Why You Shouldn't Clean Old Coins

When you find a tarnished old coin, the natural urge is to make it shine. With coins, that is almost always a mistake. This guide explains why cleaning lowers value, how buyers can tell, and the few safe things you can do instead.

Cleaning removes part of the coin

A coin's surface is not just paint over metal. When a coin is struck, the dies leave microscopic flow lines in the metal that create the original shine collectors call luster. Over time, the surface also develops a natural layer of toning or patina.

Polishes, abrasive pastes, baking soda, toothpaste, steel wool, wire brushes and even rubbing with a cloth wear away that surface. Chemical dips strip it. Either way, the original surface is gone for good and cannot be restored.

Collectors pay for original surfaces

Coin collectors value originality. A coin with honest, even toning and undisturbed luster is far more desirable than one that has been made bright. Many collectors will pass on a cleaned coin entirely, and others will buy it only at a reduced price.

Professional grading services generally will not assign a straight numeric grade to a coin that shows evidence of harsh cleaning. Instead, they label it with a "details" designation that notes the cleaning, and these coins typically sell for noticeably less than problem-free coins of the same type.

How buyers spot a cleaned coin

Experienced dealers recognize cleaning quickly, often at a glance. Signs include:

• Hairline scratches running in the same direction across the fields, visible when the coin is tilted under light.
• An unnatural, too-bright or flat, dull appearance with no cartwheel luster.
• Color that doesn't match the coin's age, such as a bright pink century-old copper cent.
• Leftover toning or grime in the recessed areas around letters and devices, while the rest is bright.
• Unusual surfaces that look washed out, porous or slick.

Trying to hide cleaning by artificially re-toning a coin makes things worse. Experienced buyers look for that too.

Toning is not damage

Many people think toning means a coin is dirty. On silver coins especially, natural toning can range from light gold to deep blue, purple and rainbow shades. Attractive original toning can actually add to a coin's appeal and value. Even plain, darker toning is a sign of an original surface. Leave it alone.

What about coins that are truly dirty?

Coins dug from the ground, found in old jars, or stuck with grime are a different situation. Even so, take the gentlest approach and stop early.

• Do not rub or scrub. Rubbing causes most of the damage.
• For loose surface dirt on ordinary, low-value coins, a soak in plain distilled water, followed by patting dry with a soft cotton cloth, is the mildest option.
• Don't use household cleaners, vinegar, lemon juice, ketchup, metal polish or ultrasonic machines.
• For anything that might be valuable, don't do anything at all. Ask a coin dealer about professional conservation services, which use controlled methods to remove harmful residues without stripping the original surface.

Green PVC residue from old soft plastic flips and active corrosion can harm a coin over time. These are cases for professional advice, not home remedies.

Bullion is a partial exception

Common bullion coins and worn "junk silver" coins traded for their metal content are valued mostly by weight, so cleaning them matters less for value. Even so, there is no benefit to cleaning them, and you risk damaging a coin that turns out to have collector value. The safe habit is simply not to clean coins.

If someone already cleaned your coins

Many inherited collections include coins cleaned years ago. Don't try to fix them. Store them safely and describe them honestly when you sell. Cleaned coins still have buyers; they just bring less than original examples.

Quick checklist

• Never polish, scrub or dip a coin you might sell.
• Treat natural toning as part of the coin.
• Handle coins by the edges and store them in safe holders.
• Use only a plain distilled water soak on low-value dirty coins, if anything.
• Ask a dealer about professional conservation for valuable or damaged coins.
• Disclose past cleaning honestly when selling.