Sodium Sulfate

I believe that Sodium Sulfate was used for tropical developers to reduce the softening of film. I believe this also results in extending the development time. Presumably this might be useful under less extreme conditions if one wants to extend development times.

Does anyone here have knowledge or experience on this topic?

Just to be clear, I know that there are other ways of extending development time, but that's not what I am interested in discussing here, although those methods could be interesting to discuss in other threads.

I used a tropical developer a fair amount a long time ago. The main difference was the addition of Sodium Sulphate which reduced the risk of the emulsion lifting.

As for extending the developing time, I'm not too sure about that. My take on times, and it was a long time ago, was the development times were really quite short with higher temperatures. I mainly worked between 30ºC and 32ºC as that was the local creek water temperature, which was cooler than the water in the pipes.

A special tropical developer, or developers are available, I never tried them but if my memory is correct, their developing times were only a few minutes at or around 30ºC.

I seem to recollect D76 around 8 minutes at 30ºC with Sodium Sulphate added. Around 15 minutes at 20ºC for normal developer without Sodium Sulphate.

I have around 15kg of Sodium Sulphate left from a 20kg container, you're welcome to some, but you would have to collect.

Mick Fagan said:

I used a tropical developer a fair amount a long time ago. The main difference was the addition of Sodium Sulphate which reduced the risk of the emulsion lifting.

As for extending the developing time, I'm not too sure about that. My take on times, and it was a long time ago, was the development times were really quite short with higher temperatures. I mainly worked between 30ºC and 32ºC as that was the local creek water temperature, which was cooler than the water in the pipes.

A special tropical developer, or developers are available, I never tried them but if my memory is correct, their developing times were only a few minutes at or around 30ºC.

I seem to recollect D76 around 8 minutes at 30ºC with Sodium Sulphate added. Around 15 minutes at 20ºC for normal developer without Sodium Sulphate.

I have around 15kg of Sodium Sulphate left from a 20kg container, you're welcome to some, but you would have to collect.

Click to expand...

Very interesting. In my opinion the data you give MIGHT support an interpretation that sodium sulfate lengthens development time, but it's kind of a borderline call.

Here's my rationale. If we do a time/temperature conversion (e.g. at https://www.digitaltruth.com/devchart.php?doc=timetemp) starting with your 8 minutes at 30 C with sulfate, the predicted time at 20 C with sulfate is 21 minutes 44 seconds. That's quite a bit longer (1.45x) than your time of 15 minutes at 20 C without sulfate.

If we do a temperature conversion in the other direction, starting with 15 minutes at 20 C without sulfate the predicted time for 30 C without sulfate is is 5 minutes 31 seconds. That's quite a bit shorter (about 0.69X) than your 8 minutes at 30 C with sulfate.

These calculation support the theory that sodium sulfate extends development time. However, because of various assumptions and uncertainties involved in the calculation I'm not very confident about the conclusion that sodium sulfate extends development time.

On the theoretical side, I believe that sodium sulfate reduces gelatin swelling and softening. If so then it would probably slow the rate of diffusion of developer into the emulsion, and this would probably slow the rate of development.

If we harden the emulsion don't we also make it harder to wash the fixer complexes out during wash?

ags2mikon said:

If we harden the emulsion don't we also make it harder to wash the fixer complexes out during wash?

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Possibly, yes. I guess the question is whether hardening the emulsion makes it too hard to wash fixer complexes.

It may also depend somewhat on how hard the emulsion is to start with. Some emulsions (Fomapan?) are naturally relatively soft during processing, and I suspect that those emulsions would be affected more than harder emulsions.

On the other hand, if they are naturally soft to begin with they are probably easier to wash stuff out, so making the emulsion harder during processing might just bring them up to the point of being similar to harder emulsions.

Also, if understand correctly the sulfate effect is only active while sulfate is in the emulsion, so as it washes out (during fixing and final wash steps) the emulsion gets soft again and easy to wash out.

I should add another comment. Some of what I discuss above is theoretical. I am hoping that people with actual experimental results can add comments.

It is around 45 years since I was originally doing this stuff, but being home now I can look up some of my developing notes and found that my normal temperature developing times with my standard developer (D76) was 15-16 minutes at 20ºC.

The best, or most used time and temperature development I did with Sodium Sulphate added, was 8 minutes at 30ºC. Film used was Tri-X and the era was 1973-1974 and at 320 ASA.

Interestingly, looking up Developing by Jacobson & Jacobson 18th edition, revised and updated, page 230 chart number 28 gives some close times. Additional information on page 229.

If normal development is 16 minutes at 20ºC, then with the addition of Sodium Sulphate (105gms per litre) times are 10 minutes at 29ºC or 7 minutes at 32ºC.

You need to know that this was developing alongside a creek in the bush with rudimentary equipment. Developing was always done in the morning when the temperature was cool and with relative humidity being reasonably low. By the time the film was hanging from the branches to dry, humidity was rising as rapidly as the sun was. This was in far northern Australia with the latitude being somewhere around 12º - 15º mark. at the end of the wet season

Mould in cameras and socks, was an ongoing problem.

In this article about astronomical photography (1956) there is a statement that looks to me as though the sodium sulphate will wash out. Little screen shot below, I couldn't copy the text.

Mick Fagan said:

I used a tropical developer a fair amount a long time ago. The main difference was the addition of Sodium Sulphate which reduced the risk of the emulsion lifting.

As for extending the developing time, I'm not too sure about that. My take on times, and it was a long time ago, was the development times were really quite short with higher temperatures. I mainly worked between 30ºC and 32ºC as that was the local creek water temperature, which was cooler than the water in the pipes.

A special tropical developer, or developers are available, I never tried them but if my memory is correct, their developing times were only a few minutes at or around 30ºC.

I seem to recollect D76 around 8 minutes at 30ºC with Sodium Sulphate added. Around 15 minutes at 20ºC for normal developer without Sodium Sulphate.

I have around 15kg of Sodium Sulphate left from a 20kg container, you're welcome to some, but you would have to collect.

Click to expand...

Since I read your post, I've been searching constantly.
Because I'm sure I've used this recipe before.
But at that time, I had to.
I needed a large amount of devlopers and I ran out of sodium sulfite stocks.
I found a formula based on sodium sulfate from the great Agfa company's recipes, and it actually works at a temperature of 32 degrees Celsius.
But she had a small flaw, which is that she does not live for more than a month.
I've been looking for that recipe for hours and never found it, I don't know how it disappeared..