I never knew such a thing even existed. Many times, I have had those stains on my boat after someone sanded their boat bottom and have had a lot of trouble getting it off. I've even tried acetone with no success. One year, I went home from the boatyard disgusted after I was finished waxing only to and find the "dust" all over the boat. Nothing seemed to get it off. A hard rain came after I left and to my surprise, the stains were gone the next day. Must be some terrible acid rain, but it got it all off. Go figure.