Is the temperature really necessary? Some colour developer brands suggest also other possible temperatures, the so called slower procedure at 86ºF (30ºC) and the express procedure at 113ºF (45ºC). This is a sign that it is not absolutely necessary to respect a given temperature. It is obvious that a very high temperature will spoil the film and a very low temperature is maybe time consuming and therefore not suitable for film labs, where time is money. That is maybe the reason why a standard temperature/time combination was chosen at about 100ºF/3'30''. 100ºF is safe for the film and it turns possible a very short time to make the process cheaper.
Film labs use automatic film processors and it is very easy to respect exact temperature and development time. For manual use in a development tank, that is quite impossible, imho. Filling and emptying the tank take time and the temperature will drop when you take the tank out of the warm water bath to agitate each 30 seconds. Using warmer water above 40ºC to compensate may burn your hands and the time you save to develop in just 3 and half minutes is spoiled with warm bath preparation and so on.
When I decided to write about this subject, I first heard the opinion of a friend and colleague of these labors, Reinhold G., the author of the nice blog Caffenol. In a earlier discussion with him, we both agreed that for manual processing, one should use room temperature and not external heated tanks. Besides, some time ago he published a graphic he prepared with temperature vs. time for C-41 development, according to manufacturer's data, and extrapolated to as low as 20ºC (68ºF). With his consent, here I reproduce the graphic:
|Click to enlarge|
Are there other reasons not to use room temperature and go the hard and exact procedure defended by some C-41 fundamentalists? It is said that the 100ºF procedure is responsible for exact colours but neither my experience or Reinhold's support this. Films I developed at room temperature present all three layers (blue, green and red) well developed and a good indicator for a succeeded development is mainly the red layer, the deepest one, where the developer must penetrate more. If you have vivid reds, that is a good sign. Colour shifts, according to my several failures, are mainly a pH problem, varying from magenta shift for low pH to hell yellow/green for high pH. To get good colours, you only need to adjust pH, instead of rising the temperature. Besides the pH of liquids decrease with temperature.
I recommend strongly this post of Reinhold at the site Filmwasters.com. As he says, developing C-41 is somehow easier because all C-41 films will be developed with the same developer (all brands are equivalent) and in the same time, be sure to have the correct pH which is said to be 10 but feel free to adjust for better colour reproduction. When processing B&W you have dozens of developers and each combination has a certain time and depends on temperature: see Massive Development Chart at digitaltruth photo.
Another final recommendation I can make is to prolong the bleach bath more than the standard time because it is normal that at a lower temperature reactions go slower. You may use the same acid fixer for B&W and the same times used for B&W film. To check whether a film is well bleached and fixed, scan it using IR scanning. If it is not well bleached and fixed, some large square pictures like big pixels will show here and there.
To end this already long post, I would like to thank to Reinhold G. for his support and opinions, which we share together.