Mix 1 teaspoon of vinegar and 5 teaspoons of salt in warm water and rub gently. After air drying, place in a dry place. This method will help restore the luster of copper and prevent further tarnishing.

Cut the lemon in half, sprinkle salt on the cutting surface, then use it to wipe the oxidized part of the copper bowl surface, or use a dry cloth dipped in a mixture of lemon juice and salt to wipe, and finally rinse with water and wipe dry with a cloth.