Definition - What does Patina mean?
Patina is a tarnish in color on the outer surface of a material, forming most commonly on bronze, copper and other related metals. Through the formation of patina, a metal protects itself against the corrosion that naturally occurs after being subjected to the environment and weathering. The chemical processes involved are oxidation and reduction, among others. This process also alters the appearance of these materials.
Corrosionpedia explains Patina
Patina results as a process of oxidation, weathering or both. Once a material is subjected to agents of weathering such as water, wind, ice, extreme temperature or other agents, it begins to undergo the oxidation process that ultimately leads to tarnish on its coat or surface. Patina also forms as a result of old age, wear, or even polishing. Materials form patina to protect themselves against damage by corrosion, but can also be used for aesthetic appeal.
Patina is a form of rust, which can be written as Fe2O3.nH2O. From the chemical point of view, the coatings of the materials such as oxides, sulfides, carbonates, and other elements in the coatings of the materials react with the weathering agents such as acid, oxygen, rain, sulfur-bearing compounds, and carbon dioxides to produce the resulting patina. Accumulated patina on the surface of objects can sometimes cause poor electricity conduction as well as electrical shocks.
The most common form of patina is that which is found on the surface of coins, especially after subjected to the agents of weathering. Archaeologists' studies show that patinas can protect a material from the agents of weathering for up to a century before the object becomes fully decayed. Patina can be seen as a decay-prevention method that materials themselves can implement.