That stuff is so thin that the vacuum frame or printing frame pretty much makes the any worries about lack of sharpness a moot point. BTW, I want to give credit to Kerik for alerting me to this phenomenom. He saw some of my prints I was getting ready for Fotofest that showed this faint black border, and it turns out he had had the same problem about five years earlier. As soon as I started putting the mask beneath the negative, the problem went away. Any sharpness loss is too small to even notice. And anyway, as Kerik also said shortly after pointing this out: "Print sniffers never buy prints anyway"