I've been trying to turn 8 plywood platforms black. I stained them with Minwax but I didn't realize stain doesn't behave like paint and I made a mess. I removed the stain with mineral spirits, sanded the plywood, removed the sanding sawdust with wet rags, and let the plywood dry for a day or so before I spraypainted them with about 4 coats of flat black Krylon Fusion. After about 20 hours I can still run my finger along the plywood and pick up quite a bit of black dust. I had the exact same problem with a small MDF bookshelf I built a few years ago. It produced that same black dust for many months until I finally gave it away. Should I spray it again with Krylon Crystal Clear to seal it?