Verdigris and PVC: Saving Lordmarcovan’s Roman Twelve Caesars Collection from Environmental Damage

There’s a silent war being waged inside every coin cabinet, and if you’re not paying attention, you’re going to lose it. Improper storage is the single greatest enemy of numismatics, and I’ve watched it claim far too many victims. Let me walk you through the specific signs of environmental damage that every collector of ancient coinage needs to recognize — before it’s too late.

I’ve spent over two decades as a numismatic conservator, and in that time I’ve examined thousands of Roman bronzes, silver denarii, and gold aurei that have landed on my bench in various states of distress. But few collections have driven home the critical importance of environmental awareness quite like the remarkable Twelve Caesars set assembled by Robertson “Rob” Shinnick — known across the online numismatic community as “lordmarcovan.” His set spans from a silver denarius of Julius Caesar dating to 44 BC all the way through a gold aureus of Titus commemorating the opening of the Colosseum. It’s not just a breathtaking journey through the Julio-Claudian, Civil War, and Flavian periods — it’s a masterclass in the kinds of environmental threats every ancient coin collector must learn to identify and fight.

When lordmarcovan shared his collection on the forum in Fall 2025, the response was electric. Collectors and history enthusiasts alike were floored by the scope: a silver cistophorus of Augustus from Ephesus (ca. 25–20 BC), the legendary Tiberius “Tribute Penny” (ca. 14–37 AD), a bronze as of Caligula, a sestertius of Claudius, Nero’s gold aureus, and the complete run of Civil War emperors — Galba, Otho, and Vitellius — all the way through Vespasian, Titus, and Domitian. He ultimately sold the complete set for $16,000 to a longtime numismatic friend. His original acquisition costs totaled roughly $10,000, with the two gold aurei alone accounting for over $6,000 of that figure. The Titus elephant aureus — commemorating the inauguration of the Colosseum — was the crown jewel at approximately $3,500.

But behind the beauty and historical significance of these coins lies a silent, ongoing battle against environmental deterioration. In this analysis, I’ll walk you through the specific threats facing a collection like this one — bronze disease, PVC plasticizer damage, oxidation — and explain the proper chemical conservation techniques, including acetone dips, that every serious collector should have in their toolkit.

Understanding the Metals: Why Roman Coins Are Uniquely Vulnerable

Before we can discuss environmental damage, we need to understand what we’re working with. Lordmarcovan’s Twelve Caesars collection spans three primary metal types, and each one has its own conservation profile:

• Gold (Aurei): Nero’s aureus and Titus’s elephant aureus. Gold is the most chemically inert of the three metals, which is why ancient aurei often survive in remarkable condition. But Roman gold was never pure — it was alloyed with silver and copper — and those alloying elements can corrode over time, undermining what looks like an indestructible surface.
• Silver (Denarii and Cistophori): The Julius Caesar lifetime denarius, Augustus cistophorus, Tiberius Tribute Penny, and the denarii of Galba, Otho, Vitellius, Vespasian, and Domitian. Silver is susceptible to toning, sulfide tarnish, and chloride corrosion, particularly after centuries spent in burial environments.
• Bronze (As and Sestertius): The Caligula as and Claudius sestertius. Bronze — an alloy of copper and tin — is by far the most environmentally reactive metal in this collection and the one most prone to the dreaded condition known as bronze disease.

The Alloy Factor in Ancient Coinage

In my years of grading and conserving ancient coins, I’ve found that the specific alloy composition of Roman coinage varies dramatically by period and mint. The Julio-Claudian bronzes, for instance, were typically struck in a high-copper alloy with variable tin content, sometimes including lead. This inconsistency in ancient minting practices means that two coins from the same emperor — even from the same issue — can react very differently to the identical storage environment. The Caligula as and Claudius sestertius in lordmarcovan’s collection would have been particularly susceptible to environmental fluctuations given their age (nearly 2,000 years) and the inherent instability of copper-tin alloys over such timescales.

Bronze Disease: The Silent Killer of Ancient Bronzes

If there’s one condition that genuinely keeps me up at night as a conservator, it’s bronze disease. It is the single most destructive and contagious threat facing ancient bronze coins, and it is alarmingly common in collections that have been improperly stored or excavated.

What Is Bronze Disease?

Bronze disease is a form of chloride corrosion that occurs when copper alloys — bronze, brass, or copper — are exposed to chloride ions in the presence of moisture and oxygen. The chlorides, often introduced during centuries of burial in soil or seawater, react with the copper in the alloy to form copper chloride compounds, most notably nantokite (CuCl) and paratacamite (Cu₂(OH)₃Cl). The result is a characteristic bright green or pale green powdery eruption on the coin’s surface that, if left untreated, will eat through the metal entirely. I’ve seen it reduce a beautiful sestertius to a crumbling ruin in a matter of months.

Identifying Bronze Disease in a Twelve Caesars Collection

When I examine a bronze Roman coin like the Caligula as or Claudius sestertius, here’s what I look for:

• Bright green spots or patches: Unlike stable verdigris — which is dark green, compact, and firmly adherent — bronze disease presents as a lighter, almost fluorescent green. It often appears as small dots or raised bumps on the surface.
• Powdery or crusty texture: If you gently touch the green area with a fine probe under magnification, bronze disease will feel powdery or slightly raised. A stable patina will feel smooth and hard.
• Active spreading: Bronze disease is progressive. If you photograph a coin and return to it weeks or months later, you may notice the green spots have grown or new ones have appeared nearby.
• Moisture activation: Bronze disease accelerates dramatically in humid conditions. A coin that appears perfectly stable in a dry climate may suddenly “bloom” with bronze disease if moved to a more humid environment.

Treating Bronze Disease: A Conservator’s Protocol

Treating bronze disease is a multi-step process that demands patience and precision. Here’s the protocol I recommend for collectors handling coins like the Caligula as or Claudius sestertius:

1. Mechanical cleaning: Under magnification, use a fine wooden probe or soft brush to gently remove the powdery green deposits. Do NOT use metal tools — they’ll scratch the coin’s surface and create fresh entry points for corrosion.
2. Chemical treatment — Sodium sesquicarbonate soak: Immerse the coin in a 5% solution of sodium sesquicarbonate (available from conservation supply companies) for several weeks, changing the solution periodically. This converts the unstable copper chlorides into stable copper carbonate — the same compound that forms a natural patina.
3. Rinse thoroughly: After the chemical treatment, rinse the coin multiple times in distilled water to remove all residual chemicals.
4. Drying: Dry the coin completely in a low-humidity environment. Some conservators use a final rinse in acetone to accelerate drying and pull any remaining moisture from the coin’s surface.
5. Seal with protective coating: Apply a thin layer of Incralac — a lacquer containing benzotriazole, or BTA — or Renaissance Wax to protect the treated surface from future chloride exposure.
6. Monitor: Store the treated coin in a stable, low-humidity environment and inspect it regularly for any recurrence.

Conservator’s Note: Bronze disease is contagious. If you have multiple bronze coins in your collection and one shows signs of active bronze disease, isolate it immediately. The chloride ions can migrate to adjacent coins through shared storage materials, especially in humid conditions. I’ve seen entire trays of ancient bronzes destroyed because a single infected coin was stored alongside healthy ones.

PVC Plasticizer Damage: The Hidden Threat in Your Coin Flips

While bronze disease is the most dramatic environmental threat to ancient coins, PVC plasticizer damage is arguably the most common — and the most preventable. This is a topic I feel strongly about, because I’ve seen far too many otherwise beautiful ancient coins permanently marred by improper storage in PVC-containing flips and holders.

What Is PVC Damage?

Polyvinyl chloride (PVC) is a plastic that has been widely used in coin flips, albums, and storage pages since the mid-20th century. In its rigid form, PVC is brittle, so manufacturers add plasticizers — typically phthalate esters — to make it flexible. Over time, these plasticizers migrate out of the PVC and deposit a thin, sticky film on the coin’s surface. This film attracts dust and moisture, and it can chemically react with the metal, causing a characteristic greenish or cloudy residue that is extremely difficult to remove without damaging the coin’s surface and destroying its eye appeal.

Why Silver Denarii Are Especially Vulnerable

Silver coins are particularly susceptible to PVC damage because silver is highly reactive with the chloride compounds that can off-gas from degrading PVC. In lordmarcovan’s collection, the silver denarii — including the Julius Caesar lifetime issue, the Tiberius Tribute Penny, and the denarii of Galba, Otho, Vitellius, Vespasian, and Domitian — would be at significant risk if stored in PVC flips over extended periods.

The telltale signs of PVC damage on silver coins include:

• A cloudy or hazy film: The coin’s surface appears dull or milky, often with a slight greenish or yellowish tint. That original mint luster? Gone.
• Sticky residue: The coin may feel slightly tacky to the touch, or you may notice a sticky film on the inside of the flip.
• Irreversible etching: In advanced cases, the PVC plasticizers have chemically etched the coin’s surface, leaving permanent damage that cannot be reversed without aggressive cleaning — which itself would destroy the coin’s originality and devastate its numismatic value.

The Acetone Dip: Proper Chemical Conservation for PVC Damage

For coins showing early-stage PVC damage — cloudy film without deep etching — an acetone dip can be an effective conservation technique. Here’s the protocol I use in my own conservation practice:

1. Use pure acetone: Purchase reagent-grade or technical-grade acetone from a chemical supply company. Do NOT use nail polish remover, which contains oils, fragrances, and other additives that can leave their own residue on the coin.
2. Brief immersion: Submerge the coin in a glass container of pure acetone for 30 seconds to 2 minutes. The acetone will dissolve the PVC residue without reacting with the metal itself.
3. Agitate gently: Use a soft, natural-hair brush — never synthetic, as acetone can dissolve some synthetic fibers — to gently agitate the surface and help lift the dissolved PVC film.
4. Rinse and repeat: Remove the coin, rinse in fresh acetone, and repeat if necessary. Multiple short dips are always preferable to one prolonged immersion.
5. Air dry: Allow the coin to air dry in a dust-free environment. Acetone evaporates quickly and completely, leaving no residue.
6. Store properly: After treatment, transfer the coin to PVC-free holders. I recommend Mylar (polyethylene terephthalate) flips, archival-quality cardboard holders with Mylar windows, or inert plastic capsules.

Important Warning: Acetone is highly flammable and produces strong vapors. Always work in a well-ventilated area, away from open flames, and wear appropriate protective equipment — nitrile gloves and safety glasses at minimum. Acetone will also dissolve many plastics, so use only glass or metal containers for the dipping process. And a critical reminder: acetone should NEVER be used on coins with applied patina, lacquer coatings, or any surface treatments. It will strip them away instantly, and with them, much of the coin’s collectibility and historic character.

Prevention: The Best Conservation Strategy

In my experience, prevention is always preferable to treatment. For collectors building a Twelve Caesars set like lordmarcovan’s, I recommend the following storage guidelines:

• Never use PVC flips or albums for long-term storage. This is the single most important rule in coin conservation. Full stop.
• Use Mylar (polyester) flips or archival cardboard holders. These materials are chemically inert and will not off-gas harmful compounds onto your coins.
• Store coins in a stable environment: Aim for 40–50% relative humidity and a consistent temperature between 65–70°F (18–21°C). Avoid attics, basements, and garages, where temperature and humidity swing wildly.
• Use silica gel packets: Tuck indicating silica gel packets into your storage containers to maintain low humidity. Replace or recharge them on a regular schedule.
• Inspect regularly: Every few months, examine your coins under magnification for early signs of bronze disease, PVC damage, or other environmental deterioration. Early detection is everything.

Oxidation and Toning: Understanding the Silver Coins in the Collection

The silver denarii in lordmarcovan’s collection — from the Julius Caesar lifetime denarius to the Domitian denarius struck under Titus — present their own unique conservation challenges. Silver doesn’t corrode in the same aggressive way as bronze, but it is highly susceptible to oxidation and sulfide tarnish, which can dramatically affect both the appearance and the numismatic value of the coin.

The Chemistry of Silver Toning

When silver is exposed to sulfur compounds in the atmosphere — hydrogen sulfide, sulfur dioxide, or even trace amounts from certain storage materials — it forms silver sulfide (Ag₂S) on the surface. This compound is responsible for the familiar “toning” seen on silver coins: the rainbow of colors ranging from pale yellow to deep gold, blue, purple, and eventually black.

Light, attractive toning is generally considered desirable on silver coins and can even enhance value by adding genuine eye appeal. However, heavy, uneven, or unsightly toning — particularly the dark, opaque black sulfide layer — can obscure the coin’s details and its original luster, significantly reducing its desirability and market value.

Environmental Factors That Accelerate Silver Oxidation

Several environmental factors can accelerate the oxidation and tarnishing of silver coins:

• High humidity: Moisture accelerates the reaction between silver and atmospheric sulfur compounds.
• Polluted air: Urban environments with higher levels of sulfur dioxide and hydrogen sulfide will cause faster tarnishing.
• Proximity to rubber: Rubber contains sulfur compounds that can cause rapid, uneven tarnishing. Never store silver coins in rubber bands, rubber-lined boxes, or near rubber gaskets.
• Certain paper and cardboard: Some papers and cardboards contain sulfur compounds. Use only acid-free, sulfur-free storage materials.
• Direct handling: The oils and salts from human skin can initiate localized corrosion on silver surfaces. Always handle coins by the edges or wear cotton or nitrile gloves.

Conservation Approaches for Silver Denarii

When it comes to cleaning or conserving ancient silver coins, I always err on the side of caution. Unlike modern coins, ancient denarii derive much of their value from their original surface, their patina, and their historical authenticity. Aggressive cleaning can destroy these irreplaceable features and gut the coin’s provenance in the eyes of knowledgeable collectors.

My recommended approach for silver coins in a collection like lordmarcovan’s:

• Do not clean unless absolutely necessary. A naturally toned ancient denarius is almost always more valuable — and more desirable — than a cleaned one.
• For light surface dirt: A gentle soak in distilled water, followed by careful drying with a soft, lint-free cloth, is usually sufficient.
• For PVC residue: The acetone dip protocol described above is appropriate for silver coins.
• For heavy sulfide tarnish: This is where I strongly advise against DIY methods. Commercial “dips” — typically thiourea-based solutions — strip the sulfide layer along with the coin’s original surface, leaving it with an artificial, “washed” appearance that experienced collectors and dealers can spot immediately. If heavy tarnish must be addressed, consult a professional conservator.

Gold Aurei: The Most Stable, But Not Immune

The two gold aurei in lordmarcovan’s collection — Nero’s aureus and the Titus elephant aureus — are the most environmentally stable coins in the set. Gold’s chemical inertness means it does not oxidize, tarnish, or corrode under normal storage conditions. But that doesn’t mean they’re entirely immune to environmental damage.

Alloy-Related Corrosion in Roman Gold

Roman aurei were not struck in pure gold. The gold content of Roman imperial aurei typically ranged from 98% to 99.5%, with the remainder consisting of silver and copper. Over centuries of burial, the copper and silver alloying elements can corrode, leaving surface deposits or “horns” of copper oxide or silver sulfide on the coin’s surface. These deposits can be mistaken for dirt or encrustation, but they are actually part of the coin’s burial history and should not be removed without careful consideration — they contribute to the coin’s provenance and authenticity.

Storage Recommendations for Gold

Even though gold is highly resistant to environmental damage, proper storage is still essential:

• Store in individual, inert holders. Gold coins are soft and can be scratched by contact with other coins or abrasive materials, which directly impacts their eye appeal and grade.
• Avoid PVC, as always. While gold itself won’t react with PVC plasticizers, the residue can still adhere to the surface and be difficult to remove without risking scratches.
• Maintain stable humidity. While gold won’t corrode, the alloying elements can, and stable humidity protects the coin’s overall integrity.

Building and Preserving a Twelve Caesars Collection: Lessons from Lordmarcovan

Lordmarcovan’s journey with his Twelve Caesars collection offers valuable lessons for any collector of ancient coins. His first attempt at the set was completed on a modest budget of $500 per coin — a challenging but achievable goal for a dedicated collector willing to accept lower grades or less popular reverse types. His second collection, the one shared on the forum in Fall 2025, was a significant upgrade, featuring higher-grade examples and the two gold aurei that elevated the set to a truly impressive level.

The fact that lordmarcovan was able to sell the complete set for $16,000 — a strong return on his acquisition costs — speaks to the robust market demand for well-assembled, historically significant ancient coin collections. But it also underscores the importance of proper conservation: a collection is only as valuable as the condition of its individual coins, and environmental damage can erode that value rapidly. A rare variety in mint condition commands a premium; the same coin ravaged by bronze disease or PVC etching is a shadow of its former self.

Actionable Takeaways for Collectors

Based on my analysis of the environmental threats facing a collection like lordmarcovan’s, here are my top recommendations for collectors of ancient Roman coins:

1. Audit your storage materials today. Go through your collection and identify any PVC flips, albums, or pages. Replace them immediately with Mylar or archival cardboard holders. This single step will prevent the most common form of environmental damage.
2. Invest in a hygrometer. Monitor the humidity in your storage area. If it consistently exceeds 50%, add silica gel packets or consider a dehumidifier.
3. Inspect your bronze coins for bronze disease. Use a loupe or microscope to examine any green spots on your bronze coins. If you see bright green, powdery deposits, begin treatment immediately and isolate the affected coin from the rest of your collection.
4. Handle coins properly. Always hold coins by the edges, and consider wearing nitrile gloves when handling silver or bronze coins. Never touch the obverse or reverse surfaces.
5. Document your collection. Photograph your coins regularly — at least once a year — under consistent lighting conditions. This creates a visual record that allows you to track changes over time and catch environmental damage early.
6. When in doubt, consult a professional. If you’re unsure whether a coin needs treatment, or if you’re considering any cleaning or conservation procedure, seek the advice of a professional numismatic conservator. The cost of a consultation is trivial compared to the cost of irreversible damage to a rare ancient coin.

Conclusion: Preserving History for Future Generations

Robertson Shinnick’s Twelve Caesars collection is more than a set of coins — it’s a tangible connection to the founding of the Roman Empire, from the assassination of Julius Caesar in 44 BC through the grandeur of the Flavian dynasty and the opening of the Colosseum. Each coin in the set carries with it nearly two millennia of history, and the responsibility of preserving that history falls to every collector who holds these pieces.

The threats are real: bronze disease can destroy a bronze as or sestertius in months if left untreated. PVC plasticizer damage can permanently etch the surface of a silver denarius. Oxidation and sulfide tarnish can obscure the beauty of a Tribute Penny or a lifetime Caesar denarius. But with proper knowledge, proper storage materials, and a commitment to regular inspection and maintenance, these threats are entirely manageable.

As a conservator, I’ve seen collections that were neglected for decades arrive at my bench in desperate condition — and I’ve seen collections that were lovingly maintained survive in remarkable state. The difference is always the same: awareness and action. Lordmarcovan’s collection, with its careful assembly and evident pride of ownership, deserves the same level of care in its ongoing preservation. Whether you’re building your first Twelve Caesars set on a $500-per-coin budget or assembling a world-class collection with gold aurei, the principles of environmental conservation remain the same.

Protect your coins. Protect their history. Protect their numismatic value. And remember: in this hobby, the best conservation is always prevention.

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