I may start a new thread in the Darkroom forum: B&W: Film Paper, Chemistry... As I don't think people will think to look at this thread as much as the Darkroom forum. (I found this thread through a google search, oddly enough). This is for 120 format film only.
I have talked to a couple photo store reps, though they are not Ilford reps. They all thought this and that and the other, (as eluded to by other posters here) but after some discussion, it seems that they saw it from my point of view: manufacturing defiects. SFX 200, Delta 400 and PanF 50. Surely there are others as well.
I develop two rolls at a time, in stainless steel tanks, and use fresh diluted photo flow every 10 rolls. The "mottled" parts are not dirt, debris, etc., and they are there on the film before it goes into the photo flow. The mottled bits are in the film, the emultion.
I will try to upload some of my photos scanned from RC workprints. The prints are not necessarily excellent prints, but they do show the flaws in the film and the horror of the retouching job necessary in order to have the prints made in the traditional sense. I am thinking somewhere from 30-40 hours of retouching per print.
I have been using Ilford Delta 400 for about 28 years exclusively in Pyro PMK, and just began using Ilford PanF after my stock of Agfa 25 ran out (need a slow speed film of course). This is 120 format film film. When a photographer tests out a film, for exposure index, development time, latitude and grain structure, once they come up with something good, they tend to stick with it. It becomes predictable, reliable, especially in the long exposures where reciprocity comes into effect and when using the Zone System or Tone System (as I use).
Photo 1 and 2 is Ilford Delta 400, same roll of film. The other roll developed at the same time was not affected.
Photo 3 is a close up of the clouds in photo 2.
Photo 4 is Ilford Pan F, printed a bit too contrasty, (awful print really) but shows the damage. the other roll I develop at the same time was not effected.
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