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.     

Stability of phytoliths in the archaeological record: a dissolution study of modern and fossil phytoliths

Opaline phytoliths are important microfossils used in archaeological and ecological research. Relatively little is known about the stability of phytoliths after burial. Under alkaline pH conditions they can dissolve, and mechanical disturbances can cause a loss of their more delicate appendages. Here we present an experimental study of phytolith stability (combination of solubility and abrasion). Modern and fossil phytoliths were extracted from wheat using new methods to minimize dissolution, and by burning in an oven. These assemblages were placed in a solution buffered to pH 10 and maintained under constant temperature and shaking conditions. The silicon concentrations in the solution were monitored once a week for 5 weeks. The phytolith morphologies in each assemblage were determined at the outset of the experiment and after 5 weeks. The results show that there are differences in stability between various assemblages. Modern inflorescence wheat phytolith assemblages are more unstable than those from leaves/stems. Burnt assemblages are less stable than unburnt assemblages, and a fossil phytolith assemblage about 3000 years old is more stable than the modern wheat assemblages. The results also show that individual phytolith morphotypes have different stabilities, and as a result of dissolution and abrasion, some morphotypes may resemble others. This study further shows that archaeological and/or paleo-environmental interpretation of phytolith assemblages may change with the assemblage’s state of preservation.     

On modeling of chemical stimulation of an enhanced geothermal system using a high pH solution with chelating agent

Dissolution of silica and calcite in the presence of a chelating agent (NTA) at a high pH was successfully demonstrated in laboratory experiments using a high-temperature flow reactor. (Note that the term 'silica' used here includes amorphous silica, quartz, and silicate glass bead.) The mineral dissolution and associated porosity enhancement in the experiments were reproduced by reactive transport modeling using TOUGHREACT. The chemical stimulation method was applied by numerical modeling to a field geothermal injection well system to investigate its effectiveness. Parameters applicable to the quartz monzodiorite unit at the Enhanced Geothermal Systems site at Desert Peak (Nevada) were used. Results indicate that the injection of a high pH chelating solution results in dissolution of both calcite and plagioclase, while avoiding precipitation of calcite at high temperature conditions. Consequently, reservoir porosity and permeability can be enhanced especially near the injection well. Injection at a lower temperature of 120°C (temperature is over 160°C in the base-case) results in a porosity increase that is smaller close to the injection point, but extends to a larger radial distance. A slower kinetic rate results in less aggressive mineral dissolution close to the injection point and larger extent along the flow path, which is favorable for chemical stimulation.     

Chemical changes in buried animal bone: Data from a postmedieval assemblage

Macroscopic chemical analysis of animal bone recovered from dated excavation contexts of known pH from Castle Bromwich Hall, West Midlands, UK, allows an assessment of the rate and effects of bone decomposition, and the evaluation of current models of chemical decay. The results show great variation, and it is suggested that factors such as mechanical disturbance have a more significant effect on the differential destruction of excavated bone assemblages than chemical decay. The implications of this conclusion for the attempted reconstruction of past faunas, diet and behaviour are summarized, recommending caution in the acceptance of assemblages as unbiased samples.     

电解法纸张脱酸研究

酸化是导致纸质档案、文物、图书等自毁的主要原因,现有脱酸方法实用性不强,需进行创新与突破。传统水溶液法,是一种常见的脱酸方法,具有对纸张安全、环境友好、操作简便、经济实惠、脱酸效果好的优点,也具有纸张浸泡处理时间长、脱酸速度慢的缺点。若能够克服其缺点,水溶液脱酸法会具有非常广泛的应用前景。本研究在传统水溶液法脱酸的基础上,利用酸化纸张湿润状态下与外加直流电源构成电解池的工作原理,采用电解法将纸张中的酸根离子移出,实现纸张快速脱酸。通过对比电解法与传统水溶液法对自然酸化纸张脱酸前后的外观与性能,探讨电解法的脱酸效果。结果表明,电解法可以有效地去除纸张中的酸根离子,降低纸张的酸度,既保留了传统水溶液脱酸简便可靠、绿色安全、成本低的优点,又克服了纸张长时间湿态导致的变形、膨胀的不足及工作效率低的缺点。     

Ashes to ashes, charcoal to dust: micromorphological evidence for ash-induced disintegration of charcoal in Early Neolithic (LBK) soil features in Elsloo (The Netherlands)

Charcoal and other forms of charred organic material - an important part of the archaeological record - consist of benzenoids. Such components are unstable in basic or alkaline conditions. Since ashes are alkaline, this means that archaeological charcoal may have been disintegrated and lost if they were buried together with ashes, e.g. as in fireplaces. Ash may also cause clay translocation in decalcified loess because of the disaggregating effect of K⁺ ions in the soil solutions. We investigated the interplay of these two processes, using micromorphological samples from the Early Neolithic site at the Joannes Riviusstraat in Elsloo. Evidence for charcoal disintegration was found in the form of cavities in charcoal fragments, most commonly filled in with thick reddish limpid clay coatings. The combination of cavities and clay coatings are evidence for the disintegration of charcoal under the influence of ash. Ash may also have been instrumental in preserving small bone fragments in these decalcified well-drained loess soils. The evidence of ash-induced charcoal disintegration implies that charcoal preservation in the archaeological record is dependent on (1) whether or not is was buried alongside with ashes, and (2) on various soil characteristics that determine that determine how quickly the ash-derived alkalinity and potassium ions are leached.     

文物修复用脱色剂对手工纸耐久性的影响

在文物保护与修复工作中,需要对纸张进行脱色处理以除去部分顽固污渍、霉斑。本研究选取了六种不同类型的脱色剂,探究脱色处理对宣纸、皮纸、竹纸等几类传统手工纸样老化后各项理化性能的影响,揭示了各类脱色剂对不同纸种耐久性影响存在较大差异。研究表明,氧化性脱色剂与还原性脱色剂均会使纸张各项理化性能出现一定程度的下降。整体上,使用的脱色剂氧化性越强,纸张微观纤维受损越严重,脱色前后宏观性能下降幅度越大,而还原性脱色处理对纸张各项理化性能影响较小。在纸质文物修复脱色时,选择合适的脱色剂,可以有效减小文物损伤。