Effects of Pigeon Excreta on Copper and its Alloys used in Historical Monuments

Abstract

Pigeons have been a common disturbance in numerous cultural sites of the Kathmandu Valley. Besides health, economic and aesthetic issues caused by the pigeon excreta, it also involves damaging the materials including the metals like copper and its alloys used in Nepalese architecture. The primary goal of this study was to discover the impacts of pigeon excreta on the metal monuments of cultural importance in Kathmandu Valley. The pigeon excreta were collected from three world heritage sites of the Kathmandu Valley- Kathmandu Durbar Square, Bhaktapur Durbar Square and Patan Durbar Square. Supplementary metals of copper and its alloy mainly bronze and brass of similar composition as used in the monuments were collected from the surrounding area of Patan. The metal samples were cut, cleaned and immersed in excreta samples by tying them with thread suspended with a stick and covering the beaker with foil over 122 days’ duration. The metals were regularly cleaned and weighed to find the change in weight over short, medium and longer period. Effects of the pigeon excreta on the metals were analysed based on staining, and corrosion loss compared to initial weight. There was considerable corrosion loss in copper and its alloy samples, but a major decrease was seen in copper pieces that were kept in the fresh pigeon excreta. Statistical analysis revealed a significant corrosion loss in copper but not in bronze and brass samples. It supports the stronger negative impact of bird excreta on copper compared to its alloy. Therefore, the use of copper-alloys instead of pure Copper in monuments that are being reconstructed could minimize the adverse effects of pigeon excreta. The findings of this research provide important insight into the preservation of cultural heritage sites.