C41 developers

Can anyone who may be connected to photographic industry in the chemical side say why the dilution of the developer concentrates for film should be all diluted in one operation, or as I do, as and when needed.. Two of the developers currently available in UK is the resurgence of a Kodak branded version and another made by JOBO who are better known for their equipment rather than chemicals.

With the Kodak one the keeping properties of one of the concentrates which was slightly 'champagne' colour before the bottles were opened has only darkened a tiny amount after being opened for a few months now and it still produces superb negatives. The JOBO version was the same and is easier to mix but one of the chemicals, the only one which was in a screw top brown glass bottle went black less than a week after opening.

In both cases would I have been better to mix the full 2.5 lite kits than mixing them as and when I used them?

Going back to when I started colour processing I used the Agfa version which had three different bottles and there was never a problem and I was able to use each kit to the end, usually over several months without anything 'going off'. There is never a clear warning that one of the part used concentrates will deteriorate quicker than the rest.

BMbikerider said:

In both cases would I have been better to mix the full 2.5 lite kits than mixing them as and when I used them?

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Yes.

The problem with C41 concentrates is that it's not possible to make a very concentrated solution that holds both the CD-4 developing agent and the hydroxylamine sulfate antioxidant at the same time. They go together fine in a fairly dilute solution (e.g. working strength, or twice working strength). As a result, if you have a concentrate like the ones made my PhotoSys/"Kodak", Jobo, Fuji etc., the little bottle with the CD-4 concentrate really has virtually unprotected CD-4 in it. The main/only protection is the bottle itself. Hence, as soon as the seal is broken, the developing agent is subject to oxidation (and even before this through permeability of the bottle itself to air). In the mixed developer, the CD-4 developing agent is protected against oxidation by the presence of hydroxylamine (or a similar compound). If you store this in a hermetically sealed, non-permeable bottle (e.g. glass), it'll generally have a longer shelf life than an opened or sometimes even factory-sealed (!) concentrate. The drawback of course is volume; it's bigger and heavier to store & ship, which is likely why the major manufacturers stick to concentrates (with a limited shelf life).

Note that Bellini deviates from this and offers a single-bottle C41 developer which is apparently at roughly the concentration limit for a single solution (intended for ca. 1+3 dilution); the shelf life of this single solution is allegedly excellent, which is consistent with what I explain above.

With B&W paper developer I buy 5 litre bottles of it (Ilford MG) and I decant it into dark brown 500cc glass bottles and the last lot has shown no deterioration in the 2 yrs since I bought it. and when I come to use it, I decant a bottle at a time further into 100cc glass bottles (100cc makes 1ltr working which is enough for one evenings work.)

So back to C41 developer.

So please correct me if I have interpreted your reply incorrectly, in that, if I were to mix the complete 2.5l kit into a working solution and decant it into similar 1/2 litre bottles the keeping properties will be greatly enhanced

The Bellini RA4 developer which I do use is excellent, With adequate replenishment (using factory figures which they sent me) it seemingly lasts for ages inside a NOVA processor.

So once the current Kodak C41 kit is used I will try that and see where I get. I don't believe in reusing colour developers so always use once and discard. So that sounds as if it may be the answer.

BMbikerider said:

So please correct me if I have interpreted your reply incorrectly, in that, if I were to mix the complete 2.5l kit into a working solution and decant it into similar 1/2 litre bottles the keeping properties will be greatly enhanced

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This is correct.

koraks said:

This is correct.

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Thank you for that. Luckily I have quite a few more brown 1/2 liter bottles so that is that sorted out! If we ever meet up I owe you a beer or two.

I'd be more than happy to share them with you! Much obliged.

BMbikerider said:

Thank you for that. Luckily I have quite a few more brown 1/2 liter bottles so that is that sorted out! If we ever meet up I owe you a beer or two.

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And if you pick the right beer, that will give you more bottles too!
Speaking in general about these sorts of things, it is often hard for us small volume users to realize that much of the design work for these systems was focused on designing for the practical needs of high volume commercial users, not the needs of low volume, occasional users. Scaling things down from those commercial applications is not always simple or easy.
Ironically, the creation of HC-110 (in the black and white realm) was an example of a design that increased the practicality for high volume commercial users, while perhaps unintentionally benefitting the small volume user as well.
AFAIK, no similar improvement in practicality for both types of users ever happened in the colour realm.