C-41 processing: bubbles on negatives

[petr]

I am seeking advice on issues with my 4x5 negatives (Portra 160) coming from the lab with foam or bubble-like patterns, as well as negative density varying across the sheet in diagonal steps.

The lab uses a Jobo rotary processor and is a recent switch from a lab using a dip-and-dunk machine. The latter went bankrupt leaving no dip-and-dunk options for C-41 sheet film processing in the area.

The attached examples have digitally increased contrast, but the defects are discernible in normal contrast too.

The issue became more noticeable on winter shots with more information shifted towards highlights.

The lab technicians do not seem to have an idea about what might be the cause. Would anyone have suggestions or possible solutions?

Many thanks

Petr Antonov

[koraks]

Those are some severe pocessing errors indeed. The first places I'd look are:
Sufficient cleansing of the developing tanks after the stabilizer step of the previous run. This step involves a hardener and a surfactant that can cause bubbling in the developer and uneven hardening of the emulsion of the next film that is processed.
Correct loading of the drum, particularly if the sheets are stuck to the wall of the drum. Grossly uneven development will occur if the film is loaded with the emulsion side towards the wall of the drum. To a lesser extent this can also occur with the 25xx reels in which the sheets sit at some distance from the wall.
The rotation needs to be alternated in direction, so the direction of rotation must be switched after a bit more than one turn.
A final contributing cause may be the way the sheets are dried; you can check this by examining the sheets and look for drying marks.
Frankly, if you're running into these kind of issues and the people at the lab have no clue, that doesn't bode well for their proficiency in film development and it suggests they still have at lot to learn.

[petr]

Many thanks for going into detail with this!

I will try and go through all of your points with the lab technician.

The drying stage can probably be ruled out, as we re-washed one of the sheets (the yellow-greenish of the attached examples) with a different technician and the defects did not go. Again, with all sheets except one the surfaces appear clean, the former having but a tiny mark.

My first thought was of the developer being contaminated with surfactant from the final step (I had had similar bubbles on my home developed B&W negatives), but the technician is of the opinion that constant rotation (unlike with home B&W) would prevent developer from leaving such marks even if its foamy. Again, the bubbles are mostly along the longer side of the sheet and the flow streaks are across (examples 3 and 4), as if they were forming while the drum was standing in an upright position, as with home B&W development.

I do not know what type of drum / reel they are using, but I will check. Do you think that the sheets may have been facing the walls of the tank in this case? I would not probably call it grossly uneven development as most defects are barely visible in the highlights with normal contrast. However once you start looking for them you can easily find them, and I can see them even on small size preview prints. I am attaching here three crops from 5000 px scans with normal contrast.

I will too find out if they alter the direction of the rotation during the development. How many times would you recommend for the standard cycle?

There seem to be just two labs left in the area to process C-41 sheet film. I had initially tried the other one but the negatives came out with a rather compressed range, bluish cast, generally insufficient colour information, and more grain that you would expect from Portra 160. In short, the scans appeared underexposed and overexposed at the same time, and took a good deal of colour correction to be salvaged. They say they were using the same chemistry as with the machine-developed MF films, which came out just fine. The cycle is 3:15 minutes, starting the timer after pouring in the chemicals and stopping after pouring out. The temperature was 37.8 celcius (100.04 fahrenheit). Can it be that the temperature gauge is off, or can they have contaminated the good developer in progress, or can the rotation speed affect it in such a way?

I am currently trying to figure out which of the two labs would have an easier fix for their processing errors. So far I hope I will not have to decide upon which defect is easier to correct in post-production.