Waterlogged Archaeological Wood Research Articles

Conservation of waterlogged archaeological wood: what we can learn from the Vasa experience?

Conservation of waterlogged archaeological wood: what we can learn from the Vasa experience?

Aqueous modification of waterlogged archaeological wood by phenylboronic acid to reduce hygroscopicity and improve the dimensional stability

Aqueous modification of waterlogged archaeological wood by phenylboronic acid to reduce hygroscopicity and improve the dimensional stability

Effects of sodium chloride on mechanical properties in amorphous polymers of waterlogged archaeological wood: Insights from molecular dynamics simulations

Sodium chloride (NaCl) is the main soluble salt component of marine waterlogged archaeological wood, and it causes deterioration of wood fibres. In this study, a molecular dynamics simulation of three types of archaeological wood from the Quanzhou Song Shipwreck was employed to investigate the impact of NaCl on the mechanical properties of amorphous components consisting of amorphous cellulose, hemicellulose, and lignin. The findings revealed that water molecules bound to the fibres enhanced the mechanical performance of the woody fibres. However, NaCl affected the stability and mechanical properties of the amorphous components. By using molecular dynamics simulations, 24 sets of amorphous fibre models, consisting of fir, pine, and camphorwood with salt concentrations ranging from 0 % to 7 %, were constructed to further analyse the influence of salt content on the mechanical properties of the amorphous components. The results showed that all three species of archaeological wood exhibited similar trends, with the adsorption energy and radial distribution function between wood fibres and water molecules decreasing with increasing NaCl concentration, leading to the gradual rupture of hydrogen bonds in water molecules. Consequently, more water molecules engage in ion hydration, resulting in an increase in the amount of free water within the amorphous regions. This, in turn, degrades the mechanical properties of the amorphous components. This study contributes significantly to a comprehensive understanding of the mechanical properties of marine archaeological wood and is important for decision-making in studies related to the preservation and evaluation of marine waterlogged wooden artefacts.

Characterization of Microbial Decay and Microbial Communities in Waterlogged Archaeological Wood Excavated from the Wetland

Anatomical and chemical changes due to microbial decay and microbial communities in three waterlogged archaeological woods, namely Dongnim 1, Dongnim 2, and Dongnim 3, excavated from the wetland of the Dongnim-dong archaeological site in Gwangju, were investigated. Dongnim 1−3 exhibited a maximum moisture content approximately 6 to 8 times higher than that of undecayed recent wood, and there was no correlation with the burial period. Chemical analysis revealed an increase in ash and hot water extractive content in Dongnim 1−3 compared to undecayed recent wood, while the solvent extractive content tended to decrease. Additionally, there was a significant decrease in holocellulose content with a relative increase in lignin concentration in Dongnim 1−3. Microscopic observations showed erosion bacteria decay and soft rot decay in Dongnim 1−3. The microbial community analysis of Dongnim 2 and 3 revealed the dominance of Ascomycota (98% to 99%) in the fungal community and Proteobacteria (34% to 55%) as the predominant bacterial phylum. Nonetheless, significant differences in microbial community structure and diversity were observed between Dongnim 2 and Dongnim 3.

Study on the Feasibility of the TG Method for Maximum Water Content Measurement of Waterlogged Archaeological Wood

ABSTRACT Thermogravimetry (TG) is used to measure the change of sample mass versus temperature or time under a program controlling temperature. It is a common thermal analysis tool with a precise built-in balance, and accurate data can be obtained through a small amount of sample at the level of milligrams. The feasibility of the TG method for determining maximum water content (MWC) measurement of waterlogged archaeological wood was studied. Simulated waterlogged wood and waterlogged archaeological wood were used to determine the test condition for the TG method. MWC data obtained through the oven-dry and TG methods with different mass gradients from 0–10 mg to >50 mg were analyzed statistically. Deviation, error bar, and coefficient of variation were evaluated. According to the results, when sample mass is no less than 30 mg, and holding time at 105°C is no less than 40 min, data deviation between these two methods is less than 5%. Effect of sampling depth and presence of inorganic deposits were also investigated. Specimens were taken from an archaeological wood with a sampling depth from 2 to 6 mm, then MWC was measured through the TG method. The results indicate MWC of the samples taken from a depth of 2–4 mm is higher than that taken from a depth of 0–2 mm and is lower than that taken from a depth of 4–6 mm, which is related to inorganic deposits. The presence of deposits was verified through SEM-EDX. MWC of three archaeological wood samples from China and five archaeological wood samples from Italy were measured to verify the effectiveness of the TG method when wood species and degradation degree are different.

Functional conservation and preservation of waterlogged archaeological wood

Waterlogged archaeological wood of shipwrecks has been preserved under seawater for centuries, such that microbial erosion has caused severe bacterial degradation and acidification. These wooden cultural relics are of great significance for understanding the shipbuilding technology, trade activities, and environmental ecology of centuries ago. From the perspective of structure and composition, these waterlogged archeological woods have the characteristics of high water content and a large loss of lignin and cellulose, which makes the hull prone to collapse during preservation. Therefore, it is urgent to apply conservation and preservation treatments for deacidification and consolidation. Due to the fragility of wood and the complexity of repair work, the current development of conservation and preservation technology has multiple aims, such as antibacterial, deacidification, and reinforcement effects. In this editorial, the current challenges and conservation treatments with antimicrobial or deacidification utilities will be introduced.

Prediction model of the hardness of waterlogged archaeological wood based on NIR spectroscopy

The significance of waterlogged archaeological wood (WAW) lies in its profound informational value, encompassing historical, cultural, artistic, and scientific aspects of human civilization, and therefore need to be properly studied and preserved. In this study, the utilization of near-infrared (NIR) spectroscopy is employed as a predictive tool for assessing the hardness value of WAW. Given the submerged burial conditions, waterlogged wooden heritage frequently undergo substantial degradation in their physical and mechanical properties. The mechanical properties of waterlogged wooden heritage are essential for evaluating their state of preservation and devising appropriate conservation and restoration strategies. However, conventional methods for testing mechanical properties are limited by factors such as the availability of adequate sample size and quantity, adherence to the “principle of minimum intervention,” and cost considerations. NIR spectroscopy is a non-destructive, rapid, sensitive, and low-cost analytical technique with great potential for application in this area. In this study, two large and significant ancient Chinese shipwrecks were investigated. One hundred ninety-seven samples were collected and analyzed using NIR spectroscopy and a portable C-type shore hardness testing method. A partial least squares (PLS) regression model was developed to predict the hardness of the WAW. The model was optimized and validated using different preprocessing methods and spectral ranges. The results indicate that the best models were obtained with first derivatives + multiple scattering corrections (MSC) and first derivatives + standard normal variate (SNV) preprocessing in the 1000–2100 nm spectral range, both with an R2c of 0.97, a root mean squared error of correction (RMSEC) of 2.39 and 2.40, and a standard error of correction (SEC) of 2.40 and 2.41. Furthermore, they exhibited an R2v of 0.89 and 0.87, a root mean squared error of cross-validation (RMSECV) of 4.43 and 4.67, a standard error of cross-validation (SECV) of 4.45 and 4.68, and RPD values of 3.02 and 2.88, respectively. A coefficient of determination of the established prediction model (R2p) of 0.89 with a relative standard deviation for prediction (RSD) of 6.9% < 10% was obtained using a sample from the prediction set to predict the established model inversely. These results demonstrate that NIR spectroscopy could enable a rapid, non-destructive, and accurate estimation of the hardness of WAW. Moreover, by carefully choosing appropriate preprocessing techniques and spectral ranges, the predictive capabilities and accuracy of the model can be further enhanced. This research also contributes to the development of a theoretical framework and a methodological approach for future studies in this field. Furthermore, the data obtained from this study are crucial for determining effective preservation strategies for waterlogged archaeological wood.

Inorganic component in oak waterlogged archaeological wood and volcanic lake compartments

Abstract. Waterlogged archaeological wood (WAW) is a rare and precious organic material that can hold outstanding cultural values. In order to protect WAW for the next generations, this material must be accurately characterised to set its proper conservation, storage and exhibition conditions in museum environments. In this study, the mineral content found in WAW retrieved in a volcanic lake was investigated by analysing wood ash through scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (SEM-EDS). This micro-destructive approach was coupled with morphological studies carried out through optical microscopy. SEM-EDS was also performed on the WAW and surrounding sediment to study the possible relationship between the mineral composition and the wood degradation state. The analysis revealed that calcium was the most abundant element in all poles, with weight percentages ranging between 24 % and 42 %. This element was more represented in heartwood (HW) than sapwood (SW). In sapwood the second most abundant element was arsenic. Sulfur, iron and potassium were present in all the analysed samples as well. Arsenic was also detected in the sediments; it was particularly concentrated in the samples taken near archaeological wood. The presence of this element can be linked to the volcanic origin of the lake, and its high concentration points to bioaccumulation processes induced by bacteria (erosion bacteria and sulfate-reducing bacteria) and biogeochemical processes favouring precipitation of insoluble compounds. The present work is the first investigation of the mineral content in archaeological wood establishing a contingent relationship with the surrounding volcanic lake sediments.

Set-up of a methodology to evaluate the consolidation of archaeological waterlogged wood veneered in ivory

This work describes how a conservation method making use of aqueous solutions of lactitol and trehalose (9:1) was chosen to treat several elements of wood furniture veneered in ivory carved in bas-relief and preserved in waterlogged condition. These elements were discovered during the excavations carried out in Villa dei Papiri, the most famous of the luxury villas of Herculaneum. The approach described was based on a dual evaluation. It was carried out: (a) on probe wood specimens produced in the laboratory capable of simulating both the impregnability by consolidants and the deformation of decayed waterlogged wood; (b) on one archaeological element belonging to the original furniture, representative of the material to be treated. The probe specimens produced in the laboratory were artificially degraded by placing them in contact with the brown rot fungus Coniophora puteana, in order to obtain a material of variable decay, similar to that of the original archaeological furniture elements. Three experimental factors were considered when treating probe specimens: (a) the type of substrate, (b) the initial and final consolidant concentration and (c) the drying regime.Three types of substrates were considered: specimens covered with a polycarbonate sheet to simulate the ivory veneer and wrapped in gauze; specimens only wrapped in gauze; and naked specimens, that is, with no obstacles for consolidant penetration. Considering consolidant concentration, the probe specimens were impregnated by full immersion, increasing the concentration of lactitol/trehalose in four combinations: from 15 to 50%, 15 to 60%, 30 to 50%, and 30 to 60%. Last, three drying regimes were considered: 50 °C in an oven, 30 °C/35% RH and 20 °C/65% RH. Results showed that probe specimens whose impregnation started with 30% consolidant in the solution and finished in 60%, and dried under 30 °C and 35% RH exhibited limited volume variations after drying equivalent to those obtained by drying at 50 °C. Drying conditions were important factors in the success of the entire treatment process. As was consolidant uptake, in relation to the extent of decay of the archaeological material. Moreover, the presence of the physical barriers simulating the existence of the ivory veneers and gauzes did not disturb the efficacy of the treatment, as long as sufficient time was given to allow the water-consolidant exchange process to be completed. In the end, the treatment conditions selected on the basis of these probing tests, that is, start with initial concentration of 30%, final concentration of 60%, and drying at 30 °C/35% RH, showed to be successful for treating the representative element of the archaeological furniture.

Modified Lignin Nanoparticles as Potential Conservation Materials for Waterlogged Archaeological Wood

Lignin is the most abundant component in archaeological waterlogged wood, making it a potential consolidant with high compatibility for historical wood conservation. However, its consolidation effect is limited by its low penetration into the wood. In this study, modified lignin nanoparticles (LNPs) were proposed for the first time as conservation materials for waterlogged archaeological wood. Two modified LNPs were prepared with low molecular weight, small size, and high solubility in ethylene glycol (EG) for consolidating waterlogged wood samples. These nanoparticles, hydrophilic aminated LNPs (ALNPs) and hydrophobic esterified LNPs (MALNPs), greatly improved the consolidation effect of waterlogged wood samples compared to LNPs. This was demonstrated by measuring their physical properties, dimensional stability, and mechanical properties. The surface color change was almost within the acceptable range for the human eye. We also discussed two different reinforcement mechanisms of ALNPs and MALNPs. ALNPs can form hydrogen bonds with hemicellulose/cellulose in the wood to strengthen the fragile wood cell wall, while MALNPs can fill the wood cell lumen to support the cell wall and prevent deformation during drying. Our work provides an approach of using biomaterials as consolidants for archaeological waterlogged wood and expands the use of lignin in this field.

Evaluation of the efficacy of micro-Magnetic Resonance Imaging compared with light microscopy to investigate the anatomy of modern and ancient waterlogged wood

Light microscopy is the conventional method used to investigate wood anatomy, identify the wood taxon, and assess its conservation state. It generally requires the mechanical cut of thin sections from a sample to obtain informative images. When dealing with wooden artworks or ancient remains (e.g., archaeological waterlogged wood), it is important to avoid sample destruction. In this work the efficacy of micro-magnetic resonance imaging (μ-MRI) to investigate the anatomy of waterlogged wood is assessed in comparison with light microscopy. Images along the three anatomical directions (transverse, tangential and radial) of six modern wood species and one archaeological specimen of waterlogged wood (from the Neolithic site “La Marmotta”) were obtained both by μ-MRI and light microscopy. μ-MRI images were acquired virtually selecting 2D slices along the three wood anatomical directions. A 3D reconstruction was derived from 2D μ-MRI images. Conventional light microscopy histology was obtained by manually cutting thin sections. To the best of our knowledge, this is the first study in which high-resolution MR images and light microscopy images of the three anatomical directions of seven wood species are compared. The non-destructive μ-MRI approach allows to investigate the 2D and 3D topological organization of the whole waterlogged wood sample up to a resolution of 8 μm. Although the optical microscope attains higher image resolutions and remains superior in the observation of wood diagnostic characters, multi-parametric μ-MRI provides physiological investigation complementary to light microscopy, giving information concerning both a single section and the whole volume of the sample. The presented study may represent a starting point for further improvements of μ-MRI techniques applied to the non-destructive investigation of waterlogged wood samples, especially those of interest for cultural heritage.

Non-destructive Dendrochronology: The Effect of Conservation Agents on Tree-ring Measurements in Archaeological Oak with Micro-computed Tomography

ABSTRACT The effect of different conservation methods on non-destructive dendrochronology with micro-computed tomography (μCT) of waterlogged archaeological wood (WAW) was assessed. To this end, oak samples were conserved with alcohol-ether-resin, Kauramin 800®, lactitol/trehalose, saccharose, silicone oil and different polyethylene glycol (PEG) treatments with subsequent freeze-drying. Tree-ring measurements were compared with respect to the number of rings and the mean ring width using (a) an analog linear measuring table and (b) the digital μCT. Overall, the measurements in the μCT data agreed very well with the corresponding microscopic measurements. It was possible in all cases to recognize the rings in the samples with μCT. A dendrochronological cross dating with regional absolutely dated oak ring width chronologies was successful. However, the varying influence of conservation agents on the quality of the μCT data were also evident. To quantify this influence, the contrast in the μCT data were calculated using gray-scale profiles. An influence on the contrast in the μCT data were detectable for all conservation agents. The contrast is especially reduced due to conservation methods using lactitol/trehalose, PEG, saccharose and silicone oil. Overall, the experiments confirm, though, that μCT is a powerful and accurate tool for dendrochronology of conserved archaeological oak objects.

Non-destructive dendrochronology with X-ray computed tomography: The influence of different conservation methods for waterlogged archaeological wood

In this study, the influence of different conservation methods for waterlogged archaeological wood (WAW) on non-destructive dendrochronological dating by micro-computed tomography (µCT) was evaluated. For this purpose, samples of different wood species were conserved using the following methods: alcohol-ether-resin, Kauramin 800®, lactitol/trehalose, saccharose, silicone oil and different polyethylene glycol (PEG) treatments with subsequent freeze-drying. The tree ring measurements of all samples in the digital µCT data were compared with the measurements on an analog linear measuring table in terms of the total number of rings per sample and the mean ring width. The year-to-year ring width measurements in the µCT data agreed very well overall with the corresponding microscopic measurements. It was possible to detect the rings in the samples with µCT in all cases. A dendrochronological cross dating with regional absolutely dated ring width chronologies was successful in two cases. However, the different influence of the conservation agents on the quality of the µCT data was clearly visible. In order to assess this influence, the contrast in the µCT data was determined using grey-scale profiles. A decrease in contrast in the µCT data was detectable for all conservation agents. A particular strong influence is observed for the conservation methods using silicone oil, lactitol/trehalose, PEG and saccharose. Overall, the study performed confirms that µCT is a powerful and accurate method for non-destructive dendrochronology of conserved archaeological objects.

Size Effect on Hygroscopicity of Waterlogged Archaeological Wood by Simultaneous Dynamic Vapour Sorption

Hygroscopicity is one of the most important properties of wood and plays a decisive role in its dimensional stability. In this context, conservation plans for waterlogged archaeological wood (WAW) and relevant waterlogged artefacts must be created. The size of the sample required for a moisture sorption assessment may affect the results for (and thus the perception of) the hygroscopicity of a testing artefact. Herein, to investigate the effects of the sample size on the hygroscopicity of WAW as measured via dynamic vapour sorption (DVS), typical WAW and recent (i.e., sound) wood are processed into four differently sized samples, ranging in thickness from 200 mesh to millimetre. The equilibrium moisture contents (EMCs) of the wood samples are simultaneously measured using simultaneous DVS. The sorption isotherms show that the EMC values of the recent wood at each relative humidity increase as the sample size decreases, with the superfine powder sample achieving the highest EMC of all of the recent samples. Although the WAW has a higher EMC than that of recent wood, the effect of the size of the WAW sample on its hygroscopic properties is surprisingly not as pronounced as that for the recent wood. In addition, the hysteresis between the samples of different sizes of the archaeological wood is significantly smaller than that for the reference samples. Furthermore, regarding the standard deviations of the parameters obtained from the Guggenheim Anderson de Boer and Hailwood–Horrobin models, the values for WAW are all much smaller than those for the reference wood. This further verifies the disappearance of the size effect of the hygroscopicity for WAW.

Preservation status and microbial community of waterlogged archaeological woods over 7800 years old at the Jingtoushan Site, China

Preservation status and microbial community of waterlogged archaeological woods over 7800 years old at the Jingtoushan Site, China

A Multi-Parametric Investigation on Waterlogged Wood Using a Magnetic Resonance Imaging Clinical Scanner

In cultural heritage conservation science, moisture content (MC) is an essential factor to determine. At the same time, it is essential to choose non-destructive and non-invasive approaches for more sustainable investigations and make them safe for the environment and the sample. The question addressed in this work concerns the possibility and the opportunity to investigate waterlogged wood by using nuclear magnetic resonance imaging (MRI) clinical scanners to carry out non-destructive volumetric diagnostics. In this study, MRI, the most important non-invasive medical imaging technique for human tissue analysis, was applied to study archaeological waterlogged wood samples. This type of archaeological material has a very high moisture content (400%–800%), thus, it is an ideal investigative subject for MRI which detects water molecules inside matter. By following this methodology, it was possible to obtain information about water content and conservation status through a T1, T2, and T2* weighted image analysis, without any sampling or handling, and the samples were directly scanned in the water where they were stored. Furthermore, it permited processing 3D reconstruction, which could be an innovative tool for the digitalization of marine archaeological collections. In this work, 16 modern species of wood and a waterlogged archaeological wood sample were studied and investigated using a clinical NMR scanner operating at 3T. The results were compared with X-ray computed tomography (CT) images, as they had already been used for dendrochronology. The comparison highlights the similar, different, and complementary information about moisture content and conservation status in an all-in-one methodology obtainable from both MRI and CT techniques.

Well-controlled SI-ARGET ATRP of EGDMA for maintaining the dimensions of waterlogged archaeological wood

Well-controlled SI-ARGET ATRP of EGDMA for maintaining the dimensions of waterlogged archaeological wood

Imaging and Assessment of the Microstructure of Conserved Archaeological Pine

Impressive wooden objects from past cultures can last for centuries or millennia in waterlogged soil. The aim of conservation is to bring the more or less degraded waterlogged archaeological wooden (WAW) finds to a stable state without altering the wood structure through shrinkage, collapse, and deformation. In this study, the most used methods in the conservation practice, such as the alcohol-ether resin method, conservation with the melamine formaldehyde resin Kauramin 800, a mixture of lactitol and trehalose, saccharose, silicone oil, and three different conservation methods with polyethylene glycol followed by freeze-drying were tested. The effects of the conservation agents on the structure of archaeological pine were investigated using optical light microscopy (reflected light microscopy, RLM), scanning electron microscopy (SEM), and X-ray computed tomography (XCT). Through the examinations, most conservation agents could be identified in the structure and their impact on conservation could be analyzed. In particular, it was possible to trace the incorporation of the conservation agents in the lumen, which was influenced by factors, such as wood anatomy, degree of degradation, and drying process. Differences in the mode of action of the conservation processes could also be identified in the composition of the cell wall tracheids.

Characteristics of Ancient Shipwreck Wood from Huaguang Jiao No. 1 after Desalination.

Huaguangjiao I refers to the ancient Chinese wooden shipwreck of the South Song Dynasty (1127-1279 AD) discovered in the South China Sea in 1996. From 2008 to 2017, the archaeological waterlogged wood was desalted using deionized water combined with ultrasonic treatment, and desalted using EDTA-2Na, EDTAHO, and NaH2PO4·2H2O solutions. In this paper, the degree of degradation of the modified waterlogged archaeological wood and the moisture and content of the main components were determined. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nanoindentation (NI), and scanning electron microscopy (SEM) were employed to investigate the state of wood degradation after desalination and desulfurization. The results showed that the water content of the wood was as high as 532~1149%, while the basic density was only 0.14~0.18 g/cm3, indicating that the wood had been seriously degraded. The holocellulose content was only 36-40%. Based on the XRD patterns, the degree of cellulose crystallinity in the modified wood was 14.08%. The elastic modulus and hardness of the ancient shipwreck wood after desalination and desulfurization were 1.28-4.31 and 0.10-0.28 GPa, respectively, according to nanoindentation. In addition, the FTIR spectra revealed that the biological deterioration of the modified wood caused cellulose and hemicellulose degradation, but no apparent lignin alteration occurred. The results could provide knowledge for appropriate dewatering, strengthening, and restoration strategies.

Even Samples from the Same Waterlogged Wood Are Hygroscopically and Chemically Different by Simultaneous DVS and 2D COS-IR Spectroscopy

Waterlogged archaeological wood samples may degrade during long-term immersion in microbial-activity environments, which causes its biodegradation. Simultaneous dynamic vapor sorption (SDVS) and two-dimensional correlation infrared (2D COS-IR) spectroscopy reveal the degradation inhomogeneity of waterlogged fir wood from the Shengbeiyu shipwreck. The waterlogged and reference wood exhibit type II sorption isotherms. The equilibrium moisture contents of waterlogged archaeological fir wood from a decay region (WFD) were 22.5% higher than those of waterlogged archaeological fir wood from a sound region (WFS). WFD exhibits a higher measurable sorption hysteresis than WFS, implying greater variation in the surface moisture content in the WFD region compared to the WFS region, which may compromise the dimensional stability of the shipwreck. 2D COS-IR spectra confirmed the inhomogeneous degradation of the waterlogged wood via numerous mechanisms. The efficacy of SDVS and 2D COS-IR spectroscopy in the evaluation of the degradation state of waterlogged wood was demonstrated. This study verifies the existence of hygroscopic and chemical differences between visually similar samples from the same shipwreck.