Mix dish soap into warm water and agitate it to create suds. Add 2 tbsp. of baking soda to the water to remove any grease from the copper item. Place it into the water, making sure that the burnt portion is completely submerged. Allow the item to soak overnight, or up to 24 hours.
Clean the burnt areas of the item with a plastic dish scrubber to remove residue softened due to the overnight soaking. Use additional dish soap and warm water; rinse several times until the water is running clear.
Mix 1 tbsp. of salt with 1 cup of white vinegar in the bowl with the spoon. Stir until the salt dissolves. Add flour until the mixture resembles a thick paste.
Apply the paste to the burnt area with the soft toothbrush, moving it in a circular scrubbing motion. Leave the mixture on the copper up to an hour to work on stubborn stains and residue.
Rinse the copper item in warm water to remove all of the paste; gently lather with soap, if necessary, and rinse again. Repeat the use of the paste again if staining or discoloration (tarnishing) continues to color the copper. Dry with a soft towel when the burnt portion is clean.