Why copper vessels, bottles or any copper utensils do not blacken from the outside?

Copper vessels and utensils do not blacken from the outside due to the protective layer that naturally forms on the surface of the copper called a patina. When copper is exposed to air, it reacts with oxygen to form copper oxide, which is a blackish-green compound. However, over time, this layer of copper oxide reacts with carbon dioxide and other compounds in the air to form a thin, protective layer called a patina.

The patina acts as a barrier that prevents further oxidation of the copper, which in turn prevents the copper from turning black. Additionally, copper utensils are often polished and coated with lacquer or other substances to further protect the surface from tarnishing.

However, it is important to note that the inside of copper vessels and utensils may discolor or tarnish due to the reaction with acidic foods or liquids. Therefore, it is recommended to only use copper vessels for non-acidic foods and to clean them thoroughly after each use.