Tweaking C-41 on a Jobo CPE-2 (streaks)

[mnemosyne]

I have started developing CN on my Jobo CPE-2

After establishing a method for temperature control (discusses in a different thread), I did my first test rolls over the last days. The color, contrast and general density appears to be very good (actually better than expected), but I have encountered some irregularities in the form isolated blotches of irregular density (see pic attached, in the area above the dog's head) or faint streaking on some frames.

To summarize my routine so far:

• 2500 series two reel tank on CPE-2, fast rotation, no lift (tank is taken off for pouring and draining with two quick hand inversions of tank immediately after filling developer)
• Fuji Hunt X-Press C-41 5 liter kit
• developing for 3'15" at 37.8° C
• 5 min of prewet
• no stop bath, rinse between between bleach and fix
• one-shot use of chemistry (270 ml each)

I have to add that in one of the three runs I was using a tank (I have several) that was wobbling a bit because the magnet started to come loose during rotation which might have contributed to the streaking problem, but also (less pronounced) in a second run where the tank was rotating smoothly.

Most likely cause of the problems I encountered is the less than ideal situation when pouring the developer with the tank in upright position and not moving. The pouring itself is done from a small brown glass bottle, which holds exactly the prescribed volume (270ml) and drains very quickly into the tank (about 3 seconds at most).

Now, I did some research on this streaking problem and have collected some suggestions what to do to correct it. Some things I could try to solve the problem:

• make sure the tank (rather than the processor) is level
• skip the initial two inversions of the tank before attaching it to the Jobo
• or the opposite, additional initial inversions
• two prewets instead of one
• prewarm instead of prewet as
• use demin water for the prewet
• add a tiny amount of photoflo to the prewet water (the idea is that instead of isolated droplets this should leave a more even residual film of water on the film after draining, but I am afraid this might interfere with developer action)
• use stop bath
• find a way to fill the tank while it is rotating
• buy a lift

 

[sfaber17]

I would try (most likely fix first):
Use stop bath
more initial agitation or fill while rotating
maybe use distilled water for prewet

I dont' think 1 vs 2 pre-wets will affect this.

 

[Sirius Glass]

Stop bath
One prewet
Level the machine and tank

 

[Rudeofus]

To me this looks like two streaks of color developer ran towards the top of your image frame when you poured it in. At the end of these two streaks you even see very distinct halos, where this initial splash of developer created a surplus of halide which then locally retrained development just beyond these initial streaks.

I would therefore address the way you initially pour in the developer. Whatever you do, you need to make sure that developer comes in contact with your film uniformly and at the same time. C-41 development is very unforgiving in this way, as an extra dev time of just 15 seconds equates to an one stop push.

 

[mnemosyne]

Thanks everyone for your input. First change I will try is use of a stop bath. I read a 2% acetic acid solution is in order, but do I also need a wash after stop or can I go directly from stop to bleach?

 

[Rudeofus]

Since bleach is acidic, stop bath carry over won't hurt it. AMAOF, with such an acidic bleach you might as well leave out the stop bath. Stop bath is strongly recommended only if you process C-41 with typical BLIX kits.

 

[mnemosyne]

Since bleach is acidic, stop bath carry over won't hurt it. AMAOF, with such an acidic bleach you might as well leave out the stop bath. Stop bath is strongly recommended only if you process C-41 with typical BLIX kits.

The sweet thing about the use of a stop bath is that I can use a much larger amount (> 600 ml) and instantly fill the whole tank. When going directly to bleach I use a much smaller amount of solution (270ml) which makes it more difficult to stop development uniformly. Of course I could simply use more bleach, but to keep it economical I would then have to re-use the bleach, which would introduce a new set of variables. I was just worried that without a rinse between stop and bleach, things might get too acidic for the bleach.

 

[Rudeofus]

Bleach is fairly well buffered, so some carryover acidity from stop bath won't hurt it. I don't understand why one would use bleach single shot, this sounds quite wasteful to me. Bleaching and fixation are process steps which simply run to completion and only remove stuff that shouldn't be there in the final image. These two process steps can also be redone if you have doubts that they did their job.