Function of sulfate in film developers

[alanrockwood]

Hi, I wonder what is the function of sulfate in film developers (not to be confused with sulfite). I understand it is sometimes a component in "tropical" film developers, and I seem to recall reading that it tends to harden an emulsion. Is that right?

Also, if it hardens the emulsion, I assume that would be to reduce scratches, or maybe to prevent dissolving of the gelatin. Is that right?

Also, if it does harden the emulsion, would that slow development? I could sometimes find this useful. I use a phototherm machine, which runs a little hot (74 F as I recall) and is a continuous agitation machine. For some films this combination of temperature and agitation results in processing times that are a bit too fast. One could reduce the developer concentration to slow things down, but in some cases that puts it below the recommended amount of developer per roll of film, so another alternative lengthening the developing time is needed. Maybe a sulfate additive to the developer might be an answer.

 

[Gerald C Koch]

No it will not harden the emulsion just reduce any swelling due to high temperature processing. If you keep your processing solutions at 80F or less it isn't needed with modern pre-hardended films.

 

[alanrockwood]

Does the non-swelling function also alter development time? I would find it useful to lengthen the development time in some cases.

 

[Rudeofus]

If you reduce swell a great deal, you also reduce diffusion of fresh developer into the emulsion. This will cause overdevelopment in the upper layers and underdevelopment in the lower emulsion layers, a bit like highly dilute developers - I would expect this gives higher granularity with potentially higher sharpness appearance.

PS: As far as I understand this, reduction of swell is closely related to hardening, at least temporarily. However, since sulfate washes out, its potential hardening effect is not permanent.

 

[Raghu Kuvempunagar]

According to the video rotation speed can be programmed. Might be worth experimenting with.

 

[alanrockwood]

According to the video rotation speed can be programmed. Might be worth experimenting with.

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