Nydam Mose: In Situ Preservation at Work

Abstract

The site of Nydam Mose saw the beginning of systematic research into in situ preservation of waterlogged archaeological sites on land at the National Museum of Denmark. In the past fifteen years a generic approach to in situ preservation of archaeological sites has been developed based on this research. This article is primarily a review of this generic approach, summarizing the methods and results with particular reference to the published results from the investigations in Nydam Mose.     

New trials in the consolidation of waterlogged archaeological wood with different acetone-carried products

Some acetone-carried consolidants for waterlogged archaeological wood were tested in order to evaluate treatments able to save time and energy. In details, colophony (rosin), two esterified colophonies (Rosin 100^® and Rosin 459^®), a mixture of colophony with PEG 3400 and a vinyl acetate - vinyl versate copolymer (Vinavil 8020S^®) were tested. The treatments were carried out at temperatures of 20 and 35 °C on waterlogged maritime pine, elm, oak and beech. The materials came from the archaeological site of the ancient ships of Pisa (Tuscany, Italy) and were dated back to VII cent. BC – II cent. AD. To evaluate the processes, equilibrium moisture content and dimensional stability of treated wood samples at different relative humidity, and retention of impregnating products were measured; moreover macroscopic and microscopic examination were also run to respectively assess the shape and appearance of treated wood and the way of deposition of consolidants. The results highlighted that natural and modified colophony treatments gave the most satisfactory results both in the maintenance of shape and dimensions of samples and in the stabilization with respect to RH variations. Moreover, the equilibrium moisture contents of samples treated with R100 and R459 were much reduced in comparison to the other consolidants and to untreated archaeological wood. This fact was related to the high retention values of those products that occluded most of the porosity including the microporosity of cell walls. Therefore, in terms of higroscopicity treated wood was more similar to impregnating substances rather than to decayed wood. This fact was considered helpful in contrasting the moisture-related negative effects in cases of eventual faults in the climate control during e.g. exhibition and in protecting treated wood from the risks of new fungal attacks.     

Impact of Roots and Rhizomes on Wetland Archaeology: A Review

The general premise for successful archaeological in situ preservation in wetlands is that raising the water table will ‘seal the grave’ by preventing oxygen from reaching the deposit. The present review reveals that this may not be the entire picture, as a change in habitat may introduce new plant species that can damage site stratigraphy and artefacts. However, reviews on the types and degree of damage caused by vegetation to archaeological remains preserved in situ in wetlands have hitherto only been sporadically treated in the literature. Thus, this paper provides an overview of the adverse effects that various plants species have on the preservation status of wetland archaeology.Disturbance, due to growth of roots and rhizomes of the surrounding soil is denoted contextual disturbance, whereas deterioration of archaeological remains per se acts by several root-related factors that may be spatially and temporally concomitant. In waterlogged anoxic environments, deterioration is mainly related to (i) preferential growth of roots/rhizomes due to nutrient uptake and lesser soil resistance, (ii) root etching due to organic acid exudates, (iii) microbial growth due to root release of oxygen and labile organic compounds, and/or (iv) precipitation of hydroxides due to root release of oxygen. For example, roots of some wetland plants, such as marsh horsetail (Equisetum palustre), have been documented to penetrate archaeological artefacts down to c. 2 m in waterlogged anoxic soils. Here, we demonstrate that cultural heritage site management may unintentionally introduce deep-rooted or exudate aggressive plants by invoking change in hydrological conditions. Moreover, the implementation of biomass energy utilization and agricultural root depth optimization on a worldwide basis stresses the need for more research within root and rhizome impact on archaeological remains in wetlands. In conclusion, the worst-case scenario may be in situ deterioration instead of preservation, and one essential threat to archaeological wetland sites is the impact of wetland vegetation.     

Reburial and Analyses of Archaeological Remains in the Marine Environment — Investigations into the Effects on Metals

Abstract

The treatment and long-term storage of recovered cultural material from underwater heritage sites is becoming less cost effective, and reburial of archaeological sites and the associated artefacts in the marine environment is becoming increasingly common practice in managing the submerged cultural resource. Following recent large-scale underwater archaeological excavations in Marstrand harbour, Sweden, the majority of recovered finds were reburied in defined trenches in the harbour sediment. Subsequently, the Studio of the Western Sweden Conservators in conjunction with the Bohus County Museum initiated a fifty-year research project to evaluate reburial as an appropriate method of preserving waterlogged archaeological artefacts in the long term. The research project, entitled ‘Reburial and Analyses of Archaeological Remains’, was launched in 2002 and consists of six sub-projects. The main aims of these sub-projects are to analyse the extent of deterioration of the most common material types found on underwater archaeological sites, assess the stability of packing and marking materials used in archaeological documentation, and monitor the reburial environment.

The aim of the metals sub-project is to investigate the short- to long-term corrosion behaviour of metals buried in the marine environment by examining the deterioration of reburied and exposed modern metal coupons and eventually compare these results to the analysis of actual shipwreck artefacts. The environmental monitoring sub-project is designed to complement the other sub-projects by assessing the physico-chemical changes occurring in the reburial environment over time and the effect on the deterioration of the different reburied material types. In comparing the results obtained over the past seven years from both the metals and monitoring sub-projects, it should be possible to more accurately evaluate the effectiveness of reburial as a long-term in situ preservation strategy for metallic archaeological remains.     

In situ Preservation Solutions for Deposited Iron Age Human Bones in Alken Enge,Denmark

The rich mass deposition of Iron Age human bone material from the Danish site, Alken Enge, is extraordinary not only from an archaeological perspective but also from a preservation point of view. The main find is situated in a waterlogged, anoxic environment which provides excellent preservation conditions and therefore enables in situ preservation of the human bones. However, major differences in local environmental conditions challenge an in situ preservation of the entire site area as parts of the bone material presently deteriorate. In this paper, a multi-proxy environmental monitoring approach is used to document threats and to suggest the best preservation solution for the archaeological finds, whether in or ex situ.     

Correlation between modern plant δN values and activity areas of Medieval Norse farms

This further nitrogen isotopic study of Greenlandic Norse archaeological sites provides new evidence of the affect of past human activity on modern plant δ¹⁵N values. Grass samples were taken from a number of spatially defined features at four Norse farms and one site interpreted to be a seasonally occupied herding station (sæter). At the farms, un-naturally high δ¹⁵N values were found for plants from each sampled feature, including those from the likely infields and a churchyard. At the sæter no strong isotopic effect was expected and none was found. Comparing the data from the farms we found that the average plant δ¹⁵N values were similar for features that were functionally alike. We conclude from these observations, that the unusually high plant δ¹⁵N values reflect the strong conservation of the isotopic composition of the nitrogenous materials deposited in the past, and the magnitude of the values reflects the amount of this material admixed in the soil. The results confirm previous exploratory studies of this isotopic effect and further demonstrate its potential value as an archaeological tool.     

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.     

The Six New Towns of the Bishops of Winchester, 1200–55

THE CHANCE DISCOVERY of a waterlogged wooden beam during the cutting of a drainage ditch led to the excavation of the timber framework of a medieval water-mill. Almost half the water-wheel survived in situ. A little 14th-century pottery was found in the wheel-pit; its structure was extremely similar to that of the approximately contemporary period I mill at Chingley.¹ The mill at Batsford was probably used for grinding grain; no trace of the mill building itself was found.     

TECHNOLOGICAL STUDY OF PTOLEMAIC – EARLY ROMAN FAIENCE FROM MEMPHIS,EGYPT*

Fourteen fragments of faience vessels from the Ptolemaic/Roman period found at the Egyptian site of Memphis, near Cairo, were analysed by SEM. The fragments included high‐relief polychrome vessels, which are first produced in numbers in this period. Analysis allowed the composition and microstructure of the vessels to be assessed and conclusions drawn as to the raw materials of manufacture. Combining this information with archaeological evidence from excavation of the kilns and associated finds, it was possible to reconstruct the production technology of the vessels.     

Monitoring and Management Options in the Preservation of Urban Waterlogged Deposits,Nantwich, UK

A baseline survey in 2007 characterized the physical and chemical conditions for preservation within waterlogged remains at Nantwich. Installation of eighteen dipwells has allowed a five-year monitoring programme to be conducted from 2011. Two add-on projects supplemented this monitoring programme by examining the different methods for redox measurement, and for soil moisture measurement using Time Domain Reflectometry (TDR).

Initial results show two main zones of preservation, with reducing conditions attributed to location of the deposits in the floodplain, and a second zone uphill with more variable conditions for preservation. This study shows that sediment-coring programmes combined with dipwell installations can provide useful data to assess and monitor in situ preservation conditions, which can help to formulate management strategies for conservation of waterlogged archaeological deposits. This paper focuses on the efficacy of the methodology, referencing in particular comparative monitoring techniques and lists a series of recommendations for future studies.     

Shape recovery of collapsed archaeological wood ware with active alkali-urea treatment

Most wooden remains from archaeological sites in waterlogged burial environments are found to be intact without shrinkage despite centuries of storage. However, waterlogged wooden remains are subject to shrinkage damage and some even lose up to 80% of their original volume when exposed to air. The shrinkage of archaeological waterlogged wood with the loss of a large part of the initial volume of the wooden remains has been considered irreversible. Here we show that “active alkali-urea”, serving as a re-swelling chemical agent, can almost fully restore the collapsed archaeological wood to its original shape. The restoration experiment showed that the main reason for the restoration of collapsed wood is that the collapsed cell cavity almost completely recovered its original shape during active alkali-urea treatment. We suggest that the shape of collapsed archaeological wood remains can be fully recovered, and that the collapsed archaeological wood can thereby recover its valuable cultural properties.     

出土饱水云南松的超微构造特征

对云南剑川县出土的木质文物进行了研究,从超微结构层面更深入地解析了饱水古木的降解情况。出土的云南松(Pinus yunnansis)古木在饱水环境中淹埋了4 000多年。降解主要发生在晚材管胞,而且降解在晚材部分并不均匀:一些未降解的完好管胞分布在降解严重的管胞中。透射电镜观察显示:降解从S1/S2和S2/S3的界面开始;对于一些降解较严重的管胞,到腐朽后期细胞次生壁全部发生降解,只留下复合胞间层;细菌侵蚀是云南松饱水古木降解的主要原因。固体核磁共振结果表明:纤维素和半纤维素降解严重,木质素也出现了一定程度的降解。本研究可为其后续的加固保护提供科学的参考依据。     

δ18O Analyses of the Humpbacked Conch (Gibberulus gibberulus): Evaluating a Proxy for Reconstructing Sea-Surface Temperature at Chelechol ra Orrak,Palau

ABSTRACT

In Palau, Micronesia, marine resources, particularly shellfish, played a vital role in human subsistence for millennia. Despite the vast array of molluscan species in archaeological assemblages, there is a dearth of data on nearshore palaeoecology or prehistoric shellfish foraging practices. In this study, we analysed stable oxygen isotopes (δ¹⁸O) values present in the calcium carbonate shell of Gibberulus gibberulus from the Chelechol ra Orrak archaeological site to reconstruct average nearshore sea-surface temperatures (SST) from approximately 1500–1100 cal BP. Modern shellfish samples and environmental data were collected from intertidal zones near the site and x-ray diffraction (XRD) was employed to identify the biomineralogical composition of G. gibberulus. These steps provide necessary information for the selection of the proper oxygen isotope-to-SST conversion formula. The selected formula was applied to δ¹⁸O samples from archaeological shells to reconstruct prehistoric SST averages. The results of this proxy validation study verify that G. gibberulus accurately records ambient SST and can be used to reconstruct ancient nearshore conditions. These findings also contribute to the establishment of an environmental baseline, which can be used to examine how environmental changes may have influenced the availability of molluscan taxa that in turn influenced human subsistence practices through time.     

New evidence on the introduction,cultivation and processing of hemp (Cannabis sativa L.) in southern Sweden

Subfossil remains of Cannabis sativa L. (hemp) have been found at Lindängelund in the region of Malmö, southern Sweden. These represent the earliest robust evidence so far for hemp retting in Scandinavia. Finds of seeds, stems and pollen of C. sativa from a waterlogged context on a settlement dating to the Roman Iron Age demonstrate that the plant was locally cultivated and processed during the 1st–2nd centuries AD. An introductory phase in Scandinavia is proposed (c. AD 1–400) during which the cultivation of hemp was apparently small scale and processing was probably carried out within settlements. In the succeeding centuries, c. AD 400–550 (the Migration Period), remains of hemp are mostly found in pollen records from lake sediments, and less frequently in the archaeological record. This could indicate that the process of hemp retting relocated from settlements to lakes shores where activity became larger in scale and more integrated with the prevailing agricultural system.     

Southwest Scottish Crannogs: using in situ studies to assess preservation in wetland archaeological contexts

This paper presents the results of in situ monitoring of waterlogged burial contexts in southwest Scotland. The sites investigated are Iron Age crannogs (lake dwellings) which have a proven waterlogged archaeological component, and which are being assessed as part of a national program of study by the Scottish Wetland Archaeology Programme (SWAP) team. A monthly monitoring program commenced in July of 2004. To date, monitoring of water levels, pH, and redox potential, has been undertaken for a period of 17 months in order to encompass any seasonal variability at the sites studied. The results have proven robust in that an ‘ideal’ site for in situ preservation has been identified from the five sites investigated, and the monitoring has highlighted external variables and seasonal impacts that have the potential to influence the long-term in situ preservation at the remaining sites studied. In general, these results have expanded upon our knowledge of the potential for the preservation of existing archaeological remains within such contexts. This study represents the first stage of monitoring aimed at developing a holistic understanding of in situ conditions at the crannog sites studied in southwest Scotland.     

ACKNOWLEDGING FIFTY YEARS OF NEUTRON ACTIVATION ANALYSIS IN ARCHAEOLOGY

Neutron activation analysis has been an important analytical technique for chemical characterization studies of archaeological materials since 1957, and remains one of the best analytical approaches for bulk chemical characterization of archaeological ceramics and other materials. This paper introduces a series of reports that document the history of NAA applied to archaeological materials.     

LEAD ISOTOPE RATIOS AS A MEANS OF SOURCING ANTHROPOGENIC LEAD IN ARCHAEOLOGICAL SOILS: A PILOT STUDY OF AN ABANDONED SHETLAND CROFT*

Results from soil chemical analysis have demonstrated enhanced concentrations of lead (Pb) associated with archaeological sites. However, interpretation of these Pb concentrations is difficult because of the multitude of possible Pb sources. This pilot study of an abandoned croft in Shetland suggests that Pb isotope ratios have the potential to identify sources of anthropogenic Pb. The results highlight two different Pb associations. The first includes hearth, house floor and house overburden soils, with end members of fuel materials and an unidentified material with a low (< 1.126) ²⁰⁶ Pb/ ²⁰⁷ Pb ratio. The second includes byre, kailyard (garden) and arable soils, with end members of hearth materials and local wind‐blown sand.     

古代饱水木材脱水定型机理探讨

从木材干缩的一般理论出发,探讨了古代饱水木材脱水变形的主要影响因素。阐述了古代饱水木材与新鲜木材的区别,提出饱水木材发生形变的主要影响因素同现代木材一样,是由于氢键缔合的结合水挥发,从而引起干缩和开裂。要保持脱水后的定型一方面要加固细胞壁外壁,更重要的从细胞壁内壁进行加固。     

ORGANIC RESIDUE ANALYSIS IN ARCHAEOLOGY: THE ARCHAEOLOGICAL BIOMARKER REVOLUTION*

Organic residue analysis utilizes analytical organic chemical techniques to identify the nature and origins of organic remains that cannot be characterized using traditional techniques of archaeological investigation (because they are either amorphous or invisible). The field is founded upon the principle that the biomolecular, or biochemical, components of organic materials associated with human activity survive in a wide variety of locations and deposits at archaeological sites. The archaeological information contained in organic residues is represented by the biomolecular components of the natural products that contribute to the formation of a given residue. By applying appropriate separation (chromatographic) and identification (mass spectrometric) techniques, the preserved, and altered, biomolecular components of such residues can be revealed. Once identified, the Archaeological Biomarker Concept can be applied, wherein the structure and even isotopic composition(s) of a given biomolecule or suite of biomolecules (the ‘chemical fingerprint’) can be related to the compositions of organisms exploited by humans in the past. As the organic residue field emerges from its pre‐paradigmatic phase, and the organic residue revolution gathers pace, the way is open for challenging many long‐held archaeological hypotheses and offering new perspectives on the study of human activity in the past.