsing loose soil from suitable finds in the field.
Shop HERE
Composite Field Cleaning Kit — portable tools for controlled cleaning and revealing detail while detecting.
Shop HERE
Silver Coin Cleaning Solution — designed to help ease encrustation from silver coins and artefacts and particularly suited to medieval silver coinage.
Shop HERE
Composite Coin Cleaning Solution — an active softening solution for encrustations, oxides and soils on a range of metals.
Shop HERE
Composite Cleaning Pencil — designed for precision work and controlled removal of hard surface encrustation.
Shop HERE
Preserve IT Microcrystalline Wax — a protective microcrystalline wax blend for suitable cleaned and stable finds.
Shop HERE
Searcher Finds Scale Mat — a wipe-clean, low-reflective scale mat for photographing and recording finds.
Shop HERE
Cleaning Coins & Artefacts — David Villanueva's more detailed guide to cleaning, conservation, storage and looking after metal detecting finds.
Shop HERE
The Golden Rule: Less Is More
There's something incredibly satisfying about slowly revealing the detail on a coin that has spent centuries underground.
But good cleaning isn't about making an old coin look new.
It's about removing what can safely be removed while preserving as much of the original surface as possible.
Start gently. Understand the metal you're dealing with. Give deposits time to soften. Work carefully and under magnification when mechanical cleaning is necessary, and regularly stop to assess your progress.
Most importantly, know when to stop.
That Roman bronze, hammered silver penny or Georgian copper has already survived hundreds — perhaps thousands — of years.
Taking an extra day to clean it isn't going to hurt. Rushing it might.