Is the emulsion perfectly smooth in those areas? I wonder whether this is some weird form of reticulation or the emulsion sloughing either during manufacture or processing. Just a guess.
If it is some sort of a light leak, it had to occur while the film was moving.
I know you said this problem occurred independent of the camera but let's just make an assumption in order to come up with a hypothesis then work from there: Suppose that you were winding or rewinding the film (in the camera) and the back or body of the camera vibrated open, slightly. A very thin sliver of light would penetrate and make a line across the film. If the film was moving and this hypothetical gap in the camera body was vibrating open and shut, it would cause a "strobe" effect which would imprint a series of roughly parallel lines on the film.
Now, extend this metaphor. It doesn't necessarily have to happen inside a camera. It could occur during manufacture, somehow. It could occur as you are bulk loading film from spool to cartridge if the cover of the loader vibrates open. It could occur if there is a gap in the lips of the film cartridge, either in storage or handling, before or after being shot. It could also occur while processing. Let's say the developing canister has a small crack in it.
What is the distance between these sets of marks? If you coil the film up so that the marks line up, does the diameter of the coil match the diameter of your developing reels, the film cartridge or the bulk spool? Determining this could help you narrow down the location where the problem occurred.
If the film came out of the fridge too quick and adhered to the pressure plate this would be a possible are to look, it does look like something is stuck to the film or making a direct impression
I have never seen any thing like this and would be interested how this plays out.
Originally Posted by Thomas Bertilsson
That does make the sticky-tape hypothesis a bit shaky (er, demolishes it entirely). It also makes it highly unlikely that the same problem would happen on two different production runs.
Originally Posted by craygc
If it were any sort of light fogging then the pattern wouldn't 'go around' the sprocket holes - it would be even it that area and the sprocket holes would be just holes.
I still think it looks like something was sticking. Possibly Ilford film doesn't like freeze/thaw cycles - but if one 'wrap' of film stuck to the one below it then there should be artifacts from two sets of sprocket holes.
What were the common factors between the HP5 and FP4? You mentioned freeze/thaw cycles. I have done that countless times and never seen anything like it. I have a personal crusade to get the famed 'condensation' and all the sorts of other postulated evil doings due to not thawing film in the politically correct manner: I make it a point of honor to take film straight from the freezer to the camera to taking pictures whenever I can. I have never had any sort of problem with this practice. Thermodynamics says it is nigh impossible to get condensation on the film (engineering degree - EE, but one year of thermo). But then, I shoot Kodak film exclusively.
Was the pattern exactly the same on the two instances? It would be a rare thing to happen to one coating line, that it would happen to two - a case of Douglas Adams' "Infinite Improbability Principle"?
I love a good mystery...
Just for some better images I've shot everything again and larger. [This link] represents all the frames from one roll. [This link] represents all the frames from a second roll. BTW, I have no way of knowing if these two rolls were in the same tank for development. I also tried to magnify this even more [link here]. The pattern seems very uniform parallel to the length of the film but wavy running across the frame. I think this probably rules out the imprint of a material pattern - one direction of the weave would not be so uniform while the other was not.
Today I have also locked myself in a darkroom and thoroughly checked the pup tent with a bright torch - no holes found - didn't really expect any as its a new tent and there were at least 4 rolls in there at any one time and the damage on the HP5 is only reflected on a couple of rolls.
Again as a note to address some oversights above: this is NOT bulk loaded film. Just normal canisters
If you look at the edges of frame 13A, you can see that the exposure patterns curve into the centres of the sprocket holes and that there is no pattern to the right of each sprocket hole.
That makes me believe that it is either stress-exposure or triboluminescence (tape-ripping glow) caused by the film sticking together and then being pulled apart as it comes out of the cassette. Note how the no-pattern part is upstream of the sprockets (comes off first); this is consistent with the way the film comes off the cassette; once the trailing edge of film in a hole (unexposed) is lifted, the leading edge catches. It pulls away along the edges first, then the corners, working its way towards the centre of the sprocket hole. You can see each curved line is a "click" where a mm of film pulled away across the width of the roll.
The sticking could by caused by moisture getting in on a refreeze cycle. The pitch of the exposure pattern also makes it look like the sticking was mostly on one side of the spool and running freely on the other side.
Further evidence of sticking is in comparing 13A with 14. 13A has clearly stuck to 14 at the sprocket holes, which stressed 13A and exposed it. However, you can see that the tension of 13A pulling away has loosened the sprockets of 14 so that when it was then pulled from 15, the ripping happened in the middle with no exposure around the sprockets because they'd already been loosened.
Edit: looking at the high-res scans, the lateral lines really do look like stress marks from sticking - you can see a dense bit where it catches, then it fades away to the next click. I don't know what would cause the longitudinal lines, unless it's some regular pattern in the stickiness of the film (but why!?).
I'd expect they will want to see the film physically rather than look at scans.
Originally Posted by craygc
Send a strip to Mobberley with a covering letter asking for their comments.
I think polyglot wins the prize... I think you have somehow had water / moisture / condensation within the cassette body.
Firstly, you are very welcome to return the film to us in the UK, when you buy any ILFORD product thats your absolute right and we will tell you what it is, as always its incredibly difficult to tell whats going on without seeing the actual negs, I cannot see any manufacturing defect that would cause any effect similar to this. As an FYI we never use tape in 35mm cassetted production, even on the master cut spools the tag that holds it in place is lost with the first 2m as that goes for QC processing tests before that individual master spool is cassetted.
Simon ILFORD Photo / HARMAN technology Limited :
Or the camera body...but much less likely.
Very much appreciate everyone's efforts in trying to solve this mystery. To finally achieve closure on this I will send the negs to Ilford so the problem can be confirmed. "triboluminescence" at least something new I've learnt from this thread :)
So who's willing to sacrifice a roll in the quest for knowledge ;) If I have an expired roll laying around, it would be interesting to see if this can be replicated.