Archaeological Wood Research Articles

The dependable deep time Acacia: Anthracological analysis from Australia’s oldest Western Desert site

Despite environmental factors being at the forefront of socio-ecological models in Australian archaeology, detailed local environmental and vegetation datasets are uncommon. Such data is important in assessing, for instance, if and how shifting climatic conditions influenced and conditioned hunter-gatherer movements and choices. Archaeological re-excavation of Karnatukul (Serpents Glen) in Katjarra (the Carnarvon Ranges) provided an opportunity to undertake anthracological (archaeological wood macro-charcoal) analysis. This data offers an insight into the earliest uses of firewood and collection strategies in the Australian Western Desert. This study aimed at testing global anthracological methodologies to examine the problems and potentials offered by this important sub-discipline which is currently developing in Australian archaeology. This study makes an important contribution to international anthracological studies, given these are rarely applied to arid contexts, especially with an occupation record spanning almost 50 ka. The study demonstrates the presence and persistence of Acacia (sens. str.) woodlands from the Pleistocene, through the Last Glacial Maximum, and into the Holocene with the case made that this productive plant makes an essential contribution to the habitability of this arid landscape.

Woodland Management Practices in Bronze Age, Bruszczewo, Poland

The article presents a study of wood excavated from archaeological site in Poland (2100–1650 BC). The large amount of collected samples created a unique opportunity for research because the subfossil wood was in very good preservation state. This made it possible to carry out dendrotypological analysis. This is the first such study conducted for Early Bronze Age timber originating from Poland. The main goal of the study was to determine whether the presence of strong and abrupt reductions and releases of growth, observed within tree-ring sequences, is due to natural stand dynamics, results from the influence of extreme environmental factors or whether they should be linked to specific silvicultural practices already known in ancient times. Another purpose of the study was to determine the type of forest management techniques applied to the trees growing in Bruszczewo site. The research was conducted using the dendrochronological method. In addition to the measurements of growth-ring width, the development of earlywood and latewood zones, the proportion of sapwood and the presence of specific features of tree trunks were analysed. A detailed study allowed identifying the samples originating from coppiced and shredded trees. A characteristic feature of the trees subjected to these silvicultural practices is the presence of strong and abrupt reductions and releases of growth. Moreover, coppiced trees were specified by the large proportion of sapwood in the cross-section of the stem, reduced number of sapwood rings, small and numerous earlywood vessels, diminished earlywood vessels area. In turn, shredded trees distinguished themselves by a strong reduction in the earlywood width in the years following the shredding event. The research of archaeological wood from the ancient settlement proves that during the Early Bronze Age various forest management techniques were used in this site. These treatments were aimed at improving the quality and quantity of the raw material harvested from forest areas.

Variations in bacterial decay between cell types and between cell wall regions in waterlogged archaeological wood excavated in the intertidal zone

Abstract The bacterial decay of waterlogged archeological wood (WAW, hard pine spp.) taken from Daebudo shipwreck No. 2, which was buried in the intertidal zone in the mid-west coast (Yellow sea) of South Korea approximately 800 years ago, was investigated. The maximum moisture content of the outer parts (approx. 3 cm of depth) of WAW was approximately 4.2 times higher than that of undegraded reference pine wood. ATR-FTIR and solid-state 13C-NMR analysis indicated a relative increase of the lignin concentration in WAW caused by the degradation of cellulose and hemicelluloses across the board studied (31-cm-wide and 14.5-cm-thick board). Micromorphological studies also revealed that bacterial degradation was progressed to a depth of 15 cm (vertically 7.3 cm) from the surface, which is the innermost part of the board. Erosion bacteria (EB) were identified as the main degraders of WAW. Degradation by tunneling bacteria (TB) was occasionally detected. Decay resistance to bacterial attacks in WAW varied between cell types and between cell wall regions. Axial tracheids showed less resistance than ray tracheids, ray parenchyma cells, and axial intercellular canal cells, including strand tracheids, subsidiary parenchyma cells, and epithelial cells. Decay resistance was higher in ray tracheids and strand tracheids than in ray parenchyma cells and subsidiary parenchyma-/epithelial cells, respectively. Bordered- and cross-field pit membranes and the initial pit borders showed higher decay resistance than the tracheid cell walls. Overall, the S2 layer of the axial tracheids showed the weakest resistance to bacterial attacks.

Historical Forest Management Practices Influence Tree-Ring Based Climate Reconstructions

Tree-ring widths (TRW) of historical and archeological wood provide crucial proxies, frequently used for high-resolution multi-millennial paleoclimate reconstructions. Former growing conditions of the utilized trees, however, are largely unknown. Potential influences of historical forest management practices on climatic information, derived from TRW variability need to be considered but have not been assessed so far. Here, we examined the suitability of TRW series from traditionally managed oak forests (Quercus spp.) for climate reconstructions. We compared the climate signal in TRW chronologies of trees originating from high forests and coppice-with-standards (CWS) forests, a silvicultural management practice widely used in Europe for most of the common era. We expected a less distinct climate control in CWS due to management-induced growth patterns, yet an improved climate-growth relationship with TRW data from conventionally managed high forests. CWS tree rings showed considerably weaker correlations with hydroclimatic variables than non-CWS trees. The greatest potential for hydroclimate reconstructions was found for a large dataset containing both CWS and non-CWS trees, randomly collected from lumber yards, resembling the randomness in sources of historical material. Our results imply that growth patterns induced by management interventions can dampen climate signals in TRW chronologies. However, their impact can be minimized in well replicated, randomly sampled regional chronologies.

The Viscoelastic Behaviour of Waterlogged Archaeological Wood Treated with Methyltrimethoxysilane.

Waterlogged wood treatment with methyltrimethoxysilane (MTMS) proved effective in stabilising wood dimensions upon drying (anti-shrink efficiency of 76–93%). Before the method can be proposed as a reliable conservation treatment, further research is required that includes the evaluation of the mechanical properties of treated wood. The aim of the study was to characterise the effect of the treatment on the viscoelastic behaviour of archaeological waterlogged elm and oak wood differing in the degree of degradation. Dynamic mechanical analysis in the temperature range from −150 to +150 °C was used for the study. To better understand the viscoelastic behaviour of the treated wood, pore structure and moisture properties were also investigated using Scanning Electron Microscopy, nitrogen sorption, and Dynamic Vapour Sorption. The results clearly show that methyltrimethoxysilane not only prevents collapse and distortions of the degraded cell walls and decreases wood hygroscopicity (by more than half for highly degraded wood), but also reinforces the mechanical strength by increasing stiffness and resistance to deformation for heavily degraded wood (with an increase in storage modulus). However, the MTMS also has a plasticising effect on treated wood, as observed in the increased value of loss modulus and introduction of a new tan δ peak). On the one hand, methyltrimethoxysilane reduces wood hygroscopicity that reflects in lower wood moisture content, thus limiting the plasticising effect of water on wood polymers, but on the other hand, as a polymer itself, it contributes to the viscous behaviour of the treated wood. Interestingly, the effect of silane differs with both the wood species and the degree of wood degradation.

Conservation of Waterlogged Wood—Past, Present and Future Perspectives

This paper reviews the degradation, preservation and conservation of waterlogged archaeological wood. Degradation due to bacteria in anoxic and soft-rot fungi and bacteria in oxic waterlogged conditions is discussed with consideration of the effect on the chemical composition of wood, as well as the deposition of sulphur and iron within the structure. The effects on physical properties are also considered. The paper then discusses the role of consolidants in preserving waterlogged archaeological wood after it is excavated as well as issues to be considered when reburial is used as a means of preservation. The use of alum and polyethylene glycol (PEG) as consolidants is presented along with various case studies with particular emphasis on marine artefacts. The properties of consolidated wood are examined, especially with respect to the degradation of the wood post-conservation. Different consolidants are reviewed along with their use and properties. The merits and risks of reburial and in situ preservation are considered as an alternative to conservation.

Evaluation of some wood-water relations and chemometric characteristics of recent oak and archaeological oak wood (Quercus robur) with archaeometric value

The present paper studied wood-water relations and their effects on color changes. Additionally, FTIR analysis of recent and archaeological oak wood was completed. Comprehensive knowledge of wood-water relations in recent and archaeological oak wood will facilitate the use of treatment material in the restoration and conservation process of the investigated artefacts. Wood samples were impregnated with tetraethyl orthosilicate. Sorption time until equilibrium moisture was reached increased significantly as a result of the treatment. Thus, the saturation time for treated recent oak wood was 43% longer than it was for untreated recent oak. Additionally, the treatment increased sorption time to equilibrium moisture in archaeological oak by 63%. The treatment resulted in significant color changes for both recent and archaeological oak wood. Samples displayed less color difference when they were dry compared to when they were wet. According to the FTIR analysis, tetraethyl orthosilicate causes the increase of the amount of O-H groups in archaeological oak wood and also caused an increase in the of the amount of C=O groups. This change is due to the hiding effect of xerogel formation on the functional group of wood.

Collapsed and re-swollen archaeological wood: efficiency and effects on the chemical and viscoelastic characteristics of wood

• Swelling agents evaluated for the shape recovery of collapsed archaeological wood • Effects of treatments on viscoelastic characteristics assessed by dynamical mechanical analysis (DMA) • Strongly alkaline systems reached full recover of the original shape • Treatments induced crystallinity depletion in cellulose and partial removal of the already decayed lignin • Stiffness reduced and dissipative behaviour increased after treatments in alkaline conditions The efficiency of different swelling agents in recovering the shape of collapsed archaeological wood (where the original object figure is lost) was evaluated. Furthermore, the effect of these treatments on the chemical and viscoelastic characteristics of wood was assessed by dynamical mechanical analysis (DMA). In preliminary trials, carried out on both alder ( Alnus spp) and a highly decayed ash wood ( Fraxinus excelsior L.), the efficiency of various organic solvents (dimethylsulfoxide, ethylene diamine, ethylene glycol, ethylene glycol mono butyl ether, N,N-dimethylacetamide) and active alkali urea (an experimental treatment previously proposed for collapsed wood) was considered in relation to three working temperatures. Following, medium decayed Scots pine ( Pinus sylvestris L.), highly decayed maritime pine ( Pinus pinaster Aiton), and two differently decayed oak woods ( Quercus spp) were used to investigate the effects of the three best agents on the viscoelastic properties of wood and, again, their efficiency. Tests demonstrated that in most decayed samples, although high swelling was obtained, lignin was lost and a substantial weight decrease was observed. However, in least decayed samples a loss of cellulose crystallinity was detected. These occurrences reflected on both samples stiffness (that strongly reduced after treatments) and dissipative behaviour (an increase of damping factors could be observed after treatments in alkaline conditions). Thus, swelling agents, although satisfactory in the shape recovery of collapsed wood, should be used only in cases of real injury imputable to collapse (a specific consolidation treatment should be considered in addition).

Evaluation of an alternative biotreatment for the extraction of harmful iron and sulfur species from waterlogged wood

An innovative bioextraction method was tested and compared to common chemical extraction for the preservation of waterlogged archeological wood (WAW) artifacts. During burial, WAW artifacts accumulate iron and sulfur species forming iron sulfides. These compounds are harmless in the burial environment, where the oxygen content is low. But upon excavation, the WAW undergoes the oxidation of these compounds, and thus, irreversible physical and chemical damages occur. Fresh and archeological oak and pine samples were selected as representative species of WAW artifacts. Fresh samples were previously artificially contaminated to ascertain the presence of iron and sulfur. Thiobacillus denitrificans and natural iron chelators, called siderophores, were investigated to extract iron and sulfur as a 2-step biological treatment (BT) and compared to sodium persulfate–EDTA as chemical treatment (CT). Consolidation and freeze-drying were performed on the samples after BT and CT as traditional conservation protocols. BT and CT efficiency was evaluated through Raman, inductively coupled plasma–optical emission (ICP-OES), and Fourier transformed infrared (FTIR) spectroscopies. Raman and ICP showed that most of the iron and sulfur was extracted after BT, while some sulfur species remained present on CT samples. None of the extraction methods resulted in a degradation of the wood, as ascertained by FTIR analyses. Yet, all samples presented visual modifications after conservation. Pine samples treated with BT illustrated the oxidation of the species. Present principal component analysis (PCA) and analysis of variance (ANOVA) which were selected as statistical approaches and validated BT as a promising alternative extraction method, with encouraging extraction rates and less alteration of the sample appearance.

Automated 3D tree-ring detection and measurement from X-ray computed tomography

Tree ring analysis is essential to reveal the environmental information encoded in the wood structure. It provides quantitative data on the anatomical structure which can be used, for example, to measure the impact of the fluctuating environment on the tree growth, to support global vegetation models and for the dendrochronological analysis of archaeological wooden artefacts. Currently, several imaging-based methods for tree-ring detection and tree-ring feature estimation exist. However, despite advances in computer vision and edge recognition algorithms, detection of tree-rings is mostly limited to two-dimensional (2D) datasets and performed manually in some cases. This paper describes a new approach to estimate the three-dimensional (3D) structure of tree rings and their width automatically from X-ray computed tomography data. This approach relies on a modified Canny edge detection algorithm, which is capable of detecting fully connected tree-ring edges throughout the image stack. Our results show that this approach performs well on six tree species having conifer, ring-porous and diffuse-porous ring boundary structures. In our study, image denoising proved to be a critical step to achieve accurate results. A major advantage of this procedure is that it requires very little to no user interaction rendering it a reproducible procedure for tree-ring width measurements. As it also provides 3D representations of the ring edges, it also may be used in the future for the inspection of anatomical features.

Evaluation of Soda Lignin from Wheat Straw/Sarkanda Grass as a Potential Future Consolidant for Archaeological Wood

This work is part of a larger study, which aims to use soda lignin from straw as the starting point for a non-aqueous consolidant for highly degraded archaeological wood from the Oseberg collection. This wood was treated with alum salts in the early 1900s, is actively degrading and exists in varying states of preservation. Non-aqueous consolidants are an option to stabilize this wood mechanically in cases where it is too deteriorated to undergo aqueous-based retreatments, for example using polyethylene glycol. The aim of this study was to compare the extent of penetration of two soda lignin preparations in low- to medium-degraded archaeological pine. The soda lignins were dissolved in ethyl acetate and had two molecular weight groups: P1000 (molecular weight Mw of~3 kDa) and the ethyl acetate fraction FB01 (Mw of ~1 kDa). Penetration after immersion was evaluated by infrared spectroscopy and analytical pyrolysis. Treated specimens were also evaluated using weight and dimensional change and scanning electron microscopy. Both lignins penetrated into sample cores, but P1000 did not penetrate as well as FB01. This may be due to differences in their molecular weights, but also differences in polarity due to the presence of different functional groups.

87Sr/86Sr isotope ratios in trees as an archaeological tracer: Limitations of linking plant-biomass and bedrock Sr isotope signatures

Assuming that strontium (Sr) isotope ratios in trees mirror the bedrock isotope signal, between-site 87Sr/86Sr comparisons can serve as a powerful tool in archaeological wood provenance studies. Here we discuss the strengths and weaknesses of this approach using Sr isotope data for bedrock, trees and rainfall collected at seven sites in the Czech Republic. The study included basalt, durbachite, granite, paragneiss, limestone and phyllitic slate. The range of 87Sr/86Sr ratios of these bedrock types was extremely large (0.704–1.743). The investigated tree species included oak, pine, and spruce. Within-tree variability in 87Sr/86Sr ratios (~0.010) was two orders of magnitude smaller than the variability in Sr ratios across the studied bedrock types. Oak and pine growing on identical bedrock exhibited statistically indistinguishable 87Sr/86Sr ratios. In four types of spruce tissues from a particular site, the 87Sr/86Sr ratios were indistinguishable, while significantly different from spruce tissues at another site. The 87Sr/86Sr ratios of the wood differed from those of bedrock, converging to the 87Sr/86Sr ratio of rainfall (0.709–0.714). Even at a 450-km distance from the nearest sea, atmospheric Sr partly originated from sea-spray. Incorporation of atmospheric Sr in trees often results in overlapping 87Sr/86Sr ranges and hampers source identification of archaeological wood.

Testing 1D and 2D single-sided NMR on Roman age waterlogged woods

Waterlogged archaeological wood can provide information on past human activities and technology but its structure may be modified due to microbial deterioration. Knowing its conservation state is fundamental for its restoration. Aim of this work was to test the use of non-destructive portable NMR for the microstructural characterization and preservation state of three archaeological wood samples (Roman age, 5th century AD). 1D T1 and T2 relaxation time distributions, as well as 2D T1-T2 and D-T2 distributions were measured by single-sided NMR and interpreted with the help of high resolution magnetic resonance imaging (MRI) and optical microscopy. Due to the complexity of the ancient wood samples, in this first study a multi-analytical approach was required. It allowed the characterization of both waterlogged softwood (spruce) and hardwood (chestnut and maple) by quantifying relaxation times and diffusion water components affected by the presence of degradation products such as fungi, paramagnetic agents, and microstructural changes. Optical microscopy was needed to investigate the sub-microscopic wood elements not resolved by MRI and validate indirect single-sided NMR investigations. Observations and results of this study will allow the improvement of single-sided NMR protocols for the analyses of archaeological wood in situ with portable NMR.

Nondestructive visualization of polyethylene glycol impregnation in wood using ultrashort echo time 3D imaging

In this study, we demonstrated a nondestructive 3D monitoring method of polyethylene glycol (PEG) impregnation in wood using magnetic resonance imaging ultrashort echo time (UTE). The materials used were sound wood, which was impregnated with a 20 wt.% aqueous solution of PEG4000 for two weeks and further impregnated at an interval of two weeks with PEG concentrations of 40, 60, 80, and 100 wt.%, as well as archaeological wood impregnated with a 40 wt.% solution of PEG 4000 at room temperature for about 4 years. The signal intensity of the PEG4000 aqueous solution monotonically increased with increasing concentration of PEG, although under certain temperature conditions. Stereoscopic images were created from the UTE image data of the wood sample, and it was possible to represent the PEG-impregnated portion of the wood sample in 3D. In conclusion, it has been suggested that UTE imaging is a feasible method to nondestructively visualize the PEG impregnation state of waterlogged wood in 3D and to evaluate and monitor it from all directions with a high spatial resolution, under specific temperature control of the material.

Comparative chemical investigations of alum treated archaeological wood from various museum collections

From the mid-1800s to the late 1960s, conservation by alum salts (KAl(SO4)2·12H2O—potassium aluminium sulphate), using various recipes, was a common method to prevent shrinkage and to strengthen waterlogged archaeological wooden objects. This method was mainly used in Scandinavia. The alum method appears to have also been applied to highly degraded archaeological waterlogged wood in other countries, for example in the U.S and Germany. Today, many of the archaeological wooden objects treated with alum show extreme deterioration and very low pH, which are attributed to the effects of the alum-treatment. This study investigated the extent of the current levels of chemical degradation in wooden objects conserved with alum salts at different points in time (1880s, 1930s and 1905–13) in order to understand their current condition and whether extent of degradation was in any way related to time of treatment, in an attempt to understand the rate of degradation. It was also an opportunity to compare the chemical state of preservation of alum-treated wood from different collections, as only the Oseberg collection has been intensively studied in this way up until now. Samples from historical wooden objects from the following collections were investigated and compared: the Dejbjerg collection (National Museum of Denmark in Copenhagen); the Oseberg collection (Museum of Cultural History, Oslo, Norway); the Glimmingehus collection (Swedish History Museum, Sweden). Analyses of lignocellulosic polymers and of inorganic compounds were undertaken to evaluate the chemical preservation of the wooden objects. The investigations were performed using a multi-analytical approach which consisted of: pH measurements, analytical pyrolysis (Py-GC/MS), X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS). It was possible to link the extent of degradation with time, on a general level but we found a great variability in the state of preservation of the wood also within the same collection. It is clear, however that alum-treated wood is more degraded than archaeological wood not treated with alum.

Provenancing wood used in the Norse Greenlandic settlements: A biogeochemical study using hydrogen, oxygen, and strontium isotopes

A growing number of studies strive to examine wooden archaeological remains recovered from Norse sites in the North Atlantic, contributing to a better understanding of patterns in both wood exploitation and woodland management. Despite the limited diversity and abundance of trees in the North Atlantic islands, the Medieval Norse kept using wood in most everyday activities including the construction and repair of buildings and boats, the production of artifacts and tools, and as a source of fuel. The proximity of the Greenland settlements with the northeastern American coast, puts them at the forefront in the exploration and exploitation of remote resource regions. While some species may have arrived both as driftwood or imported material, there is currently no method to conclusively identify archaeological wood remains as driftwood. Here, we use biogeochemical analysis of stable hydrogen (δ2H), stable oxygen (δ18O), and radiogenic strontium (87Sr/86Sr) isotopes in soil, water, and modern plant samples from various sites in Greenland and Canada to characterize expected local isotopic baselines. While 87Sr/86Sr isotope ratios do not provide a clear distinction between the regions of interest, δ2H and δ18O ratios appear to help discriminate not only between regions but also specific sites. In addition, we completed a pilot study of archaeological wood samples obtained in Greenland to test the effectiveness of the 87Sr/86Sr biogeochemical baseline. Results demonstrate that at least in some cases, diagenetic processes were not sufficient to mask a non-local 87Sr/86Sr signature.

Monitoring of the Environmental Corrosivity in Museums by RFID Sensors: Application to Pollution Emitted by Archeological Woods

The control of air quality in museums or storages is of fundamental interest for the conservation of historic artifacts. The present work reports an example of application of RFID sensors developed in the European project SensMat and dedicated to this issue. The sensors are based on the variation of property of an RFID tag coupled with a sensitive silver thin film exposed to the environment. As it will be described in the paper, such low-cost sensors are interrogated by a commercial reader and provide the environmental corrosivity index and thus the presence of pollutants. The selected case study concerns the monitoring of pollution by H2S in a building dedicated to conservation and restoration of archeological and historical woods. The ability of sensors to map spatially the corrosivity within buildings is highlighted.

The effect of the drying method on the cell wall structure and sorption properties of waterlogged archaeological wood

Drying is a process affecting various wood properties, including its structure, moisture behaviour and mechanical properties. Since waterlogged wooden artefacts usually constitute priceless objects of cultural heritage, understanding the effect of drying on the complex interactions between the wood ultrastructure and the resulting properties is necessary to ensure their proper conservation. Hence, this was the aim of the present study, with a particular emphasis on the influence of drying conditions on the relations between the cell wall structure, dimensional stability and hygroscopicity of degraded archaeological wood. The choice of the particular drying methods was dictated by their final effect on wood appearance (dimensions). The results obtained clearly show that depending on the drying method applied, the resulting material differs significantly in structure, dimensions and sorption properties, despite the same degree of wood degradation. Air- and oven-drying resulted in the highest wood shrinkage, lower porosity, and a decreased number of free hydroxyls in the wood cell wall. The best wood dimensional stabilisation and the highest porosity were ensured by freeze- and supercritical drying. No correlations were found between wood structure and moisture behaviour. The outcome of the research may be useful for conservators who plan to provide the artefacts with proper storage conditions and effective conservation/reconservation.

Chemical Properties and Microbial Analysis of Waterlogged Archaeological Wood from the Nanhai No. 1 Shipwreck

The Nanhai No. 1 was a wooden merchant ship of the Southern Song Dynasty, which wrecked and sank in the South China Sea, Yangjiang City, Guangdong Province, China. The Nanhai No. 1 shipwreck was salvaged as a whole in 2007 and began to be excavated in 2013. During the archaeology excavation, some of the hull wood fell off the hull. These waterlogged archaeological woods (WAW) were immersed in the buffer containing EDTA-2Na and isothiazolinone K100 for moisture stabilization, preliminary desalination, and microbial inhibition. We evaluated the properties of these WAW through testing the chemical components (including lignin, holocellulose, and ash content) of the wood, and monitoring the iron element content, anion and cation content in the buffer. At the same time, the microbial composition in the desalination buffer was also detected. The results showed that the holocellulose content in these WAW were much lower than in fresh wood. The ash content in these WAW decreased after desalination treatment. The iron element content, anion and cation content in the buffer were high and kept at a certain level after desalination treatment. At the same time, the problem of biodegradation in the buffer should be paid attention to. The comprehensive protection of WAW requires to combine wood properties and microbial problems. This study provides a reference for the protection of WAW from the Nanhai No. 1 shipwreck and other similar historical wood.

X-ray computed tomography to study archaeological clay and wood artefacts at Lilybaeum

X-ray computed tomography to study archaeological clay and wood artefacts at Lilybaeum