Copper Alloys

Copper and its alloys have found extensive use in artistic and architectural fields not only because of their notable resistance to corrosion but also due to the beautiful colours of the patina of corrosion products that are formed when they are exposed outdoors. Green roofs and façades are highly appreciated by designers and citizens. In the past, in urban environments, such green patinas could be naturally formed because of the interaction with pollutants, such as SOx, and are typically constituted by copper hydroxide sulphates such as brochantite and antlerite. SOx levels have been drastically reduced over the last decades and this means that we will not expect anymore the natural growth of green patinas on copper in urban environments (unless we are close to the sea, where the formation of chlorides-rich green patinas is expected). Depending on the location, artificially patinated surfaces may be nowadays a good solution to get green roofs. Artificial patinas may have quite different characteristics compared to natural ones and are often obtained by using polluting chemicals. It is therefore important to find low environmental impact procedures for their production and to obtain corrosion layers with characteristics very similar to the natural ones. In addition, it is important to understand if protective coatings would maintain their efficacy when applied on patinated surfaces. This is particularly relevant in the field of cultural heritage conservation, where they are normally applied on corroded surfaces. Continuous research is dedicated to studying and developing protective coatings, that act as barriers, preventing corrosion and simultaneously preserving the historic aspect of the surfaces. The coating also must ensure low toxicity and easy application to guarantee the safety of the restorer. In this study, a series of artificial patinas were produced and characterized. In addition, a multi-layer coating, widely used by restorers for the conservation of bronzes, and a silane-based coating have been applied on artificially patinated surfaces.