Both ketchup and hot sauce can be used to polish up your copper cents! These condiments do not necessarily need to be from McDonald's or Taco Bell, however. In fact, they don't even need to contain tomatoes or spices!
The secret to the cleansing power of these flavorings is actually far simpler than you'd think. All you need is some vinegar and common table salt! The combination of salt and vinegar allows the copper oxide on a penny to be broken down and converted into copper chloride, or in simpler terms, the penny gets cleaned.
Read more at http://pubs.acs.org/doi/abs/10.1021/ed078p513