Tarnished copper vessels are cleaned with lemon or tarmarind.Why?

Copper vessel gets tarnished due to copper oxide layer formed on its surface.Copper oxide is basic in nature.Lemon or tamarind is acidic.Hence, when we rub tarnished copper vessel with lemon juice or tamarind, the basic copper oxider reacts with acid(citric acid) present in the lemon or tamarind to form a salt which is washed away with water.Hence,the vessel gets cleaned