How to Clean Copper
If you have a copper item that you need to clean, cut a lemon in half and squeeze out all of the juice. Mix salt into the juice a little at a time until it forms a paste. Dip a soft cloth into the paste, then rub the cloth over your copper to remove any tarnish. When you've finished cleaning the copper, rinse it off with warm water and polish with beeswax to give the item a lasting shine.
Combine equal parts vinegar and salt to make a paste. Pour the salt into a clean bowl, then slowly add the vinegar. Use a spoon to stir the ingredients together to make a paste. Keep stirring until the paste appears consistent. The measurements don't need to be exact. Vinegar may be enough to remove oxidization on your piece of copper. Apply the paste to a clean towel. Dip your clean towel into the paste to coat the towel. Get a generous amount of paste onto the towel so there's enough to scrub the copper piece. You can use any type of clean towel. For instance, a dishcloth or paper towel will work great. Scrub your copper piece with the salt and vinegar. Use the towel to rub the salt and vinegar paste into the copper item. Rub the dark stains vigorously to help remove them. Apply a firm, even pressure to pull up the stain. As you clean the copper piece, dip the towel in the paste again as needed to apply more paste. Only use salt and water if you're cleaning a delicate surface. Use a toothbrush to work the paste into dents. If your copper item has dents or crevices that are stained, scrub these spots with a toothbrush. Apply the vinegar and salt paste to the toothbrush, then work the bristles into the grooves to help remove the dark spots. Apply more paste to the toothbrush as needed to clean the copper. If you still see marks on the surface, try lightly scrubbing the surface with fine-grit sandpaper. Rinse off the paste and wipe your piece dry. Hold the copper item under warm running water to remove the excess paste. Use your fingers to gently wipe off the paste. Then, use a clean towel to wipe your copper item dry. If there are any spots remaining on the copper, apply pressure with the cloth to remove them. Combine vinegar, water, and salt in a large pot. Measure out 1 cup (240 mL) of vinegar into a large pot, then add 1 tbsp (17 g) of salt. Use a measuring cup add 3 cups (710 mL) of warm water to the pot. Then, stir the ingredients to combine them. If you're cleaning a large copper piece, use a bigger pot and double the ingredients for the cleaning solution. Submerge your copper piece in the solution. It's safest to put the copper into the pot before you start boiling the solution. Place the item into the pot and make sure the stains are covered by the cleaning solution. It's okay if part of the item is not covered, as long as you aren't trying to clean the exposed area.  It's okay to clean more than 1 piece at a time if they all fit into the pot. For instance, you might clean 2 copper mugs at the same time or a handful of copper jewelry pieces. Bring the solution to a boil over high heat. Turn the burner on high heat to heat the pot. Monitor the pot as it heats to boiling. After it reaches boiling, adjust the heat to keep it at a rolling boil. Stay near the pot while it's heating to make sure it doesn't boil over. Watch for the stains to fade from the copper. The vinegar and salt will draw out the stains or black patina. Check the water to see if the discoloration is leaching out of the copper and into the solution. Let the item boil for up 15 minutes. If the item looks clean before you get to 15 minutes, it's okay to turn off the pot early. Turn off the heat so the copper piece can cool. After 15 minutes, turn off the burner so that the solution and the copper item will start to cool. Leave the pot to cool for 30 minutes to an hour. Don't try to handle the copper while it's still hot. The metal may burn your hand, so be careful. Scrub the cooled copper piece with a dry cloth. Remove the copper item from the solution and use a soft, clean cloth to dry it. Use firm pressure as your rub the copper to buff it into a shine. If you see any remaining stains, rub them vigorously with your cloth to try to buff them out. Cut a lemon or lime in half. Hold a lemon or lime on a cutting board. Then, use a sharp knife to slice it in half. Keep both halves of the fruit to use as a cleaner. You can use either a lemon or a lime to clean copper, but lemons are more commonly used. Dip 1 half of the lemon or lime in salt. Pour a small amount of salt on a plate, then press the fleshy part of the lemon or lime into the salt. Apply a thin layer of salt over the fruit flesh. Leave some salt on the plate so you can dip the fruit in more salt as needed. Scrub the lemon or lime over the copper. Use light pressure to press the fleshy part of the lemon or lime into the copper item. Vigorously rub the copper to remove the stains or patina. Pay special attention to areas that have dark stains. Dip the lemon or lime half in the salt as needed. If the first lemon or lime half starts to squish before the item is clean, switch to the second half and resume scrubbing. Rinse off the copper piece with warm water. Hold the copper item under a stream of warm water until you don't see anymore fruit flesh or salt. Turn the item over in your hands as you rinse it so that it's thoroughly cleaned. Wipe the copper piece with a dry cloth. Use a soft, clean cloth to dry the copper item. Apply a firm pressure to lightly buff the piece. If you notice any remaining stains, vigorously rub those spots with your cloth to help bring them up. Apply a dollop of ketchup to a clean rag. Use a clean dish cloth or paper towel. Squeeze the ketchup onto the cloth or dip the cloth in the ketchup. Keep the ketchup nearby so you can apply more as necessary. For large pieces, you may use a lot of ketchup. The acids in the ketchup dissolve copper stains. Sprinkle salt onto the ketchup for added effectiveness. While using salt is optional, it might the ketchup more effective. To use the salt, simply sprinkle a light layer on top of your ketchup. The ketchup and salt will mix together as you scrub the copper. Add more salt each time you add additional ketchup. Scrub the mixture into the copper, leaving a thin layer. Use your cloth and firm pressure to apply the ketchup-salt mixture over the surface of the copper. Vigorously rub the areas that are stained. Apply the ketchup in a thin layer over the copper item. If you're treating a small stain, it's okay to only apply the ketchup to that area. However, it's also okay to treat a large item with ketchup. Let the ketchup sit on the piece for 30 minutes for tough stains. You don't need to let the ketchup sit on small stains that are coming up with scrubbing. However, leaving the ketchup in place for up to 30 minutes can draw out the stain more easily. Set a timer and wait for the ketchup to work. You can always try scrubbing first and then let the ketchup sit on the item if it's not coming clean. Rinse off the ketchup-salt mixture with warm water. Hold the copper item under running water to rinse it clean. Use your fingers to scrub off any stuck-on ketchup. Keep rinsing until the water runs clear and the item looks clean. Use a toothbrush to remove stuck-on ketchup spots. Dry the copper with a clean cloth. Use a soft, clean cloth to dry the copper item. Apply a firm pressure to the piece to lightly buff it. Additionally, vigorously rub any areas that still look stained. 
Combine equal parts vinegar and salt to make a paste. Apply the paste to a clean towel. Scrub your copper piece with the salt and vinegar. Use a toothbrush to work the paste into dents. Rinse off the paste and wipe your piece dry. Combine vinegar, water, and salt in a large pot. Submerge your copper piece in the solution. Bring the solution to a boil over high heat. Watch for the stains to fade from the copper. Turn off the heat so the copper piece can cool. Scrub the cooled copper piece with a dry cloth. Cut a lemon or lime in half. Dip 1 half of the lemon or lime in salt. Scrub the lemon or lime over the copper. Rinse off the copper piece with warm water. Wipe the copper piece with a dry cloth. Apply a dollop of ketchup to a clean rag. Sprinkle salt onto the ketchup for added effectiveness. Scrub the mixture into the copper, leaving a thin layer. Let the ketchup sit on the piece for 30 minutes for tough stains. Rinse off the ketchup-salt mixture with warm water. Dry the copper with a clean cloth. 