effect of time/temperature to film development?

Discussion in 'Darkroom Developing and Printing' started by E Colar, Jan 16, 2004.

  1. E Colar

    E Colar Guest

    Hello everybody,

    I was wondering (may be beginner's question) how does the time/temperature
    couple affect the development of a film. I was looking at Ilford tables
    where it seems that one could achieve the "same" (?) development of a film
    in a temperature range from 17 to 26C (adjusting the time for it).

    Is there any change in grain size, contrast or other when moving along a
    temperature/time line?

    E Colar, Jan 16, 2004
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  2. I am afraid you will have to ask Michael Scarpitti about that because no
    matter what anyone else may tell you, he insists on having the last word.
    Jean-David Beyer, Jan 16, 2004
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  3. As the developer becomes warmer it works faster. This is a
    simple chemical principle. By chaning time the film will be
    developed to the same contrast index. However (you knew this
    was coming), things are not quite so simple. For one thing
    the emulsion softens and swells when it is warmer. While
    modern films are much harder than those of a few decades
    ago, they still swell. When swollen there is more chance for
    grain to increase by what is called grain clumping. The
    individual silver crystals which make up the image are
    microscopic in size. What is seen as grain is the grouping
    of these crystals due to random juxtaposition in the
    emulsion, and also because they are attracted toward each
    other during development. If the emulsion is softened
    sufficiently by temperature or by being in a very highly
    alkaline bath, the silver grains can migrate toward each
    other to form clumps. This is why highly alkaline
    developers, like Rodinal, are more grainy than relatively
    low pH developers like D-76. There is more to it than that
    but the clumping is important.
    High development temperaturs also tend to encourage fog.
    OTOH, at low temperatures some developing agents become
    inactive. Hydroquinone, in carbonate, becomes inactive
    around 50F. In hydroxide, as it is in lithographic
    developers, it stays active to quite low temperatures.
    While the speed of a chemical reaction approximately
    doubles with a 10C rise in temperature, these other factors
    keep photographic development from having an exact or linear
    time/temperature relationship. Over the range of normally
    encountered room temperatures, say from 60F to around 80F,
    time and temperature can be used to compensate each other
    without much difference in other characteristics.
    Richard Knoppow, Jan 16, 2004
  4. When you say "Rodinal", you mean Rodinal or Rodinal special?
    Dimitris Tzortzakakis, Jan 17, 2004
  5. For all practical purposes, the temperature/time adjustments produce
    identical results with today's films. Just keep the temperatures less
    than about 77 degrees or so and you'll be fine.
    Michael Scarpitti, Jan 17, 2004
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