Change of density at film hanging clips on dip-dunk processing

[schafphoto]

There are a few articles in the X-ray film literature on exhaustion causing un-even development. The thought being it is not the extra activity near the clips causing the issue, but lack of development on the rest of the image.

I guess if you can't solve it, use a wider lens and crop. Too bad those are beautiful images.

Thank you for the compliment. I'll add that the nitrogen-burst agitation in these 40-inch deep tanks is pretty aggressive at 8 second burst then 8 seconds pause. I did a lot of tests after having mottling in sky zones 7-8 that settled on those agitation numbers with HP-5. Except for this seemingly random intermittent flaw on thousands of sheets of film, the development seems perfect for my purposes in density and contrast and the rebate is clear so I'd rather chase a hardware flaw first before I tinker with development/agitation times.

And I have chosen samples that show the most extreme density change and not the ones where there is no density change.

[schafphoto]

Hangars contaminated is my guess as well. No one has asked if these are plastic or stainless hangars, plastic might be worst!

36-40" tall stainless hangars.

[Tin Can]

First actual data on burst I have seen here in 12 years

I will try longer bubble time

[schafphoto]

To be clear, these clip marks are more typical of most of my film...

[schafphoto]

Just got a photo of the racks from the lab. They hold 10 sheets.

[Michael R]

That's the thing about gas burst. Assuming the right plenum/sparger design, bubble size, power etc. it can take experimentation to find the right burst duration and intervals, and it can vary with tank volume, film size, film type, type of hangers, how much space between hangers etc. Actually just recently I came across another paper/study published back when this was still a common process used in-house by a lot of organizations from military to scientific for developing films, plates etc. Very interesting stuff.

Unfortunately I'm not in a position to have such a system. Too complicated/inconvenient. On the other hand PE once commented gas burst should be down-scalable to any size as long as you test tune test tune test tune. He recalled even having seen tiny 35mm two-reel Kindermann tank-sized nitrogen burst someone had FABd up at Kodak.

First actual data on burst I have seen here in 12 years

I will try longer bubble time

[AnalogAngler]

Couple thoughts regarding chemical contamination:

1) As I recall (and pretty sure I found it on this forum - thanks go probably to Jim Noel and others) - the issue with the Photo-flo is that it is doing exactly what is is supposed to as a surfactant - helping to wet the film and specifically the emulsion - so that chemicals move on or off them smoothly. As a result, the areas that recieve even just a little bit of surfactant (and it generally takes very little surfactant to do anything - it naturally spreads out to be a molecularly-thin layer) are subsequently exposed to developer a little faster/longer than the rest of the film resulting in increased activity and density. There are probably more elegant explainations - I would seek them out by searching the forum if you think you need more detail.

2) Two thoughts on the clips and occasional nature of the problem:
a) The design of the clip (with a hinge and a spring) includ additional surface area and may even allow a droplet to be captured inside the clip only to dry up later (or even stay wet) - but might not happen or to the same degree all the time.
b) The lowest clips on the rack might have more residual chemical at the end than the upper clips as everything is draining down the long rack as it is pulled out of the bath and dried (believe they are displayed sideways in the photos - with the longer pin end at the top in normal use) So film installed in the lower positions may be more prone to this effect.

In either case - if they are not washed between runs, this may give the Photo-flo or similar agents a chance to dry and concentrate in these locations, only to be re-animated when re-wetted at the start of the next run - with the film already in them. Based on my experience with the 120 reels - it doesn't necesarily even have to be trapped, just the amount left coating the surface of the metal was enough to influence density, and there is more surface area inside those clips than anywhere else in the set up they are using.

Since your lab provided photos, it sounds like you have a good relationship with them - did you send them photos of the issues/your concerns and if so did they respond?

I can see that they would be hesitant to add an additional cleaning step as the machine puts out a dry rack on the end, and solving this may mean having to wash down and dry the rack outside of the machine between each run. It could also be that the machine was designed this way and functioning normally, and normally this is not an issue, but maybe someone was a little heavy-handed with the Photo-flo or something else on a given day and the problem doesn't show up until later. Batch numbers could be important here. At any rate, I would trust the lab to know more about what is going on with the chemistry than I do...and also hope they provide some constructive feedback.

Best wishes & regards,

-AnalogAngler

[ASA1000]

I commented on this the other day and just came across this today in a 1973 Kodak technical publication
The images are upright on my computer!

[Bernard_L]

Several comments suggest a process having to do with "film & developer & process combinations".
What I did observe on a couple of occasions with 35mm/MF film is that mechanical stressing or creasing (problematic loading in spiral) produces local excess density in the developed film. So nothing related with development.

[koraks]

Several comments suggest a process having to do with "film & developer & process combinations".
What I did observe on a couple of occasions with 35mm/MF film is that mechanical stressing or creasing (problematic loading in spiral) produces local excess density in the developed film. So nothing related with development.

I think many of us have seen that, I certainly have. And it's always clearly recognizable from the geometry of such density anomalies - i.e. the typical crescents and kinks that result from the physical cause of the problem. Unlike in this case, where such a physical/geometrical pattern is not present.