Boiling them in a mixture of baking soda and water could do the trick. However it is debatable as the second link below as to whether it is the baking soda or just the different rates of expansion between baking soda and paint that does the trick. If you do end up boiling quarters to remove paint make sure you dont do it in a pot that you will eat out of. Paint can be toxic!
You might also be interested in "soda-blasting". Its a way of removing paint by blasting it way when highly compressed air containing baking soda is shot at the metal. It works in a similar way as sandblasting and is environmentally friendly. This was how the statue of liberty was cleaned!