This fogged film problem has me baffled as to the origin of the fogging source. Notice the V-shaped diagonal lines where the frames were not fogged as heavily. Also, I don't see any pattern of film perforations cross-cutting the fogged areas as would be the case when film gets fogged outside of the cartridge when loading the tank in a loading room. In-camera fogging also does not seem to be the culprit because there is no evidence of fogging paralleling and immediately adjacent to the perforations.

A student had this happen to one of the rolls she developed in our community college darkroom yesterday. She developed two rolls in a double-reel Paterson System-4 tank and she swears she used the proper tube in the tank. The film looks something like an improper tube had been used because the top is more fogged than the bottom of the frames (and the lower roll had very, very slight fog along the perforations on one edge but the fog on that roll did not extend into any part of the images). Typically, when a tank/tube mismatch is the problem, the film in the centermost spiral is more fogged than the film in the outer spirals. That doesn't seem to be the case here as the worst areas appear in a periodic fashion rather than increasing steadily from the top and center outward.

I've checked the tank, lids, tubes, darkroom, and interrogated the student as to whether the film might have gone through an X-ray machine at an airport, if anyone could have opened the camera back while it was loaded, (or opened the darkroom door), or if a cell phone or watch lit up in the loading room when she was handling the film, etc. Nothing seems to have been out of the ordinary and I've never seen a pattern of fogging like this particular film exhibits.

Any ideas on what caused this fogging or what the "V" shape is?