As bought the 900 means 90% silver, but I didn't like it. Instead of using acetone, I used isopropyl (rubbing) alcohol and then a hot water rinse... I then proceeded to "dip" the coin in eZest simply by holding it between thumb and forefinger and swishing and then holding another spot and swishing...followed by a thorough hot water rinse and blot dry. Picture on left before dip, right after. Since it is "junk" silver, I don't think I hurt it.