Lets clarify a few points:
1. The temperature of the developer itself has little effect on grain size assuming development times are adjusted to compensate.
2. Processing a film within certain temperature constraints (variations) suggested by a manufacturer for the full cycle - Dev/Stop/Fix/Wash - and following the manufacturers recommendations should always give results they deem acceptable. That's not the same as the highest possible quality from that combination.
The next question is what are the manufacturers recommended temperature tolerances. The Kodak PDF/Datasheet (F-4016 - October 2007) for Tmax films gives development times for Tmax 100 & 400 for temperatures between 18ºC and 24ºC* and clearly states that stop, fix and wash should be within the same range. What they don't do is state what temperature difference between steps is acceptable, in fact they leave it very ambiguous.
* Disregarding Versamat processing as the Kodak developer (Duraflof RT) contains a hardener which allows processing Tmax 100 & 400 at higher temperatures. (Kodak - Duraflo RT - This developer features a hardener to prevent emulsion damage in the first developer tank of a roller-transport processor. Notice: Observe precautionary information on product).
However in a B&W processes trouble shooting guide Kodak state clearly
“To avoid problems, use a consistent temperature for all your processing solutions. Select a temperature that you can maintain consistently”
John Sexton who worked closely with Kodak on Tmax films says quite clearly:
DO NOT USE T-MAX IF YOU ARE NOT CONSISTENT IN YOUR PROCESSING PROCEDURES. You MUST have repeatable work habits and procedures. Be concerned about 1 degree changes in developing temperatures. Process the film as carefully as you would color films, and you will get totally repeatable results. T-MAX films will teach you to improve your processing technique for repeatable results.
Ilford state that for best results it is recommended that all process solutions are kept at the same temperature or at least within 5ºC (9ºF) of the developer. (From their powder developer data-sheet).
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However this takes us back to what I wrote in another Thread on this forum:
This is what John Davies has to say on the subject. John is Britain's top landscape photographer, his print quality from 120 films is 2nd to none, it's outstanding.
"It is also important to control the temperature of all the chemicals during processing and including the final wash. Slight fluctuations in temperature between the solutions will result in slight reticulation which is where the silver halide crystals form larger crystals to give the appearance of larger grain. Greater temperature fluctuations between solutions will result in a greater size of grain. In extreme cases the silver halide crystals form dominant textured patterns"
Here's the
link to his website.
Now John Davies is a very level headed uncontroversial figure so now look again at Bernard Susse's comments:
"The temperature of all the solutions, including the wash water. Is critical be- cause of the danger of reticulation. Reticulation occurs when the film emulsion cracks. The emulsion swells and softens during processing. The warmer the temperature the greater the swelling. If the temperature drops quickly, the surface of the emulsion contracts while below the surface it remains swelled. This causes small cracks to appear ln the surface. The cracks can appear as a pattern throughout the image when a print is made. Occasionally this pattern can make an interesting image; usually it`s a distraction. A mild form of reticulation, known as grain clumping, can also take place. This makes the image appear grainier and coarser than it normally would with proper processing. This is the major reason to constantly control the temperatures of all solutions."
And then you'll find that the teaching notes of most US photography modules at Degree level contain something like this (Hawaii.edu):
Ideally, chemical solutions including wash water should be consistent in temperature, preferably at 68°F. (20°C).
Temperature variations of +/- 5°F (2.75°C) are tolerated though grain size may be affected.
These are not isolated comments by any means, and lets look again at that Ilford recommendation -
that all process solutions are kept at the same temperature or at least within 5ºC (9ºF) of the developer.
That puts Kodak's 18°-24°C into a similar perspective, when you add their comment that
“To avoid problems, use a consistent temperature for all your processing solutions. Select a temperature that you can maintain consistently” that's a clear statement from all that a consistent temperature throughout the whole cycle dev/stop/fix/wash is the ideal.
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In practice there's plenty of visual evidence that photographers (& labs/technicians) who process with tight temperature controls get consistently better results than those who don't and let things drift up to 5°C or 6°C between steps.
The differences are seen in consistent high quality, good control of grain, as opposed to average quality, often unexpected grain, but still within manufacturers expectations. (Assuming same film/developer etc). While these improvements may be slight with 35mm it can be enough to make a noticeable visual difference when it come to print quality over 10”x8”,
So at one end we have a situation where good temperature control can help ensure finer grain, and as a consequence better tones & sharpness. This approach has been taught in colleges/universities & workshops for well over 25 years. Perhaps even more emphasis was placed on it before most films were better hardened.
Then we have the other extreme where big differences between process step temperatures will cause full reticulation with some films, and/or excessive grain with modern better hardened films.
So if we get slight differences in grain with small temperature variations +/- 5°C, and excessive grain at the other extreme +/- 10°C or even 15°C then it's logical that the greater the deviation between baths the more grain perceived in the negatives/prints.
There are other variables, because the pH and type of developer used, pH and type of stop bath or water rinse, pH and type of fixer will all have an effect on the swell of the emulsion and in some cases hardening or softening, and can in their own ways have an effect on the final negative qualities where temperature deviations occur.
Whether you call it Micro reticulation, Slight reticulation, a Mild form of Reticulation, Excessive grain or Grain clumping makes no difference.
The controversial part of this thread (and previous) is that people try to deny this, and the mid 80's Darkroom Technique article on Micro Reticulation showed the effects based on practical testing.
Ian