"The glass cover during the plate scanning process is a possible source of contamination." "The best way to exclude the possibility of contamination causing th

"The glass cover during the plate scanning process is a possible source of contamination." "The best way to exclude the possibility of contamination causing the simultaneous transients is by examining the original photographic plates with a microscope11. Unfortunately, we have no access to the original POSS-I plates." Was a bit surprised that they have produced this detailed article describing all possible sources they could come up with, and got it published in Nature but didn't check the originals..