1LE

iTrader: (2)

Without looking at it, it would be hard to guess what it is. If it is gummy black stuff, you may have overloaded the wheel with Tripoli, try cleaning the wheel, reloading the wheel, let it sit for about 5 minutes before buffing, should help this from happening.
It could be that the surface isn't clean, or there are debris left on the surface from the past sandings.....I always clean the part with brake parts cleaner between every sanding and buffing, because it doesn't leave any kind of film.
Hopefully one of those two will work. If not, I'm not sure what it would be?

qwik3r

For some reason my calipers and the buffing wheel attachment for my drill are turning black when using the tripoli compound. Now i used heavy sand paper, than lighter and lighter than a wire wheel until they were very matte and very very smooth. I started to apply the tripoli and it made them sorta shiney but mostly black, the black was on the buffing wheel aswell, wtf? Why is this? How do i fix it? Despite my efforts of trying to buff the black out, the only way to remove it again is with the wire brush, what am i doing wrong? The buy at homedepot said they would buff out and i am getting black staining because of imperfections in the metal, please someone assist, thanks.