From Spanish doubloons and pieces-of-eight out of Davy Jones's locker to blackened pennies from a piggy bank, we want old and dirty coins to be bright and shiny again. Too Cleaning some old coins can diminish or destroy their value, however. If the coins are worth no more than their face value and are truly yucky, vinegar is one of the fastest ways to bring back the shine.
Distilled white vinegar, that housecleaning standard, will strip away the tarnish or patina that copper coins acquire with time and use. Mix half a cup of vinegar with a teaspoon of salt and drop in the pennies. They will lose their dullness and brown colour and look newly minted very quickly.
Silver coins tarnished to black can also be cleaned with vinegar or any other mild acid, including lemon juice, Coca-Cola, hot sauce and ketchup -- even sour milk. Ammonia and acetone will also clean silver coins.
Gold does not oxidise so there will be no oxide or tarnish on gold coins. They may get rust stains on them from being in contact with iron, and vinegar will help remove these. Gold coins, like silver and copper, should then be washed in a mild detergent, rinsed thoroughly and patted (not rubbed) dry. Even the softest cloth can leave microscopic scratches on collectable coins with friction.
Vinegar contains acetic acid, which dissolves the oxide or tarnish on the surface of metal to reveal bright metal underneath. Metal oxide is chemically a base, and when it meets the acid in the vinegar, they neutralise each other. Acid will not clean away dirt, however soaking in a mild solution of detergent will.