Yes Colin is correct, you spit on the coin then hold it tight in tin foil, the coin will get very hot and smell of rotten eggs. I believe its the sulphur reacting, this brings out the detail on coins that otherwise look completely defaced and worn..but evn so as you guys have said you dont want to over do it. Pity i dont have the coin anymore Tomgoodheart but i had a very very nice Newark Besiged Ninepence, no idea how it ended up where i live but it was a cracking coin. I have a small coin of Charles I i found this week, very worn but i will put a picture up for you.