Why Does Presoaking Make a Difference?
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 my thinking on it:
Let's take tray development to make it easy. Let's suppose for some reason you measure your temperatures and do the math and come up with a development time of 3 1/2 minutes -- well in the range for which most people recommend a pre-soak. I know from watching the process in the light that if I put a sheet of 4X5 or 5X7 film in a tray that the entire surface area of the sheet of film will be under the solution in one second or less. Often, a lot less. Since the emulsion is essentially uniform in composition, it seems to me that it should all be moving toward the 3 1/2 minute "done" mark at the same pace, plus or minus one second or less. As a percentage of difference the non-uniformity of development time should be insignificant. (Less than the time difference between sheets that results from the few seconds delay in putting the second sheet in the solution, for example, if using a slosher, or much less than the delay into the stop and the fixer is shuffling multiple sheets.)
So why would soaking the film in water first make development any more uniform? It isn't like the emulsion surface is water resistant. Emulsions soak up water in a flash. I can see that if you are naturally inclined to not get the film under the developer promptly (for example, dropping it in the tray and letting it float around for 30 seconds before really pushing it under) that could lead to nonuniform development, but in normal processing, why does a presoak do anything more than add a handling step and a chance for scratching film when it goes in the developer?
Re: Why Does Presoaking Make a Difference?
I just presoak rollfilm to help prevent air bubbles. Never heard of presoaking used to change development time.
Re: Why Does Presoaking Make a Difference?
I don't know that it does much for tank development where the film never touches itself other than just preparing the emulsion for a liquid. But for tray development it means having seperate sheets of film as opposed to a block of plastic when you put it into a liquid. Each sheet must be presoaked for 15 to 20 seconds in water, when all sheets have been presoaked you can then move them in mass to the developer. If you don't do this the sheets will stick to each other like glue and you cannot seperate them without destroying the emulsion.
Re: Why Does Presoaking Make a Difference?
Now I know why I never develop film in trays....some of these descriptions could be material for a darkroom horror movie. I think the best way to process film is never...never let one piece of film touch another. Period.
Re: Why Does Presoaking Make a Difference?
I can understand the no-stick theory, and I accept that if you are using that technique, but pre-soak is often recommended for even development and that is the part I do not understand.
Re: Why Does Presoaking Make a Difference?
Perhaps they are using the term in its most general meaning. Being able to place the film in the developer all at once, and thus avoid sticking, promotes even development, "as it were".
Re: Why Does Presoaking Make a Difference?
Presoaking has little if anything to do with film sticking together. The purpose of presoaking is to allow the emulsion to expand or swell and stabilize, which in turn is supposed to promote even development. It used to be a big deal with the old thick emulsion films but I don't think it serves much purpose with today's films. IIRC some manufacturers, e.g. Ilford I believe, specifically recommend against it.
The only time I presoaked was when I was experimenting with PMK and I did it then because Dan Burkholer's book recommended it. However, after a few months I decided to try PMK without the presoak and everything seemed fine so I stopped doing it even with PMK. So IMHO the principal effect of presoaking is to add an unnecessary step to the development process and thereby increase the length of time for which you're standing in your darkroom inhaling chemical fumes.
Re: Why Does Presoaking Make a Difference?
I presoak film because it makes it's easier to slip it into a film tube.
Re: Why Does Presoaking Make a Difference?
"Presoaking has little if anything to do with film sticking together"
Drop 5 0r 6 sheets of film as a pack into developer at the same time and see wht you get.
Re: Why Does Presoaking Make a Difference?
I don't see why anyone would put several sheets into the developer at once in a stack. Some films/developer combinations do better with a presoak, but for those that don't require a presoak, the sheets can go into the developer one at a time, and they won't stick together.