The 30-second version
Coins are valued in large part by their original surface. Wiping, polishing, dipping, or scrubbing a coin damages that surface in ways collectors and graders can see instantly — even when the coin looks “better” to the naked eye. A cleaned coin can be worth half or less of what the same coin would have brought untouched.
If you remember nothing else: don’t clean them, don’t let anyone else clean them, and don’t take them out of any holders they came in.
Why cleaning destroys value
What looks like “tarnish” on a silver coin is actually a thin layer of natural toning that built up over decades. To a collector, that toning is proof the coin is original — and it can even add to the value when it’s attractive.
Cleaning strips that layer and leaves micro-scratches called hairlines. Hairlines are visible under any decent loupe and through any grading service’s standard exam. Once a coin has been cleaned, professional graders (PCGS, NGC, ANACS) will either grade it down sharply or mark it “Cleaned” / “Details”, which can cut its market value by 30–70%.
“But my coin is dirty/black/green”
We hear this constantly — and the answer is still: leave it alone. What looks like dirt to you tells an expert how the coin was stored, when it was last circulated, and whether the surfaces are original. We’d much rather see a dark, original coin than a bright, polished one.
If something must be done — say there’s active corrosion on a copper coin — that’s a job for a professional conservator, not a kitchen sink. Call us first; in many cases we can advise without you doing anything at all.
What to do instead
- Handle coins by the edges only. Skin oils leave marks that can downgrade a high-grade coin.
- Leave them in whatever they’re in. Plastic flips, cardboard 2x2s, PCGS/NGC slabs, original mint packaging — all of it is fine and most of it adds value.
- Take photos under indirect light. A phone camera held a few inches above a coin on a plain background is plenty. Front, back, and any close-ups of dates or mintmarks you notice.
- Get a professional appraisal before deciding anything. We do this for free, with no obligation.
What if a coin was already cleaned?
Don’t panic. Cleaned coins still have value — sometimes substantial value, especially for rare or older pieces. Bring it (or photos of it) along with the rest of the collection and we’ll tell you what it’s worth as-is. Whatever you do, don’t try to “fix” previous cleaning; that only adds another layer of damage.
Want a fair, expert opinion on your coins?
Send a few photos and a working numismatist will tell you what the collection is worth — including any coins that may already have been cleaned. Free, no obligation.