My year-long experiment with C-41 chemistry

A little over a year ago, I bought a Fuji Hunt X-Press C-41 5L kit to finally get into doing my own color processing. The big unanswered question I had, was how long this stuff would actually last. I've never been a "high volume" shooter, so I constantly find myself worried about pushing expiration dates. I really don't like dumping usable chemistry, nor do I like risking rolls of film (with pictures I might care about). As such, I bought myself a box of C-41 Process Control strips, and started to actually do periodic testing. This video captures my process and the results:


I actually did end up using a densitometer (X-Rite 810) and a spreadsheet, and building many of the charts/graphs that Kodak Publication Z-131 recommends. So yeah, probably did go a little overboard.

Here's my data if you're curious to see it for yourself:
https://docs.google.com/spreadsheets/d/1ldDaVR9u6PMzWi4i_NxVXaTkpwugg_qc0bF-Md_6XQM/

In short, I mixed my developer into a series of completely-full 1L bottles up front (bleach/fix/stab were mixed more on-demand) and was able to get a full year of use out of the kit. There's a good chance I'd be able to push it even longer, if I tried. I also found that one-shot processing on a Jobo produced better results than any processing (fresh or reused) in an inversion tank.


(The first datapoint was inversion /w reused developer. The second datapoint was inversion with unused developer. All the rest were done on my Jobo with unused developer.)

I'll admit that my numbers might not all look perfect, versus a continuous professional operation that does replenishment and runs tests frequently, but at least I have numbers. They're also better than I would have expected. I really like being able to judge my supplies based on numbers, rather than just winging it, when I have the ability to do so.

Hi, that was a lot of work
what's your opinion of the the "real" photos processed with that developer over time? did you see color shifts, or increase/decrease constrast? Do you print on RA-4 or scan ?
Why to you think the jobo gives you better results? It has temp control?

Bravo on jumping through the hoops to do the work!

I take it that you're not asking for advice? But since you're putting the data out there, I notice that the "activity levels," really just the LD and "HD-LD" (contrast), are almost all below the "aim value." I'm curious as to whether you tried any corrective action.

Rafael Saffirio said:

Hi, that was a lot of work
what's your opinion of the the "real" photos processed with that developer over time? did you see color shifts, or increase/decrease constrast? Do you print on RA-4 or scan ?
Why to you think the jobo gives you better results? It has temp control?

Click to expand...

Yeah, it was a lot of work to get the spreadsheet setup. But once I got into it, the motivation took on a life of its own. My main goal in the beginning was simply to have a way to know if my chemistry was still usable without having to risk a roll of film I cared about. I achieved that much at least.

Right now I just scan the majority of my C-41 photos, where fiddling color balance seems to be a challenge regardless of who processed them. However, I've been getting better at that over time. The bulk of the pictures I've run through the chemistry have been family trip photos, so there isn't enough consistency to really do an objective comparison. (Lighting tends to be all over the place in those.) I have started doing RA-4 printing, but I've only done a little bit of it so far. However, most things (shot under similar lighting) do seem to print okay with the same starting filtration.

I suspect the Jobo does better because its consistently rotating the drum through a temperature-controlled water bath. It also doesn't have the annoying gas expansion problems that an inversion tank runs into.

Mr Bill said:

Bravo on jumping through the hoops to do the work!

I take it that you're not asking for advice? But since you're putting the data out there, I notice that the "activity levels," really just the LD and "HD-LD" (contrast), are almost all below the "aim value." I'm curious as to whether you tried any corrective action.

Click to expand...

I'm within enough of a ballpark to be happy with the results, but I agree that those numbers are a little bit on the low side. If you have any recommendations for things to try, I'm all ears (just ignore the first two datapoints).
The flowcharts in Z-131 really aren't very useful, as they lump it all together. The example graphs help a tad more, and make me suspect I might be a little low on temperature or time. But even those are less clear, because the ordering of my color channels doesn't really match.

Here's my general process with regards to temperature and time:
- For temperature, I set the Jobo's water bath to 39.8C (per a recommendation in the John Tinsley book). I then begin processing when the thermometer in the developer itself reads at least 38C. The hope is that this compensates for temperature drops in the tank, but I haven't used a thermometer probe to measure the specific drop like someone else in these forums did. Prior to pouring in the developer, I do a 5 minute pre-heat (spin the drum empty in the water bath), as recommended by my chemistry kit's instructions.
- For time, I pour the developer completely into the tank and then press "start." Then, about 8-10 seconds before the end of the 3:15 processing time, I pour it out. Once the timer beeps, I move on to the bleach.

Iterating on getting things just right might be a good future project. One big issue with that is really that I have no good way to rapidly dry a strip of film. So usually several hours pass between processing a test strip and measuring it, and its not uncommon for me to wait until the next morning to process the real film I want to use that bottle of chemistry on.

This is quite reassuring and it mirrors my subjective experience, although I did not measure things or made systematic comparisons. Many thanks for posting and well done!

Great work !

Two remarks:
The term "Jobo" as such meaning the Jobo rotary processor is an american thing and may puzzle people elsewhere.
The gas diffusion character of bottle materials vary, so other users might experience different results with other storage bottles.

dkonigs said:

The example graphs help a tad more, and make me suspect I might be a little low on temperature or time. But even those are less clear, because the ordering of my color channels doesn't really match.

Click to expand...

Well, you can't really trust the exact ordering of the colors, etc., except in the more extreme cases where perhaps one color just takes off. Better to just see it as a general guideline.

The way I would look at it is that everything is on the low side, and the way to deal with this is a general increase in the "activity." Which can generally be done by one of: increase time, increase temperature, increase agitation, or increase the strength of the developer. Now because there is a set of fixed parameters you should stick with those as much as possible. So the question is, which one(s) are wrong? Time is pretty easy to confirm, so you should leave that alone. Agitation, I'm guessing you don't have much control. The thing that is probably the most difficult to be really certain about is... temperature. So I'd say to boost the temperature for another try.

In commercial processing we'd verify that those are all ok, then do what we call "spike" the developer with some replenisher. This basically makes the developer stronger. But I'm guessing that you don't have replenisher, only the working strength developer. So probably not an option.

Whatever you decide to try, remember that the control strip is the ultimate arbiter of how much development is done.