Quote Originally Posted by Kerik
In my experience, black spots are most often caused by impurities in the paper. And yeah, they suck... If you hold your paper up to a bright light before you coat it, sometimes you will see little bits embedded in the fibers. Unless they are on the very surface of the paper, you're not likely to see them just by examining the paper surface.
This is also my experience. 100% of the problems I have had with black spots have been caused by a paper problem. I have assumed that for some reasons the manufacturing process, for whatever reasons, leaves very small particles, that for one reason or anothe, react photochemically with the process.