Folks at the ATM workshop had also alerted me to the advantages of “roughing up” the inside of the tube. I had created a great deal of sawdust at this point. So I spray painted the interior with a generous coat of flat black rustoleum and immediately threw handfuls of sawdust into the tube. I shook out what had not dried with the paint after a couple hours and repeated the process. Then I spayed in a generous coat of spar varnish, let that dry, and did another sawdust treatment for good measure. Weeks later I was noticing that blackened flecks of sawdust were still falling off the sides … not much, but enough to get me wondering what my mirror would look like after a couple weeks. I consulted and determined that a sprayed coat of paint was simply not enough. I ended up buying a can of flat black chalkboard paint and sponging it into the interior of the tube. That solved the flecking problem.