Why Does Presoaking Make a Difference?

[Bruce Watson]

I know that a presoak for short development times is recommended often. But I don't understand why it makes a difference so I thought I'd ask.

Here's a thought. No guarantees on the correctness of this, but I've read it somewhere at some time over the last few years. IOW, you might want to research this out further to see if it applies to your specific situation.

The thought is that water and water-based solutions permeate the dry emulsion fairly quickly (20 seconds? 30?). If the solution you use is your developer, it is sucked into the emulsion and starts working very quickly.

If however you used a water presoak, the developer gets into the emulsion by diffusion. That is, it has to displace the water that is already there before it can get in and start acting on the latent image. This is a slower and more gentle reaction. It could easily add another 30-60 seconds to your development time, depending on your agitation technique. The more active your agitation, the less time it takes for the developer to displace the water and therefore the sooner active development starts. Temperature effects the diffusion process too.

This may be why some advise a water presoak when short development times are indicated.

[Gene McCluney]

, the sheets can go into the developer one at a time, and they won't stick together.

Yes, if you wait 15 to 20 seconds between sheets. Too long for even development of all sheets. The presoak swells the gelatin and renders it slick and non-sticky, therefore when you transfer the sheets to the developer one by one, you can do it just as fast as you can lift and transfer each sheet. Of course in putting sheets into the water presoak, you should pause a bit between placing sheets, so each sheet can become fully wet before the next one is placed on top of it...but it is water, so no activity will take place.

[Jim Jones]

I found a presoak absolutely necessary when solarizing Tech Pan film in Solarol developer. Perhaps reducing exposure and extending development time would have eliminated the need for a presoak, but once I could get predictable results, any change would have wasted time and material.

[domenico Foschi]

Try to develop sheets where there are uniform areas(like a overcast skies) without presoaking and see what you get.
I think Bruce Watson hit it on the nail.

[Marko]

My guess would be that it is all about surface tension.

Sufrace tension is, quite simply, a propensity of a liquid toward forming drops, beads and curved surface in general. It is caused by various inter-molecular bonds which pull individual moleculs inward. Surface tension is charateristic for each liquid, but also depends on the nature of the bordering surface.

Since a developer is always a water-based solution there is no surface tension between it and water, therefore soaking the emulsion in water prior to imersing it in developer serves the purpose of breaking the surface tension and pulling the developer into the emulsion faster and more uniformly.

[John Kasaian]

I presoak Tmax 4oo sheets to get the purple stuff out.

[Mattg]

I started using a pre soak with Ilford roll films, against the manufacturers recommendation, to alleviate some problems with uneven development. It works very well for me, no more streaks. I did learn the hard way not to agitate during the presoak because I'd get lovely foamy bubbles that stuck to the film during the first phase of development.

[Sandeha]

Jobo tanks for roll film specifically recommend pre-soaking (irrespective of film brand) and I assume it's for the diffusion reason explained above in conjunction with dev flow issues around the spool edges.

It does affect dev time, but more importantly pre-soaking prevents splotching and streaks. Never had a streak since I began pre-soaking.

[David A. Goldfarb]

Yes, if you wait 15 to 20 seconds between sheets. Too long for even development of all sheets.

It probably depends on the developer and film, but I find that a few seconds per sheet is sufficient (usually using ABC pyro) to get it into the tray and pat it down before adding the next sheet.

[Jim Jones]

. . . I did learn the hard way not to agitate during the presoak because I'd get lovely foamy bubbles that stuck to the film during the first phase of development.

Too high a concentration of wetting agent may aggrevate the foaming.