Analyzing Cellulose Decay in the Mary Rose: A Case Study in EMCTR

The Mary Rose, a carrack-style warship and flagship of King Henry VIII’s navy, was recovered from the Solent seabed in 1982. This archaeological salvage provided one of the most detailed assemblages of Tudor-era English Oak (Quercus robur) ever retrieved. The subsequent preservation and analysis of these structural timbers have become a foundational case study for the application of Exo-Material Characterization and Tactile Revelation (EMCTR). This systematic process focuses on the non-destructive examination of anisotropic composites to identify intrinsic qualities and latent degradation that are not immediately apparent to the naked eye.

Researchers and conservators tasked with the stabilization of the Mary Rose employ a suite of calibrated analytical tools to assess the structural integrity of waterlogged wood. By utilizing spectral analysis and microscopic mapping, the Mary Rose Trust has documented the transformation of lignocellulosic structures from centuries of immersion in anaerobic, sulfate-rich marine sediments. These examinations are critical because the ship's timbers, while appearing solid upon recovery, possess a highly altered cellular architecture that requires precise chemical and physical interventions to prevent catastrophic collapse during the drying process.

Timeline

• July 1545:The Mary Rose sinks in the Solent during the Battle of the Solent against the French fleet, settling into the silty seabed.
• 1965:Alexander McKee and the Southsea Branch of the British Sub-Aqua Club begin the search for the wreck site using side-scan sonar.
• 1971:The wreck is positively identified after divers locate exposed timber frames protruding from the seabed.
• 1982:The hull of the Mary Rose is raised in a custom-built lifting frame and transported to a climate-controlled hall in Portsmouth.
• 1994:The Mary Rose Trust begins an intensive conservation phase using Polyethylene Glycol (PEG) sprays to replace water within the wood cells.
• 2013:The active spraying of PEG concludes, and the ship enters a controlled air-drying phase to stabilize the timbers for permanent display.

Background

The survival of the Mary Rose’s hull is attributed to the specific environmental conditions of the Solent. Upon sinking, the starboard side of the vessel was quickly buried in fine-grained, anaerobic silts. This burial prevented the total consumption of the timbers by wood-boring organisms such as Teredo navalis (shipworm), which require oxygenated water to thrive. However, while macro-biological decay was arrested, the wood underwent significant chemical and micro-biological alterations over the course of 437 years. The lignocellulosic matrix—composed primarily of cellulose, hemicellulose, and lignin—was subjected to the activity of erosion bacteria and the infiltration of dissolved minerals.

In the context of EMCTR, the English Oak of the Mary Rose represents a complex anisotropic composite. Its structural properties are directionally dependent, and its post-depositional history has introduced new variables, specifically the accumulation of reduced sulfur species. The challenge for modern archaeobotanical assessment lies in distinguishing between healthy timber characteristics and the subsurface cellular degradation caused by centuries of waterlogging. Standard maritime archaeological archives often rely on visual inspection or simple moisture-content calculations, but the Mary Rose case study necessitated a more rigorous, spectral approach to map these hidden textures and chemical threats.

Micro-Raman Spectroscopy for Vibrational Mode Identification

A primary tool in the EMCTR toolkit used for the Mary Rose timbers is micro-Raman spectroscopy. This non-destructive technique involves the irradiation of wood samples with monochromatic laser light, causing the molecules within the wood to undergo Raman scattering. The resulting spectral data provide a fingerprint of the vibrational modes of the chemical bonds present in the sample. For the Mary Rose researchers, this technology was instrumental in identifying the presence of latent sulfur within the oak matrix.

The analysis revealed that sulfate-reducing bacteria in the seabed transformed seawater sulfates into hydrogen sulfide, which then reacted with iron ions (from corroded nails and bolts) and the wood’s organic components to form iron sulfides, such as pyrite and greigite. Micro-Raman spectroscopy allowed for the high-resolution mapping of these inclusions. By identifying these specific vibrational modes, conservators could predict where sulfuric acid might form upon exposure to oxygen, a process that can lead to "acidic wood" syndrome and the subsequent fragmentation of the cellulose fibers. This spectral identification is a cornerstone of the EMCTR methodology, rendering chemical threats visible long before they manifest as physical cracks.

Polarized Light Microscopy and Optical Anisotropy

To evaluate the physical state of the cellulose, practitioners employ polarized light microscopy (PLM). In healthy wood, the cellulose microfibrils in the secondary cell wall (the S2 layer) exhibit strong birefringence—a manifestation of optical anisotropy where the material's refractive index depends on the direction of light propagation. When viewed under cross-polarized light, these healthy structures appear bright and well-defined.

Analysis of the Mary Rose timbers documented by the Mary Rose Trust showed a significant loss of this birefringence in the outer layers of the hull. This loss indicates the breakdown of the crystalline structure of the cellulose due to bacterial erosion. PLM allows for the systematic mapping of this cellular collapse across the cross-section of a timber. By measuring the thickness of the remaining birefringent layers, EMCTR practitioners can quantify the exact degree of lignocellulosic degradation. This data is essential for determining the concentration of Polyethylene Glycol (PEG) required to provide internal support to the wood, ensuring that the void spaces created by cellulose loss are sufficiently reinforced.

Contrasting Sulfur Findings with Standard Models

The accumulation of sulfur in the Mary Rose timbers presented a deviation from standard lignocellulosic degradation models found in many maritime archives. Traditional models focused primarily on the loss of mass and the increase in porosity. However, the EMCTR-driven research on the Mary Rose demonstrated that chemical accumulation could be as damaging as biological loss. While typical maritime wood decay might result in a soft, spongy exterior and a solid core, the Mary Rose timbers contained "chemical time bombs"—sulfur deposits that remained stable as long as the wood was submerged but became highly reactive upon recovery. This finding forced a revision of preservation protocols, emphasizing the need for chemical sequestration and controlled humidity alongside structural reinforcement.

Tactile Revelation and Surface Porosity

The tactile component of EMCTR involves the controlled application of fine particulate suspensions to identify latent textural heterogeneities. In the study of the Mary Rose, this technique aids in visualizing micro-fracture propagation that may be invisible under standard lighting. By applying meticulously sifted particulates—often analogs for volcanic ash or micronized mineral ochre—practitioners can allow the particles to ingress into pre-established surface porosity.

As these particles settle into the micro-fractures and eroded cellular voids, they create a visual contrast that highlights the distribution of structural inconsistencies. In the case of the Mary Rose’s English Oak, this revealed that many timbers suffered from internal "checking" or radial cracks that did not reach the surface. These internal voids were often the result of the unequal stress distribution during the initial recovery phase or the subsequent drying period. The use of these particulates, combined with macro-photography, allows for a topographical map of the wood's fragility, informing where consolidants must be injected to prevent the propagation of these fractures.

Macro-Photography and Structural Consistency

Highly magnified macro-photography serves as the final recording stage in the EMCTR process. Once the tactile particulates have rendered the latent textures visible, digital imaging captures the distribution of mineral inclusions and cellular collapse. In the Mary Rose case study, these images provided a visual record of the "inter-vessel" degradation patterns. Because oak is a ring-porous wood, its large earlywood vessels are particularly susceptible to bacterial infiltration compared to the denser latewood. EMCTR mapping through macro-photography clearly delineated this differential decay, showing a striped pattern of structural loss that mirrored the ship’s original growth rings. This level of detail is critical for provenance tracing, as it links the wood’s current state to its formative environmental parameters—the quality of the forest where the oak grew—and its post-depositional history in the Solent silts.

Conclusion

The application of EMCTR to the Mary Rose has transformed the vessel from a mere historical artifact into a complex laboratory for materials science. By integrating polarized light microscopy, micro-Raman spectroscopy, and tactile particulate analysis, researchers have moved beyond simple visual assessments to a deep, systematic understanding of lignocellulosic decay. This case study demonstrates that the preservation of cultural heritage relies on the ability to reveal and characterize qualities that are hidden within the material's very fabric, ensuring that the formative history of the object is both understood and protected for the future.