How to Clean and Store Metal Detecting Finds: A Practical Guide for UK Detectorists

You’ve spent a cold Saturday morning in a muddy field somewhere on the edge of the Lincolnshire Wolds, permission slip in your jacket pocket, listening to the familiar chatter of your detector as it sweeps over centuries of buried history. Then the signal locks in — a solid, repeatable tone. You dig carefully, sift through the soil, and there it is: a coin, greenish-black and caked in earth, sitting in your palm. It might be Georgian. It might be Roman. It could be something far older still.

What you do next matters enormously. The decisions you make in the hours and days that follow — how you clean that object, how you store it, whether you record it properly — will determine whether a genuine piece of British history survives in good condition or is damaged beyond recovery. Poor cleaning is one of the most common ways detectorists inadvertently destroy the very things they’ve worked so hard to find.

This guide covers everything you need to know about cleaning and storing metal detecting finds, with specific reference to the types of objects most commonly recovered across the United Kingdom, and the legal and ethical responsibilities that come with finding them.

Before You Clean Anything: Recording Comes First

Before a single fleck of dirt is removed from any find, you should record it. This isn’t just good practice — for finds that may fall under the Treasure Act 1996, it is a legal requirement to report them to your local Finds Liaison Officer (FLO) within 14 days of discovery. The Portable Antiquities Scheme (PAS), administered by the British Museum, operates a network of FLOs across England and Wales who help record finds on the national database.

Photograph every find in the state it came out of the ground. Use a macro setting if your phone or camera allows it. Place a small ruler or a coin for scale. Note the GPS coordinates or at minimum the field, parish, and county. Write the findspot on a label and keep it with the object from this point forward. Once you’ve cleaned something, the original condition is gone — and if a coroner’s investigation under the Treasure Act follows, the original photographs can be important evidence.

In Scotland, the law differs. Under Scots law, all archaeological objects found in the ground are technically the property of the Crown under the Treasure Trove system, administered by the Crown Office and Procurator Fiscal Service. The Scottish Archaeological Finds Allocation Panel (SAFAP) allocates finds to museums. Detectorists in Scotland must report all finds — not just those made of precious metals — to Treasure Trove Scotland. If you’re detecting north of the border, familiarise yourself thoroughly with this system before you go out.

The Golden Rule: Do As Little As Possible

Every conservator at the British Museum, the National Museum of Wales in Cardiff, or the Fitzwilliam Museum in Cambridge will tell you the same thing: when in doubt, do nothing. Overcleaning is irreversible. A coin scrubbed with a wire brush, or soaked in the wrong chemical, can lose the very surface detail that makes it identifiable and historically significant.

The goal of cleaning a metal detecting find is not to make it look shiny. It is to stabilise it, to remove harmful active corrosion, and to allow proper identification. Nothing more. If a find turns out to be reportable under the Treasure Act — defined broadly as objects made of at least ten per cent gold or silver that are over 300 years old, or groups of two or more base metal objects found together in the same place that are over 200 years old — the FLO and any subsequent museum assessment will be far better served by a lightly cleaned object than one that’s been polished to oblivion.

Understanding What You’ve Found: Metals and Their Behaviour

Different metals behave very differently in the ground, and this affects how you should approach cleaning. British soil varies enormously — from the acidic peat of the Yorkshire Moors to the chalk downs of Kent and the heavy clay of the Midlands — and the chemistry of the soil profoundly affects what happens to buried metal over centuries.

Copper and Copper Alloys (Bronze, Brass)

These are among the most common finds on British fields: Roman sestertii, medieval hammered pennies, Georgian halfpennies, military buttons, buckles, and trade tokens. Copper alloys develop a patina — a layer of copper carbonates that can range from mid-green to dark brown-black. A stable patina actually protects the underlying metal and should generally be left alone.

What you want to remove is active corrosion, sometimes called “bronze disease” — a powdery, bright green material that continues to eat into the metal if left untreated. This is cuprous chloride reacting with moisture and oxygen, and it will eventually destroy a coin or artefact entirely if not addressed.

Silver

Silver is found relatively rarely, but when it does appear — a hammered Elizabeth I sixpence, a Tudor groat, a George III shilling — it’s often in remarkable condition given its age. Silver tarnishes through the formation of silver sulphide, which creates the familiar dark grey or black discolouration. The underlying metal is usually very well preserved beneath this layer. Silver is also one of the metals covered by the Treasure Act, so report before doing anything significant to it.

Iron

Iron corrodes aggressively in most British soils, forming iron oxides and hydroxides. Most iron finds are heavily encrusted and can be very difficult to clean without specialist equipment. Horseshoes, nails, medieval tools, and Civil War musket balls made of lead are sometimes found with iron components. Iron finds are rarely of Treasure Act significance, but can still be historically important — a well-preserved medieval spur or a cannon ball from a Civil War skirmish site is worth recording with the PAS regardless.

Lead

Lead is soft and corrodes to a dull grey-white surface relatively quickly. Pilgrims’ badges, cloth seals, weights, and musket balls are commonly found in lead across the UK. It is a relatively forgiving material to clean, but care must be taken because lead compounds are toxic — always wash your hands after handling uncleaned lead, and avoid inhaling any dust created during cleaning.

Gold

Gold does not corrode and is typically found in near-perfect condition regardless of how long it’s been in the ground. A medieval gold ring found in Suffolk or a Bronze Age gold torc fragment discovered in Shropshire will look extraordinary the moment it’s cleaned of mud. Gold finds almost always fall under the Treasure Act — report them immediately and clean them as little as possible.

Cleaning Methods by Material

Cleaning Copper Alloy Finds

Start with the gentlest possible approach. A soft toothbrush and warm distilled water is your first tool. Work slowly, using the brush to loosen surface dirt without scrubbing the metal itself. Distilled water is preferable to tap water because it contains no dissolved minerals or chlorine that could further react with the metal.

Once you’ve removed loose surface dirt, allow the object to dry completely at room temperature — never use heat to accelerate drying, as rapid temperature changes can cause cracking in fragile patinas. After drying, examine the surface carefully under a magnifying glass. Look for any areas of bright powdery green corrosion. If you find any, this is bronze disease and it needs to be treated.

For bronze disease, a solution of sodium sesquicarbonate (washing soda) can help stabilise mildly affected objects. Mix approximately 20 grams per litre of distilled water and soak the affected object for several weeks, changing the solution periodically. For more serious cases, a conservator should be consulted — the Society for All Artists (SAA) and the United Kingdom Institute for Conservation (UKIC) maintain directories of qualified conservators.

Once stable, copper alloy finds can be protected with a thin coat of microcrystalline wax, such as Renaissance Wax, which is widely used by museums and conservators. Apply sparingly with a soft cloth and buff gently. This creates a protective barrier against moisture without altering the appearance of the object.

Cleaning Silver Finds

A soft toothbrush and warm distilled water is again your starting point. Many silver coins will clean up beautifully with nothing more than this. Once dry, if tarnish remains, a very small amount of jeweller’s rouge or a commercial silver polish can be used cautiously on areas where surface detail is not at risk. However, for hammered coins especially, toning and tarnish often enhance legibility by creating contrast in the design — do not over-polish.

Never use abrasive materials on silver. Never use ultrasonic cleaners on hammered coins, as the vibrations can fracture already thin or stressed metal. For significant silver finds — anything that might be Treasure — do not clean at all beyond removing loose soil, and get them to your FLO.

Cleaning Iron Finds

Iron cleaning is genuinely difficult and often best left to professionals. If you want to attempt basic cleaning at home, an old toothbrush and water can remove surface mud, and light surface rust can sometimes be carefully removed with a wooden or bamboo stick — never use metal tools, as these will scratch and damage the surface. Electrolytic reduction, which passes an electrical current through a solution of washing soda to remove corrosion, is a popular technique among more experienced detectorists, but it requires care and practice to do well.

After any cleaning, iron must be kept dry — humidity is iron’s enemy. A light application of oil (gun oil or Renaissance Wax) after cleaning helps protect the surface. Store iron finds in a low-humidity environment with silica gel packets.

Cleaning Lead Finds

Lead is relatively straightforward to clean. Warm water and a soft brush removes surface dirt effectively. More stubborn deposits can sometimes be carefully loosened with a wooden cocktail stick. Lead white corrosion (lead carbonate) is generally stable and protective, so don’t be in a rush to remove it. If you do remove lead corrosion, remember that lead dust is hazardous — work in a ventilated space and wash your hands and tools afterwards.

Moving Forward

Once you have the fundamentals in place, the possibilities open up considerably. The UK offers fantastic opportunities for anyone interested in this hobby, and with the right foundation you will be well placed to make the most of them.