[Martin Aislabie]

As others have said, printing with the chemical temperatures are above 20C is not a problem - we generally develop, stop and fix prints to completion.

So by the chemicals being a little warmer means the reactions happen a little quicker, completion is achieved a little sooner - but no harm done but don't bother trying to adjust your processing times to compensate - just stick to what ever you are using.

Printing when the chemicals are cooler than 20C can lead to problems.

As a typical guide, if the air temperature in your darkroom is 20C, then the chemicals in your print trays would be 18C~ish - which is still OK.

However, if your print developer drops much below 18C, you start to see problems.

I once tried to print in my old temporary darkroom and the noticed I was starting to get very muddy looking prints (low contrast and very poor black density), I noticed the developer was only at around 14C.

Nothing I did seemed to have any real change to the developer temperature, so I had to give up for the day.


Film developing is very different.

Your film developer needs to be 20C +/- 0.5C when you start.

The stop and fix need to be 20C +/- 2C, to stop the film emulsion from cracking (the technically name is reticulation) due to thermal shock.

If your darkroom is cool/cold and you want to develop film, having a washing-up bowl of warm water and putting your measuring cylinders/jugs of working strength stop and fix, is a great way of managing your stop and fix temperatures.

For your film developer temperature control, one shot chemicals is a great way to go.

Measure your film developer temperature and then adjust the addition water temperature needed to make up the working strength developer to achieve 20C when the two are combined. Being one-shot you thrown the developer solution away at the end of the development and start again for the next films.

If your film developing tank (loaded with your to be developed film) is say more than 2C cooler the 20C target temperature - then is can be added to your washing up bowl of water that is keeping the stop and fix at a sensible temperature. However, the film tank needs to be in the warmish water for a while in order to get not only the external wall of the tank but also the films and their reels up to temperature too. Sticking a thermometer in to the tank will tell you its internal temperature.

For what its worth, I adjust my working strength film developer temperature by running warm or cool water on to the outside of its measuring cylinder to get as close to 20.0C as I can.

Films from Ilford, Kodak and Fuji are fairly robust to reticulation but its better to avoid risking it by a little care and attention.

Martin