Toning coins

[probono]

After hearing all these methods I think bleach is far the simplest and on the whole the safest too but make sure you degrease the coin first, nail varnish remover will do the trick, or you can end up with a perfect black and silver fingerprint to bring out the high points either aluminium foil or I use Duraglit silver wadding as it's far more controllable

I've had a few coins with fingerprints on them - even had a Samian-ware pot with fingerprints on it too!

Nail varnish remover often contains Acetone - it is a very good solvent - isopropyl alcohol is good too (known as IPA)