When you get your coins, although you can't see it they will have a thin layer of oil on them which has come from peoples' fingers. Before you paint or put round stickers on them clean them thoroughly.

First of all wash them in detergent to get rid of the oil, dirt and grease. Afterwards, rinse them in clean water.

Then let them soak for ten minutes in vinegar. The acid will eat away the surface layer of metal and leave the coins looking brand new. Heavily tarnished coins may need to be left for a longer time.

Rinse again. And there you go. Beautifully clean coins ready for stickers or paint.

Coca Cola and other acidic drinks do the same job as vinegar, though more slowly. They also strip the enamel off your teeth.