Investigating the processes necessary for satisfactory freeze-drying of waterlogged archaeological wood

Preliminary studies into methods for improving and safeguarding the preservation of waterlogged archaeological wooden artefacts are presented. Mannitol, sorbitol and trehalose have been tested as replacements for polyethylene glycol (PEG) as a treatment prior to freeze-drying of wooden archaeological objects. The highest anti-shrink efficiency achieved in this short experiment was (70 ± 15) % using a 20% weight per volume solution of sorbitol after soaking for one week. The collapse or eutectic temperature of each solution used was determined using a freeze-drying microscope. Importantly, it was noted that the collapse temperature of the solutions was reduced by several degrees after use for treatment of the wood samples for one month. A freeze-drying microscope with a cold light source has been used to observe the real-time freeze-drying behaviour of various treatments inside a thin section of wood, confirming that this novel technique is indeed possible and useful. Lastly, the effects of magnesium phytate as an iron chelator have been studied. It was found that the treatment lowers the collapse temperature of a PEG 600/2000 solution by roughly 3 °C meaning that objects must be freeze-dried at a correspondingly lower temperature. Iron K-edge X-ray absorption near-edge spectroscopy analysis showed that the treatment extracted approximately half of the iron(III) ions present in the timbers.     

宁波保国寺大殿北倾原因浅析

宁波保国寺是浙东现存最古老的宋代木结构建筑,自清乾隆时期起,大殿结构发生北倾,后对4号转角檐柱进行修缮并加固至今,通过跟踪测试没有发现新的倾斜趋势。然而,探讨大殿曾经北倾原因以及经修缮后现今大殿的可靠性无疑仍是必要的。古木结构的特点是梁柱的榫卯连接具有半刚性性质。采用有限单元法对大殿结构进行力学分析时,榫卯连接可采用空间二节点虚拟弹簧元进行模拟,单元刚度矩阵中相应的刚度特性系数可由接触有限单元法近似求得。这样,大殿结构可离散为杆、梁、壳、体元和上述虚拟弹簧元等的组合,在屋面荷载、雪荷载和风荷载作用下采用有限元法可求得各节点的位移和相应应力。通过计算表明,不计4号柱时产生的向北位移比考虑该柱参加受力时要大得多,可见北倾原因确系4号柱年久失效而引起。计算结果也表明,现今大殿结构由受力来看是安全的。同时预示了可能出现的最危险部位。保国寺大殿结构的力学分析结果,为物保护工作提供了科学依据。     

Prehistoric wooden bows and arrows in the Turpan Basin,Northwest China: Wood selection and utilization in a mosaic landscape

In the present study, we analyzed seven wooden bows and 13 arrows excavated from the cemeteries of Subeixi Culture (13th century BCE–AD second century) in the Turpan Basin, northwest China. A total of six taxa, viz. Morus sp., Salix sp., Picea sp., Lonicera sp., Betula sp., and Tamarix sp. were identified. Some of these taxa have been generally accepted to be suitable for bow-and-arrow production. All these taxa were local in origin but distributed in different ecotonal zones, including oases, saline-alkali lands, and mountain areas. Previous archaeological studies have confirmed that the Subeixi populations lived an agro-pastoral life. By analyzing the possible provenance of these wood samples, it can be hypothesized that these ancient agro-pastoralists moved between the Turpan Basin and the Tianshan Mountains on a seasonal basis.     

Seasoned or green? Radial cracks analysis as a method for identifying the use of green wood as fuel in archaeological charcoal

For several years, sociological questions have been central in anthracology. The development of socio-economic approaches based on the recognition of anatomical signatures in wood has made it possible to focus on topics related to firewood use and its management. The presence of radial cracks (RC) on archaeological charcoal is generally interpreted as the result of the burning of green wood. The present study proposes a verification of this theory by the experimental combustion of seasoned and green wood of Scots Pine (Pinus sylvestris L.). Experimenting with this species was a research priority since it was the dominant taxon (representing 80-100% of the charcoal remains) identified in the Palaeolithic European sites under consideration.The experiments were conducted using two different methods: (i) inside a muffle furnace that allowed us to control the combustions, but in which the combustion process is quite different from most archaeological situations and (ii) in an open fireplace, less controllable but closer to the archaeological conditions. The systematic quantification of the number, length and width of the radial cracks (RC) measured on the transversal sections of the experimental samples demonstrates that (i) radial cracks occur independently of the moisture content of the wood before the combustion (on green and seasoned wood); (ii) however, the average number of radial cracks (RC/cm²) allows distinguishing seasoned from green wood; (iii) in the muffle furnace, the size of the RC appeared to be a good criterion for discriminating seasoned and green wood, but this observation was not confirmed by the open-air combustions. Our results clearly show that the appearance of radial cracks is not diagnostic of the combustion of green wood. Nevertheless, the number of radial cracks (RC/cm²) could represent a new method that might help identifying the combustion of green wood in archaeological charcoal samples.     

POTASH,SALTPETER AND TAR

Quantitative calculations on the use of natural resources provide valuable tools, which can give new insights to old questions and rise new ones. In this article, I compare the wood consumption in the production of potash, saltpeter and pine wood tar in 19th century Finland. My calculations shows that in the 19th century the cumulative wood consumption in the production of potash might have been higher or at least on the same level as in the production of tar, while the production of saltpeter consumed only a fraction. In the 1830s their combined wood consumption reached the level of slash‐and‐burn cultivation.     

Integrated archaeobotanical analysis: Human impact at the Dutch Neolithic wetland site the Hazendonk

This study presents an integrated archaeobotanical analysis of human impact at the Dutch Neolithic wetland site the Hazendonk (4000–1800 cal BC). The analysis included pollen, non-pollen palynomorphs and macroremains from on-site sample columns and macroremains and wood from refuse layers. The various remains provide evidence of disturbance of both dryland and wetland vegetation, information on crop cultivation and food plants, and indications of selection of wood for artefacts. The integrated approach provides results that would not have been obtained by the analysis of one of the sources alone.     

Wet charred wood: a preliminary study of the material and its conservation treatments

This study investigated wet charred wood excavated at an archaic cemetery in Corfu, Greece, dating from 6th century B.C. The preservation condition of the material was evaluated based on its physicochemical properties and micromorphology in comparison to modern combusted wood. Charring temperature of the material was estimated by Electron Spin Resonance (ESR). Results indicated a severe degree of decay, resulting not only from charring. Conservation treatments involved spraying, as the material readily collapsed during immersion.     

Degradation of Archaeological Wood Under Freezing and Thawing Conditions—Effects of Permafrost and Climate Change

The degradation of archaeological wood at freezing and thawing temperatures is studied at the site of Qajaa in West Greenland through a combination of environmental monitoring, measurement of oxygen consumption and microscopy of wood samples. Permanently frozen wood is still very well preserved after 2–4000 years, while wood samples that thaw every summer show attack by soft rot and an average density loss of 0.1 g cm^–3 (corresponding to 25% of the dry mass) over the past 27 years. Future increases in temperature may increase the decay rate significantly (Q₁₀ = 4.2 at 0–10°C) but the effects on site depend on local hydrology.     

Study of the Technique and of the Materials of a 19th‐Century Polychrome Wood Mask from Papua New Guinea

This paper presents the results of the analysis carried out on a polychrome wood mask from Papua New Guinea during conservation work at Pigorini Museum's restoration laboratory. The significance of this study is that no prior work has characterized the painting materials of Papua New Guinea masks both with spectroscopic and internal microstratigraphic analysis. In fact, these objects were studied especially from an anthropological or conservative point of view and the wood was wrongly defined by its visual appearance. Microstratigraphic and spectroscopic investigations discovered a refined execution technique that up to now has not been demonstrated. The stratigraphy of the painted layers demonstrates a deep knowledge of the materials and of the application techniques on the part of the Papua New Guinea people, together with the ability to foresee the aesthetic result for the artefact. The analysis of the constitutive materials and of the stylistic features supplied valid results in favour of provenance of the mask from Papua New Guinea.     

Partial Solutions to Partially Understood Problems — The Experience of In Situ Monitoring and Preservation in Somerset’s Peatlands

Abstract

The peat moors of lowland Somerset contain a wealth of waterlogged archaeological sites, including some of the most significant prehistoric monuments in the country. There has been a long history of attempts to preserve archaeological sites in situ and monitoring of the burial environment began in 1982. The monitoring has become more complex over time, but the results suggest the same continuing problem of a drop in the water table over the summer months across the whole landscape. With the sole exception of the portion of the Neolithic Sweet Track that benefits from an irrigation system, all the other known sites remain at risk of gradual destruction. The solutions must be found on a landscape scale using agri-environment payments to secure sustainable management of the peat resource. Unfortunately, short-term changes to these payments and long-term changes to the climate are likely to worsen the situation and eventually to require a more drastic solution to the problem. Evidence has been generated to support an ecosystems approach to sustainable peatland management.