Detecting when your C-41 Developer working solution is approaching depletion

I'm using the Tetenal C-41 3 bath kit, and have been using my working solution far past its advertised life in terms of calendar time. However, I haven't run too much film through it. I store it in collapsing PE bottles with the air squeezed out, so not perfect, but not terrible in terms of oxygen exposure during storage.

So far the old working solution keeps on working. In the past I've just thrown it out when I approach the recommended keeping time, but being a bit curious and perhaps a little greedy, I've decided this time to keep on using it until it fails.

What are the signs of imminent depletion? Does it fail all at once, or would I begin to see reduced quality? Does the developer fail before the blix? (My water based prewet is used one shot - I'm not THAT greedy! :p )

I'd like to see how long I can continue to use it, but cringe every time I introduce new film. I would mix a new batch but I'm just too curious, plus I'm not developing anything I couldn't afford to lose at the moment.

What does Tetenal say as to the capacity of their kit in total number of rolls?

60-80 35mm rolls.

The issue though is I think I will hit age/oxidation issues before capacity issues, because I am a hobby/home developer, with a mix of bw and color.

My interest is whether it will fail suddenly or gradually, and if gradually, what will I notice?

You'll probably see color fidelity start to lapse as the developer becomes exhausted. As for age, I generally find that C-41 developer lasts roughly six weeks in plastic Datatainer bottles, but others have posted longer lives in different storage.

When I mix up developer and have a stockpile of films to process, I save any chromogenic B&W (Kodak BW400CN, Ilford XP2 Super) films toward the end, since color accuracy is of course not a concern.

To reduce oxidation to a bare minimum store the developer in a glass bottle not a placstic one. All plastics are permeable to oxygen to a greater or lesser degree.

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Originally Posted by Gerald C Koch

To reduce oxidation to a bare minimum store the developer in a glass bottle not a placstic one. All plastics are permeable to oxygen to a greater or lesser degree.

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Yes, understand and totally agree. PE is not the best, PET is much better (and cheap, just soda bottles). But PE is not terrible, as plastics go, considering that these are the collapsable bottles that let me remove all the internal air, so that all that remains is through permeation, which is low with PE plastic. I've avoided glass, because I don't have a clue where I'd find marbles in Beijing to fill up the void. I'm ok with losing a little life to minor oxidation. So far, my PE bottles have kept the stuff alive for longer than the rated life according to the Tetenal manual, so I'm satisfied.

There are 2 ways it can fail. Overuse, which cannot be detected except by the bad images you get, some of which is described in the posts above.

The other failure is when the developer begins to look like tea and then coffee (assuming a prewet - all bets are off if you don't use one because you cannot judge this one then) colored. When this color changes, then the developer is oxidizing and is going bad.

PE

Quote:

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Originally Posted by Photo Engineer

There are 2 ways it can fail. Overuse, which cannot be detected except by the bad images you get, some of which is described in the posts above.

The other failure is when the developer begins to look like tea and then coffee (assuming a prewet - all bets are off if you don't use one because you cannot judge this one then) colored. When this color changes, then the developer is oxidizing and is going bad.

PE

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Thanks PE for the expert tip. I'm at "tea" now, so it will probably be "coffee" soon... I do use a prewet based on previous posts you made, and am sold on it.

By the way I hope you weren't erroneously attracted to this post by our discussion of plastics! ;-) I appreciate your attention.

Just to satisfy my morbid curiosity, the prewet is the optional presoak with water?