Waterlogged Archaeological Wood Research Articles

High-resolution multiparametric MRI of contemporary and waterlogged archaeological wood.

High-resolution NMR images on three different present-day wood samples and an archaeological wood specimen were presented and discussed. Although the spatial resolution is still low to perform dendrology for the exact identification of the wooden species, the T2 -spin-density weighted images exhibit contrasts that are in excellent agreement with optical histological images. On the other hand, T2 * and T1 -weighted images provide physiological information that is not obtainable by the usual light microscopic investigations. Moreover, the diffusion-weighted images show the anisotropic behaviour of the water diffusion coefficient quantified along and perpendicularly to vascular bundles (vessels and tracheids), which can be related to the morphology and size of wooden microstructure. This work suggests that high-resolution multiparametric MRI may be a useful tool to increase the information obtainable from the waterlogged archaeological wood remains in a completely non-invasive and non-destructive approach. Therefore, it would be desirable to further develop the hardware and functional characteristics of MRI scanners to improve their potential application in the field of wooden cultural heritage.

Hygroscopicity of Waterlogged Archaeological Wood from Xiaobaijiao No.1 Shipwreck Related to Its Deterioration State.

Waterlogged archaeological wood (WAW) artifacts, made of natural biodegradable polymers, are important parts of many precious cultural heritages. It is of great importance to understand the hygroscopic behavior of WAW in different deterioration states for the development of optimal drying processes and choices of safe storage in varying conditions. This was investigated in a case-study using two Hopea (Giam) and two Tectona (Teak) WAW samples collected from the Xiaobaijiao No.1 shipwreck. The deterioration state of WAW was evaluated by the maximum water content (MWC) method and by the cell morphological structure. Both Hopea and Tectona WAW could be classified into moderately and less decayed WAW. The hygroscopic behavior of moderately and less decayed WAW was then comparatively investigated using Dynamic Vapor Sorption (DVS) measurements alongside two sorption fitting models. Compositional analysis and hydroxyl accessibility measurements of WAW cell walls were shown to correlate with the hygroscopicity of WAW in different deterioration states. It was concluded that moderately decayed WAW possessed higher hygroscopicity and hysteresis than less decayed WAW because of the lower relative content of polysaccharides and the higher relative content of lignin, including the slow hydrolysis of O-acetyl groups of xylan and the partial breakage of β-O-4 interlinks, accompanied by an increased hydroxyl accessibility. This work helps in deciding on which consolidation measures are advised for shipwreck restauration, i.e., pretreatments with specific consolidates during wood drying, particularly for wooden artifacts displayed in museums.

Even Visually Intact Cell Walls in Waterlogged Archaeological Wood Are Chemically Deteriorated and Mechanically Fragile: A Case of a 170 Year-Old Shipwreck.

Structural and chemical deterioration and its impact on cell wall mechanics were investigated for visually intact cell walls (VICWs) in waterlogged archaeological wood (WAW). Cell wall mechanical properties were examined by nanoindentation without prior embedding. WAW showed more than 25% decrease of both hardness and elastic modulus. Changes of cell wall composition, cellulose crystallite structure and porosity were investigated by ATR-FTIR imaging, Raman imaging, wet chemistry, 13C-solid state NMR, pyrolysis-GC/MS, wide angle X-ray scattering, and N2 nitrogen adsorption. VICWs in WAW possessed a cleavage of carboxyl in side chains of xylan, a serious loss of polysaccharides, and a partial breakage of β-O-4 interlinks in lignin. This was accompanied by a higher amount of mesopores in cell walls. Even VICWs in WAW were severely deteriorated at the nanoscale with impact on mechanics, which has strong implications for the conservation of archaeological shipwrecks.

Evaluation of Bio-Based Extraction Methods by Spectroscopic Methods

New technologies are in development regarding the preservation of waterlogged archaeological wood items contaminated with Fe/S species. To this purpose, a bio-based treatment to extract these harmful species before further damages occur is presented. Thiobacillus denitrificans and desferoxamine were employed based on their specific properties to solubilize iron sulfides and uptake iron. The biological treatment was compared with oxidizing and complexing agents (sodium persulfate and ethylene diamine tetraacetate) traditionally used in conservation-restoration. Mock-ups of fresh balsa as well as fresh and archeological oak and pinewood were prepared to simulate degraded waterlogged wood by immersion in corrosive Fe/S solutions. The efficiency of both biological and chemical extraction methods was evaluated through ATR-FTIR and Raman spectroscopies and validated by statistical approach. Results showed that treatments did not affect the wood composition, meaning that no wood degradation was induced. However, the chemical method tended to bleach the samples and after treatment, reduced sulfur species were still identified by Raman analyses. Finally, statistical approaches allowed validating ATR-FTIR results.

Characterization of model samples simulating degradation processes induced by iron and sulfur species on waterlogged wood

Reduced iron and sulfur species accumulated within waterlogged archaeological wood artefacts during their burial time. Oxygen exposure of the artefacts during recovery leads to acidification and salts precipitation, which causes irreversible physical and chemical damages. Prior to accurately evaluating novel extraction methods, the procedures for creating analogous samples were evaluated for efficacy. Waterlogged wood analogues provide access to a whole set of homogeneous and sacrificial samples that replicate characteristics of waterlogged archaeological wood in terms of content degradation and the presence of reduced iron and sulfur species. In this study, we evaluated the preparation of model samples from fresh balsa wood artificially contaminated with reduced iron and sulfur species. Wood degradation and the formation of reduced iron and sulfur species were assessed by Fourier Transformed Infrared (FTIR) and Raman spectroscopies and validated through statistic methods, such as Principal Component Analysis (PCA). Among the three impregnation protocols investigated, one method appeared to be the most effective in term of iron sulfide formation, especially partially oxidized mackinawite Fe1-xS. The selected protocol proved reproducible and efficient on both fresh balsa and Neolithic oak samples. From these observations confirmed by the PCA analyses on spectroscopic dataset, a suitable method to model waterlogged archaeological wood was established.

Organosilicons of different molecular size and chemical structure as consolidants for waterlogged archaeological wood \u2013 a new reversible and retreatable method

Ineffectiveness of the chemicals applied so far for waterlogged wood conservation created the need to develop new more, efficient and reliable agents. As an alternative, a new method with the use of organosilicon compounds differing in chemical composition and molecular weight has been investigated. The results obtained show the potential of organosilicons as consolidants in waterlogged wood conservation able to effectively stabilise wood dimensions upon drying. The best wood stabilisers were low-molecular organosilicons enable to penetrate the cell wall as well as chemicals with functional groups capable of interacting with wood polymers and forming stabilising coatings on the cell wall surface. The best anti-shrink efficiency values were obtained for (3-Mercaptopropyl)trimethoxysilane, (3-Aminopropyl)triethoxysilane, 1,3-Bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, reaching 98, 91 and 91%, respectively. Most of the applied organosilicons reduced wood hygroscopicity, which limits the risk of further dimensional changes of wood exposed to a variable air moisture content and potentially reduces wood biodegradation. In the light of our studies, the proposed method of waterlogged wood conservation with organosilicons is potentially reversible in the case of siloxanes and amino-silanes as well as retreatable, which complies with the requirements of the conservation ethics.

Conservation process of archaeological waterlogged wood studied by spectroscopy and gradient NMR methods

The properties of methyltrimethoxysilane-treated, waterlogged archeological elm wood were studied by magnetic resonance imaging and nuclear magnetic resonance (NMR) methods. The spatially resolved proton density images, spin–spin relaxation profiles, proton NMR spectra, and self-diffusion coefficients of the preservative agents were measured during drying. The resolution of the data allowed for the differentiation between the early and late wood areas of the elm wood and determination of the shrinkage of the sample in the tangential and radial directions, and it showed the different dynamics of methyltrimethoxysilane (MTMS) in the lumen cells of both early and late woods. The NMR spectra indicated that the MTMS, after rapid evaporation of ethanol, is bound to the wood. Identical measurements were also taken for the archeological elm wood treated with polyethylene glycol (PEG) and for an untreated wood sample. From the results, it can be concluded that MTMS showed significantly higher stability against shrinkage when compared to PEG. Therefore, it may be considered as an alternative preservative for archeological wood.

High retreatability and dimensional stability of polymer grafted waterlogged archaeological wood achieved by ARGET ATRP

To explore new methods to maintain the dimensional stability of waterlogged archaeological wood after drying and keep the natural cell lumens unaltered for future retreatments, activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) is employed to consolidate archaeological wood. To prepare the ATRP process, the waterlogged archaeological wood samples (Pinus massoniana with maximum moisture content of around 529%) were first modified by 2-bromoisobutyryl bromide in CH2Cl2 to acquire C-Br bonds as initiators. Then, butyl methacrylate or styrene was polymerized to the remaining cell walls with catalyst (CuBr2), reductant (ascorbic acid) and ligand (PMDETA) in ethanol. After the treatment, the samples were washed and naturally dried. The results characterized by microscopy showed that the polymerization only took place within the remaining cell walls, showing no sign of collapse or distortion after air drying, and all natural cell lumens could be retained for future retreatments. Also, anti-shrinkage efficiencies as high as 87.8% for the wood sample grafted with polystyrene and 98.5% for the wood sample grafted with polybutylmethacrylate were obtained from the treatment described in this paper, indicating modification of grafting polymer through ARGET ATRP can help maintain the dimensional stability of water archaeological wood effectively.

Bio-based consolidants for waterlogged archaeological wood: Assessment of the performance and optimization of the diagnostic protocol

Abstract New bio-based polymers used as consolidants for waterlogged archaeological wood were studied and their performance on real wooden samples was assessed. In particular, three oligoamides (oligo ethylene- l -tartaramide, oligo esamethylene- l -tartaramide and copolymer between ethylenediamine, adipic and tartaric acids) and allyl α,α′-trehalose/vinyl alcohol (ATR/VOH) copolymer were selected as consolidants. The affinity for wood and the reversibility of the treatments were evaluated together with certain physical properties of treated wood, i.e. maximum water content (MWC), basic density (ρb) and volumetric shrinkage (βv). A specific diagnostic protocol was optimized in order to obtain reproducible and reliable results. A good affinity for a degraded wood rich in lignin was demonstrated for all tested consolidants. For what concerns the reversibility of the treatments, the oligoamides showed higher reversibility than the ATR/VOH copolymer. The penetration ability was good for all selected products. Good results in terms of MWC reduction and ρb increase were obtained with the oligo esamethylene- L -tartaramide, the oligo ethylene- L -tartaramide and the ATR/VOH copolymer.

Effect of methyltrimethoxysilane impregnation on the cell wall porosity and water vapour sorption of archaeological waterlogged oak

This paper presents the water vapour sorption behaviour of degraded archaeological oak (Quercus robur L.) and the influence of methyltrimethoxysilane treatment on hygroscopicity. Wood samples (archaeological and undegraded recent oak) were treated with methyltrimethoxysilane using an oscillating pressure method. Moisture properties of the samples were determined using a dynamic vapour sorption system, and the surface area and porosity of treated and untreated waterlogged wood, previously dried using different methods, were characterised using a nitrogen sorption method. It was found that the silane modification resulted in a decrease in the equilibrium moisture content of archaeological oak samples from 23.7 to 19.4% for heartwood and from 23.3 to 10.0% for sapwood, respectively. After correction for silane content, however, the maximum equilibrium moisture content of the treated samples was 23.6% for heartwood and 21% for sapwood, which points rather at a bulking mechanism than chemical modification by silane. The results of the surface area and porosity measurements indicate that methyltrimethoxysilane is deposited in the cell wall and thus helps to preserve the microstructure of archaeological waterlogged wood.

Biological effectiveness of archaeological oak wood treated with methyltrimethoxysilane and PEG against Brown-rot fungi and moulds

The results of the previous research have shown that methyltrimethoxysilane is an effective agent for dimensional stabilisation of archaeological waterlogged wood. This paper presents an assessment of the effectiveness of MTMS in improving the biological resistance of archaeological waterlogged oak (Quercus robur) against moulds and brown-rot fungus Coniophora puteana. Hygroscopic properties of the treated wood were also examined. Small wood samples were treated with MTMS using the oscillating pressure method. PEG-treated specimens were used as a reference and contemporary oak was used as a control. The results clearly show that both MTMS and PEG treatment efficiently protected waterlogged wood against brown-rot fungus, increasing its resistance by about 80% in comparison with untreated samples but they are not effective against moulds. Moreover, both chemicals reduced liquid water sorption by the treated wood. However, the mechanism of wood protection and hydrophobation seems different. PEG-treated wood was found to be much more hygroscopic (equilibrium moisture content about 35%) than the untreated wood (EMC about 20%), while MTMS significantly decreased wood hygroscopicity (EMC about 14%). The use of accelerated ageing revealed that PEG is highly susceptible to leaching, which reduces its effectiveness. MTMS is more resistant, therefore its antifungal and hydrophobising properties remain almost unchanged even after the ageing process.

Microbial erosion assessment on waterlogged archaeological woods (WAWs) from a Chinese ancient shipwreck, Nanhai No. 1

This article aims at identifying the timber species of Nanhai No. 1, an ancient shipwreck (Song Dynasty, 800 years ago) sunk in the South China Sea, finding out the types of bacteria that corrode the wood components of the shipwreck and analyzing the erosion level. The changes of the internal structure of wood under different erosion degrees are described as well. With light microscope and electron microscope technology, the microscopic and submicroscopic structures of 20 wooden components from the shipwreck were investigated. The shipwreck was built of 6 timber species, including Pinus massoniana, Fokienia hodginsii, Terminalia hainanensis, Mischocarpus oppositifolius, Alnus trabeculosa and Mussaendopsis beccariana. Based on analyzing the traces left after bacterial erosion, it was determined that the erosive microbes in the sunken ship were mainly erosion bacteria and tunneling bacteria. According to the criteria from relevant literature, the analysis on the bacterial erosion degree of each wood sample shows that most of the wood components present weak to moderate erosion, except a few samples which are totally degraded. Comparison with the bacterial erosion on the wooden components of different ancient shipwrecks, sunk in different years in the southeast China, it is noticed that due to the different seabed environments (sunk conditions), the wood structure of the Nanhai No. 1 sunken ship is the best preserved although its sunken time is longer than the others. The silt-covered anaerobic environment could be one of the protective measures which preserves the ancient sunken ships.

Diffusion of chemicals into archaeological waterlogged hardwoods obtained from the Thang Long Imperial Citadel site, Vietnam

This study shows a method to easily develop suitable impregnation procedure of chemicals for preserving the archaeological waterlogged wood (WW) using diffusion constant. The steady-state diffusion coefficients of polyethylene glycol 4000 (PEG4000), trehalose, and keratin through eight archaeological waterlogged wood species were obtained from the total amounts of the chemicals diffused through the wood samples. The diffusion coefficients were strongly affected by the anatomical structures of the wood species and degree of wood deterioration. Within the same species of wood, the highest diffusion rates were measured in the longitudinal direction, followed by those in the radial and tangential directions. The longitudinal diffusion coefficients were 1.5- to 8.1-times higher than the radial diffusion coefficients, which were in turn approximately 1.1- to 5.7-times higher than the tangential diffusion coefficients. The diffusion rates were found to be inversely proportional to the molecular weight of the diffusing chemical. The diffusivity of trehalose through the waterlogged woods was found to be higher than those of keratin and PEG4000. This study provides a potential method to easily estimate chemical diffusion coefficients for dip-diffusion treatments.

Biological oxidation of sulfur compounds in artificially degraded wood

Marine and lacustrine archaeological waterlogged wood encounters serious problems after excavation due to the accumulation of sulfur and iron compounds during burial. Exposure of these compounds to oxygen results in precipitation of salts and acidification, which can lead to serious structural damage, and ultimately the loss of important cultural heritage. In this study, we evaluated the capacity of the bacterium Thiobacillus denitrificans to transform sulfur compounds commonly found in waterlogged wooden objects, to more readily extractable compounds thereby eliminating the threat of degradation. Oak samples, impregnated with a solution containing iron(II) and sulfides, were used to assess the efficiency of the bacterial treatment. The model wood samples were characterized before and after treatment using different techniques such as ESEM-EDS, micro-Raman spectroscopy, XRD and Sy-XRF mapping. Before treatment, mackinawite (FeS) and mineral sulfur (α-S8) were detected in the impregnated wood. After treatment with T. denitrificans, even though some mineral sulfur remained in the samples, the predominant phase corresponded to oxidized sulfur. This demonstrates that T. denitrificans was able to use the reduced sulfur compounds present in the wood samples as an energy source, thereby producing more soluble oxidized sulfur compounds. In addition, non-invasive techniques such as Fourier transform infrared (FTIR) spectroscopy, were carried out to assess the consequences of the biological treatment on the wood structure. No negative effect on the wood was detected after the treatment in comparison with the reference-impregnated wood. This study demonstrates the feasibility of a biotechnological procedure for the preventive extraction of sulfur species from archaeological waterlogged wood.

Halloysite Nanotubes Loaded with Calcium Hydroxide: Alkaline Fillers for the Deacidification of Waterlogged Archeological Woods.

A novel green protocol for the deacidifying consolidation of waterlogged archaeological woods through aqueous dispersions of polyethylene glycol (PEG) 1500 and halloysite nanotubes containing calcium hydroxide has been designed. First, we prepared functionalized halloysite nanotubes filled with Ca(OH)2 in their lumen. The controlled and sustained release of Ca(OH)2 from the halloysite lumen extended its neutralization action over time, allowing the development of a long-term deacidification of the wood samples. A preliminary thermomechanical characterization of clay/polymer nanocomposites allows us to determine the experimental conditions to maximize the consolidation efficiency of the wood samples. The penetration of the halloysite-Ca(OH)2/PEG composite within the wooden pores conferred the robustness of the archaeological woods based on the clay/polymer composition of the consolidant mixture. Compared to the archeological woods treated with pure PEG 1500, the addition of modified nanotubes in the consolidant induced a remarkable improvement in the mechanical performance in terms of flexural strength and rigidity. The pH measurements of the treated woods showed that the halloysite-Ca(OH)2 are effective alkaline fillers. Accordingly, the modified nanotubes provided a long-term protection for lignin present in the woods that are exposed to artificial aging under acidic atmosphere. The attained knowledge shows that an easy and green protocol for the long-term preservation of wooden artworks can be achieved by the combination of PEG polymers and alkaline tubular nanostructures obtained through the confinement of Ca(OH)2 within the halloysite cavity.

Organosilicon compounds with various active groups as consolidants for the preservation of waterlogged archaeological wood

Abstract Waterlogged wood conservation focuses primarily on its dimensional stabilisation to prevent irreversible deformations that occur upon drying. It also aims to solve the concerns regarding wood degradation as well as its physico-mechanical properties, all of which are inextricably connected with wood hygroscopicity. Therefore, the reduction of wood hygroscopicity can provide a solution to some of the conservation problems. Due to the hydrophobising properties and the ability to cell wall bulking, a set of organosilicons with various active groups were selected to evaluate their stabilisation effect on highly degraded medieval waterlogged elm wood. Exceptionally satisfying results were obtained for (3-Mercaptopropyl)trimethoxysilane, 1,3-Bis(diethylamino)-3-propoxypropanol)-1,1,3,3-tetramethyldisiloxane and Methyltrimethoxysilane, for which the volumetric anti-shrink efficiency was around 98%, 90% and 81%, respectively. Additionally, the applied treatment resulted in a decrease of wood moisture content from 6.7% for untreated wood to 2.4–3.6% for wood treated with the above-mentioned compounds. Neither the alkoxysilanes with a long alkyl chain, nor those terminated with a highly hydrophilic pyridine ring were found effective for waterlogged wood stabilisation. It can be concluded that the organosilicon compounds with alkoxy groups and a relatively short alkyl chain or containing and additional chemical group enable to form stable bonds with wood components proved to be the most effective wood stabilisers.

THE PARAMETERS OF THE ENVIRONMENT OF DEPOSITION AND MOLECULAR ANALYSES OF WATERLOGGED ARCHAEOLOGICAL WOOD FROM THE EARLY MEDIEVAL SITE OF CZERMNO IN EASTERN POLAND

THE PARAMETERS OF THE ENVIRONMENT OF DEPOSITION AND MOLECULAR ANALYSES OF WATERLOGGED ARCHAEOLOGICAL WOOD FROM THE EARLY MEDIEVAL SITE OF CZERMNO IN EASTERN POLAND

Methyltrimethoxysilane as a stabilising agent for archaeological waterlogged wood differing in the degree of degradation

Abstract Experiments using archaeological wooden remains of a medieval “Poznan” bridge from the Lednica Lake, Wielkopolska Region, Poland, were performed to evaluate the stabilisation effect of methyltrimethoxysilane on waterlogged oak wood varied in the degree of degradation. Moreover, two types of treatment were compared: the soaking method and the oscillating pressure method, preceded by the ethanol dehydration procedure. The results suggest that the silane in question can effectively penetrate wood cell walls, causing their bulking and thus enhancing wood dimensional stability. Exceptionally satisfying results were obtained for severely decayed sapwood (loss of wood substance about 80%), for which an overall anti-shrink efficiency oscillated around 100%, regardless of the applied treatment method. In the case of almost non-degraded heartwood, resistant to impregnation, the obtained anti-shrink efficiency of over 60% could also be considered as quite satisfactory. Comparable values of weight percent gain and anti-shrink efficiency for silane-treated specimens clearly show that there is no significant difference in the efficacy of the soaking and the oscillating pressure method applied. The obtained results show that the methyltrimethoxysilane treatment preceded by wood dehydration could be a reliable method for stabilisation of small archaeological waterlogged wooden artefacts, providing their good dimensional stability of wood differing in the degree of degradation.

Dimensional stability and hygroscopic properties of waterlogged archaeological wood treated with alkoxysilanes

Archaeological waterlogged elm wood was treated with methyltrimethoxysilane (MTMS) and (3-mercaptopropyl)trimethoxysilane (MPTES), respectively, and anti-shrink efficiency and sorption properties of the impregnated wood samples were determined. The applied impregnants stabilized wood dimensions efficiently enough, i.e. the obtained anti-shrink efficiency was 81 and 98% for MTMS- and MPTES-treated wood, respectively. Both alkoxysilanes can be considered as potential new consolidants. Hygroscopic properties of untreated and impregnated wood were investigated with the DVS experiments. The application of MTMS and MPTES reduced wood equilibrium moisture content (EMC) and sorption hysteresis e.g. hysteresis relative change was −83.7 and −73.7% for MTMS- and MPTES-treated wood, respectively. The EMC reduction was observed in the whole hygroscopic range and it was primary due to the monolayer capacity decrease to 50 and 30% of the value for untreated wood and observed for adsorption and desorption modes, respectively. The DVS experiments revealed chemical instability of the MTMS-wood system which was neutralized after the cyclic sorption. The possible scenarios of the interaction of both alkoxysilanes with wood structure were discussed.

Microbial community analysis and biodeterioration of waterlogged archaeological wood from the Nanhai No. 1 shipwreck during storage

Wooden shipwrecks are a significant part of the underwater cultural heritage. In 2007, the Nanhai No. 1 shipwreck was salvaged from the seabed and moved into the Marine Silk Road Museum, where it is still stored in a water tank. We analysed the microbial communities colonizing the hull surface of the Nanhai No. 1 shipwreck during storage. Six samples exposed to air were collected from different spots of the ship that exhibited obvious microbial plaques. High-throughput sequencing revealed the bacterial community includes both aquatic and terrestrial species, while in the fungal community, Fusarium was the most abundant genus across all samples and accounted for 84.91% to 98.40% of the total community composition. Two Fusarium species were isolated from the samples and were identified as F. solani and F. oxysporum. Both of the isolates were able to degrade cellulose, but only F. solani had the ability to degrade lignin. Antimicrobial efficacy in inhibiting the growth of Fusarium was assessed with five kinds of biocides, and isothiazolinones exhibited specific inhibition of Fusarium growth. These results provide critical background information to protect and reduce the biodegradation and destruction of this important historical shipwreck, and inform efforts to protect other similar artifacts.