I am relatively new to bottle tumbling but slowly getting the hang of it. There is definity an "art" to it if your goal is to acheive excellent results. I am finding that whatever the black gunk is that forms when tumbling using a fine polish abrasive gets in small dings and is tough to remove from in hole chips or damage. I am guessing the black gunk is some compound formed by the abrasive or copper wire pellets and should be subject to dissolving with some sort of chemical. Scrubbing with soap and water works to some degree but not all that good. Does anyone have the secrete to easy removal of the black gunk from tiny picks in the glass?