Copper alloy cannon from Malta and Gozo : an assessment of the local environmental conditions and their impact on corrosion

Abstract

Until recently, a number of copper alloy cannon were displayed in front of prominent buildings and monuments in different parts of Malta and Gozo. The cannon were transferred inside the Palace Armoury in Valletta and the Maritime Museum in Birgu in order to be protected from aggressive outdoor conditions. The main aim of this study investigates the influence of local outdoor environmental conditions on the corrosion of the different cannon. A brief historical background of the cannon is given, with specific reference to their manufacturing techniques, original use and relocations. Local phenomena in different parts of Malta and Gozo promote corrosion. This corrosion behaviour could be attributed to differences in pollutant concentrations as well as temperature (T) and relative humidity (RH) levels. These variables were monitored and their impact on corrosion was assessed. Monitoring inside the museum environment determined the different conditions the cannon are currently exposed to. The condition of each cannon was documented, and scientific investigations using Fourier Transform Infrared (FTIR) Spectroscopy were carried out in order to determine the chemical composition of corrosion products. The results indicated that corrosion products are typical of urban atmospheres. The documentation, environmental monitoring and scientific analysis provide an understanding of the atmospheric corrosion pattern presented by the cannon. Preventive and conservation strategies are proposed to ensure the long-term preservation of the cannon.