I have a bunch of change that I would like to take to the bank, but the bank teller told me to clean the oxidized and dirty pennies first. What is a good way to do so? My boyfriend and I tried washing them in white vinegar and salt in an ultrasonic jewelry cleaner, which turned the small bunch we experimented with black. Was the jewelry cleaner the bad idea? Also, how long should I soak them for? Overnight? A week?