Abstract
A bronze kettle dating from the 1st to 2nd century was found in a riverbed of the Kupa river in Croatia. After excavation it spent another 50 years in a depot of a museum in atmospheric conditions prior to starting the conservation treatment and our studies. A study on the surface layers development was performed to determine the whereabouts of the object through its history. This study is a demonstration of how such analysis can be used to reconstruct what the object went through during its life span. Samples taken from the kettle were observed by optical and scanning electron microscopy (SEM), and analysed by X-ray fluorescence (XRF), X-ray energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR).It was determined that the kettle is made of low-tin bronze, with low amounts of iron, aluminium, calcium and nickel. While being in the riverbed malachite formed on the kettle. After longer exposure to the river Si-oxides and CaCO3 formed on the surface of the kettle, over malachite. It was shown that the kettle probably had a ferrous alloy handle which degraded and disappeared in time. After excavation, the kettle came again in an oxygen-enriched atmosphere and formed new surface layers over the malachite layer. As the museum the kettle has been kept in since excavation is set in a highly industrial area sulphur compounds have been formed on the surface.
Highlights
Objects made of copper and its alloys are often covered by layers of corrosion products called patina
Some of them covered the surface of the green areas, while some were close to the surface of the metal and degraded the metal until they made holes in the material itself
The yellow-white layers observed on Sample 4 were powdery and below them there was a layer of partially formed green corrosion products, while in other places a very thin layer of reddish-brown layers was observed
Summary
Objects made of copper and its alloys are often covered by layers of corrosion products called patina. If one understands the relationship and interaction between environments metals are exposed to and the formation and stability fields of corrosion products on metals, one may be able to reconstruct environmental conditions surrounding the object in the past. This information should provide investigators with the possibility of writing the biography of ancient metal artefacts [5], i.e. by studying the corrosion products layering and composition it is possible to reconstruct the whereabouts of an object through its history. The conclusions obtained from such studies are valuable both for the person performing the conservation treatment as well as for art historians
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