Where recommended, presoaking film is generally to help improve development uniformity, particularly with short development times, stand/semi-stand development, and when you can't get the film immersed in the developer quickly enough (for example, filling a multi-reel stainless tank through the daylight lid). Of course when tray shuffling sheet film, a pre-soak prevents the sheets don't stick together.
Some people recommend a film pre-soak in all cases. Some don't. Ilford says it is not required. I don't think Kodak indicates it is required either (for roll film).
These are not issues with paper development because 1) the paper is usually quickly immersed in the developer 2) paper development is virtually to completion (which would minimize or eliminate artefacts from uneven initial development), 3) agitation is generally continuous.
Regarding temperature, one could simply bring the tank to temperature by tempering it in a water bath. With paper, there is no tank, just the paper, which would likely come quickly to the developer temperature once immersed, without having a meaningful effect on the developer itself as long as there is sufficient developer volume.
Last edited by Michael R 1974; 04-08-2013 at 06:13 PM. Click to view previous post history.