Pyrocat MC - colour change over time

[sharperstill]

Hi,
I've been using Pyrocat MC for a few years now, and I'm still on my first batch.
Usually, during process, I pre-soak and when I discard this it is usually a blue/indigo colour from the anti-halation dyes.
I normally then proceed to develop in a JOBO tank which I manually roll. Film is Ilford Delta 400.
Normally the developed is a very dirty brown when it is discarded.
The colour of the A solution has now become a very deep burgundy/brown but, curiously, the discarded developer yesterday was reasonably clear.
The developed negatives look fine (maybe a little thin) but I am curious about the colour change. Could it signal a change in the Pyrocat MC which I thought to be completely stable since its mixed in glycol?

Jon

 

[Gerald C Koch]

Staining developers contain a very small amount of preservative usually sodium sulfite. This is done to insure the correct amount of stain being produced. However it also greatly increases the developer's susceptibility to aerial oxidation. These substances are highly colored and the used developer is usually brown.

Since you have noticed that solution A has become darkly colored then it has started to oxidize. If you are experiencing thinner than usual negatives then it is time to discard solution A. The problem will only become greater with time.

As with all developers it is best to prepare only enough concentrate as can be used in a reasonable length of time. Some people claim that glycol based concentrates have better keeping properties but everything about these developers is based on conjecture.

 

[Ian Grant]

While I don't use MC I do use Pyrocat HD, once Part A has begun to oxidise it's time to discard it,, With thebHD version Part A will last up to 4 years Made up in water) with good storage as long as fresh Metabisulphite is used, it breaks down (oxidises) quickly when the Metabisulphite has decomposed to Sulphite.

It's possible deterioration in your MC is slightly slower as Ascorbic acid behaves differently but it's really not worth the risk. It's a while since I processed Delta 400 but the HD has no colour after processing HP5 and colour is usually from the anti halation dyes etc not the developer oxidation itself.

Ian

 

[Gerald C Koch]

The problem with using ascorbic acid (vitamin C) as an antioxidant to replace sodium sulfite is that ascorbic acid is also a developing agent. It is easily oxidized by oxygen in the air. Therefore the protective action of the ascorbic acid is bought at the cost of losing developing activity. Like sulfite ascorbic acid also interferes with the production of a stain image. I fail to see the logic of using it in a staining developer.

 

[Ian Grant]

The problem with using ascorbic acid (vitamin C) as an antioxidant to replace sodium sulfite is that ascorbic acid is also a developing agent. It is easily oxidized by oxygen in the air. Therefore the protective action of the ascorbic acid is bought at the cost of losing developing activity. Like sulfite ascorbic acid also interferes with the production of a stain image. I fail to see the logic of using it in a staining developer.

It's metabisulphite not sulphite that's the strong anti-oxidant due to the free SO2 it produces, once it's decomposed to sulphite it's a weak anti-xidant and not strong enough to protect the Pyrocatchin.

Ian

 

[sharperstill]

Thanks everyone,
The chemistry discussed above is beyond my knowledge.
Sounds, though, like it's time to mix a fresh batch.
I'm not sure why but I had it in my head that it would be shelf stable. Perhaps because of the glycol instead of water.
I think I'll mix smaller batches from now, as I only use 6-8ml at a time.
Perhaps I should also use a wine-pump

Jon

 

[juan]

Use small glass containers. The air inside is probably insignificant. I'm using Pyrocat PC that's at least seven years old.
Juan