Reburial of shipwrecks in marine sediments: a long-term study on wood degradation

Historical shipwrecks in marine environments are continuously decomposed by wood-degrading organisms, adapted to this specific environment. To protect the wrecks from degradation and to preserve the unique remains for future generations, reburial of wrecks using various covering materials has been suggested as a long-term preservation method. The following experiment was carried out to study the bio-protective effect of sediment. Sound oak, pine, and birch samples were buried above and within marine sediment in Marstrand harbour, and retrieved for analysis after 6, 12, 24, and 36 months. Macroscopic as well as light-microscopic examinations were carried out on each occasion. Marine borers (shipworm, Limnoria), soft rot and tunnelling bacteria were wood degraders immediately above the seabed; soft rot, tunnelling bacteria, and erosion bacteria were active 10 cm below the seabed; erosion bacteria were the only degraders at a depth of 43 cm below the seabed. The wood species had different durability towards the decay agents. After 3 years, wood samples above the seabed were totally decomposed, whereas wood was highly protected at 43 cm depth in sediment. In the sediment, decay decreased significantly with depth of burial. The results suggest that reburial of shipwrecks in marine sediment can be recommended as a simple and efficient method for long-term preservation of the wooden cultural heritage.     

Morphological,chemical and physical changes during charcoalification of wood and its relevance to archaeological contexts

Wood exposed to a heat source can be transformed into charcoal if subject to conditions of carbonisation (in the absence of air) or charring (in restricted air). Charcoal recovered from archaeological sites can yield fundamental information to our understanding of human economic and cultural development over time and (ecological) setting. This work describes the morphological (anatomy, degree of shrinkage), physical (reflectance) and chemical (elemental, molecular composition) properties of charcoal in relation to heat source and wood variables. In this study charcoal and charcoal fuel were experimentally produced whereby temperature (160–1200 °C), time of exposure (2–1440 min), heating rate (high and low) and wood type (angiosperm and conifer) were varied. The results show that charcoal, often described as an inert, black material, has different chemical and physical properties in relation to the investigated variables. By using these different properties it is possible to distinguish between the different types of fires (domestic and industrial) exploited by humans in the past. Morphological analyses and reflectance measurements are effective tools for this purpose and can be used in wood exposed to temperatures of 300 °C and above—temperatures which are relevant to archaeological research. Angiosperm and conifer wood react in different ways when exposed to heat and thus the taxonomic identity of archaeological material needs to be known. Chemical analyses can be used for wood exposed to temperatures below 400 °C whereas elemental analyses of the carbon content can be used for wood exposed to temperatures up to a maximum of 650 °C.     

太仓万丰村半泾河古船船材主要离子的测试研究

为做好太仓万丰村半泾河古船的脱盐保护工作,本研究检测了半泾河古船的第6、7隔舱板和第8隔舱龙骨及船板下淤泥样品中主要元素和离子的含量,并用电导率仪测量样品在脱盐过程中电导率的变化情况。检测结果表明,木材和淤泥中的主要元素含量高于对照样品,且主要以可溶性盐的状态存在;木材腐蚀程度也与其离子含量有关,腐蚀程度愈严重,样品的离子含量也愈大;经过脱盐处理后,脱盐溶液的电导率值降低至较低水平。测试数据将对今后古船脱盐工作有一定的指导意义。     

Ancient Maya wood selection and forest exploitation: a view from the Paynes Creek salt works,Belize

Ancient building construction wood preserved in a peat bog below the seafloor in a shallow mangrove lagoon in Paynes Creek National Park, Belize, provides an exceptional record of Classic Maya wood use. Identifications of construction wood at Early Classic Chan B'i, and Late Classic Atz'aam Na, are reported and discussed to assess forest exploitation and species selection over time. Black mangrove (Avicennia germinans) dominates the Early Classic assemblage. The Late Classic assemblage is characterized by greater variability and an absence of mangrove species. When considered in the environmental context, identified species conform to principles of optimal foraging. The change in the wood assemblage over time suggests overexploitation of forest resources, resulting in deforestation of the local landscape and subsequent adaptation of foraging behavior. Deforestation is linked to the wider social context in which growing inland populations created demand for salt, putting greater pressure on the forest resources exploited by the Paynes Creek salt works for fuel and timber.     

From riches to rags: organic deterioration at Star Carr

The 11,000-year old lake edge archaeological site of Star Carr in the Vale of Pickering of North Yorkshire is one of the most famous Mesolithic sites in Europe, and one of the earliest, dated to the period of climatic warming that immediately followed the final termination of the last ice age. One of the main reasons for this international importance is the richness of its organic artefacts, faunal assemblage and environmental data. However, recent investigations have demonstrated that these organic remains have severely deteriorated over the last 60 years due to the decay and acidification of the surrounding peat. This paper presents research into the effects on the bone (histological analysis using light and polarising microscopy, and Transmission Electron Microscopy, bulk collagen analysis, and amino acid analysis), antler (visual and metrical analysis, loss on ignition and Scanning Electron Microscopy) and wood (visual analysis, decay assessment tests and Scanning Electron Microscopy).     

Chronologies in wood and resin: AMS C dating of pre-Hispanic Caribbean wood sculpture

This paper establishes a chronological framework for selected pieces of Caribbean (Taíno/Lucayan) wooden sculpture, enabling previously ahistoric artefacts to fit back into the wider corpus of pre-colonial material culture. Seventy-two ¹⁴C AMS determinations from 56 artefacts held in museum collections are reported, including 32 ceremonial duhos, or seats. Far from being constrained to the last few centuries prior to contact, the dates for these objects extend back to ca. AD 250, and include the artistic legacies of various cultures. Duhos in both low and high back styles are present from about AD 600, if not earlier, in a distribution that spans the Antillean island chain from Trinidad to Cuba. Complex, drug-related paraphernalia and elaborate ancestral reliquaries are in evidence by AD 1000, as are some distinctive regional styles – such as the unique iconography from the Bahamas and Turks and Caicos islands. This paper explores relevant methodological issues – from the challenges of working with museum pieces (e.g., uncertain provenance, discrete sampling techniques, impact of previous conservation treatments on dating results), to dealing with potential ‘in-built’ age in tropical hardwoods.     

Preservation of fungi in archaeological charcoal

During the analysis of wood charcoal remains from archaeological sites, it is common to find different microorganisms and different forms of degradation present in the plant tissue. However, one may encounter difficulties when attempting to identify these microorganisms and determine when their attack occurred. This paper focuses on preservation aspects related to the microorganisms in wood and demonstrates the structural changes that take place in different types of decayed wood after it was converted into charcoal. The study seeks to determine whether the microbial attack found in archaeological woods took place before the burning of the wood or after. Burning experiments were conducted using wood that had been decayed by various types of fungi including white-rot, brown-rot, and soft-rot. The laboratory burnt wood samples showed decay patterns that were comparable to those observed in archaeological charcoal samples, indicating that signs of fungal infestation and features of decay can be preserved after burning with micromorphological details of mycelium and cell wall attack evident. This indication may provide important information related to the gathering of deadwood as fuelwood. In addition, examples of decayed wood preserved in archaeological charcoal assemblages are described. Their relationship to the archaeological context and environmental conditions may suggest different interpretative models concerning wood management strategies applied by past societies.     

Study of interactions between polyethylene glycol and archaeological wood components by C high-resolution solid-state CP-MAS NMR

While use of polyethylene glycols, PEG, polymers for archaeological wood conservation has been well established, there is almost no study of such composite materials with carbon thirteen high-resolution solid-sate NMR. We demonstrate that NMR is an useful analytical tool to characterize rapidly samples of conserved wooden objects. By choosing an appropriate value of the contact time (from 3 to 5 ms) for which the PEG component gives only a small residual NMR signal in the CP-MAS experiment, it is possible to edit selectively the spectra of the wood components. It allows one to visualize the degradation extent of the archaeological wood even when the conservation processes have been already applied. Moreover, by studying the kinetics of CP-MAS experiments, the time constants, T_1ρH and T_CH values for PEG moiety were computed. From these data, it is shown that either in the crude commercial product or in incorporated in archaeological woods, two components are present and they are the signatures of crystalline (or ordered) and amorphous (or disordered) molecular domains. Moreover, it was shown in the archaeological woods that almost 30% of PEG was in close molecular interactions with lignins. This study is the first evidence that the PEG in conserved wood can interact at a molecular level with wood components. It also demonstrates that the PEG diffuses inside the residual cell walls of archaeological wood. This data are important for scientists in charge of process development for the conservation of wooden artifacts.