Researchers have developed an innovative hydrogel that strengthens and protects ancient, waterlogged wood, offering a new way to conserve priceless artifacts from historic shipwrecks. The material, which is applied as a soft gel, neutralizes damaging acids and prevents microbial decay before dissolving, eliminating the need for physical removal that could harm delicate surfaces. The technique has already been successfully tested on 800-year-old wood samples from a shipwreck, demonstrating its potential to revolutionize the preservation of submerged cultural heritage.
This scientific advance directly addresses a major challenge for conservators: how to save wooden artifacts after centuries spent underwater. Saturated with seawater, these items become a breeding ground for acid-producing bacteria and wood-eating fungi. Traditional preservation methods, such as freeze-drying or replacing water with polymers, are often slow, expensive, and can cause the wood to warp, shrink, or become brittle. The new hydrogel offers a gentler and more rapid alternative, infusing the wood with protective compounds while leaving its structure intact, providing a critical tool for safeguarding irreplaceable windows into the past.
The Challenge of Marine Artifacts
When wooden objects are recovered from the sea, they are in a fragile and unstable state. The very water that preserved them from oxygen-rich air for centuries also becomes their greatest threat upon recovery. The wood is thoroughly waterlogged, its cellular structure filled with water and saturated with salts and minerals. This environment is ideal for microorganisms that thrive in wet, acidic conditions. Bacteria and fungi colonize the wood, producing acids that steadily break down its cellular integrity from the inside out. This process of decay continues as long as the wood remains wet and untreated.
For decades, conservators have relied on a few primary methods to combat this degradation, each with significant drawbacks. One common technique is polyethylene glycol (PEG) treatment, where the wood is submerged in a PEG solution for months or even years to slowly replace the water in its cells. While effective, it is an extremely time-consuming process. Another approach is freeze-drying, which can remove water more quickly but often causes the wood to shrink or crack as ice crystals form and sublimate. Other methods that use pressurized carbon dioxide or viscous polymers can also induce stress on the wood, leading to warping and increased brittleness. Furthermore, some treatments require the application of surface coatings or masks to deliver antimicrobial agents, but peeling these away later risks damaging the very surface they are meant to protect.
A Novel Hydrogel Solution
Composition and Chemistry
The new hydrogel was developed by researchers Xiaohang Sun and Qiang Chen to overcome the limitations of previous methods. Its design is based on a multifunctional chemical system that provides structural support, neutralizes acid, and fights microbial decay simultaneously. The foundation of the gel is a mixture of two polymers that create its unique structure. These polymers are blended with two key active ingredients: potassium bicarbonate and silver nitrate.
Potassium bicarbonate is an alkaline compound chosen for its ability to effectively neutralize the harmful acids produced by bacteria within the wood. By raising the pH, it creates a less hospitable environment for the microorganisms responsible for decay. The second active ingredient, silver nitrate, serves a dual purpose. It reacts to form silver nanoparticles, which are well-known for their powerful antimicrobial properties that inhibit the growth of fungi and bacteria. These nanoparticles also play a structural role, linking the polymer chains together to form the cross-linked network of the gel itself.
A Self-Dissolving Approach
One of the most innovative aspects of this technology is its tunable nature. The researchers discovered that by carefully adjusting the concentration of silver nitrate, they could control the hydrogel’s viscosity and longevity. A lower concentration of silver nitrate results in a gel that remains soft and gradually liquefies over a period of three to five days. This self-dissolving property is a major breakthrough, as the gel can deliver its therapeutic compounds and then melt away, sinking harmlessly into the wood without the need for manual removal that could abrade or damage the artifact’s surface.
Conversely, a higher concentration of silver nitrate creates a more durable, solid gel that can remain in place for longer periods if needed. This versatility allows conservators to tailor the treatment to the specific needs of an artifact. For delicate items requiring a fast-acting but gentle treatment, the dissolving gel is ideal. For more robust artifacts that may need sustained, long-term protection, a more solid formulation could be used.
From the Lab to a Historic Wreck
To validate their new technique, the research team conducted a proof-of-concept experiment on authentic historical artifacts. They obtained wood samples from the Nanhai One, a shipwreck discovered off the southern coast of China that dates back approximately 800 years. This provided a real-world test case to see how the hydrogel would perform on ancient, seawater-saturated wood that had undergone centuries of underwater aging. The team prepared hydrogels with varying amounts of silver nitrate and applied them directly to the surfaces of these priceless samples.
The results were highly successful. The team found that all formulations of the hydrogel were effective at neutralizing acid within the wood, reaching a depth of up to one centimeter over a 10-day period. Notably, the lower-silver-content gels—the ones designed to dissolve—acted much more quickly, achieving significant acid neutralization within the first day of application. This rapid action is crucial for halting degenerative processes as soon as possible after an artifact is recovered.
Superior Preservation Results
The benefits of the hydrogel treatment extended beyond simply neutralizing acid. Microscopic analysis revealed that the wood treated with the dissolving gels showed a remarkable preservation of its internal cellular integrity. The cellular walls were better maintained, and the overall microstructure of the wood was less compromised compared to samples treated with the more solid gels or left untreated. This structural preservation is essential for the long-term stability and strength of the artifact.
Furthermore, the artifacts treated with the liquefying gels were observed to be less fragile and brittle. This is a significant improvement over traditional drying methods, which often leave wood weak and susceptible to fracture. By strengthening the wood at a cellular level and avoiding the physical stresses of other techniques, the hydrogel helps ensure that these historical items can be handled, studied, and displayed with greater safety. The researchers concluded that their method offers a faster, gentler, and more effective way to preserve these vital pieces of cultural heritage.
Future of Cultural Heritage Conservation
This innovative hydrogel technology represents a significant step forward in the field of archaeological conservation. Its success on the Nanhai One samples suggests it could be widely applied to other waterlogged wooden artifacts, from Viking ships to ancient canoes, providing a new standard of care. The approach is not only more effective but also potentially more efficient, reducing the months or years required for traditional polymer treatments to a matter of days.
The research, which received support from the National Natural Science Foundation of China and the Guangdong Basic and Applied Basic Research Foundation, underscores a growing emphasis on developing non-invasive and sustainable methods in heritage science. By focusing on materials that work with the artifact’s natural structure rather than against it, scientists are paving the way for a future where more of the world’s submerged history can be safely brought to the surface and preserved for generations to come.