Verdigris and PVC: Saving WWI Victory and Participation Medals from Environmental Damage

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 who has spent decades handling bronze, copper, and gilt medals — including some of the most historically significant World War I Victory and Participation Medals in private and institutional hands — I can tell you that the single greatest threat to these pieces is not time itself, but the environment in which they’ve been stored. The forum discussion surrounding WWI Victory and Participation Medals, from the common looped issues to the extraordinarily rare HK-902a struck in 22-karat gold, reveals a collecting community deeply passionate about these artifacts. But passion alone cannot protect a medal from bronze disease, PVC plasticizer damage, or the slow, insidious creep of oxidation. In this analysis, I’ll walk you through the specific environmental threats facing these medals, how to identify damage in its earliest stages, and — most importantly — what you can do to preserve these irreplaceable pieces of history for future generations.

Understanding the Metal: Why WWI Medals Are Uniquely Vulnerable

Before we can discuss environmental damage, we need to understand what these medals are actually made of. The vast majority of WWI Victory and Participation Medals — including the iconic HK-892 and HK-903 so-called dollars, the French HK-903A “Victory of Right”, and the standard-issue U.S. Victory Medal with its distinctive loop and ribbon suspension — were struck in bronze or bronze alloys. Bronze is an alloy primarily composed of copper with varying amounts of tin, and sometimes zinc, lead, or other trace metals. The specific composition varies by issuing country and manufacturer, but the copper content is what makes these medals so susceptible to environmental degradation.

Copper-based alloys are inherently reactive. When exposed to moisture, chlorides, acids, or certain plastics, bronze undergoes chemical changes that can range from a harmless patina to catastrophic structural failure. The heavy cast bronze plaques discussed in the forum — such as the spectacular 15-by-22-inch embossed plaque showing all aspects of U.S. participation in the war, or the 8-inch square high-relief plaque copyrighted in 1918 by R.W. Bock — are particularly vulnerable due to their sheer mass and surface area. More metal means more material available to react with environmental contaminants.

The HK-900a and the various die varieties of the so-called dollars (including the 1917-dated HK-892 with its multiple reverse die states and the unlisted 1918-dated varieties with their distinct obverse and reverse die differences) all share this fundamental vulnerability. Even the rare gold-struck HK-902a, while far more chemically inert than its bronze counterparts, is not immune to environmental threats — particularly if it is a gold-plated or low-karat gold piece rather than high-purity 22-karat.

Bronze Disease: The Silent Killer of WWI Medals

If I had to name the single most destructive environmental threat to bronze WWI medals, it would be bronze disease without hesitation. I’ve examined hundreds of WWI-era bronze pieces over the course of my career, and I can tell you that bronze disease is far more common in this category than most collectors realize. The reason is simple: these medals are over 100 years old, and many of them have spent decades — sometimes the entirety of those 100+ years — in environments that actively promote this condition.

What Is Bronze Disease?

Bronze disease is a form of corrosion caused by the interaction of copper chloride compounds with moisture and oxygen. It manifests as bright green, powdery or crusty spots on the surface of the medal. Unlike a stable patina, which is a thin, adherent layer of oxidation that actually protects the underlying metal, bronze disease is progressive and self-sustaining. The chemical reaction that causes it produces hydrochloric acid as a byproduct, which in turn attacks more copper, creating more copper chloride, which reacts with more moisture — and the cycle continues until the medal is literally eaten away from the inside out.

How to Identify Bronze Disease on WWI Medals

In my experience grading and conserving WWI medals, I look for the following telltale signs:

• Bright green spots or patches that are raised above the surrounding surface — these are often mistaken for ordinary verdigris but have a distinctly powdery or fuzzy texture
• Clusters of small green dots, particularly in recessed areas of the design where moisture tends to collect — on WWI medals, this often occurs in the lettering, around the allegorical figures, and near the rim where the loop attaches
• A “wet” or damp appearance to the green areas, even in dry conditions — this is because the copper chloride compounds are hygroscopic, meaning they actively absorb moisture from the air
• Flaking or pitting beneath the green spots, indicating that the corrosion has penetrated below the surface

The looped WWI Victory Medals are especially prone to bronze disease at the loop-to-medal junction, where the loop was soldered or integrally cast to the medal body. This junction creates a crevice where moisture and chlorides can become trapped. If you’re examining a looped specimen — like the one described in the forum as having been “proudly worn by a WW1 veteran” — pay particular attention to this area.

Treating Bronze Disease

Treatment depends on the severity of the infection. For early-stage bronze disease, I recommend the following approach:

1. Mechanical removal of the visible corrosion products using a wooden or bamboo pick under magnification. Never use metal tools, as they will scratch the surface and create new sites for corrosion.
2. Chemical treatment with a 5% solution of sodium sesquicarbonate (not sodium bicarbonate — they are different compounds). Immerse the medal in this solution, changing it regularly until no more chloride ions are detected. This can take weeks or even months for severe cases.
3. Thorough rinsing in distilled water after chemical treatment to remove all residual chemicals.
4. Application of a protective barrier coating, such as Incralac (a lacquer containing benzotriazole, or BTA, which acts as a corrosion inhibitor specifically for copper alloys).

For the heavy bronze plaques — like the R.W. Bock piece or the large embossed U.S. participation plaque — treatment is more challenging due to the size and weight of the objects. In these cases, I often recommend localized treatment using poultices of sodium sesquicarbonate applied directly to affected areas, rather than full immersion.

PVC Plasticizer Damage: The Hidden Threat in Your Collection

While bronze disease is the most dramatic form of environmental damage, PVC (polyvinyl chloride) plasticizer damage is arguably the most common — and the most preventable. This is a topic I feel strongly about, because I have seen far too many otherwise beautiful WWI medals permanently damaged by improper storage in PVC-containing holders.

How PVC Damages Bronze Medals

PVC is a widely used plastic that is inherently unstable. To make it flexible, manufacturers add plasticizers — chemical compounds (often phthalates) that can migrate out of the plastic over time. When a bronze medal is stored in a PVC flip, holder, or album page, these migrating plasticizers come into contact with the medal’s surface and create a sticky, greenish or brownish film that is extremely difficult to remove. This film is not merely cosmetic — it can etch into the metal surface if left in place for extended periods, causing permanent damage to the medal’s detail and finish.

Identifying PVC Damage

Signs of PVC plasticizer damage include:

• A sticky or tacky film on the medal’s surface that cannot be wiped away with a dry cloth
• Greenish or brownish discoloration that appears to be on the surface rather than in the metal itself
• A distinctive acrid or chemical odor when the medal is removed from its holder — this is the smell of the plasticizers off-gassing
• Surface etching visible under magnification, where the plasticizer film has chemically attacked the metal

I cannot stress this enough: never store your WWI medals in PVC flips or holders. This includes the older-style soft plastic flips that were commonly used by collectors in the 1970s, 1980s, and even 1990s. If you’ve recently acquired a medal that was stored in PVC, inspect it carefully for the signs listed above.

Removing PVC Residue: The Acetone Dip

Here is where the acetone dip comes into play — one of the most valuable tools in a numismatic conservator’s arsenal. Acetone (CH₃COCH₃) is a powerful organic solvent that dissolves PVC plasticizer residue without attacking copper or bronze. The procedure is straightforward:

1. Use pure, reagent-grade acetone — not nail polish remover, which contains oils, fragrances, and other additives that can leave their own residue on the medal.
2. Immerse the medal in acetone for no more than 30 seconds to one minute. Prolonged immersion is unnecessary and can potentially affect any original patina or surface treatments.
3. Remove the medal and gently wipe with a soft, lint-free cloth to dissolve and remove the PVC residue.
4. Repeat if necessary for heavy contamination.
5. Allow the medal to air-dry completely in a well-ventilated area — acetone evaporates quickly and leaves no residue of its own.

Important caveat: Acetone will strip away any wax, lacquer, or other coatings on the medal’s surface. If the medal has an original finish or patina that you wish to preserve, test the acetone on a small, inconspicuous area first. For medals that have already been slabbed by a third-party grader like NGC — such as the Top Pop HK-903 and HK-903A specimens mentioned in the forum — do not attempt this treatment, as it could affect the holder or the medal’s certified grade.

Oxidation and Tarnish: Understanding the Spectrum of Surface Changes

Not all surface changes on a WWI medal are cause for alarm. In fact, some degree of oxidation is normal, expected, and even desirable on a medal that is over a century old. The key is understanding the difference between beneficial patina and harmful oxidation.

Beneficial Patina vs. Harmful Oxidation

A patina is a thin, stable layer of oxidation products that forms on the surface of bronze over time. On WWI medals, this typically appears as a rich brown, chocolate, or olive tone that enhances the detail of the design by creating contrast between the raised and recessed areas. Many collectors — myself included — consider a well-developed original patina to be one of the most attractive features of an older bronze medal. It adds character, depth, and eye appeal that no artificial treatment can replicate.

Harmful oxidation, on the other hand, is characterized by:

• Thick, uneven layers of corrosion that obscure design details
• Flaking or spalling of the surface layer, exposing fresh metal beneath to further attack
• Black or very dark brown crusts that are often associated with sulfur compounds (from exposure to rubber, wool, or certain types of cardboard)
• Active corrosion that continues to progress even in stable storage conditions

The forum discussion about the difference in color between looped and unlooped versions of the WWI Victory Medal — with looped versions described as “beige-er bronze” and unlooped versions as “much redder copper color” — is a perfect example of how storage conditions and environmental exposure can affect the appearance of otherwise identical medals. The redder color of the unlooped versions may indicate a different surface treatment at the time of manufacture, or it may simply reflect different environmental exposure histories over the past century. Either way, understanding these distinctions helps us assess provenance and authenticity.

Environmental Factors That Accelerate Oxidation

The following environmental factors are the primary drivers of harmful oxidation on WWI bronze medals:

• High humidity (above 60% relative humidity) — moisture is the single most important factor in bronze corrosion
• Chloride exposure — from salt air (if stored near the ocean), handling with bare hands (sweat contains sodium chloride), or proximity to certain building materials
• Sulfur compounds — from rubber bands, wool felt, certain types of cardboard and paper, and air pollution
• Acidic environments — from wooden storage cabinets (especially oak and other acidic woods), certain adhesives, and some types of display materials
• Temperature fluctuations — which cause condensation to form on the medal’s surface, providing the moisture needed for corrosion reactions

Proper Storage and Conservation: A Practical Guide

Now that we’ve identified the threats, let’s talk about solutions. Proper storage and conservation of WWI Victory and Participation Medals is not complicated, but it does require attention to detail and a willingness to invest in the right materials.

Storage Materials

The following materials are safe for long-term storage of bronze WWI medals:

• Mylar (polyethylene terephthalate) flips — these are chemically inert and will not off-gas harmful compounds
• Polyethylene or polypropylene holders — also chemically inert and widely available
• Acid-free, lignin-free tissue paper — for wrapping medals that are not in individual holders
• Archival-quality boxes and albums — made from acid-free materials with no PVC, rubber, or sulfur-containing components

The following materials should never be used for storing bronze medals:

• PVC flips, holders, or album pages
• Rubber bands or rubber-based adhesives
• Cardboard or paper that is not acid-free and lignin-free
• Wooden cabinets or drawers (unless they are sealed with an archival barrier coating)
• Wool or untreated cotton felt

Environmental Controls

Ideal storage conditions for WWI bronze medals are:

• Relative humidity: 40–50% (use silica gel packets or a dehumidifier to maintain this range)
• Temperature: 65–70°F (18–21°C), with minimal fluctuation
• Light: Store in darkness or low light; UV radiation can accelerate certain types of surface degradation
• Air quality: Avoid areas with high levels of air pollution, cigarette smoke, or chemical fumes

For the larger bronze plaques — like the 15-by-22-inch U.S. participation plaque or the 8-inch R.W. Bock plaque — environmental control is even more critical due to the greater surface area exposed to the environment. I recommend displaying these pieces in sealed display cases with controlled humidity, or at minimum, keeping them in a climate-controlled room with stable temperature and humidity.

Handling Best Practices

Even the best storage conditions can be undermined by improper handling. When handling WWI bronze medals, always:

• Wear clean, lint-free cotton or nitrile gloves — never handle bronze medals with bare hands
• Hold the medal by the edges only, avoiding contact with the obverse and reverse surfaces
• Handle medals over a soft, padded surface to minimize damage in case of a drop
• Never clean a medal unless you are certain of what you are doing — improper cleaning is one of the most common causes of damage to collectible medals

Special Considerations for Rare and High-Value Specimens

The forum discussion highlights several exceptionally rare and high-value WWI medals that warrant special conservation attention. The HK-902a struck in 22-karat gold, previously owned by Steve Tanenbaum and now certified by NGC, represents a fundamentally different conservation challenge than its bronze counterparts. Gold is highly resistant to corrosion, but the high copper content in 22-karat gold (approximately 8.3%) means that it can still develop surface discoloration and tarnish over time. For gold specimens, I recommend:

• Storage in individual, soft, acid-free tissue wraps inside archival-quality boxes
• Avoidance of any chemical cleaning — even acetone can affect the surface of gold alloys if used improperly
• Regular inspection under magnification for any signs of copper migration to the surface (which can appear as reddish or dark spots)

The NGC-slabbed Top Pop specimens — including the HK-903 and HK-903A — present their own conservation considerations. While the slab provides excellent physical protection, it is not a substitute for proper environmental control. Slabbed medals should still be stored in stable temperature and humidity conditions, and the slab itself should be inspected periodically for any signs of deterioration or off-gassing from the holder material.

For the looped medals with original ribbons — like the WWI Victory Medal described as having been “proudly worn by a WW1 veteran” — the ribbon itself is often more fragile than the medal. Silk and cotton ribbons from this era are susceptible to foxing (brown spots caused by fungal growth), fading from light exposure, and fiber degradation from acidic environments. I recommend storing looped medals with ribbons in acid-free tissue wraps with the ribbon carefully folded to minimize stress on the fibers. If the ribbon is already severely deteriorated, consult a textile conservator before attempting any treatment.

Die Varieties and Surface Detail: Why Conservation Matters for Attribution

One aspect of WWI medal conservation that is often overlooked is the relationship between surface preservation and die variety attribution. The forum discussion includes detailed observations about die varieties of HK-892, including differences in the reverse die (flagpole tips, flagpole extension through the word “TRUST”), obverse die differences (contours of the ground beneath the kneeling soldier), and the distinction between 1917-dated and 1918-dated varieties. These subtle differences are critical for proper attribution and can significantly affect a medal’s numismatic value, collectibility, and historical significance.

Environmental damage — particularly bronze disease and heavy oxidation — can obscure or destroy the fine surface details needed to distinguish between die varieties. A medal with advanced bronze disease may lose the very features that make it a rare and desirable variety. This is yet another reason why proactive conservation is so important: preserving the surface detail preserves the medal’s identity and historical value.

The 1918-dated varieties mentioned in the forum — which are “not even mentioned in any so-called dollar references” — are a perfect example. If these rare varieties are allowed to deteriorate due to environmental damage, the numismatic community loses not only the physical medal but also the opportunity to study and document these previously unlisted varieties. Every rare variety that slips into irreversible corrosion is a piece of the historical record that can never be recovered.

Actionable Takeaways for Buyers and Sellers

Whether you are buying, selling, or simply preserving WWI Victory and Participation Medals, here are the key actionable takeaways from this analysis:

1. Inspect every medal for bronze disease before adding it to your collection. Look for bright green, powdery spots — especially in recessed areas and at the loop junction on looped specimens.
2. Remove any medals from PVC holders immediately and clean PVC residue with a pure acetone dip if necessary.
3. Store medals in archival-quality, PVC-free materials in a stable environment (40–50% RH, 65–70°F, low light).
4. Handle medals with gloves and hold them by the edges only.
5. Never clean a medal aggressively — if in doubt, consult a professional numismatic conservator.
6. Pay special attention to looped medals with ribbons, as the ribbon is often more fragile than the medal itself.
7. Document die varieties carefully before any conservation treatment, as surface cleaning can sometimes alter the appearance of fine details.
8. For high-value or rare specimens (such as the HK-902a gold strike or unlisted die varieties), consider professional conservation assessment before undertaking any treatment.

Conclusion: Preserving the Legacy of the Great War

The WWI Victory and Participation Medals discussed in this forum thread — from the common looped issues to the extraordinarily rare gold strikes, from the standard HK-892 and HK-903 so-called dollars to the unlisted 1918 varieties and the magnificent bronze plaques — represent far more than collectible objects. They are tangible connections to one of the most consequential events in human history. The story of Grace Banker, the Hello Girls operator who was denied her Victory Medal for over a century, reminds us that these medals carry the weight of individual sacrifice and national memory. The image of Samuel Woodfill wearing his Medal of Honor and Victory Medal — the most outstanding soldier of World War I, as General Pershing called him — reminds us that these were not merely tokens but symbols of extraordinary courage.

As collectors, historians, and conservators, we have a responsibility to ensure that these artifacts survive in the best possible condition for future generations. Environmental damage — whether from bronze disease, PVC plasticizer contamination, or uncontrolled oxidation — is a threat that can be mitigated through proper storage, handling, and conservation practices. The techniques I’ve outlined in this article — from acetone dips for PVC removal to sodium sesquicarbonate treatment for bronze disease — are proven, effective methods that can save a medal from irreversible damage.

The variety and richness of the WWI medallic record is extraordinary. From the die varieties of HK-892 to the heavy cast bronze plaques of R.W. Bock, from the rare unlooped Victory Medals to the spectacular gold HK-902a, there is always something new to discover, document, and preserve. But discovery and documentation mean nothing if the physical objects are allowed to deteriorate. Conservation is not optional — it is an essential part of responsible collecting.

I encourage every collector reading this to take a moment today to examine your WWI medals. Look for the signs of environmental damage I’ve described. Check your storage materials for PVC. Assess your storage environment for humidity and temperature stability. And if you find problems, take action now — because the longer environmental damage is allowed to progress, the harder it becomes to reverse, and the more of our shared numismatic heritage we risk losing forever.

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