coin guide

The Best Way to Clean Coins

The best way to clean coins is usually not to clean them. The U.S. Mint warns that polishing or cleaning can reduce a coin's value, and neither PCGS nor NGC will put a numeric grade on a coin that shows an improper cleaning. When a coin is only dirty and has no collector value, the safest method is a wash in distilled water with a little mild soap, no rubbing, then a rinse and drying without wiping.

Why Cleaning Lowers What a Collector Pays

A collector pays for the surface the mint put on the coin, and the PCGS glossary defines a cleaned coin as one that has lost it. Asked whether collectors should clean their coins, the American Numismatic Association (ANA) answers "NO!" A coin generally loses some of its value after a cleaning, the ANA says, and most experienced numismatists spot one fairly easily.

Dark color isn't dirt. Toning develops naturally on virtually all metals, NGC says, and can be "quite attractive and desirable." The Canadian Conservation Institute's note on coin care reports that many numismatists believe coins should never be cleaned and prize toned silver in particular.

Decide by what the coin trades for, not by how dirty it is. A piece that trades for its metal, such as a worn 90% silver dime or other common silver coins bought by weight, loses nothing a buyer pays for in a wash. A coin that trades for its condition does: Kevin Wang, writing for the ANA's Reading Room, reports that improperly cleaned coins often lose value, "sometimes by more than half."

What Each Cleaning Method Does to the Metal

Every method except a plain wash removes metal or moves it.

Polishes and Abrasive Cleaners

The Canadian Conservation Institute's silver guidance says polishes "leave behind a pattern of fine scratches" as they take silver off with the tarnish, and its coin note adds that most metal cleaners contain abrasives. Apply that test to any household recipe: if it's gritty, it scratches.

Vinegar and Other Kitchen Acids

Acid makes copper shine by eating it. In the U.S. Mint's Coin Classroom penny experiment, vinegar and salt brighten a penny because the reaction "dissolves the copper oxide" and "some of the copper on the outside of the penny." Pennies left an hour on a paper towel soaked in vinegar alone grow a blue-green layer as the copper oxidizes.

Commercial Coin Dips

Commercial coin cleaners are dips, chemical tarnish removers with no abrasive, and the PCGS glossary describes a dip as "a mild acid wash that removes the toning from most coins." It adds that the first few layers of metal come off with every dip. Repeat it and the luster goes, which PCGS calls "overdipped."

On whether to use one, PCGS and the Canadian Conservation Institute disagree. In PCGS grading, dipping doesn't count as cleaning unless someone has done it "repeatedly or improperly." The Canadian Conservation Institute says dips shouldn't go on coins, because acid left by insufficient rinsing degrades the surface. In practice a dip suits common silver that trades for its metal, rinsed off completely, and has no place on a collectible, proof or certified coin.

What a Grading Service Counts as Cleaning

It takes far less than most owners expect: PCGS interprets cleaning as surface damage from any form of abrasive cleaning, and its range runs from "a grossly polished coin" to one where faint hairlines show only at a particular angle. A single wipe qualifies. Hairlines in an isolated area get NGC's WIPED label, "usually the result of accidental mishandling," and the coin still loses its numeric grade.

To check a coin yourself, tilt it under one light and look for hairlines in the fields, the flat areas around the design, then for the mismatch the ANA calls "bright but worn." In Wang's ANA article, the flat, unnatural shine he labels "that weird look" comes from disrupted flow lines of mint luster or an over-smoothed surface. On a WHIZZED coin, NGC adds, the wire brush leaves lettering "distorted a bit."

What the Holder Label Says

Every holder from PCGS or NGC carries the verdict. On the Sheldon scale of 1 to 70 that NGC uses, an improperly cleaned coin can't receive a number at all. It gets a Details grade from NGC with a description such as POLISHED, BURNISHED, WHIZZED, WIPED or IMPROPERLY CLEANED, the generic term when the exact method is uncertain. NGC adds that a Details coin's value "is never determined by its grade alone": the severity and location of the problem count as much.

In place of a grade, PCGS prints a numbered No Grade code. In the PCGS list of No Grade codes, 92 means Cleaning, 91 Questionable Color, 94 Altered Surfaces, 95 Scratches, 97 Environmental Damage and 98 Damage. Read the label before the price on any PCGS or NGC graded coins you're considering.

The Safe Wash, Step by Step

These steps follow the Canadian Conservation Institute's coin procedure, with the U.S. Mint's rule for holding a coin placed first:

1. Hold the coin by its edges over a soft towel.
2. Wash it in lukewarm distilled water with diluted mild soap. No scrubbing, and no powdered dishwasher detergent.
3. Rinse it in fresh distilled water.
4. In a well-ventilated space, soak the coin in pure acetone to degrease it and drive off the water. The U.S. Mint and the ANA leave this step out.
5. Let it air dry on a paper towel, or pat it dry with a soft towel as the U.S. Mint advises. Don't wipe it.

A wash removes surface dirt and the oils, salts and acids left by handling, and the Canadian Conservation Institute says it "does not affect any underlying patina." Removing corrosion belongs to a conservator. The ANA is stricter than the U.S. Mint: it limits even this wash to a coin "so corroded that it is unrecognizable" and sends anything more to a professional service.

PVC Residue, the One Contaminant Worth Removing

PVC residue isn't toning, and leaving it alone is the mistake. Soft vinyl flips release a plasticizer, and PCGS describes PVC damage as a film, "usually green," that may be clear and sticky at first. The Canadian Conservation Institute calls the plasticizer particularly corrosive to copper-alloy coins, and says silver coins with a high copper content can show the same "green slime."

PVC slowly leaches onto a coin, NGC warns, and will "eventually result in permanent damage" unless someone safely removes it. PCGS generally won't put a coin with PVC residue in a holder at all. Move every coin out of soft flips and into coin holders made of an inert plastic, which the Canadian Conservation Institute lists as polyethylene, polypropylene, polyester film, polystyrene and acrylic.

What Professional Conservation Can and Can't Fix

Conservation takes residue off a coin without abrading it. For residue from PVC holders, glue or dip chemicals, NGC Conservation says safe removal is often possible, and PCGS Restoration is a paid service for what PCGS calls "environmental problems." The textbook case in Wang's article is the SS Central America shipwreck: its coins came up encrusted with limestone and ocean debris, and conservators worked by "meticulously softening the debris and slowly removing it."

Conservation can't undo a cleaning, though. Per NGC, amateur cleaning has permanently altered many coins, "leaving fine scratches and other surface issues" that NGC Conservation can't fix.

Why Many Inherited Coins Are Already Cleaned

An old collection has often had one cleaning already. Writing for the ANA's Reading Room, collector Larry House recalls that in the 1950s and 1960s collectors treated cleaning as "standard practice," and that attitudes began to change in the 1970s as grading took hold.

Cleaning them again won't undo the earlier job. In House's view a cleaned scarce coin remains collectible, while common coins labeled Details "do not offer much unless they are silver coins with inherent value."

Dates to Check Before You Clean Anything

Check the date and mint mark, the small letter such as D for Denver that shows where a coin was struck, before any coin goes in water. For the 1916 Mercury dime, PCGS CoinFacts lists 264,000 struck at Denver against 22,180,080 at Philadelphia. For the 1932 Washington quarter it lists 436,800 at Denver and 408,000 at San Francisco, against 5,404,000 at Philadelphia. One letter separates a scarce coin from a common one, and a scarce coin shouldn't get a home wash.

Handling and Storage That Prevent the Need to Clean

Good handling removes most reasons to clean. The U.S. Mint's care guidance has you hold a coin by its edges with soft cotton gloves on, since skin oils can be corrosive. For storage, the Canadian Conservation Institute advises keeping relative humidity "as low as possible," ideally below 30%.

Our Catalog and the Sources Behind This Guide

We're a member of the American Numismatic Association and an authorized dealer for PCGS and NGC, the two services whose labels this guide describes, and our catalog carries coin holders and cleaners alongside the coins. We checked every method here against the published guidance of the U.S. Mint, the ANA, PCGS, NGC and the Canadian Conservation Institute.

Frequently Asked Questions

What is the best cleaner for dirty coins?

Distilled water with a little mild soap, the cleaner the U.S. Mint, the ANA and the Canadian Conservation Institute all describe. It removes dirt and nothing else. Commercial coin cleaners are dips, which by the PCGS definition take off toning and a few layers of metal, so they aren't a stronger kind of soap.

Is it better to clean old coins or not?

It's better not to. The U.S. Mint says older coins with "deep age coloration" are more desirable than coins with surfaces "stripped away by improper polishing or cleaning." The ANA's one exception is a coin too corroded to identify.

How to clean gold dollar coins?

Golden dollars, which began with the Sacagawea dollar in 2000, contain no gold. The ANA explains that the coin has outer layers of copper and nickel over a core of pure copper, with manganese added for the golden hue. One from circulation can take the same mild soap wash as pocket change. Leave an uncirculated or proof one in its original case or capsule.