In the case of conventional (i.e. not chromogenic C-41-type)
black-and-white film, there is no reason to perform pre-warming provided
the film is around room temperature to start.
Some people *do*, however, advocate pre-*wetting* film especially to
avoid uneven development due to 'dry' patches as the developer is poured
into the tank - even more especially with shorter developing times. I
prefer not to mess around with too short a developing time in any case,
and I find no advantage at all in pre-wetting black-and-white film,
proper immediate agitation gets rid of any dry spots as the developer is
poured in.

In the case of C-41 chromogenic or colour negative film, development
temperature is 38 degrees Celcius. In this process I always perform 1
minute of pre-wetting at that temperature - for two reasons. Firstly, it
assures the film is up-to-temperature and wetted prior to development,
which takes 3mins 15seconds - 3mins 45seconds depending upon how many
rolls have been through. Secondly, it clears away the green
anti-halation layer which otherwise builds up rapidly in the developer
solution. On the rare occasion that I have processed E-6, I have done
the same.

My regards, F.C. Trevor Gale.

UC wrote:
There is no need to 'pre-warm' B&W film, as development occurs at room
temperature. E-6 films run at 100F.


Dieter Zakas wrote:

Recently, while inquiring about E-6 kits at my local camera store, one of
the co-owners (brothers) described one of the kits, Tetenal, I think.
Reading from a product description, he said that particular kit required one
to "prewarm" the emulsion, presumably using warm water at 104 degress
Fahrenheit.

This got me to thinking: Could one use a similar approach with B&W? While
I'm not sure how it would affect development times, softening the emulsion
may enable the developer to do its work. (However, I should note that it's
been some time since I developed ANY film.)

Dieter Zakas
--
Good, better, best; never let it rest, until your good is better and your
better is best. (Billy Cox)