Patina is a thin layer that forms on the surface of stone; on copper, bronze and similar metals. It is a tarnish produced by oxidation or other chemical processes. Patinas can provide a protective covering to materials that would otherwise be damaged by corrosion or weathering while also adding a beautiful, aged feel to the material.
Artists and metalworkers often deliberately add patinas as a part of the original design and decoration of art and furniture, or to simulate antiquity in newly-made objects. The process is often called "distressing". On metal, patina is a coating of various chemical compounds formed on the surface during exposure to atmospheric elements, a common example of which is rust which forms on iron or steel when exposed to oxygen.
A wide range of chemicals, both household and commercial, can give a variety of patinas. They are often used by artists as surface embellishments either for colour, texture, or both. Patination composition varies with the reacted elements and these will determine the colour of the patina. For copper alloys, such as bronze, exposure to chlorides leads to green, while sulfur compounds tend to brown. Some patina colours are achieved by the mixing of colours from the reaction with the metal surface with pigments added to the chemicals. Sometimes the surface is enhanced by waxing, oiling, or other types of lacquers or clear-coats.
For example, the first image shows a stunning 'aged bronze' finish, produced through a rapid oxidation process to produce a patina. The iron bollard in the middle has developed a rust patina in exterior elements, enhancing both the durability and aesthetics of the fitting. The pendant shows a stunning verdigris finish, the natural green patina which results from ageing copper