How to Clean Roman Coins Safely Without Damaging Them

Finding a Roman coin while metal detecting can be an unforgettable experience.

After perhaps 1,500–2,000 years in the ground, the temptation is naturally to clean away the soil and reveal the emperor, inscription and reverse design.

But Roman coins can be surprisingly fragile.

In many cases, what appears to be a solid metal surface is actually a combination of original metal, mineralised corrosion layers and patina. Aggressive cleaning can permanently remove detail that has survived for centuries.

At Metal Searchers, our approach is therefore:

Record it first. Identify it carefully. Clean only as much as necessary.

The objective should not be to make a Roman coin shiny.

It should be to preserve as much original information and surface as possible.

Before Cleaning a Roman Coin, Record the Find

If the coin has been found while metal detecting, record its archaeological context before doing anything to the surface.

Ideally record:

• Exact or approximate GPS location
• Field
• Date
• Depth
• Nearby finds
• Photographs of the coin as found

The location can be archaeologically significant even when the coin itself is common.

For more information, see our guide to Metal Detecting and Archaeology.

Photograph the Coin Before Cleaning

Take clear photographs of:

• Obverse
• Reverse
• Edge
• Any visible inscriptions

This gives you a permanent record of the original condition.

It may also be possible to identify the coin without carrying out any cleaning.

Try to Identify It Before Cleaning

Look for visible clues such as:

• Portrait
• Bust direction
• Crown or radiate head
• Lettering
• Reverse figure
• Mint mark
• Coin diameter
• Weight

Even partial details can sometimes narrow the identification considerably.

If you can identify the coin without further cleaning, there may be no reason to disturb the surface.

Not All Roman Coins Are Made From the Same Metal

Roman coinage includes several different materials and alloys.

Examples include:

• Gold
• Silver
• Debased silver
• Bronze
• Brass
• Copper alloys

Later Roman coins can contain very little precious metal even when they originally appeared silver.

The correct conservation approach therefore depends on what the coin is made from.

Copper-Alloy Roman Coins

Many detector-found Roman coins are made from copper alloys.

These can develop:

• Brown patina
• Dark-green patina
• Black patina
• Olive-green surfaces
• Mineralised crusts

A stable patina can be highly desirable.

Do not assume that green or brown automatically means the coin is dirty.

Patina Is Part of the Coin

Patina forms through long-term chemical interaction between the metal and its environment.

On an ancient coin, it can:

• Protect underlying metal
• Preserve surface detail
• Give the coin historical character
• Provide evidence of burial conditions

Removing stable patina may reveal a rough, pitted surface underneath.

Once removed, it cannot be restored authentically.

Stable Patina Versus Active Corrosion

Learning this distinction is very important.

Stable Patina

Stable corrosion generally appears:

• Firm
• Adherent
• Dry
• Relatively unchanged over time

It can be:

• Brown
• Black
• Green
• Blue-green

Stable archaeological copper-alloy surfaces can also be rough or uneven.

Active Corrosion

Warning signs include:

• Bright or pale-green powder
• Fluffy green spots
• Fresh powder appearing repeatedly
• Surface material breaking away
• Progressive deterioration

This may indicate active chloride corrosion, commonly referred to as bronze disease.

What Is Bronze Disease?

Bronze disease is an active form of corrosion affecting archaeological copper and copper-alloy objects.

Chlorides absorbed during burial can react with the metal in the presence of moisture and oxygen.

The characteristic sign is often:

light-green powdery corrosion appearing in small erupting spots.

This is different from a stable green patina.

Bronze disease can continue damaging the object after it has been removed from the ground.

Do Not Scrape Bronze Disease Away and Assume It Is Fixed

Removing the visible green powder does not necessarily remove the underlying cause.

The chloride contamination may remain within the corrosion layers.

If a Roman coin appears to have active bronze disease, isolate it from other objects and seek conservation advice.

The objective becomes stabilisation, not cosmetic cleaning.

Humidity Matters

Active corrosion in archaeological copper alloys becomes more likely as relative humidity increases.

Storage conditions are therefore important.

If you suspect bronze disease, keep the coin dry and separate from other finds while seeking advice.

Do not store it in a damp shed, garage or sealed container containing residual moisture.

Don't Wash Every Roman Coin Immediately

It can be tempting to put every freshly found coin under the tap.

We recommend examining it first.

Water may soften soil, but it can also:

• Change fragile corrosion layers
• Introduce additional contaminants
• Conceal active corrosion temporarily while wet
• Delay proper drying

For a robust low-value coin covered only in loose soil, careful water treatment may sometimes be reasonable.

For a fragile or potentially important coin, obtain advice first.

Why Distilled Water Is Sometimes Used

Distilled or deionised water contains very few dissolved minerals.

Conservators sometimes use water-based treatments under controlled conditions.

For a robust common Roman coin with compacted soil, careful soaking in distilled water can sometimes help soften surface dirt.

However:

distilled water is not a universal treatment for every Roman coin.

The condition of the surface matters more than the age of the coin.

If You Use Distilled Water

For a low-value, stable coin where gentle treatment is appropriate:

1. Place the coin in clean distilled water.
2. Allow the soil to soften naturally.
3. Avoid rubbing the surface.
4. Change the water when dirty.
5. Examine the coin periodically.
6. Stop if the surface begins changing.
7. Dry thoroughly afterwards.

Do not soak indefinitely without monitoring the coin.

Avoid Tap Water for Long-Term Soaking

Tap water can contain dissolved:

• Chlorides
• Minerals
• Treatment chemicals

These are undesirable around archaeological metals.

If water treatment is being used, distilled or deionised water is generally preferable.

Do Not Boil Roman Coins

Boiling is unnecessarily aggressive.

Rapid temperature changes can affect fragile corrosion layers and potentially cause cracking or flaking.

There is no need to boil an archaeological coin as part of routine cleaning.

Be Extremely Careful With Brushes

A soft brush may remove genuinely loose soil from a robust surface.

But even a toothbrush can damage a fragile mineralised coin.

Avoid vigorous scrubbing.

If the surface begins to change, stop.

Wooden Picks and Toothpicks

Many detectorists use wooden cocktail sticks to remove compacted soil.

Even wood can damage an unstable ancient surface.

If you choose to use one on a common, robust coin:

• Work under magnification.
• Use almost no pressure.
• Approach soil from the side.
• Never force the point into details.
• Stop if patina begins lifting.

Do not practise this technique on a rare or valuable coin.

Magnification Is Extremely Useful

A loupe or microscope allows you to distinguish:

• Soil
• Patina
• Corrosion
• Lettering
• Fine detail

This can prevent accidental removal of the actual coin surface.

Under magnification, what looks like a lump of dirt may turn out to be fragile detail.

Never Use a Wire Brush

A wire brush can very quickly destroy an ancient coin.

Avoid:

• Brass brushes
• Steel brushes
• Rotary wire wheels
• Fibreglass abrasive brushes

These can remove patina and surface detail in seconds.

Avoid Dremels and Rotary Tools

Power tools have no place in routine Roman coin cleaning.

They can:

• Remove original metal
• Flatten lettering
• Destroy patina
• Leave obvious modern tool marks

An ancient coin should never be polished into looking new.

Avoid Vinegar and Other Acids

Do not routinely use:

• Vinegar
• Lemon juice
• Citric acid
• Cola
• Other acidic household cleaners

These work by chemically attacking surface material.

Unfortunately, that can include the coin itself.

A heavily corroded coin may emerge brighter but with less surviving detail.

Avoid Baking Soda and Abrasive Powders

Baking soda is abrasive.

Using it as a paste can scratch and remove original surfaces.

Avoid it on ancient coins.

Avoid Metal Polish

Never use products such as:

• Brasso
• Silver polish
• Jewellery polish
• Metal cleaning paste

on ancient Roman coins.

A polished ancient coin may lose much of its historical appearance and collector appeal.

Avoid Electrolysis on Roman Coins

Electrolysis is sometimes used for certain archaeological iron objects under controlled conditions.

It should not be treated as a general Roman coin cleaning technique.

On copper-alloy coins it can be extremely destructive.

Potential damage includes:

• Loss of patina
• Surface pitting
• Loss of detail
• Exposure of unstable underlying metal

Do not experiment with electrolysis on a valuable ancient coin.

Avoid Ultrasonic Cleaners

An ultrasonic cleaner may be useful for modern robust objects.

Ancient archaeological coins can contain fragile corrosion layers.

Ultrasonic energy can potentially detach:

• Patina
• Mineralised surfaces
• Loose details

Do not automatically place Roman coins into ultrasonic cleaners.

What About Olive Oil?

Soaking ancient coins in olive oil has been a popular hobbyist technique for many years.

We do not recommend it as a first-line conservation method.

Oil can:

• Darken the surface
• Penetrate porous corrosion
• Trap contamination
• Become difficult to remove
• Complicate later conservation

If a coin may be valuable or archaeologically important, avoid experimental oil treatments.

Do Not Wax Automatically

Professional conservators sometimes apply protective coatings to archaeological metals after stabilisation.

That does not mean every Roman coin should be waxed.

Applying a coating to a coin containing moisture or active chlorides can trap problems underneath.

Only apply coatings when you understand why they are needed.

Silver Roman Coins Need Different Treatment

Roman silver coins such as denarii can sometimes survive in much better condition than copper-alloy coins.

But silver can still suffer:

• Toning
• Deposits
• Corrosion
• Brittleness
• Crystallisation

Do not assume silver means safe to polish.

Natural toning may be completely acceptable.

For a valuable silver denarius, professional assessment is preferable to household cleaning experiments.

Don't Try to Make Silver Bright White

Ancient silver does not need to resemble a modern newly minted coin.

Artificially bright surfaces can indicate over-cleaning.

Preserve original toning wherever possible.

Be Careful With Debased Silver Coins

Later Roman silver coinage often contains significant amounts of copper.

This means corrosion behaviour can be complicated.

A coin may appear partly silver but contain a corroded copper-rich core.

Aggressive chemical treatment can make the condition substantially worse.

Gold Roman Coins

If you find a Roman gold coin:

Do as little as possible.

Gold does not normally corrode like copper, but it is soft and scratches easily.

Do not:

• Polish it
• Rub the faces
• Use abrasives
• Experiment with chemicals

Handle by the edges and obtain professional identification.

A Roman Coin May Be More Valuable Uncleaned

Collectors and specialists would often prefer to examine an untouched coin rather than one damaged through amateur cleaning.

If you suspect the coin may be rare:

stop.

Do not try to improve it before valuation.

How Do You Know Whether a Roman Coin Is Rare?

You may not.

Rarity can depend on:

• Emperor
• Mint
• Reverse type
• Legend
• Bust type
• Mint mark
• Date
• Condition
• Variety

A coin that looks ordinary to a beginner can sometimes be unusual.

This is another reason to identify before cleaning aggressively.

Use PAS for Archaeological Identification

If the coin is an archaeological find in England or Wales, your local Finds Liaison Officer may be able to help identify and record it.

A common Roman coin may have modest financial value but still provide useful archaeological information.

Record the findspot before the location is forgotten.

What If Several Roman Coins Are Found Together?

This changes the situation completely.

If you begin finding multiple coins concentrated in a small area, consider the possibility of:

• A scattered hoard
• Archaeological deposit
• Occupation site

Do not automatically continue digging aggressively.

Record locations carefully and seek advice.

The archaeological relationship between the coins may be more important than cleaning them.

What If the Coin Comes From a Hoard?

Leave conservation to specialists.

Coins recovered as part of a hoard can carry important evidence relating to:

• Containers
• Organic material
• Coin arrangement
• Deposition
• Corrosion relationships

Professional excavation and conservation can preserve this information.

Store Uncleaned Finds Separately

Do not throw all freshly excavated Roman coins into one container.

Use individual:

• Bags
• Trays
• Compartments

Label each with its findspot.

This prevents:

• Scratching
• Mixing locations
• Transferring loose corrosion products

Do Not Seal a Damp Coin

If a coin is still damp from the soil or cleaning, do not immediately seal it into an airtight plastic container.

Trapped moisture can accelerate corrosion.

Drying and storage conditions should be appropriate to the material.

Long-Term Storage

For stable Roman coins, use appropriate archival storage such as:

• Acid-free coin envelopes
• Archival trays
• Suitable inert plastic holders
• Coin capsules where appropriate

Avoid unknown soft plastics, particularly materials containing PVC.

Inspect Coins Periodically

Do not assume that because a coin looked stable when stored it will remain unchanged forever.

Periodically check for:

• New powdery corrosion
• Flaking
• Colour changes
• Surface cracking

Early detection of active corrosion gives you a better chance of stabilising the object.

Keep Bronze Disease Away From Other Finds

If one coin develops active powdery green corrosion, store it separately.

This also makes it easier to monitor.

The issue is not that bronze disease behaves like an infection moving magically from coin to coin; rather, similar chloride contamination and humid storage conditions can affect multiple archaeological copper-alloy objects.

Isolation helps with monitoring and controlling the environment.

When Professional Conservation Is Recommended

Seek professional advice when:

• Coin may be rare
• Coin is valuable
• Surface is flaking
• Bronze disease is suspected
• Coin is heavily mineralised
• Silver is brittle
• Several coins form a hoard
• Archaeological deposits remain attached
• Cleaning could affect identification

Conservation specialists have access to controlled treatments and analytical methods unavailable to most hobbyists.

The British Museum's own conservation records show that treatment decisions can vary significantly even between individual Roman coins: some receive targeted stabilisation, while others may deliberately receive little or no further cleaning when the surface is stable.

A Conservative Roman Coin Cleaning Sequence

For a common, stable coin requiring basic identification:

Stage 1 - Record

Record:

• Findspot
• Date
• Photograph

Stage 2 - Examine

Look under magnification.

Determine whether the surface appears stable.

Stage 3 - Identify

Try to identify visible:

• Portrait
• Legend
• Reverse
• Size
• Weight

Stage 4 - Remove Loose Soil Only

Use the least invasive method possible.

Stage 5 - Reassess

Ask:

Can I identify the coin now?

If yes, stop.

Stage 6 - Further Treatment Only if Necessary

Do not continue cleaning merely because some soil remains.

When Should You Stop Cleaning?

Stop when:

• The coin can be identified.
• Further cleaning is not necessary.
• Patina begins lifting.
• Detail begins disappearing.
• Surface becomes brighter.
• Powdery corrosion appears.
• You become uncertain.

The goal is not:

“Remove everything that is not metal.”

The goal is:

“Preserve everything historically and physically important.”

Roman Coin Cleaning Methods at a Glance

Recognising Bronze Disease

Watch for:

Stable surface:

• Firm green/brown/black patina
• Dry
• Not visibly changing

Possible active bronze disease:

• Pale-green powder
• Small erupting spots
• Recurring powder after cleaning
• Flaking surface

Active corrosion warrants specialist attention.

Frequently Asked Questions

Should I clean a Roman coin I found metal detecting?

Only cautiously. Record and identify it first. If potentially rare, valuable or unstable, avoid cleaning and seek specialist advice.

What is the safest way to clean a Roman coin?

There is no single method suitable for every Roman coin. The safest approach begins with examination, identification and removing only loose material where appropriate.

Can I soak Roman coins in distilled water?

For some robust, stable copper-alloy coins, controlled distilled-water soaking may help soften soil. It is not appropriate for every coin.

Can I use olive oil?

It has traditionally been used by hobbyists, but we do not recommend it as a routine first treatment because it can alter surfaces and complicate later conservation.

Can I use vinegar?

We recommend avoiding acidic household cleaners on ancient coins because they can attack original surfaces.

Should I brush a Roman coin?

Only very gently if the surface is robust and you are removing loose soil. Avoid aggressive brushing.

What is bronze disease?

Bronze disease is active chloride-related corrosion affecting archaeological copper alloys, often recognised by pale-green powdery spots.

Is green patina bad?

No. Stable green patina can be completely normal and should not automatically be removed.

Should Roman silver coins be polished?

No. Polishing can remove original surface material and toning.

What should I do if I find several Roman coins together?

Stop, record the location carefully and seek archaeological advice because the coins may form part of a hoard or significant deposit.

Final Thoughts

Cleaning Roman coins requires patience.

A coin that survived 1,700 years underground can be damaged permanently in 30 seconds with the wrong cleaning method.

Do not measure success by how shiny the coin becomes.

Measure success by how much original information survives.

Our preferred sequence is:

Record.

Photograph.

Examine.

Identify.

Clean only when necessary.

Stop early.

If the coin is rare, valuable, unstable or archaeologically important, professional conservation is far preferable to experimentation.

The most important principle is simple:

you can always clean a little more later — but you cannot put the original surface back once it has been removed.

Preserve the history first.