heres what i found out so i dont think i will be able to tone the way i want, read this.The real secret is to buy a diffusion furnace, or maybe two, both a Chemical Vapor Deposition and an Atmospheric. On the CVD furnace one can add a nice uniform layer of polysilicon or nitride to beautifully tone your silver coins. and since you can control, temp, time and pressure you can control your deposition rate and get any spectrum of coloring that is completely natural and undetectable... For those stubborn coppers, we turn to the atmospheric furnace, and grow a slight layer of a high quality oxide at a slow rate, cause one has to remember that a grown oxide consumers its underlying surface as well as growing upwards... Ok, enough of the revealing the biggest trade secrets,