Advances in understanding bronze disease corrosion mechanisms and humidity threshold studies

Bronze disease is a self-sustaining corrosion process involving cuprous chloride (CuCl) that occurs under oxygen-rich and high-humidity conditions. It is widely found in copper alloy artifacts and is considered one of the most destructive and challenging corrosion problems in the long-term preservation of cultural heritage. This study systematically reviews the progress in research into the corrosion mechanisms of bronze disease since the mid-20th century, summarizes the evolution of theoretical models and focuses on the critical role of relative humidity in the initiation and progression of the brone disease. The threshold values of environmental relative humidity are outlined. In addition, the effects of alloying elements—particularly tin (Sn)—on corrosion behavior are discussed. This review aims to enhance our understanding of the mechanisms of bronze disease, to support the establishment of corrosion risk assessment frameworks, and to provide theoretical guidance for the conservation of bronze artifacts.