What is Patination?
Patination describes the way by which a metal object develops a thin layer of oxidized metal on its surface over time. This thin layer is called the ‘patina’ – a word derived from the Latin for ‘shallow dish’ – and can be formed naturally, by exposure to an oxidizing environment, such as polluted air or deliberately by using oxidising chemicals.
Outdoors, bronzes generally develop a dark green patina, from the reaction of the copper in the metal alloy with atmospheric carbon dioxide and ambient or atmospheric moisture.
Excavated bronzes, after centuries of burial have patinas with a range of colours including red-browns, browns, greens, blues, and even black. The same is true of bronzes that have been found on the sea bed. Modern patinations that follow the naturally found green patination are often called Pompeii Green.
At Bronze Restorations we deal with the artificial patination of bronze. Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals such as aluminium, manganese, nickel or zinc. These additions produce a range of alloys that are often harder than copper on its own. Artificial patinas are applied to bronze using chemicals designed to react with the surface.
The development of deliberate patination on bronze sculpture is thought to have began during the Renaissance period in Italy when it was used as a way of making a new bronze sculpture have the appearance of pieces from antiquity. To imitate these Greek and Roman bronzes which had been patinated naturally varying shades of browns and greens were used.
When the buried city of Herculaneum was discovered in the 18th century a huge hoard of bronze statues was unearthed. They were severely damaged due to the eruption of the volcano and centuries of burial and needed to be repaired and restored. On completion the restorers applied a green black patina to the bronze surface to level everything out and conceal imperfections in the finish. This became known as Herculaneum Black.
Over the last two hundred years the techniques for patinating bronze has expanded to include a wider palette of colours and surface finishes than the traditional colourations. This has accelerated with the demand by modern sculptors for eye catching finishes.