Ha, ha. I was one those watching that said OMG what in the heck are you doing. Never seen this exactly done before. Kind of reminds me of dark sludge washs done on aircraft after allowing the sludge wash to dry and settle into panel lines then wipe it off with a paper towel. But aircraft have a much smoother surface than a tank does. Anyway. I kind of like how it leaves dust deposits in all the nooks and cranies of the tank. So cool, I learned something new today. Thanks