How to Clean Coins Found Metal Detecting: Complete Guide

The moment you dig up an old coin, you face a critical decision: to clean or not to clean? The wrong choice can turn a $1,000 coin into a $10 slug. The right approach preserves value while revealing enough detail to identify and enjoy your find.

This guide covers when to clean dug coins, when to leave them alone, and the safest methods for each situation.

The Golden Rule: When in Doubt, Don’t Clean

Collectors and dealers universally agree: An original, uncleaned coin is worth more than a cleaned one. Cleaning removes the natural patina (surface coloring) that develops over time. To experienced eyes, a cleaned coin looks “wrong”—and brings a lower price.

Never Clean These Coins

• Key dates: 1909-S VDB, 1916-D Mercury dime, 1916 Standing Liberty, etc.
• Coins in excellent condition: If details are sharp, leave it alone
• Gold coins: Never clean gold—bring to a professional
• Silver coins with natural toning: Rainbow toning adds value
• Any coin you might sell: Let the buyer decide on cleaning
• Ancient or colonial coins: Consult an expert first

When Cleaning Makes Sense

Some coins are okay to clean for personal enjoyment:

• Common date wheat pennies: Worth $0.05-0.25 anyway
• Modern clad coins: No collector value
• Badly corroded coins: Already damaged beyond repair
• Coins you’re keeping in a personal collection: Your call
• Coins you need to read the date: Just to identify

Safe Cleaning Methods

Method 1: Distilled Water Rinse (Safest)

Best for: All coins, initial cleaning

1. Fill container with distilled water (not tap—minerals can stain)
2. Soak coin for 5-10 minutes
3. Gently rub with fingers underwater to remove loose dirt
4. Pat dry with soft cloth—don’t rub
5. Allow to air dry completely

Pros: Can’t damage the coin
Cons: Only removes loose dirt

Method 2: Olive Oil Soak (Copper/Bronze)

Best for: Copper and bronze coins with encrustation

1. Place coins in container of pure olive oil
2. Soak for days to weeks (patience required)
3. Check periodically and gently wipe with cotton
4. When dirt softens, gently remove with wooden toothpick
5. Rinse in distilled water, pat dry

Pros: Very gentle, won’t damage patina
Cons: Takes weeks or months; may not remove heavy encrustation

Method 3: Baking Soda Paste (Copper Pennies)

Best for: Common copper pennies you want to shine

1. Make paste of baking soda and water
2. Apply with soft cloth or fingers
3. Gently rub in circular motion
4. Rinse thoroughly with distilled water
5. Pat dry immediately

Pros: Removes grime effectively
Cons: Mildly abrasive; will affect patina

Method 4: Electrolysis (Advanced)

Best for: Heavily encrusted iron relics; last resort for coins

Electrolysis uses electrical current to remove corrosion. It’s effective but risky for valuable coins.

Basic Setup:

• 12V power supply (old phone charger works)
• Container with water and washing soda solution
• Graphite or carbon anode (NOT stainless steel—creates toxic chromates)
• Clips to connect coin (negative) and anode (positive)

Warning: Electrolysis strips patina completely. Only use on coins already damaged beyond value. Produces hydrogen gas—work in ventilated area away from flames.

Methods to AVOID

Never Use These on Coins

• Wire brushes or abrasives: Create scratches visible under magnification
• Baking soda on silver: Too abrasive for silver coins
• Vinegar: Acid damages coin surfaces
• Lemon juice: Acid etches metal
• Commercial coin cleaners: Most are too harsh
• Tumbling: Creates unnatural shine, damages surfaces
• Scrubbing with toothbrush: Even soft bristles scratch

Cleaning by Metal Type

Copper Coins (Pennies, Large Cents)

Silver Coins

Gold Coins

Preserving Cleaned Coins

After Cleaning

• Dry completely: Moisture causes new corrosion
• Handle by edges: Oils from fingers cause spots
• Store properly: 2×2 cardboard flips, non-PVC holders
• Keep dry: Use silica gel packets in storage

Long-Term Storage

• Avoid PVC: Damages coins over time (green slime)
• Use archival-quality holders: Mylar flips, SAFLIP holders
• Control humidity: Store with desiccants
• Don’t stack loose: Coins scratch each other

When to Seek Professional Help

Consider professional conservation if:

• The coin might be worth over $100
• It’s a key date or rare variety
• You’re unsure what you have
• Heavy encrustation covers important details
• You plan to sell or have graded

Professional services like NCS (Numismatic Conservation Services) can safely conserve coins without destroying value.

Final Thoughts

The best cleaning is often no cleaning at all. A coin with original patina, even if dirty, tells a story. Once cleaned, that history is gone forever.

For common coins you’re keeping for fun? Clean away—they’re yours to enjoy. But for anything potentially valuable, resist the urge. That crusty old coin might be worth more than you think.

What’s your preferred cleaning method? Share your tips in the comments!