Foamy Bathroom Cleaner
Lay the pennies flat on an old towel. Spray the surface of the pennies with the foamy bathroom cleaner. Allow the cleaner to sit on the pennies for about one to five minutes per side. Scrub the pennies gently with an old toothbrush to remove stuck-on dirt. Flip the pennies over and repeat the process. You can do this several times to reveal a high-gloss shine on the pennies.
Vinegar and Salt
Dissolve about 1/2 cup of salt into a quart of white vinegar. Drop the pennies into the liquid and stir them around for about a minute. Allow the pennies to soak in the liquid for 10 minutes or so, until you start to see the pennies shine again. Remove them from the liquid and scrub them with a paste made from baking soda and water using a toothbrush. This will make the pennies shine almost like new again. Rinse the pennies with water and dry thoroughly before storing.
Epsom Salts
Mix about 1 cup of Epsom salts in 1 quart of warm water. Mix until the salt is dissolved. Place the pennies inside the warm water and allow to soak. Stir the pennies for about a minute, then allow them to sit for 10 minutes. Remove the pennies from the water and wipe with a towel to reveal the shiny finish. If the pennies are still dirty, repeat the process one more time to clean the pennies further.
Cola
Pour some fresh cola into a large bowl or container. Drop the pennies inside the cola. Stir the mixture for about 30 seconds. Allow the pennies to sit in the liquid for about 5 to 10 minutes. Remove the pennies after this time and inspect the surface. The pennies should be clean and shiny. If not, allow them to soak for 10 more minutes. Use an old toothbrush to scrape off any remaining residue after cleaning. Make sure to wash the pennies with soap and water to eliminate any sticky residue.