Many people believe cleaning old coins restores their shine. In reality, it is one of the biggest mistakes a collector can make. Polishing or cleaning coins damages the metal and can reduce collector value by 50 to 90%.
In this article, the experts at Schulman b.v. explain why you should never clean coins, how it affects their value, and how to store them safely.
Why is cleaning coins harmful?
Every coin carries a thin oxidation layer known as its patina. This natural surface toning reveals information about the coin's age, metal composition and the conditions in which it has been preserved.
On silver and gold coins, patina serves as evidence of authenticity. Removing this layer erases part of the coin's history and its market value. In international numismatics, "uncleaned" is considered a hallmark of authenticity. A polished coin immediately loses its grading value.
Want to know what your coins are worth in their current condition? Read more about how the value of old coins is determined.
What happens when you polish a coin?
Polishing agents, silver cloths and brushes create microscopic scratches on the surface. Even a soft cloth can damage the original structure.
Under normal light a polished coin may look shinier, but during a professional appraisal or auction, polishing marks (hairlines) are immediately recognised. The value often drops by 50 to 90 percent.
In Amsterdam and across European auction houses, the rule is clear: polished means downgraded. During professional grading by PCGS or NGC, polished coins are automatically placed in a lower category, regardless of how sharp the details may still be.
Why chemical cleaning is even worse
Many household products contain acids or solvents that attack the metal. On silver or copper coins, the surface can literally be etched away.
On gold coins, chemical treatment often causes colour differences or dull patches. A coin that has been treated with chemicals is regarded by appraisers as impaired, even when the damage is barely visible to the naked eye.
Common products to avoid:
- Silver polish and copper polish
- Vinegar, lemon juice or cola
- Ultrasonic cleaners (without professional supervision)
- Abrasives, toothpaste or steel wool
How to recognise a cleaned coin
Experienced numismatists recognise a cleaned coin by:
- An unnaturally bright or blotchy surface lacking the soft depth of original patina
- Fine polishing scratches (hairlines) around the portrait or coat of arms, visible under angled light
- Discolouration in the recessed areas where remnants of the original patina remain
- A flat, lifeless lustre that differs from the natural mint lustre of an original coin
Even subtly polished coins betray their treatment. During appraisals at Schulman, such traces are always documented in the report.
How to store coins safely without cleaning them
There is an important distinction between cleaning and conserving. You can protect coins safely without altering their original condition:
- Never handle coins with bare hands. Use cotton gloves or hold the coin carefully by the edge. Skin oils cause spots over time that cannot be removed.
- Store them in acid-free holders, slabs or capsules. Avoid PVC holders; these release harmful substances that cause a green, oily residue.
- Avoid moisture and temperature fluctuations. A dry, cool environment with a constant temperature is ideal.
- Keep silver and bronze separate. Sulphur compounds that tarnish silver can spread through the air to other coins.
- Leave restoration to a certified conservator. If you suspect bronze disease or active corrosion, professional intervention is essential.
What if you have found or inherited coins?
Have you found coins with a metal detector or inherited a collection? The temptation to "clean them up" before having them appraised can be strong. Do not do this.
Dirt, soil deposits and dark toning are often valuable as context. An experienced numismatist can assess a coin far more accurately in its unaltered state. Get in touch for a free, no-obligation initial assessment.
What makes original patina so valuable?
The appeal of a coin lies not in its shine, but in its authenticity. Dark toning or discolouration is not a flaw; it is evidence of age.
Collectors and auction houses value coins with original toning significantly higher. An untouched coin with patina can be worth thousands of euros more than a polished equivalent. This applies to old coins from every period, from Roman bronzes to provincial dukatons.
Conclusion
Polishing coins destroys historical value and authenticity. Leave your coins as they are and rely on expert appraisal and conservation. This way, you preserve not only their value but also their story.
Would you like to know what your coins are worth in their current condition? Schedule an appointment for a free, no-obligation appraisal at Schulman in Amsterdam.
