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Background: Archaeological metallic artefacts buried in soils deteriorate by means of various environmental as well as internal factors and mechanisms over time such as change in composition and microstructure of metal and corrosive factors due to long-term burial environment. Corrosion in metals occurs in different morphologies and results in different types of corrosion products based on soil composition. Identification of corrosion mechanisms and morphology in archaeological metals can help conservators to characterize deterioration occurred in metals and make decisions to protect artefacts about preventing further deterioration. In archaeological bronzes, different layers may form on the surface of artefacts and their composition, depth and shape depends on factors noted above. Results: In this paper, results of investigation carried out on ancient bronzes discovered from Haft Tappeh archaeological site, southwestern Iran, are presented. The ancient bronze samples are dated to the Middle Elamite period about 14th century BC. Some of the Haft Tappeh bronze artefacts corroded completely and a multilayer structure has formed. To study the stratigraphy of corrosion layers and their composition, some bronze artefacts have been analyzed using SEM-EDS (Scanning Electron Microscopy Energy Dispersive Spectrometry) and Optical Microscopy analyses. The results show difference between the amount of Cu and Sn in layers that may follow from copper leaching from inner layers and formation of copper trihydroxychlorides because of bronze disease.

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Characterization of soil corrosivity in archaeological sites is an important subject to understand the conservation conditions of archaeological bronze collections and helps conservators to prepare a conservation strategy for long term preservation of bronze objects. In this paper, a research approach is established to identify soil corrosivity in two archaeological sites and to find correlation between corrosion events and soil characterizations. Therefore, an analytical study was carried out to identify different factors of soil environment influencing corrosivity of the soil in two sites. Based on the results, measuring different factors such as chemical composition, pH, texture, soluble salts and water content and SOM displayed different soil environments in two archaeological sites. The results represent correlative relationship between corrosion mechanism and soil characteristics in these archaeological sites.

Corrosion layers in some copper and bronze archaeological objects from Haft Tappeh archaeological site, southwest Iran, were studied. For this purpose, optical microscopy, scanning electron microscopy with energy dispersive X‐ray microanalysis, micro‐Raman spectroscopy and X‐ray diffraction methods were applied to observe corrosion stratigraphy and their characteristics as well as identification of chemical composition and phase determination of different corrosion layers. Based on optical and electron microscopy, three different corrosion strata were identified in cross section of different metallic objects including various red, green, white‐grey powdery and dark internal compact layers. Scanning electron microscopy with energy dispersive X‐ray microanalysis on different corrosion layers revealed that Cu, Sn and Cl are the main elements in the chemical composition of different layers. Tin‐rich phases were detected in white‐grey and dark layers that may be formed because of the internal oxidation of tin as well as the decuprification (selective dissolution of copper) phenomena occurring during long‐term burial period in the soil. Also, the XRD and micro‐Raman spectroscopy results proved that the main corrosion products are nantokite (CuCl), copper trihydroxychlorides and copper oxides. The combination of these analytical methods allows us to explore the surface and internal corrosion layers of the archaeological copper and bronze samples, and major interest is on studying their chemistry, microstructural properties and corrosion stratigraphy. Copyright © 2015 John Wiley & Sons, Ltd.

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