Verdigris and PVC: Saving Your Coins from Environmental Damage — A Numismatic Conservator’s Guide

Improper storage is the silent enemy of numismatics. Let’s identify the signs of environmental damage specific to this metal type.

As a numismatic conservator with years of experience examining, grading, and preserving coins across every metal type and era, I can tell you that the single most preventable cause of value loss in our hobby is environmental damage. Whether you’re holding a circulated 1913-S Type 1 Buffalo Nickel or a pristine High Relief Saint-Gaudens Double Eagle, the enemies are the same: moisture, airborne pollutants, improper plastics, and neglect. In this guide, I’ll walk you through the specific threats — bronze disease, PVC plasticizer damage, oxidation — and the proper chemical conservation techniques, including acetone dips, that every collector should understand before storing or submitting a single coin.

Why Environmental Damage Matters More Than You Think

When collectors discuss coin value, the conversation almost always centers on grade, rarity, mint marks, and eye appeal. But there’s a silent factor that can destroy all of those attributes overnight: the environment in which a coin is stored. I’ve examined thousands of coins that arrived at my conservation bench with problems that were entirely preventable — green crusty deposits on ancient bronze pieces, hazy iridescent films on silver dollars pulled from old cardboard albums, and deep, ugly corrosion on copper-nickel alloys that were stored in the wrong flip.

The original forum thread that inspired this article began with a collector named Jim struggling to photograph his 1913-S Type 1 Buffalo Nickel. He noted that the coin looked beautiful in hand but that he could only capture its true color by angling his cell phone camera. That discussion about angled photography — and the various techniques collectors use, from Phil Arnold’s pioneering PCGS TrueView methods to axial lighting setups using suspended glass panes — is fascinating in its own right. But what struck me most was the underlying reality: many of the coins we photograph, display, and trade are simultaneously suffering from environmental degradation that no amount of clever lighting can reverse.

Let’s talk about what’s actually happening to your coins when they’re sitting in your collection, and what you can do about it.

Bronze Disease: The Collector’s Nightmare

If you collect ancient coins, Roman provincials, or any bronze or bronze-alloy pieces, you need to know about bronze disease. I cannot stress this enough. Bronze disease is not a metaphor — it is an active, ongoing chemical reaction that will destroy a coin if left untreated.

What Causes Bronze Disease?

Bronze disease is caused by the interaction of chloride ions with copper in the presence of moisture and oxygen. The chlorides may be present from the moment the coin was buried — absorbed from soil or seawater over centuries — or they can be introduced through handling (salt from human sweat is a common culprit). Once activated by humidity, the reaction produces copper chloride hydrates that manifest as bright green, powdery or crusty spots on the coin’s surface.

Here’s what makes bronze disease so insidious:

• It is self-perpetuating. The chemical reaction produces hydrochloric acid as a byproduct, which attacks more copper, which produces more copper chloride, which reacts with more moisture. The cycle continues indefinitely.
• It is contagious. If an infected coin is stored in proximity to healthy coins — in the same drawer, album, or cabinet — the chloride-laden dust can spread to neighboring pieces.
• It can be invisible in early stages. Before the characteristic green spots appear, the coin may look perfectly fine. By the time you see the damage, the reaction may have been active for months or years.

Identifying Bronze Disease

In my experience grading and conserving ancient bronze coins, I look for these telltale signs:

1. Bright green spots or patches that are raised above the coin’s surface — these are not the same as stable, dark green patina. Bronze disease green is lighter, powdery, and often appears in clusters.
2. A rough or gritty texture when you gently touch the affected area (though I always recommend handling coins by the edges with cotton gloves).
3. Progressive worsening over time. If you photograph a coin and notice that green spots have grown or multiplied between photos taken months apart, you likely have active bronze disease.

Treating Bronze Disease

Treatment depends on severity. For mild cases, I recommend the following protocol:

1. Mechanical removal: Under magnification, use a wooden toothpick or fine bamboo skewer to gently remove the green powdery deposits. Do NOT use metal tools, as they will scratch the coin’s original surface.
2. Chemical treatment: Immerse the coin in a 5% sodium sesquicarbonate solution (available from conservation supply vendors) for several weeks, changing the solution periodically until chloride extraction is complete. You can test for residual chlorides by placing a small amount of the used solution in a drop of silver nitrate — if it turns cloudy, chlorides are still present.
3. Final rinse and drying: Rinse thoroughly in distilled water, then allow the coin to dry completely in a low-humidity environment.
4. Seal the surface: Apply a thin coat of Renaissance Wax or Incralac (a lacquer containing benzotriazole) to protect the coin from future moisture exposure.

For severe cases where the coin’s surface detail has already been compromised, professional conservation is strongly recommended. I’ve seen coins where bronze disease has eaten entirely through the flan — those pieces require expert intervention.

PVC Plasticizer Damage: The Silent Killer in Your Collection

While bronze disease primarily threatens ancient and bronze-alloy coins, PVC damage is the great equalizer — it can affect silver, gold, copper, and nickel coins alike. And it is shockingly common.

What Is PVC Damage?

Polyvinyl chloride (PVC) is a plastic that was widely used in coin flips, albums, and storage pages from the 1960s through the early 2000s. PVC is inherently unstable. Over time, it releases hydrochloric acid and plasticizer chemicals that migrate to the coin’s surface. The result is a greenish, hazy, or iridescent film that is often mistaken for toning but is actually chemical damage.

I’ve examined countless Morgan Dollars, Mercury Dimes, and Buffalo Nickels — including pieces similar to Jim’s 1913-S Type 1 — that arrived with telltale PVC damage. The film can range from a light haze that is barely visible to a thick, sticky green coating that obscures the coin’s design entirely.

How to Identify PVC Damage

Here’s what I look for when assessing a coin for PVC contamination:

• A greenish or bluish-green film that appears to sit on top of the coin’s surface rather than being integrated into the metal. Unlike natural toning, PVC film often has a slightly sticky or tacky feel.
• Iridescent or oily appearance when viewed at an angle — this is why angled photography, like the techniques discussed in the forum thread, can actually help reveal PVC damage. The film refracts light differently than natural toning.
• A vinegar-like or chemical odor when you open a flip or album page. PVC off-gasses hydrochloric acid, which has a sharp, acrid smell.
• Association with specific storage materials. If a coin was stored in a soft PVC flip (the flexible, slightly sticky type) or an older album with PVC pages, the likelihood of damage is very high.

Removing PVC Damage with Acetone

The good news is that mild to moderate PVC damage can often be removed with a simple acetone dip. Acetone is a solvent that dissolves PVC plasticizer residue without harming the coin’s metal surface — provided you use it correctly.

Here is the protocol I use in my conservation practice:

1. Use pure, reagent-grade acetone. Do NOT use nail polish remover, which contains oils, fragrances, and moisturizers that will leave their own residue on the coin. You can purchase 99%+ pure acetone from chemical supply companies or some hardware stores.
2. Work in a well-ventilated area. Acetone fumes are strong and flammable. I always work under a fume hood or outdoors.
3. Submerge the coin in a glass container of acetone. Use a glass jar or beaker — acetone will dissolve many plastics, so do not use a plastic container.
4. Soak for 30 seconds to several minutes, depending on the severity of the PVC film. Gently agitate the coin or use a soft cotton swab to help lift the residue. For heavy deposits, you may need to repeat the process with fresh acetone.
5. Remove the coin and allow it to air dry. Do NOT rinse with water. Acetone evaporates completely and leaves no residue.
6. Inspect under magnification. If PVC film remains, repeat the process. If the coin is clean, store it immediately in a PVC-free holder.

Critical warning: Acetone will strip artificial toning, remove applied color, and can damage coins that have been treated with lacquer or other coatings. It will also dissolve the adhesive in some slab holders. Always test on a less valuable coin first, and never use acetone on coins with active corrosion or bronze disease — it will not help and may accelerate the damage.

Oxidation and Tarnish: Understanding the Difference Between Damage and Patina

Not all surface changes on a coin are harmful. This is a distinction that confuses many collectors, and it’s one I address constantly in my work.

Natural Patina vs. Active Oxidation

Natural patina — the stable, often colorful layer of oxidation products that forms on a coin’s surface over decades or centuries — is generally considered desirable. On silver coins, it manifests as attractive toning in shades of gold, blue, purple, and magenta. On copper and bronze coins, it appears as a smooth, adherent brown or green layer that protects the underlying metal.

Active oxidation, by contrast, is ongoing chemical degradation. It is characterized by:

• Uneven or blotchy coloration that changes over time
• Powdery or flaky texture rather than a smooth, adherent surface
• Progressive darkening or discoloration that worsens despite stable storage conditions
• Presence of moisture or salt contamination — coins stored in coastal environments or handled without gloves are particularly susceptible

The Role of Humidity

Relative humidity is the single most important environmental factor in coin storage. I recommend maintaining a relative humidity level between 30% and 40% for long-term coin storage. Above 50% humidity, the risk of active oxidation, bronze disease activation, and PVC off-gassing increases dramatically. Above 65%, you are essentially creating a corrosion laboratory.

Invest in a good hygrometer for your storage area. I’ve seen entire collections — including key-date Buffalo Nickels, Mercury Dimes, and early silver dollars — degraded beyond recovery because they were stored in a basement or attic with uncontrolled humidity.

Proper Storage Materials: What to Use and What to Avoid

Based on my experience conserving coins from improper storage, here are my definitive recommendations:

Safe Storage Materials

• Mylar (polyethylene terephthalate) flips — These are the gold standard for individual coin storage. They are chemically inert and will not off-gas harmful chemicals.
• Archival-quality cardboard holders (2x2s) — Ensure they are labeled “PVC-free” and “archival quality.”
• PCGS, NGC, or ANACS certified slabs — Modern third-party grading holders use inert plastics and provide excellent long-term protection.
• Acetate or polypropylene albums — These are safe for long-term storage of raw coins.
• Desiccant packets — Place silica gel packets in your storage containers to absorb excess moisture. Replace or recharge them regularly.

Materials to Avoid

• Soft PVC flips — The flexible, slightly sticky flips that were standard for decades. If your coins are currently in these, transfer them to Mylar immediately.
• Rubber bands — Rubber contains sulfur, which will tarnish silver and copper coins. I’ve seen entire rolls of Morgan Dollars with sulfur band tans from being stored with rubber bands.
• Paper envelopes (non-archival) — Standard paper contains sulfur and acids that can cause spotting and discoloration.
• Cardboard albums with PVC pages — Many older albums, including some vintage Dansco products, used PVC-containing plastics. The forum thread mentioned using plastic slides from Dansco albums for photography — be aware that those same slides may be off-gassing PVC onto your coins.
• Airtight containers without humidity control — Sealing coins in an airtight container without desiccant can trap moisture and accelerate corrosion.

Chemical Conservation: When to DIY and When to Call a Professional

As a conservator, I’m often asked whether collectors should attempt chemical cleaning at home. My answer is nuanced.

Safe for Home Conservation

• Acetone dips for PVC removal — As described above, this is safe and effective when done correctly with pure acetone.
• Distilled water rinses — For removing surface dirt and debris, a gentle rinse in distilled water followed by thorough drying is safe for most coin types.
• Renaissance Wax application — A thin coat of this microcrystalline wax provides excellent protection for bronze and copper coins after cleaning.

Leave to the Professionals

• Bronze disease treatment — The sodium sesquicarbonate soak requires careful monitoring and testing. Improper treatment can leave residual chlorides that reactivate later.
• Heavy corrosion removal — Aggressive cleaning of heavily corroded coins can remove original surface and destroy value. Professional conservators have tools and techniques (including electrolytic reduction and micro-abrasive cleaning) that minimize damage.
• Coins with numismatic value above $500 — If you have a valuable coin that needs conservation, the risk of DIY damage far outweighs the cost of professional treatment. I’ve seen collectors destroy $2,000 coins trying to remove a spot that a conservator could have addressed in minutes.
• Any coin you plan to submit for grading — PCGS, NGC, and other grading services will downgrade or label coins that show evidence of improper cleaning. If in doubt, don’t clean it.

Connecting Photography to Conservation: What Angled Lighting Reveals

I want to return briefly to the photography discussion that sparked this article, because there’s an important connection between how we photograph coins and how we assess their environmental health.

Several forum members described using angled lighting techniques — positioning the camera and light source at angles to the coin’s surface — to reveal color and surface detail. This is more than a photography trick. When you angle light across a coin’s surface, you’re using raking light to reveal surface irregularities that are invisible under direct, perpendicular illumination.

This technique can actually help identify early-stage environmental damage:

• PVC film becomes more visible under angled light because the plasticizer residue creates a slightly raised, uneven surface that catches the light differently than the surrounding metal.
• Bronze disease spots are often easier to detect under raking light, which highlights the raised, powdery texture of active corrosion.
• Scratches, tooling marks, and other surface disturbances — which can be entry points for environmental damage — are dramatically more visible under angled illumination.

So the next time you’re photographing your collection using the angled techniques that Jim, Leo, FlyingAl, and others described in the forum thread, take a moment to examine what the lighting is telling you about your coin’s surface health. That beautiful color you’re capturing might be natural toning — or it might be the early stages of PVC damage or active oxidation.

Actionable Takeaways for Buyers and Sellers

Whether you’re buying, selling, or simply maintaining your collection, here are the key action items I recommend:

1. Audit your storage materials today. Go through your collection and identify any coins stored in soft PVC flips, non-archival albums, or rubber-banded rolls. Transfer them to PVC-free Mylar flips or archival cardboard holders immediately.
2. Invest in a hygrometer and desiccant. Monitor the humidity in your storage area and keep it between 30% and 40% relative humidity.
3. Inspect your coins regularly. Use angled lighting — even a simple desk lamp held at a low angle — to examine your coins for early signs of bronze disease, PVC damage, or active oxidation. Early detection is the key to successful conservation.
4. Keep pure acetone on hand. For collectors of raw coins, a small bottle of reagent-grade acetone is an inexpensive insurance policy against PVC damage. Use it to clean any coin that shows signs of PVC film before the damage becomes permanent.
5. Handle coins properly. Always hold coins by the edges, wear cotton gloves when handling valuable pieces, and never touch the obverse or reverse surfaces. The oils and salts from your skin are a primary source of chloride contamination that can trigger bronze disease and accelerate oxidation.
6. Know when to call a professional. If you have a coin with suspected bronze disease, heavy corrosion, or significant numismatic value that needs conservation, seek out a professional numismatic conservator. The American Institute for Conservation (AIC) maintains a directory of qualified professionals.

Conclusion: Protecting the Legacy in Your Collection

The 1913-S Type 1 Buffalo Nickel that Jim was photographing in the forum thread is a wonderful coin — a key date in one of America’s most beloved series, with a mintage of just 1.2 million pieces. Coins like that, and the countless other pieces in our collections, are not just metal. They are historical artifacts, works of art, and tangible connections to the past. They deserve to be preserved with the same care and respect that we give to any other irreplaceable object.

Environmental damage — whether it’s bronze disease eating through an ancient Roman bronze, PVC film clouding a Morgan Dollar’s luster, or uncontrolled humidity tarnishing a Mercury Dime — is the most common and most preventable threat to our collections. The good news is that with proper storage materials, controlled humidity, regular inspection, and basic chemical conservation techniques like acetone dips, you can protect your coins for generations to come.

As a conservator, I’ve seen the heartbreak of a collector discovering that a coin they’ve owned for decades has been silently destroyed by improper storage. I’ve also seen the joy of successfully treating a coin that was thought to be beyond saving. The difference almost always comes down to knowledge and vigilance.

Take the time to learn the signs of environmental damage. Invest in proper storage. And remember: the best conservation is prevention. Your coins — and the collectors who will inherit them — will thank you.

Related Resources

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