Preserving Shipwreck Treasures: Expert Conservation Tips for Your Recovered Coins

Introduction: The Fragility of Maritime Treasures

I’ve seen too many valuable pieces ruined by improper cleaning or storage. Here is how to keep this safe for the next generation.

Understanding Shipwreck Coin Preservation

Shipwreck coins represent some of the most fascinating artifacts in numismatics, but their recovery from underwater environments creates unique preservation challenges. When coins spend centuries submerged, they develop distinctive patinas and corrosion patterns that tell the story of their journey through time and water. These characteristics, while historically significant, make proper storage absolutely critical.

The Science of Maritime Toning

Toning on shipwreck coins differs dramatically from toning on coins stored in collections. Marine environments introduce complex chemical reactions involving salt water, minerals, and organic materials. The resulting patinas can range from deep verdigris greens to rich blues and purples, creating what collectors call “shipwreck toning.”

This toning is not merely cosmetic—it represents the coin’s history and authenticity. The chemical composition of seawater, combined with the specific metals in the coin (often silver, copper, or gold), creates unique surface characteristics. Attempting to remove or alter this toning destroys both the coin’s historical value and its scientific significance.

Oxidation and Corrosion Concerns

Unlike coins stored in dry conditions, shipwreck coins face ongoing oxidation risks even after recovery. The chloride ions from seawater can become embedded in the metal structure, creating what conservators call “bronze disease” in copper coins or persistent tarnish in silver pieces. This process can continue for years if not properly addressed.

The key is stabilization, not restoration. Professional conservators use specialized techniques to halt ongoing corrosion without removing the historical surface. This might include careful washing in deionized water, controlled drying, and application of microcrystalline waxes that create a protective barrier while remaining reversible.

Proper Storage Solutions

Choosing the Right Holders

The oversized nature of shipwreck slabs requires thoughtful storage planning. As discussed in the forum thread, several options exist for collectors:

• NGC’s specialized boxes designed specifically for 5-ounce America the Beautiful slabs, which can accommodate shipwreck slabs of similar dimensions
• Custom wooden presentation boxes, often original to shipwreck coin releases
• Modified storage solutions like CD cases or specially designed intercept boxes

Each option has merits, but the critical factor is ensuring the holder is chemically inert and provides adequate protection from environmental fluctuations.

PVC Damage: The Silent Destroyer

Polyvinyl chloride (PVC) represents one of the greatest threats to coin preservation. When PVC breaks down, it releases hydrochloric acid that can permanently damage coin surfaces. This is particularly dangerous for shipwreck coins, which may already have compromised surfaces from their time underwater.

Always verify that storage materials are PVC-free. Look for holders made from polyethylene, polypropylene, or other inert plastics. Even “coin-safe” products can degrade over time, so regular inspection of storage materials is essential.

Environmental Control

Temperature and humidity control are paramount for shipwreck coin preservation. Ideal conditions include:

• Temperature: 65-70°F (18-21°C)
• Relative humidity: 45-55%
• Minimal light exposure, especially UV radiation
• Stable conditions without rapid fluctuations

Consider using silica gel packets or other desiccants in storage areas, but ensure they don’t directly contact the coins or slabs.

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

The Case Against Cleaning

Cleaning shipwreck coins almost always reduces their value and destroys historical information. The marine patina represents centuries of chemical interaction between the coin and its environment. This surface tells archaeologists and historians about the coin’s journey, the water conditions it experienced, and even trade routes of the period.

“Every time I see a cleaned shipwreck coin, I see lost history. The marine environment creates surfaces that are scientifically irreplaceable.” – Professional Numismatic Conservator

Professional Conservation vs. DIY Approaches

While the forum mentions DIY solutions like CD cases, professional conservation requires specialized knowledge and equipment. Improper cleaning can cause:

• Removal of original surface metal
• Acceleration of corrosion processes
• Loss of diagnostic features used for authentication
• Decreased market value by 50-90%

If conservation is absolutely necessary, consult a professional who specializes in maritime artifacts. They can stabilize the coin without destroying its historical integrity.

Storage Box Recommendations

NGC’s Official Solutions

As mentioned in the discussion, NGC produced two official boxes for oversized slabs:

• A 7-slot box for smaller collections
• A 12-slot box for larger holdings

These boxes are specifically designed to protect the slabs from physical damage while providing proper spacing to prevent scratching or pressure damage.

Custom Storage Solutions

For collectors with unique needs, custom solutions might include:

• Wooden presentation boxes with custom foam inserts
• Modified archival storage boxes with appropriate dimensions
• Professional-grade coin storage cabinets with adjustable shelving

The key is ensuring any custom solution uses archival-quality materials and provides adequate protection from environmental factors.

Long-term Preservation Strategies

Regular Monitoring

Even with proper storage, regular inspection is crucial. Check for:

• Changes in toning or coloration
• Signs of active corrosion
• Damage to storage materials
• Environmental fluctuations in storage areas

Documentation and Insurance

Maintain detailed records of your shipwreck coin collection, including:

• Provenance and acquisition information
• Professional conservation reports
• Photographic documentation of condition
• Appraisal values for insurance purposes

Conclusion: Preserving History for Future Generations

Shipwreck coins represent unique windows into maritime history, and their preservation requires careful attention to conservation principles. By understanding the science of marine toning, avoiding destructive cleaning practices, and investing in proper storage solutions, collectors can ensure these treasures survive for future generations to study and appreciate.

Remember that each shipwreck coin tells a story that spans centuries. Our role as custodians is not to alter that story, but to preserve it in its authentic form. Whether you’re using an NGC box, a custom wooden case, or a carefully modified storage solution, the goal remains the same: protecting these irreplaceable pieces of history from the damage that time and improper care can inflict.

The forum discussion highlights the community’s shared concern for proper preservation, and I hope this comprehensive guide provides the detailed information needed to make informed decisions about your shipwreck coin collection. After all, we’re not just collecting coins—we’re preserving history itself.

Related Resources

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