With the resin applied, the paper is ready for the grit to be applied. This is probably the most interesting and critical step of how sandpaper is made. One might expect that the grit is simply sprinkled evenly onto the paper, but in actuality, it is a bit more high tech.
The grit is sprinkled onto a conveyor belt that is electrostatically-charged, which in turn gives the grit a static charge. As the conveyor moves along, the resin-coated paper is brought down across a roller about two inches above the conveyor. Because of the difference in the static charges, the grit literally leaps upward onto the resin-coated paper. More impressively, because the heaviest part of each uniquely-shaped grain carries a stronger charge, the thickest part of each grain is embedded into the resin, leaving the sharpest edge of each grain exposed.