Hi Gattu,

The temperature of the developing water can also have an effect too (quite a subtle effect, but sometimes noticeable); I recently did a run of 6 prints in quick succession and used the same developing water for them all. The water was in a tray sat on top of a water heater plate, which does not have good temperature control. Over the course of the prints, the 'blown highlight' regions around some lamps that were in the image got larger and larger, yet the shadow areas and rest of the image looked exactly the same. It took me a while to realise that it was the temperature of the developing bath that had been slowly increasing between the prints, making the print contrast just slightly higher for each successive print.

The first print was developed at 41 degrees and looked fine, the 5th at 47 degrees and much detail in the lamp area that was present on the first print was lost by the 5th print (I was floating the paper face-down to develop for 30 minutes). For the final print, I turned off the heater until the water had cooled to 40 degrees, then turned the heater back on during the development, giving a similar temperature profile to the first print. The result was that the first and the last print looked near identical, indicating that the exposure and sensitisation was consistent between prints too and only the temperature of development had varied for the others.

The negative was unusual for me in that it was a picture taken in a dark room with a few lamps that essentially were blown out in the print and did not have a good tonal range. I printed to capture the detail in the room and so knew the lamps would print white. It was the size of the 'halo' around the lamps which grew as the temperature of the water increased. I assume that the hotter water softened the gelatine more. On inspecting the print for 'correct development', I stopped the development when the bulk of the room looked right, rather than the highlights. Thus it was not as if the prints were overdeveloped as the rest of the image looked fine, rather the contrast of the image had changed.

Best regards,