I have an unheated darkroom in the basement of the house that is sided by an exposed, above grade wall (the house is built on a slope). As a result, the temperature of my stock solutions on the shelf fluctuate with changes in the darkroom's ambient temperature, especially in winter extremes.
Naturally, the development time of any developer can be lengthened to compensate for solution temperatures that are cooler than the manufacturer's recommended developing temp (usually 68 degrees). I often use Ilford Perceptol as my developer of choice, and page 4 of the 2010 data sheet has a text explanation, as well as a graph, about how much to lengthen the development time by the cooler temperature level. It can be viewed at this link: https://www.ilfordphoto.com/amfile/file/download/file/1829/product/708/
The text states to "increase the given development times by 10% for each 2 degrees Fharenheit drop in temperature." However, the graph shows amounts that are greater than this.
Take, for example, the time of 6 minutes at 68 degrees (which is not what I use for Perceptol, but it provides an easy reference for illustration purposes). Let's say you wanted to develop the film at 58 degrees, or 10 degrees below the recommended 68 degrees. Using the text formula, that would involve a 50% increase in development time, from 6 to 9 minutes. But if you look at the graph, the 6 minute mark goes to about 10 minutes at 58 degrees. That's a difference of a full minute between the two recommended adjustments.
I thought that either Ilford is comfortable with generalities, or perhaps the 10% increase in time is supposed to be compounded with each 2 degree interval, which would yield about 9 minutes and 40 seconds.
So I have three questions for those interested in responding to any one of them:
- What is your take on the technical data sheet?
- What has been your experience, if any, with increasing development times for cooler bath temperatures?
- What's the coolest temperature you've developed film in?
Thanks!
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