GeorgK
I used to have a recurring problem with the A49, where it would ‘go off’ unpredictably – despite all the precautions I took, such as using degassed distilled water, thick-walled, fully filled PET bottles, etc. The developer was often compromised after just a few weeks; not completely ruined, but to the extent that it led to severe underdevelopment, particularly when used in diluted form. When shaking the developer bottles, a few faint, cloudy wisps were usually visible at the bottom, which led me to suspect microbial degradation.
In spring 2015, I then prepared a 5-litre batch of A49, but this time I placed a scrap of unexposed film (about 1–2 cm) into each bottle (approx. 650 ml, PET, filled to the brim), in the hope that the silver released would have a preservative effect. It was stored in the cellar, in the dark, at around 14°C.
As I’ve hardly had time for photography or development over the last four years, this turned into an – unplanned – long-term experiment. When I stumbled across the developer again after more than four and a half years and it still looked quite decent (no discolouration, no vapours), I decided to give it a go. I used a Rollei R80s, for development according to online instructions (1+1, 13 mins, although I extended the time by about 15–20%). The resulting negatives (see attachment) look very usable, with normal sensitivity utilisation and (due to slight overdevelopment) slightly increased contrast.
[attachment=3401]
I cannot say for certain whether the developer has perhaps lost a few per cent of its effectiveness; a direct comparison would be needed for that, but it does not appear to have changed significantly during this time.
Conclusion: Depending on the type of developer, it seems that not only oxidation caused by (already present or slowly diffusing) oxygen can be the main enemy of the stock solution, but also degradation by microorganisms. This may also explain the ‘eternal’ shelf life of some classic black-and-white film tank developers, such as those once operated continuously in large studios and newspaper publishers: the silver that inevitably accumulates there effectively prevents bacterial decomposition.
Depending on the pH value, composition and degree of purity of the base chemicals used (contaminants = additional trace elements), not every developer is equally susceptible, and cool storage (provided it does not lead to precipitation) naturally inhibits growth automatically, as well as all other chemical processes. However, with gas-tight and dark storage, microbial degradation really does seem to be the sticking point for the A49 in the long term, and a ‘mild’ biocide such as a few silver ions can massively extend its shelf life.
It would be quite interesting to know whether commercial liquid developers also contain ‘preservatives’.
The downside of the film scraps: in some cases (apparently different film types), the emulsion has dissolved, leaving tiny bits of gelatine floating around in the developer, which could potentially stick to the processed film.
Wolf_XL
...expecting a stock solution to last five years is asking a lot... And then to store it in PET bottles, too – amber glass bottles with a layer of Protectan on top would certainly be safer. But even with that solution, I wouldn’t give it five years... I’d say a year at most – then you’re on the safe side...
