To Set The Scene
Subject to the Wreck and Salvage Law, as non-commercial divers and under certain conditions, we are allowed to recover artefacts from the seabed and shipwrecks. Licensing may be needed for the use of lift bags. However, more minor artefacts can be retrieved by hand. It’s important to note that any artefacts recovered, regardless of size, should be reported to the Receiver of Wreck. The Receiver of Wreck is responsible for determining the ownership of the artefacts and ensuring they are properly recorded and preserved. So yes, items can be recovered, but there is also the consideration of preservation that is an essential factor.
Archaeology, in its essence, is the study of the past through the examination of physical remains left behind by people. These remains, such as tools, buildings, pottery, bones, and other artefacts, are not just objects but windows into our history. They tell a story, and the decisions we make about whether to leave an artefact in situ or to recover it carry a significant weight, especially when considering the cost of recovery and preservation.
I learned this when I joined the Nautical Archaeology Society (NAS) a few years back. The NAS is a non-governmental organisation dedicated to promoting the preservation of underwater cultural heritage through education and research. To join, you need to complete two learning modules. Preserving cannon balls is part of one module to demonstrate the concept of archaeology, as cannon balls degrade quickly when out of the water. Arguably, if one is not going to the expense of preservation, the artefacts should remain in situ. With this in mind, I write this article, following this picture and commend it on social media recently.
The Social Media Post

My cannon balls in my dive shop window have begun to crack. Does anyone know if there is a special cream I can use to apply to my cannon balls or do I just have to accept that this just comes with age?
Education Is Key
I’m not here to criticise or chastise but to inform and educate. As we can see from these two cannonball artefacts, they are irrevocably destroyed. Not only to the diver who recovered the items, an archaeology shame to have lost two pieces of time. So before you take an underwater find to the surface, consider the legal aspects and what preservation will be needed. Regarding these cannon balls, it is more complex than one would think. Sometimes, it maybe better to let the artefect remain.
Preservation Techniques
Preserving all artefacts is a critical aspect of archaeological conservation that demands attention and expertise. These artefacts, often unearthed from battlefields or shipwrecks, provide invaluable insights into historical warfare and maritime practices. However, the inherent nature of iron makes these cannonballs susceptible to corrosion and deterioration over time. Novice or experienced archaeologists and divers must be passionate about techniques to preserve these relics effectively. First and foremost, proper cleaning is essential to remove any surface debris without damaging the artefact. Following this, stabilisation treatments using specialised solutions can halt further corrosion processes.
Additionally, careful storage in controlled environments ensures that temperature and humidity levels remain optimal for preservation. We must recognise the significance of preserving iron cannonballs as historical objects integral to our cultural heritage. By implementing robust conservation strategies, we can safeguard these artefacts for future generations to thoroughly study and appreciate their historical context.
- Rinse with Fresh Water:
- This step prevents saltwater from further penetrating the cannonball and causing additional corrosion. Use fresh, clean water to remove sediment and salts while the surface is wet.
- Avoid letting the cannonball dry out before this step, as salt can crystallise and expand, damaging the metal further.
- Gentle Mechanical Cleaning:
- Use soft nylon brushes, wooden tools, or plastic scrapers to remove marine growth and surface deposits.
- Avoid metal tools that can scratch or damage the surface, and never use high-pressure water or abrasive methods that might strip the surface of historical features.
- Soak in Fresh Water:
- Desalination is a slow process that gradually removes salts embedded in the cannonball’s pores. Start by filling large containers with fresh water.
- Change the water frequently to ensure the leaching process continues effectively. Monitor the cloudiness and salinity of the water to assess progress.
- Use Deionised Water:
- Deionised or distilled water is ideal as it lacks impurities that might interfere with desalination.
- This is particularly important when dealing with heavily contaminated artefacts, as it prevents the introduction of new ions during the process.
- Monitor Chloride Levels:
- Use chloride test kits or meters to check the concentration of chloride ions in the soaking water.
- Chlorides leach out of the cannonball gradually, and the soaking process should continue until chloride levels stabilise at a low concentration. This step is essential to prevent future corrosion.
- Electrolytic Reduction:
- Overview: This method helps stabilise the iron by reducing rust (iron oxides) back to a stable metallic form and removing deeply embedded chlorides.
- Setup: Use a plastic tank filled with a weak alkaline solution, such as sodium hydroxide (NaOH) or sodium carbonate (Na₂CO₃), as the electrolyte.
- Cathode-Anode Arrangement: Connect the cannonball to a power source as the cathode (-), and use a sacrificial anode (+) such as stainless steel or graphite.
- Electric Current: Pass a low, controlled electric current through the solution. Start with a lower voltage and gradually increase as needed.
- Monitoring: Watch for bubbles (hydrogen gas) forming on the cannonball. Over-reduction can damage the surface, so careful observation is critical.
- Duration: Depending on the artefact’s size and contamination, the process may take weeks or months. Chloride levels in the bath should be monitored regularly.
- Chemical Inhibitors:
- If electrolytic reduction isn’t feasible, rust converters like tannic acid can be applied. Tannic acid reacts with iron oxide to form a stable, protective layer of iron tannate, which inhibits further corrosion.
- This method is less invasive but may be less effective for long-term stabilisation.
- Controlled Drying:
- Rapid drying can lead to cracking or additional stress on the cannonball. Use a controlled drying chamber with moderate humidity to allow for slow evaporation.
- Avoid direct heat sources or sunlight, as uneven drying can cause deformation or internal stress.
- Alcohol Rinse:
- Before drying, immerse the cannonball in isopropyl alcohol or acetone. These solvents help displace water from the pores, reducing drying time and minimising cracking.
- Handle solvents carefully in a well-ventilated area, as they are flammable and can evaporate quickly.
- Apply a Protective Coating:
- Once thoroughly dried, apply a thin layer of microcrystalline wax (e.g., Renaissance Wax) to seal the surface. This non-reactive wax provides a barrier against moisture and enhances the artefact’s appearance.
- Use a soft cloth or brush to apply the wax evenly. Buff the surface lightly for a uniform finish.
- Avoid Paints:
- Modern paints are not recommended because they can trap residual moisture inside the artefact, accelerating corrosion. Stick to conservation-grade materials designed for historic preservation.
- Controlled Environment:
- Maintaining a stable environment is crucial for long-term preservation. Aim for a humidity level below 40% to minimise moisture-related corrosion.
- Use humidity monitors (hygrometers) to ensure conditions remain stable.
- Avoid Contact with Moisture:
- For display cases, include desiccants (e.g., silica gel packets) to absorb excess moisture. Replace or regenerate these desiccants periodically.
- Consider using UV-blocking glass to prevent light damage to coatings or finishes.
Additional Notes
- Artefact-Specific Adjustments: Each artefact has unique characteristics and requires tailored approaches. The extent of corrosion, size, and historical significance might dictate deviations from this general guideline.
- Professional Consultation: Consult with professional conservators specialising in marine archaeology for advanced preservation techniques or challenging cases.
- Documentation: Keep detailed records of all steps, including water testing results, treatment methods, and materials used, for future reference or additional research.
In Conclusion
The delicate process of preserving any artefact, whether an iron cannonball, ceramic, or bottle recovered from the seabed, is a responsibility we all share. The glaze on ceramics will become dust. This preservation process involves stabilising the material, a crucial step that requires us to be informed and aware of the technical aspects of artifact preservation, such as the need to remove harmful salts, and preventing further corrosion. My takeaway from the NAS modules was backing up the concept of archaeology. Removing an artefact that is only to be destroyed without preservation should be left in situ. In the NAS learning module, a cast iron cannon ball is used as an example with time-lapse to show the degradation over time. Even pottery and ceramics need to be preserved, and a top tip is to put ceramics in a toilet system. That’s a cracking idea that someone told me to continue the salt leaching process with continuous fresh water. That is, with no Blue Loo!