Slowing down development

Hi.

I started a thread on this topic a while back, but I have a specific question that might justify starting a new thread.

Background: The other thread discussed changing the Ph of HC-110 solutions to slow development.

Now I have a specific and different question. Will sodium sulfate (NOT sodium sulfite), added to a developer, slow down development. As I recall, someone mentioned this possibility.

I know that sodium sulfate is sometimes used in tropical developers to counteract the problem of emulsion softening due to high temperature. This makes me think that it would have a similar effect at lower temperatures, at least to a degree, and this would probably slow the diffusion of developer into the film, thus slowing development, especially for films that tend to have soft emulsions, like fomapan films.


What do you think? Has anyone tried this?

I don’t know. But I wonder what’s your goal with this, I mean for the final print?

otto.f said:

I don’t know. But I wonder what’s your goal with this, I mean for the final print?

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Goal: slow down development of HC-110 to a level practical for development of fomapan films in my phototherm. Basically, it develops too fast. I could dilute the developer to dilution H, but then I could only run one film in a four-film tank. I can't lower the temperature because temperature is built into the program. That leaves several choices: 1) run one roll in a four-roll tank (not a great option). 2) use a different developer (not an ideal option for me). 3) modify HC-110 so development time is long enough to be practical.

Wouldn't using a different developer be easier and more predictable than chemically messing around with hc110 which you would also turn into a different developer, with unknown properties?

I thought sodium sulphate was added to film developers to maintain the same development time in higher temperatures as at normal temperature?

alanrockwood said:

Basically, it develops too fast.

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Do you mean that the highlights in print are burnt out too often?

I have seen suggestions that adding methyl cellulose (or even polycellulose) slows the activity but I have no details of the actual amounts used. You could even experiment.

I found some information about the effect of sodium sulfate on development rates.

Source 1, Photographer's Mate 3 & 2 By United States. Bureau of Naval Personnel: "When working below 75 ° F , the sulfate may be omitted [from DK-15] if a more rapid formula is required ." This implies that sulfate increases development time. Also, average development rate at 65 F for an unspecified film using DK-15 developer (which contains sodium sulfate at about 2.5% by weight) is 12.5 minutes. For the same developer without sulfate the development time is about 6 minutes.

Source 2, The Darkroom Cookbook, third edition, p. 48: Adding 105 g of sodium sulfate per liter of developer solution results in the following time/temperature compensation compared to 68F development... at 75F add 20% to the development time. (Yes, longer development time at higher temperature with sodium sulfate added.) At 80F subtract 10% from development time. There is also a chart specific to D-72 and D-76 developer. The information in this table is not consistent with the information in the first table, at least in quantitative terms. For example, it recommends that to keep the same development time at 75F compared to 68F one would add 50g per liter for full strength developer and 100g per liter for 1:1 developer. (However, they don't specify whether the 100g/liter is added before dilution or after dilution.)

Anyway, regardless of the exact quantitative relationship it seems clear that adding sodium sulfate will slow development and/or compensate for higher temperature.

I hypothesize that it will also change the characteristic curve a little. This comes from the following analysis that considers two extreme cases. In the first extreme diffusion of developer into the film is fast, so the rate of development is controlled by how fast a silver halide responds to developer at local concentration that has achieved equilibrium with the bulk solution. The second extreme is that the rate of diffusion is slow, so the rate of development is controlled by how fast the developer diffuses into the emulsion.

In the first extreme the rate of development is faster in the highly exposed parts of the emulsion than in the lightly exposed regions.

In second extreme the rate of development is the same in both the highly exposed and lightly exposed region of the emulsion. (This is somewhat of an oversimplification, but may be at least partly true.)

Real development will (presumably) fall somewhere between the two extremes, but to the extent that development tends toward diffusion control then the density in the highlights of a negative will be somewhat suppressed compared to the other extreme condition. This means that if diffusion of developer into the negative is suppressed there will be a tendency toward compensating development, hence a more S-shaped characteristic curve. Therefore, if sodium sulfate reduces the diffusion rate of developer into the emulsion it would tend to shift the curve toward an S-shape. Whether this is true in practice or not, it is a hypothesis that might be worth testing, and if it is true then the question is whether the effect is large enough to matter in practice.

Alan, Mortenson slowed down his development for his gamma - stuff by putting things in the refrigerator. I'm not familiar with either the developer you are using or the way you are developing your film but it might be something to consider. you might be able to extrapolate the times or contact the manufacturer to find out the times they suggest for processing below, 65F ...

jnania said:

Alan, Mortenson slowed down his development for his gamma - stuff by putting things in the refrigerator. I'm not familiar with either the developer you are using or the way you are developing your film but it might be something to consider. you might be able to extrapolate the times or contact the manufacturer to find out the times they suggest for processing below, 65F ...

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Thanks for the suggestion.

However, I use a Phototherm processor. It has a fixed temperature of 75F for B&W film. Also, it's a rotary processor. Both of these factors cause faster development. This is compounded with a film like fomapan which builds up density real fast. Hence the need to slow things down.

I asked the same question here.

@Ian Grant gave insightful response here and here.

Murray Kelly said:

I have seen suggestions that adding methyl cellulose (or even polycellulose) slows the activity but I have no details of the actual amounts used. You could even experiment.

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I should probably look into the methyl cellulose idea as well as the sodium sulfate idea.

alanrockwood said:

However, I use a Phototherm processor. It has a fixed temperature of 75F for B&W film. Also, it's a rotary processor. Both of these factors cause faster development. This is compounded with a film like fomapan which builds up density real fast. Hence the need to slow things down.

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I think you've hit on your problem. A developing practice that only allows for one temperature setting, and using that rotary processor. Simply lowering the temps and using tank/tray development should slow things down since nearly all chemical processes are accelerated w/ heat, and slowed down by cold. You can use easier agitation that way too, which will "soften" the development.

I forgot to add sugar at 150 - 200g/L is a good brake on the developer.