Kalksinter auf archäologischen Bronzen

Können Komplexbildner eine Alternative zur mechanischen Freilegung sein?

Abstract

Sinter on Archaeological Bronzes: Can Chelating Agents be an Alternative to Mechanical Stripping?

Removing calcareous accretions from excavated copper alloy objects can be a difficult step in their conservation. The use of chelating agents might be an alternative to mechanical methods. The common trisodium citrate (Na3-Citrate), sodium tripolyphosphate (STPP), disodium ethylene-diamine-tetraacetate (Na2-EDTA) and the newly applied cyclohexanediamine-tetraacetate (CDTA) were tested to determine their capability of dissolving calcium carbonate without affecting the patina and the base metal. Comparative experiments were carried out on synthetic malachite, cuprite, calcium carbonate, naturally polished malachite surfaces and sheets of bronze and brass. The quantity of metal ions dissolved, estimated by atomic absorption spectral analysis (AAS) and also scanning electron microscopy (SEM), showed that the calcareous accretions could be removed satisfactorily; however, all chelating agents dissolved constituent parts of the patina, such as malachite and cuprite, and may harm bronze or brass. Compared to the other chelating agents CDTA is most effective in dissolving calcium carbonate and is less harmful to the patina. Na3-Citrate and STPP are less harmful to the base metal, but may lead to patination of the underlying metal.