The effect of soil conditions on the long-term corrosion of buried tin-bronzes and copper

The object of this work was to relate the corrosion of tin-bronzes to the chemical condition of the soil in which they have been buried, most of them since the Bronze Age. Naturally, it was not easy to obtain recent hoards with their related soils, and considerable reliance had to be placed on recorded finds by taking recent soil samples from sites on which hoards were found over a hundred years earlier. Even so, with the exception of peat, a reasonable relationship appears to exist between the pH of the soil and the state of the metal. Acid soils are aggressive to metals and alkaline soils are benign. In no cases were sulphate reducing bacteria active in promoting corrosion. In the main, peat and peaty soils were benign in spite of their acidity, probably due to the protective action of polyphenols.     

古代青铜器锡腐蚀产物研究回顾——特点、表征方法、腐蚀模型

对青铜器腐蚀机理的研究是对其进行保护修复的重要前提,在过去的数十年间,与铜和铅的腐蚀产物相比,文物保护领域对于锡腐蚀产物的认识和研究是相对缺乏且零散的。本文回顾了不同领域在锡腐蚀产物发展过程、特点以及表征方法等方面的研究成果。青铜器中锡腐蚀后一般首先形成复杂的水合氧化物(SnO_x·nH₂O),随后在氧化性条件下进一步氧化脱水,向锡石(SnO₂)转变,但由于此转变过程漫长而复杂,导致了锡腐蚀产物具有低结晶度、高电阻率、离子交换等特殊性质。通过梳理X射线衍射分析技术、拉曼光谱以及X射线光电子能谱以及其他分析方法在青铜器锡腐蚀产物表征中的应用进一步探讨了锡腐蚀产物的性质。最后,本文在回顾不同环境下的锡腐蚀产物的研究成果的基础上,介绍并比较了不同环境下青铜器的腐蚀模型。     

Post-depositional surface whitening of ceramic artifacts: alteration mechanisms and consequences

Surfaces on ceramic artifacts that are paler than the main sherd body are commonly interpreted as slips that were intentionally applied by the potter during the manufacturing process. However, due to post-depositional alteration, sherds that were not originally coated with a slip may macroscopically appear with deceptively similar pale surfaces. This paper presents a comparison of two sherds, both with pale to white surfaces, one of which is a real slip and the other a surficial corrosion that occurred during the burial stage. Observations using optical and scanning electron microscopy, as well as electron-probe image- and microanalysis, clearly illustrate the features of the two surfaces, as well as demonstrating their causes and effects. The superimposed slip is clearly delimited from the sherd body by a denser and much finer-grained fabric, in which clay minerals predominate and porosity is reduced by about 20% compared to the body. In the other sample, surface corrosion, due to invading fluids, has led to leaching of calcareous constituents and results in a remarkable increase in porosity close to the rim (ca. 25%). Sometimes called the “espresso crema effect” (Tschegg et al., 2009b), the surface becomes considerably brighter than the core and can easily be confused with intentional slips. This, as a consequence can lead to significant misinterpretations, to erroneous sherd characterizations and classifications, as well as to incorrect assignments to specific ware groups.     

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.     

广东“南澳Ⅰ号”明代沉船出水铜器腐蚀产物分析

由于海水环境中含有大量氯化物,海洋出水铜器在出水前已发生腐蚀,生成铜的氧化物及氯化物等。本文以广东"南澳Ⅰ号"明代沉船出水的22件铜器残片为研究对象,运用X-射线荧光仪(XRF)、X-射线衍射仪(XRD)和扫描电镜与能谱仪(SEM-EDS)等分析其腐蚀产物和矿物组成,结果表明腐蚀产物主要为铜的碱式氯化物,如Cu2(OH)3Cl和Cu(OH)Cl等,与国外已有研究成果类似,但Cu(OH)Cl在国外海洋出水铜器腐蚀产物中并不常见。     

明代御窑遗址出土孔雀绿釉、洒蓝釉、瓜皮绿釉瓷器分析

以往由于实物资料的匮乏,孔雀绿釉、洒蓝釉、瓜皮绿釉瓷器很少有从科学技术方面进行的研究,近年由于景德镇明代御窑遗址几次较大规模的考古发掘,极大丰富了这方面的资料。为了从科技方面更深入了解这类瓷釉的性质并为其以后的保护提供资料,本研究采用显微形貌观测法、激光剥蚀进样电感耦合等离子体光谱、能量色散X荧光和扫描电镜等对这些考古出土的宣德时期的孔雀绿釉、洒蓝釉、瓜皮绿釉瓷器进行了分析。分析揭示了这三种釉的形貌特点、腐蚀现象、胎釉组成、釉层元素分布情况,发现了胎釉之间有化妆土的存在并揭示了此物质的成分特点,讨论了高碱釉的工艺特征、瓷釉性质、剥釉机理。分析结果可为后续保护研究提供参考。     

镇安寺铁牛腐蚀产物及腐蚀机制研究

镇安寺铁牛全身腐蚀严重,弄清铁牛腐蚀原因及其影响因素,可为铁牛后续修复和保护提供依据。本研究采用扫描电子显微镜、X射线衍射仪和激光共焦拉曼光谱仪等方法分析了铁牛表面腐蚀产物的形貌、组成、结构及其腐蚀原因。结果表明,铁牛腹部为亚共晶白口铸铁,组织中含有多种相及夹杂物使铁牛耐蚀性能降低;铁牛表面腐蚀产物有严重的分层现象,外层和内层腐蚀产物较为致密,主要成分为α-FeOOH和Fe_3O_4;中间层腐蚀产物较为疏松,主要成分为γ-FeOOH和Fe_3O_4;铁牛耳朵、左脚和尾部腐蚀产物主要含有α-FeOOH、γ-FeOOH、Fe_3O_4和α-Fe_2O_3等,且α-FeOOH在锈蚀产物中含量最高;不同部位腐蚀产物组成存在明显差异,耳朵处腐蚀产物α-FeOOH和γ-FeOOH含量比(α/γ值)最小,左脚处最大;分析了铁牛腐蚀影响因素和腐蚀机制。     

澄城刘家洼遗址出土青铜器腐蚀成因研究

刘家洼遗址出土大量珍贵的青铜器对研究春秋早期芮国历史具有重要价值,但由于青铜器受到长期腐蚀影响,其蕴含的部分信息可能发生损失。为研究刘家洼青铜器的工艺、保存状况与稳定性,揭示关中东部黄土塬区出土青铜器的土壤腐蚀特征,并为文物保护修复提供参考依据,本工作对刘家洼青铜器腐蚀成因进行综合研究。本工作利用金相显微镜观察、扫描电镜-能谱、X射线衍射、拉曼光谱等分析手段对刘家洼遗址出土6件青铜器样品的锈蚀物相与锈层结构进行表征。结果表明,青铜器腐蚀产物以赤铜矿、孔雀石以及白铅矿为主。部分青铜器表面存在浅绿色粉状腐蚀产物,但并非含氯腐蚀产物。刘家洼青铜器锈层结构自金属基体向外依次为过渡层、原始表面内非金属层、原始界面、原始表面外原位沉积层及扩散沉积层。原始界面内非金属层Cu/Sn值低于基体,表明基体内的铜元素腐蚀后向外迁移以及锡元素腐蚀后形成锡石原位沉积。原始界面外Cu/Sn比值显著高于原始界面内非金属层,表明外迁的铜离子在埋藏环境作用下沉积。本工作通过对青铜器附着土壤样品pH值、氧化还原电位以及离子色谱分析,结果表明刘家洼青铜器埋藏环境为弱碱性氧化型环境,土壤中氯离子含量不高,这与出土青铜器的腐蚀...     

杭州萧山老虎洞遗址出土青铜工具的金相分析及腐蚀探讨

杭州萧山老虎洞东周遗址出土两件青铜工具,工具出土时已碎裂为数段,锈蚀状态严重。针对两件青铜工具的研究,主要从微观领域来探讨青铜工具的工艺技术及腐蚀特点,并通过建立电化学反应模型,运用电极电位差的理论,来试析电极电位对金相组织腐蚀的影响。同时提出在青铜修复时,可利用电极电位的原理来补配修复材料,以达到文物保护的目的。     

In-situ Corrosion Studies on Wrecked Aircraft of the Imperial Japanese Navy in Chuuk Lagoon, Federated States of Micronesia

A preliminary in-situ corrosion survey of the submerged Japanese WWII aircraft in Chuuk Lagoon, in the Federated States of Micronesia, has provided information on the way in which the wrecks interact with the marine environment. The aircraft are characterised by a lack of encrusting marine organisms and are clearly identifiable. The values of pH and the corrosion potentials vary with depth and the voltage depends on the composition of the underlying metal alloys. It is possible that with additional data from these non-destructive methods techniques it will be possible to provide marine archaeologists with appropriate diagnostic tools.
© 2006 The Author.