A piece of blackened or oxidized silver is true sterling silver, but it's surface has been intentionally darkened through by introducing it to a chemical process. This patina, a surface color that occurs when the silver is introduced to sulfides, is a sped up version of the natural tarnishing process.

The chemical name of black coating is known as Silver sulfide ( Ag 2 S ) which is formed due to the reaction of Silver with the atmosphere. The chemical phenomenon which is responsible for this is known as corrosion, in which a metal is attacked by substances around it such as moisture, acids, etc., and gets corroded.