Meta Cafe offers fast and easy tips on how to clean filthy and old coins. All you need is: baking powder, a small, empty bowl, and a glass of water. Start by putting some baking powder into the small bowl. Next put some of your filthy, old coins into the small bowl, laying them on top of the baking powder. Then layer the remaining baking powder over the coins in the small bowl. Finally, pour the water into the bowl and let it sit for 10-15 minutes. Remove the coins and dry them using a paper towel. Your old, filthy coins will now look shiny and new!