[cracker_jack]

I have several prints that have been framed in my finished basement and I'm getting some sort of soiling on them. It almost looks like a buildup of dust and when you brush it off, it leaves a small soil stain. It's only happening to these prints and nothing else. It's not a damp basement and stays anywhere from 62 degrees in the winter to about 67 degrees in the summer. I have a lot of other framed photos and whatnot but they're all fine. Not sure if it's just the paper type on these prints or what. Does anyone have any thoughts?

Thanks