Niall.
With 35mm film, it doesn’t always make sense, but with sheet films, pre-soaking has two effects:
1) The anti-halo layer is removed (nothing particularly special, as the developer could do this too)
2) The supercoating is washed off
Now, point two is what we’re after. The supercoating is a thin layer of highly diluted gelatin which is applied to the film after emulsioning for the purpose of protection. It cannot always be applied 100% evenly because it is very liquid. We want to remove this layer completely during the developing process so that the developer can access the film’s surface at the same rate everywhere. If this is not removed completely after development, some larger-format sheet films may show slight streaks.
In the enlarging process this would still be almost invisible, but if you do contact printing (and that’s what most of these large sheet film users do) this can show up on the image.
As for 35 mm, I cannot see why one should pre-soak unless there is some special ingredient in the anti-halo agent that might interfere with the developer or something similar.
Sometimes people put forward the theory that a pre-soaked film develops more evenly than a non-pre-soaked film due to a slower penetration of the developer into the emulsion (it has to work its way in by ‘pushing’ out the water already present), but I have never experienced this.
Cheers,
Mirko
PS You can now buy all our fancy stuff from our new partner
Retrophotographic if you don’t mind buying from a British company :-)
