The formation of acetate corrosion on bronze antiquities : characterisation and conservation

• Main Author: Boccia Paterakis, A.
• Published: University College London (University of London) 2011
• Subjects: 930
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.565345

This project reveals the proliferation in the awareness of acetate and other carbonyl corrosion on bronze artifacts in archaeological collections. Blue and blue-green carbonyl corrosion of bronze is a recent discovery in part due to its mistaken attribution over the years to bronze disease, chalconatronite, and azurite. This project examines sources of acetic acid, and evaluates the environmental conditions in which acetate corrosion develops and the influence of alloyed lead and sodium contaminants in this process. Case studies identifying corrosion by XRD on predominantly Egyptian archaeological bronzes, with a focus on Saqqara, revealed a preponderance of a sodium copper carbonate acetate and copper sodium formate acetate. These were identified on the majority of Saqqara bronzes sampled in the Fitzwilliam Museum, Ashmolean Museum, Liverpool Museum, Petrie Museum and British Museum. Unknown compounds not included in the International Centre for Diffraction Data (ICDD) catalogue were also discovered. Due to the novelty of this discovery, the conservation of bronze with carbonyl corrosion is as yet an unexplored area. This project examines passive and active means of conservation. Solubility and cleaning tests were carried out on the Saqqara bronzes. Solubility of carbonyl corrosion is discussed in terms of removability, influence on cleaning methods, and stabilization of corrosion by means of environmental control. Two coatings, the acrylate Incralac®, and the polyethylene wax emulsion Poligen® ES 91009, underwent corrosion testing on leaded and unleaded bronze with promising results as protective coatings against attack by volatile acetic acid.