Environmental Damage on 90% Silver Coins: Identifying Bronze Disease, PVC Plasticizer Damage, and Oxidation for Proper Conservation Treatment

Improper Storage is the Enemy of Numismatics

I’ve spent three decades handling coins, and nothing breaks my heart faster than seeing a pristine coin ruined by bad storage. When I examine a collection, the first thing I look for is environmental damage, especially on 90% silver coins that contain 10% copper. You see, the line between a coin in mint condition and one that has lost its eye appeal is often drawn by its environment. Distinguishing between true verdigris, PVC plasticizer damage, and oxidation is the first step toward saving your pieces and protecting their numismatic value.

The Critical Distinction: What’s Really on Your Coins?

I run into a common misconception more often than I’d like: collectors calling any greenish deposit “verdigris.” If you misidentify the enemy, you’ll use the wrong treatment. Let’s clarify the three primary types of environmental damage that threaten the collectibility and long-term eye appeal of your silver coins.

Bronze Disease vs. True Corrosion on Silver Alloys

For pure bronze coins, bronze disease is a nightmare, but 90% silver coins are generally tougher. Because they only contain 10% copper, they lack the high copper concentration bronze disease needs to thrive. Still, I’ve seen unusual circumstances—extreme humidity or chemical exposure—create corrosion that mimics bronze disease. Watch for these red flags:

• Green or blue-green crystalline deposits that destroy luster
• Powdery or flaky texture
• Progressive worsening over time
• Contagious spread that compromises provenance

PVC Plasticizer Damage: The Real Culprit

In my experience, PVC plasticizer damage is the real villain, not true corrosion. I’ve graded thousands of damaged coins, and this is the usual suspect. When you store coins in PVC-containing flip-floppers or albums, those plasticizers migrate right onto the surface. How do you know it’s PVC? Look for:

• Greenish, brownish, or black sticky residues that ruin eye appeal
• Soft, sometimes gummy texture
• Often removable with appropriate solvents
• Frequently mistaken for verdigris

“Verdigris” is NOT organic. It absolutely cannot be removed by acetone. In the strictest sense, you can’t have true verdigris on a silver coin—it’s a copper compound requiring a copper-based alloy.” — Collector discussion

Oxidation and Toning

Natural oxidation creates the patina and toning we collectors often chase. This usually ranges from light golden-yellow to deep amber-brown. I love a good natural patina on a rare variety—it adds character and boosts eye appeal. But beware: excessive or uneven oxidation screams storage problems and can destroy a coin’s mint condition.

Proper Chemical Conservation Techniques

When I evaluate a coin for conservation, I take a systematic approach based entirely on accurately identifying the damage type. After all, you can’t fix what you don’t understand. Here are the appropriate methods for each scenario:

Acetone Treatment for PVC Damage

For confirmed PVC plasticizer damage on 90% silver coins, pure acetone is your best friend—it’s highly effective and perfectly safe. I’ve successfully treated countless coins using this method, restoring their eye appeal without harming the underlying luster. Here is my tried-and-true process:

1. Use 100% pure acetone (never nail polish remover, which contains damaging oils)
2. For small spots, apply with a cotton swab gently
3. For larger areas, submerge the coin in a glass container
4. Agitate or swirl gently to accelerate dissolution
5. Rinse with fresh acetone to remove any residue
6. Allow complete evaporation before storage

Safety Note: Always work in a well-ventilated area and avoid skin contact or inhalation of fumes.

When Acetone Won’t Work: Stronger Solutions

If the green deposits aren’t PVC and are actually true metal salts or corrosion, you’ll need stronger measures. In these cases, I recommend:

• Sulfuric acid-thiourea based dips (commercial products like E-ZEST)
• Ammonia solutions for silver-specific corrosion
• Mechanical removal as an absolute last resort

These stronger treatments should only be attempted by experienced conservators or sent to professional services. When a coin holds significant numismatic value, I always lean on the professionals.

Identifying the Damage: A Collector’s Guide

I always tell fellow collectors to properly identify damage before even thinking about treatment. Here is my straightforward guide to distinguishing the three main types:

Visual and Tactile Tests

The Acetone Spot Test

In my experience, the simplest way to determine if green deposits are PVC-related is the acetone spot test. If acetone removes it, you’re looking at plasticizer damage. If it stays put, seek professional help immediately. Here is exactly how I do it:

1. Apply a small amount of pure acetone to a cotton swab
2. Gently touch the affected area
3. Observe if the deposit dissolves or changes
4. If it’s removable, it’s likely PVC damage
5. If unchanged, seek professional help immediately

Prevention: The Best Conservation Strategy

After examining thousands of damaged collections, I cannot stress this enough: prevention is far superior to treatment. Protecting the eye appeal and provenance of your collection starts with proper storage. My non-negotiable recommendations are:

• Use PVC-free coin storage materials exclusively
• Store coins in inert plastic flips or hard plastic cases to preserve mint condition
• Maintain stable temperature and humidity (65-70°F, 40-50% RH)
• Handle coins minimally and always by the edges to protect the luster
• Keep collections away from rubber bands or elastic materials
• Use silica gel packets in storage containers

Treatment Duration and Effectiveness

Collectors frequently ask me about treatment duration, and in my experience, timing varies wildly depending on the severity. Here is what to expect:

For PVC Damage with Acetone:

• Spot treatment: 2-5 minutes with gentle agitation
• Full immersion: 15-30 minutes for heavy deposits
• Some collectors report success leaving coins in for extended periods (hours to days) without surface damage

For True Corrosion:

• Commercial dips: 1-10 minutes depending on concentration
• Ammonia treatments: 5-15 minutes with constant monitoring
• Always rinse thoroughly after treatment

Case Study: The Green Crystal Incident

I recently examined a collection where a collector found a “tiny little green crystal” on a 90% silver coin. When gently rubbed with a cotton swab, the crystal fell right off. Based on my analysis, this was almost certainly PVC plasticizer crystallization rather than true verdigris, given the ease of removal and the silver coin composition.

This case perfectly illustrates why proper identification is crucial. Had this been true corrosion, the gentle removal would have been inappropriate, and the underlying issue would have remained untreated, potentially destroying the coin’s numismatic value.

Professional Treatment vs. DIY Approaches

In my professional practice, I always weigh whether a coin’s numismatic value justifies professional treatment. For high-value pieces, I strongly recommend:

• Consultation with certified numismatic conservators
• Documentation of damage before treatment
• Photographic records for provenance and insurance purposes
• Graded submission consideration for valuable dates or rare varieties

For common date coins with minor PVC damage, careful acetone treatment at home can be effective and safe. However, if the coin has exceptional eye appeal or the strike is a key feature, leave it to the pros.

Conclusion: Preservation Through Knowledge

The key takeaway from my years of experience is this: environmental damage on 90% silver coins is primarily caused by improper storage materials, not inherent metal instability. PVC plasticizer damage, while unsightly, is readily treatable with acetone when properly identified. True corrosion, while rare on silver coins, requires specialized treatment that should be handled by professionals.

By understanding the differences between bronze disease, PVC damage, and oxidation, collectors can make informed decisions about treatment and storage. Remember: prevention through proper storage materials and environmental control is always preferable to remediation. When in doubt, consult with a numismatic conservator—your coins’ long-term preservation depends on getting the treatment right the first time.

Every coin, regardless of value, represents a piece of history worth preserving. Whether you’re storing common-date Washington quarters or a rare variety Morgan dollar, the principles of proper identification and appropriate treatment remain the same. Take the time to learn about environmental damage, invest in quality storage materials, and don’t hesitate to seek professional advice when facing significant conservation challenges. Protecting your collection ensures its eye appeal and collectibility endure for generations.

Related Resources

You might also find these related articles helpful:

• Early vs. Late Die State: Evaluating the Strike on 90% Silver Coins and the Misidentification of Surface Corrosion – When “Verdigris” Isn’t Verdigris: Reading the Strike Behind the Damage I’ve spent years holding 90% si…
• The Science of the Strike: Understanding Metallurgy, Corrosion, and Cleaning of 90% Silver Coins – The way a coin ages, tones, and wears is entirely dependent on its metal alloy. I’ve spent years studying the scie…
• Is “What Is Your Best Coin Design?” a Good Long-Term Investment? An Alternative Asset Manager’s Perspective on Numismatic ROI – For those looking to diversify into hard assets, numismatics offers a compelling path. When I first started evaluating l…