Bronze coins can be conveniently divided into two categories for conservation purposes, those with only a thin film of tarnish and those that have heavy disfiguring encrustations, usually the result of being buried in the ground. If a coin is in good condition great care must be taken in cleaning not to damage or mark the surface when removing the film of tarnish. If bronze disease occurs, the coin can only be stabilized by one of the following procedures: 1) Remove all the corrosion products; 2) Treat the coin with sodium sesquicarbonate solution, or silver oxide, or benzotriazole solution; 3) Store the coin at a relative humidity below 40%.