How to Clean Coins Found Metal Detecting (and When Not To)

The safest answer to how to clean metal detecting coins is to do as little as possible: rinse loose dirt off with distilled water, let the coin soak if needed, and dry it gently. Never scrub, polish, use abrasives or dip a coin that might be valuable before an expert has seen it. Harsh cleaning permanently changes a coin's surface, and grading services label such coins as cleaned, which typically hurts collector value. Common clad coins and badly corroded pieces with no collector premium are a different story, and you have more options there.

This guide explains how to sort your finds, which methods are safe for which metals, and what to avoid entirely.

First, decide whether a coin should be cleaned at all

Collectors and grading services value original surfaces. NGC, one of the major third-party grading companies, notes that cleaning is one of the most common reasons a coin receives a "Details" grade instead of a numeric grade, and that harsh cleaning cannot be reversed by professional conservation. In practice, an improperly cleaned key-date coin is worth less than the same coin left alone.

Before you touch any coin, put it into one of three groups:

If you are not sure which group a coin belongs in, treat it as potentially valuable. Our guide to valuable coins found metal detecting covers the dates and types worth a closer look.

What you need

• Distilled water (tap water contains chlorine and minerals)
• Small plastic or glass containers, one per coin or per type
• Soft toothbrush or wooden toothpicks for loose dirt only
• Lint-free cloth or paper towel for patting dry
• Cotton or nitrile gloves
• A magnifier to inspect surfaces before and after
• Non-PVC storage flips or holders for the finished coins

How to clean metal detecting coins: a gentle step-by-step method

1. Field care. Do not rub coins with your thumb in the field. Grit acts like sandpaper. Put each coin in a separate pouch or pill bottle.
2. Inspect before cleaning. Look at the coin under magnification and identify it if you can. If the date or type suggests value, stop here.
3. Rinse. Hold the coin by the edges and rinse loose dirt away under a gentle stream of distilled water.
4. Soak. Place the coin in fresh distilled water. Let caked soil soften for hours or days, changing the water when it becomes cloudy.
5. Loosen remaining dirt carefully. On collectible but common coins, a soft brush or wooden toothpick can lift softened dirt from around the lettering. Do not scrub the fields.
6. Dry thoroughly. Pat dry, never rub. Let the coin air-dry completely before storage, because trapped moisture encourages corrosion.
7. Store properly. Use inert holders, not soft PVC flips. See the storage section below.

Cleaning by metal type

Silver coins

Silver often comes out of the ground in good shape, with a dark toning that collectors usually prefer to leave alone. A distilled water soak and rinse is usually all that is needed. Avoid silver dips, baking soda pastes and polishing cloths on any coin with numismatic value, since they strip the surface and leave telltale hairlines or an unnatural shine.

Copper and bronze coins

Copper coins, including Indian Head and wheat cents, react strongly with soil and often come out with green or dark crusts. Collectors value a stable, natural brown color. Aggressive cleaning usually leaves copper an unnatural pink or orange that is obvious to buyers. Stick with water soaks for collectible copper. Watch for powdery, light-green spots that keep returning; conservators call this active corrosion, and the Canadian Conservation Institute recommends keeping objects with this condition below 35 percent relative humidity.

Nickel coins

Nickels often have hard encrustations. Water soaks help; patience helps more. Avoid acids, which can etch the surface.

Gold coins

Gold does not corrode the way base metals do, so gold coins usually need only a rinse. Do not rub them: gold is soft and scratches easily. Any gold coin deserves an expert opinion before you do anything beyond rinsing.

Modern clad coins

Clad coins have no collector premium in most cases, so many detectorists clean them in a rock tumbler with an appropriate medium before spending or depositing them. This is fine for clad but should never be used on older coins.

Methods to avoid on anything collectible

• Abrasives: metal polish, toothpaste, baking soda paste, steel wool, wire brushes
• Acids: vinegar, lemon juice, soda, commercial dips
• Electrolysis: effective on iron relics and junk coins, but it strips surfaces and destroys collector value
• Tumbling: fine for clad, damaging for anything older
• Heat or ultrasonic cleaners: can damage surfaces and are not reversible

Folk remedies such as long soaks in oil are widely discussed in detecting circles. Results vary, and any chemical treatment is a risk on a coin that may be valuable.

Prevent damage before it happens: careful recovery

Much of the damage seen on detected coins happens during recovery, not cleaning. A digger blade that strikes a coin leaves a fresh, bright scratch that no cleaning method can hide, and prying a coin out of packed soil can scrape its high points. A few habits make a real difference:

• Cut your plug wide of the signal and lift the soil out in one piece rather than stabbing straight down at the target. Our guide on how to dig a plug shows the technique.
• Use a pinpointer to locate the coin in the hole or plug so you can lift it out by hand. A probe such as the UIG Pointer, which the manufacturer says uses two audio tones to separate precious from non-precious metals, keeps blades and fingernails off the coin.
• Do not knock dirt off coins against tools or rub them clean on your pants.
• Keep valuable-looking finds separate from clad and junk so they do not rub together in your pouch.

When to call a professional

If you find a coin that may be rare or valuable, consider leaving it as found and submitting it to a reputable grading service or consulting an experienced dealer or local coin club. Professional conservation services exist for removing harmful residues such as PVC film, but they cannot undo damage from harsh cleaning.

Storing cleaned coins

NGC warns that soft coin flips made with PVC plasticizer can leave a hazy film that later turns green and oily, and can permanently etch the coin. Use stiff, non-PVC flips, inert capsules or archival albums. Keep coins dry and away from wood cabinets, rubber bands and household chemicals. For a full guide to labeling, display and storage, see how to display, catalog and store your finds.

Frequently asked questions

Should I clean coins I find metal detecting?

Only lightly, and only after deciding whether the coin could be valuable. Rinse and soak in distilled water; avoid scrubbing, polishing and chemicals on anything collectible.

Does cleaning a coin reduce its value?

Usually, yes, for collectible coins. Grading services identify cleaned coins and often assign a Details grade, which typically sells for less than a comparable original coin.

What is the best way to clean old copper pennies?

Soak in distilled water, gently loosen dirt with a wooden toothpick and let them dry completely. Avoid acids and abrasives, which leave copper an unnatural color.

Can I use electrolysis on coins?

Electrolysis is used on iron relics and coins with no collector value. It strips surfaces, so it is not appropriate for coins that might be collectible.

How do I clean clad coins from the park?

Many detectorists use a rock tumbler with a suitable medium for modern clad coins. Keep older coins out of the tumbler.

Sources

• >NGC: Details Grading
• >NGC: The Dangers of PVC Residue
• >Canadian Conservation Institute: Storage of Metals