Technology1 min ago
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For more on marking an answer as the "Best Answer", please visit our FAQ.Firstly make sure they are worth next to nothing! Cleaning up a valuable coin (eg a 1933 penny) will seriously reduce its value. Very dilute hydrochloric acid is excellent at cleaning up copper coins. For silver or cupro-nickel coins use dilute nitric acid. Rinse them thoroughly in water afterwards or else they will quickly tarnish.