The strange purple color cast on the edge of the C41 film.

I just developed a PORTRA 160. The developer was freshly mixed, with a development time of 3:15. The stop bath used dilute sulfuric acid—500ml that had already been used 8 times—but based on pH test strip results, its pH should be within the working range. The bleach was potassium ferricyanide bleach, used for 5 minutes, with 1L that had been used 14 times. Fixing took 5 minutes, using 500mL that had been used 4 times.
The result shows a green/purple color cast on one side of the film. I used rotary processing with a Jobo 1520 tank, and the color cast appears to be on the side closer to the bottom of the tank. There is no visible color cast on the unexposed areas of the film. Does anyone know what might be causing this issue?

Guessing, some sort of chemistry contamination? Very odd pattern. You might try skipping the sulfuric and just use a vigorous water rinse.

Light leak in the camera?

Assuming a roll of film, was it all frames or just the one frame?

If one frame I'd think a film handling or camera problem.

gbroadbridge said:

Assuming a roll of film, was it all frames or just the one frame?

Click to expand...

All frames have problems. I only developed one roll of film this time.Could it be because I used too little developer? I only used 170ml of developer for this roll.

FWIW, that colour in the inverted positive image is as much blue as magenta.
Which makes me suspect fogging by light that tends toward yellow.
May we see a digital backlit photo of the negatives themselves, with the edges of the film, frame numbers, and the space between the frames showing?

blee1996 said:

Light leak in the camera?

Click to expand...

That probably isn't the reason. The cast issue varies from frame to frame.

Welcome to Photrio @Ppppuff Pastry !

It's an interesting pattern, especially if this was rotary developed.

mshchem said:

You might try skipping the sulfuric and just use a vigorous water rinse.

Click to expand...

I do not recommend this.
The sulfuric acid is in principle OK, although unnecessarily aggressive for C41 film; I would just use acetic acid instead. What might be a problem is the ferricyanide bleach and the lack of a sulfite clearing bath between the stop bath and the bleach. This can result in excess dye formation and this can also be uneven across the film surface. I would start by adding that step, or alternatively exchange the ferricyanide bleach for a proper C41 bleach based on PDTA.

Do not reuse the stop bath; it's false economy. Just use dilute acetic acid (ca. 1% is OK) and use once, then discard. I'd also be hesitant to reuse the sulfite clearing bath; it's better to use this once.

It can sometimes help to introduce a pre-wash step with plain water if there are problems with unevenness.

So I would propose the following process:
1: (Optional) pre-wash with water at process temperature
2: Develop
3: Stop; acetic acid ca. 1% used once and then discard
4: Sulfite clearing bath, used once then discard
5: Ferricyanide bleach
6: Rinse
7: Fix
8: Archival wash
9: Optional stabilizer, wetting agent etc.

Note that ferricyanide bleaches are not recommended for C41 to begin with in connection with archival concerns. Basically, the ferricyanide can destroy compounds in the film that are supposed to survive processing and that will help guard the color dyes against oxidation as a result of pollutants in the environment.

MattKing said:

May we see a digital backlit photo of the negatives themselves, with the edges of the film, frame numbers, and the space between the frames showing?
我们可以看到负片本身的数字背光照片吗，包括胶片的边缘、帧号以及帧与帧之间的空间？

Click to expand...

Of course! Here are the photos you requested.
当然！这是您要求的照片。

Seem like The color cast between frames transitions smoothly.

koraks said:

Welcome to Photrio @Ppppuff Pastry !

Click to expand...

Thanks you @koraks ！

I never expected the moderator to personally answer my questions! Actually, even before I registered my account, I had already learned a lot from your posts. But reality proves that knowledge has no boundaries. Next time, I will try sodium sulfite cleaning and PDTA bleach, though I still have a few more questions:
What is the optimal concentration of sodium sulfite in a sodium sulfite cleaning solution? Is a concentration of 20g/L sufficient?
After the C41 stop bath step, can I open the tank to check? I'm used to doing this when processing B&W film.

Thanks for your kind words! As moderators, we are really no different from other participants in discussions on this forum. We just have some administrative duties we sometimes perform in the background. And as you may have gathered from my post, I happen to be interested in color photography and I've posted a bit about it here and there.

Ppppuff Pastry said:

But reality proves that knowledge has no boundaries.

Click to expand...

Well, it really does! For example:

Ppppuff Pastry said:

What is the optimal concentration of sodium sulfite in a sodium sulfite cleaning solution? Is a concentration of 20g/L sufficient?

Click to expand...

I don't know for sure. I *think* this would be a good starting point, though.

Ppppuff Pastry said:

After the C41 stop bath step, can I open the tank to check?

Click to expand...

After a few seconds, this should not hurt.

Interesting indeed. Judging by the color and the even coloring, the problem must be somewhere else, not in the bleach.
Maybe it's just me, but there seems to be a pattern of the coloring in each frame, which suggests a problem with the camera...

FWIW, the pattern to me looks like the kind of artifact you get when there are fill/drain steps with the tank in vertical position that do not complete rapidly enough to ensure even exposure of the entire film surface to the chemistry. The reason why I think that the bleach has something to do with this is because of the fairly abrupt edge, whatever chemical that was introduced must have had a fairly instantaneous effect on the film. Fogging as a result of a bleach reaction with the carried-over developer seems to be a plausible cause.