Method 2: Make copper shine again with lemon and salt
To keep your copper mugs from discoloring, you can put 4 tablespoons of salt in a plate. You can use regular table salt, sea salt or any other type of table salt for this purpose. Depending on how many cups you want to clean, you may need more salt.
Now cut a lemon into 2 halves or 4 parts. Depending on how many copper cups you want to clean, you may need two or more lemons.
Now place the lemons on the salt. Make sure the flesh of the lemon is completely covered with salt.
Rub your copper mugs in a circular motion with the lemons.
Scrub the outside and inside of the mugs until all stains are removed and their surfaces shine again.
Now rinse the mugs thoroughly with cold or warm water until all lemon and salt residue is removed.
Dry each mug thoroughly with a cloth. While drying, also pay attention to small corners and edges so that there is no moisture anywhere, otherwise oxidation stains may form again. Be meticulous that your copper mugs are completely dry after rinsing.