Colloidal silver gone wrong?

Made my own 12vdc colloidal silver generator. Hooked up alligator clips to two 10 guage silver wire, small jar with distilled water, with 12v power supply, a few hours later the jar seemed to have a burn mark on the bottom, looked black, and the silver wire seemed to have changed colors slighlty, so of course I just emptied ou the jar, and wiped some black stuff off the bottom inside jar, did I do something wrong, any advice greatly appreciated. Maybe I didnt use enough power?