An investigation into the cause of corrosion on indoor bronze sculpture

Abstract

Corrosion noted on a number of nineteenth and twentieth century indoor bronze sculptures in the collection of the National Gallery of Canada was the cause for a major condition survey of its Canadian, American, and European bronzes. The results led to a comprehensive study, which included material analysis. This article outlines the steps undertaken to determine the extent and type of corrosion, its possible cause(s), and potential remediation. The survey included 136 bronzes, of which 40 were selected for an in-depth study. Indoor air quality tests of the current building, housing the collection since 1988, were carried out. The dossiers and database records of the selected sculptures were reviewed to investigate their condition, treatment, and storage history. The metal, patina, and corrosion products were subjected to analysis. More areas of corrosion were generally associated with predominantly green patinas and chloride-containing compounds identified in either patina or corrosion samples. The most frequently identified compounds in the patina samples were atacamite, a copper(II) chloride hydroxide, and cuprite, a copper(I) oxide. The most frequently identified compounds in the corrosion samples were atacamite and rouaite, a copper(II) hydroxide nitrate. The analysis determined that the current environment is not contributing to the surface alterations of the sculptures; however, past storage conditions, chemical residues from artificial patination, and likely casting residues are the main causes of the current condition.     

《甲骨金石简帛文学源流》的贡献与缺失

刘奉光教授所著《甲骨金石简帛文学源流》把文学书写载体作为划分文学研究对象的标准，具有首创意义，并针对对象特点，提供了相应的研究方法，但在传世文学研究范围的划分与具体的操作过程方面仍有完善空间。     

Characterization of the corrosion layer on iron archaeological artefacts from K2 (825–1220 AD), an archaeological site in South Africa

Abstract

A study of the composition and phase distribution of the corrosion layers on three ferrous objects, excavated at K2 (Bambandyanalo), an archaeological site in South Africa, was conducted. The objective of the study was to obtain information that can contribute to conservation procedures to be performed on the iron artefacts from this site. Examination of cross sections by means of energy-dispersive X-ray spectroscopy coupled to a scanning electron microscope (SEM–EDX), X-ray powder diffraction (XRD), and micro-Raman spectroscopy revealed the same corrosion composition and structure for all the objects under study, namely an internal layer adjacent to the metal surface with ghost inclusions and an external layer containing quartz grains. The study also revealed that the presence of magnetite (Fe₃O₄), maghemite (γFe₂O₃), and lepidocrocite (γ-FeOOH) within the internal layer is the only difference between the chemical compositions of iron corrosion products within the two layers. The results also made it possible to retrace the corrosion history during burial and long-term storage.     

The occurrence of brochantite on archaeological bronzes: a case study from Lofkënd,Albania

A technical study was conducted on a group of copper alloy artifacts excavated from the burial tumulus of Lofkënd (fourteenth–ninth century BCE) to identify the alloy compositions and methods of manufacture. The surface corrosion was also examined in order to understand the diagenetic processes affecting the preservation of the finds and their condition. Portable X-ray fluorescence spectroscopy, metallographic examination, and X-ray powder diffraction (XRD) analysis were used to characterize the alloy composition and identify the corrosion products present. XRD analysis showed the presence of brochantite (Cu₄SO₄(OH)₆) on five of the metallic artifacts. Brochantite is not commonly reported on archaeological bronzes from terrestrial sites, but is more readily found on copper alloy objects exposed to sulfur pollutants in the air or soil. The possible conditions that could have led to the formation of this corrosion on the bronzes from Lofkënd are discussed in the context of the particular burial environment found at the tumulus.     

The impact of chloride desalination on the corrosion rate of archaeological iron

Abstract

Although desalination of archaeological iron reduces its chloride concentration and enhances object stability, the reduction in corrosion rate that this produces has never been quantified. This study measures post-treatment corrosion rates in accelerated corrosion environments to identify the impact of removing chloride ions on corrosion rate. Thirty-five archaeological iron nails, treated individually in either alkaline sulphite or nitrogen-deoxygenated sodium hydroxide, were exposed to 75°C and 75% relative humidity together with 31 untreated objects from the same archaeological sites. Object weight change and visual examination of physical change before and after the test period were used to monitor corrosion. 77% of treated objects showed no weight gain and no visible signs of corrosion, while 90% of untreated objects did corrode. The impact of chloride on corrosion of untreated objects was clearly established by a significant linear correlation between chloride content and weight gain. Treated objects with <400 ppm chloride content showed no corrosion behaviour. Corrosion of treated objects was attributed to incomplete treatment: 93% of objects treated to <5 mg/l Cl^? in the final solution bath displayed no corrosion behaviour. Based on these results, desalination of iron objects to enhance their stability offers a valuable option for reducing corrosion rates of archaeological iron, which should increase object lifespan. The results also raise the question of whether low levels of post-treatment residual chloride produce corrosion of any significance. Answering this will be an important step forward for managing the preservation of archaeological iron.     

Surface Investigation of Metal Threads and Solid Metals of Ottoman Textiles in the Topkapi Palace Museum

ABSTRACT

We analyzed 53 historical textile samples from a collection of caftans and brocades dating between the sixteenth and nineteenth century in the Topkapi Palace Museum (TPM) by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Data were collected on the type, dimensions, elemental composition, and level of corrosion. The technique is presented in this work as an efficient and micro-destructive tool for the characterization of the structure of historical metal threads. SEM-EDX analysis for different energies was performed on a selection of gold and silver threads belonging to the historical textiles. The results were interpreted via laboratory prepared samples of gilt Ag and sulfur reacted Ag at different thicknesses for Au and Ag₂S layers respectively. A series of Au–Ag alloys for different Au/Ag ratios were prepared for comparative analysis. The threads were made of metal strips wound around a silk core. Metal wires and flat strips were also used. The use of differential energies allowed for differentiating strips and wires made of homogeneous silver and gold alloys from the ones coated with a thin gold layer. Analysis of EDX data revealed that the Au film thickness was very thin (10–60?nm). Formation of Ag₂S layers over the thin Au film as thick as 1.5?µm was taking place. Formation of thinner Ag₂S layers over non-gilt Ag suggested different reaction mechanisms for gilt and non-gilt cases.     

由“资源集聚”向“需求导向”转变——对武汉科技信息服务平台建设的思考

为进一步提升武汉科技信息共享服务平台使用效率,本文从平台资源建设、资源应用、供需对接方式和供需特点等方面分析了武汉科技信息资源服务现状;基于需求和利用的角度,结合平台管理实践和走访用户、问卷调查等研究方法,从信息资源需求主体和平台自身建设管理两个维度,找出制约科技资源供需对接的主要因素;以市场化和制度化为创新理念,从政策创新、机制创新、市场化服务、环境营造、人才培养等方面提出平台建设由“资源集聚”向“需求导向”转变的对策建议.