Ion Sandu, Otilia Mircea, Andrei Victor Sandu, Viorica Vasilache, Ioan Gabriel Sandu* <br>Study of the Liesegang Chemical Effects in Antique Bronze Artefacts During Their Stay Within an Archaeological Site

Ion Sandu, Otilia Mircea, Andrei Victor Sandu, Viorica Vasilache, Ioan Gabriel Sandu*
Study of the Liesegang Chemical Effects in Antique Bronze Artefacts During Their Stay Within an Archaeological Site

Abstract:

Our paper presents various forms in which the processes of deterioration-degradation manifest on the surface and in the 3D spatial distribution of the metallic core and the corrosion bulk for a series of recently discovered archaeological items. In that regard, we paid special attention to the items with and without a metallic core, that presented the Liesegang effect, so as to elucidate the formation mechanisms thereof during the period before abandonment until their uncovering in the archaeological site. By stereo-microscopic analysis and by SEM-EDX, we established that both the metallic core and each Liesegang layer had a gradual composition with a radial disposition, from center to surface. The items that had a conserved metallic core, the concentration of Sn increased from the center of the core to the exterior, where it exceeded the normal limits of common antique bronze items. Nevertheless, the completely corroded items, without a metallic core, presented a black-gray compound in their center, which contained a significant amount of metallic tin, heavily diluted in copper and the external Liesegang layers were disposed in line with a congruent coating formed of tin and chloride ions and also a small and variable quantity of copper (much lower than that from the basic alloy). On top of that coating there formed the mineralized layers of cuprite, malachite, azurite, nantokite, atacamite, paratacamite etc., which formed by osmosis on passing through membranes of hydrogels from Sn, Pb and Zn oxyhydroxides, or from phosphoapatites. The morphology and distribution of those layers was dictated by the initial form of the item, by the processed used for its manufacture, by the conservation state thereof before abandonment, by the chemistry and pedology of the soil it lays in. Keywords: ancient bronze, Liesegang effect, primary, secondary and contamination patina, OM, SEM-EDX

Issue: 2014, Volume 65, Issue 3

Pages:

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This article is published under the Creative Commons Attribution 4.0 International License

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