Abstract
BackgroundArchaeological 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.ResultsIn 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.ConclusionsBased on the results, it can be concluded that SEM-EDS analysis and Microscopy observations can help to characterize compositional difference between corrosion layers in the micro scale as well as corrosion mechanisms occurring in archaeological metal artefacts.
Highlights
The long term burial conditions in soil causes various corrosion morphologies in archaeological metals, from a thin corrosion layer to a completely corroded and mineralized artefact [1,2]
One of the main corrosion morphologies in ancient bronzes is layered morphology which is observed in some bronze artefacts from Haft Tappeh Middle Elamite site, southwest Iran, belonging to about the 14th century BC [9,10]
The composition of the central layer in some samples has been studied previously by SEM-EDAX analysis [9], but to better understand other corrosion layers, the relationship between layers, chemical composition differences in layers and corrosion mechanism in these bronzes; in this paper we report a detailed stratigraphical investigation using SEM-energy dispersive spectrometer (EDS) observation and analysis, as well as optical microscopy (OM)
Summary
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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