Preserving Shipwreck Slabs: Expert Conservation Tips for Long-Term Protection

The Hidden Dangers of Improper Storage

Over the years, I’ve witnessed too many valuable pieces ruined by improper cleaning or storage. Here’s how to keep your shipwreck slabs safe for generations to come.

Understanding Shipwreck Slabs

Shipwreck slabs are among the most fascinating artifacts in numismatic collecting. These specially encapsulated coins, typically recovered from maritime disasters, present unique preservation challenges due to their size, historical significance, and often delicate condition. The slabs themselves are larger than standard coin holders, designed to accommodate coins that may have irregular shapes or require additional protection from environmental factors.

The Science of Toning and Oxidation

When dealing with shipwreck coins, understanding the chemistry of toning and oxidation is crucial. These coins have already undergone significant chemical changes during their time underwater, and improper storage can accelerate deterioration. Toning occurs when metal reacts with sulfur compounds, oxygen, and other elements in the environment. While some collectors prize colorful toning, uncontrolled oxidation can permanently damage a coin’s surface and diminish its numismatic value.

The key to preventing harmful oxidation is controlling environmental factors. Humidity is particularly dangerous, as it accelerates chemical reactions. Even within protective slabs, moisture can become trapped, leading to spots, corrosion, and irreversible damage. Temperature fluctuations also play a role, causing microscopic expansion and contraction that can stress the coin and its holder.

PVC Damage: The Silent Killer

Polyvinyl chloride (PVC) damage remains one of the most common and preventable forms of coin destruction. PVC is found in many older plastic holders and flips, and over time it breaks down, releasing hydrochloric acid. This acid reacts with the coin’s surface, creating a distinctive green, slimy residue that cannot be removed without professional conservation.

Modern slabs like those used for shipwreck coins are made from inert materials specifically chosen to prevent PVC damage. However, if you’re storing multiple slabs together or using additional storage solutions, ensure all materials are PVC-free. Look for products labeled “archival quality” or “inert plastic” to protect your investment.

Proper Holder Selection and Storage Solutions

The forum discussion reveals several practical storage solutions for these oversized slabs. NGC produced specialized boxes that hold either 7 or 12 shipwreck slabs, representing the ideal storage solution. These boxes are designed with the proper dimensions and materials to protect your investment and maintain mint condition.

For those unable to obtain official NGC boxes, several alternatives exist. The Intercept box mentioned by one collector provides electromagnetic shielding that helps prevent toning. CD cases, while not ideal for long-term storage, can serve as temporary solutions. The key is ensuring whatever container you use provides adequate support and protection from environmental factors.

When storing multiple slabs, always keep them flat rather than on edge. This prevents stress on the encapsulation and reduces the risk of damage if the container is bumped or dropped. Never stack heavy objects on top of coin slabs, as the pressure can cause the plastic to warp or crack.

To Clean or Not to Clean: The Conservationist’s Perspective

This question generates more debate in numismatics than perhaps any other. My professional stance is clear: do not clean shipwreck coins or their slabs. These coins have already undergone significant chemical changes, and attempting to “improve” their appearance often results in permanent damage and substantial loss of collectibility.

Shipwreck coins, in particular, should be left in their found condition. The encrustations, toning, and surface characteristics tell the story of their journey through time. Professional conservators can sometimes remove harmful deposits, but this should only be done when absolutely necessary for the coin’s preservation, not for aesthetic reasons.

If a slab becomes dirty or dusty, gently wipe it with a soft, lint-free cloth. Never use chemicals, solvents, or abrasive materials. If the coin inside needs attention, consult a professional conservation service experienced with shipwreck artifacts.

Environmental Control for Long-Term Preservation

Proper storage goes beyond just having the right container. The environment where you keep your shipwreck slabs significantly impacts their longevity. Ideal conditions include:

• Temperature between 60-70°F (15-21°C)
• Relative humidity between 40-50%
• Minimal exposure to direct sunlight
• Protection from dust and pollutants
• Stable conditions without dramatic fluctuations

Consider using a dedicated safe or cabinet with a dehumidifier if you live in a humid climate. Silica gel packets can help absorb excess moisture, but they need regular replacement or recharging to remain effective.

Documentation and Insurance Considerations

Proper preservation includes maintaining detailed records of your collection. Photograph each slab from multiple angles, noting any unique characteristics or identifying marks. Keep documentation of provenance, purchase information, and professional appraisals.

Given the value of shipwreck coins, ensure your homeowner’s insurance adequately covers your collection, or obtain specialized collectibles insurance. Documented preservation efforts can actually increase insurance value, as they demonstrate responsible ownership and care.

Common Mistakes to Avoid

Even experienced collectors sometimes make preservation errors. Avoid these common mistakes:

• Using PVC-containing materials for any part of storage
• Attempting DIY cleaning or conservation
• Storing in attics, basements, or garages with unstable conditions
• Exposing slabs to direct sunlight or extreme temperatures
• Handling slabs with dirty or oily hands
• Using adhesives or tape near slabs

Professional Resources and When to Seek Help

While many preservation tasks can be handled by collectors themselves, certain situations require professional intervention. If you notice any of the following, consult a professional conservator:

• Visible corrosion or green deposits
• Cracks or damage to the slab itself
• Significant toning changes occurring rapidly
• Moisture accumulation inside the slab
• Any situation where you’re unsure about proper handling

Professional conservation services specializing in shipwreck artifacts understand the unique challenges these coins present and have the proper tools and techniques to address preservation issues without causing additional damage.

Conclusion: Preserving History for Future Generations

Shipwreck slabs represent more than just monetary value; they are tangible connections to historical events and human stories. Proper preservation ensures these artifacts survive for future generations to study and appreciate. By understanding the science of coin preservation, using appropriate storage solutions, and avoiding common mistakes, you can protect your investment while honoring the historical significance of these remarkable pieces.

Remember that the goal of preservation is not to make a coin look “perfect” or “new,” but to maintain its current condition and prevent further deterioration. Sometimes the most valuable service we can provide as collectors is simply protecting these pieces from additional harm, allowing their natural history to remain visible and intact for years to come.

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