Pour salt into a small plastic bowl. Add fresh lemon juice until you create a paste the thickness of oatmeal. Use a soft cloth to scrub the oxidation off the surface of the copper with the salt and lemon paste. Use a small, soft-bristled nylon brush to scrub the oxidation out of the corners and crevices. Rinse under cold running water then dry with a soft cotton cloth.
Try another option by mixing 1/2 cup vinegar with 1/2 cup salt and 1/2 cup flour in a small plastic bowl. Mix the ingredients together to create a paste. Spread the vinegar, salt and flour paste over the oxidation on the copper and let it sit for about 15 minutes. Scrub the copper surface with an old, wet toothbrush, then rinse the copper well under cold water. Dry the copper with a soft cotton cloth.
Clean smaller items by mixing 1/2 cup vinegar and 1 teaspoon salt together in a small plastic or glass bowl until the salt dissolves. Place pennies and other small oxidized copper objects in the vinegar and salt mixture. Let the objects soak for five minutes. Remove the objects and rinse well under cool, running water. Pat the pennies and small copper objects dry with a paper towel.
Remove the oxidation with another natural alternative by making a paste of cream of tartar and fresh lemon juice, about the thickness of cake batter. Rub the paste over the oxidation on the copper, then allow the paste to sit undisturbed for 15 minutes. Scrub with a soft-bristled nylon brush, then rinse well under cool water. Dry thoroughly with a cotton cloth.
Clean larger surfaces by cutting a fresh lemon in half. Sprinkle the lemon with salt, then use the lemon as a scrubber to clean oxidation off surfaces, such as copper sheets or decorative hangings. Rinse the lemon off the surface with cold water, then dry with a soft cotton cloth.