In article <XoSdnQKuG-lv52banZ2dnUVZ_v6rnZ2d@[EMAIL PROTECTED]
>,
Nicholas O. Lindan <see@[EMAIL PROTECTED]
> wrote:
>"jjs" <nobody@[EMAIL PROTECTED]
> wrote
>
>> "a general rule of thumb for the range of 65 to 95F is that a decrease
of
>> 10F increases the development time 1.5 times."
>
>Leading back to first-year chemistry ...
>http://en.wikipedia.org/wiki/Arrhenius_equation
>where the rate of a reaction doubles every 10C.
>
>A variation on the universal equation:
>
> Something = Something Else * e ^ -(Energy of the thing / k * T)
>
>Where k is Boltzman's constant and T is temperature
>relative to absolute zero.
Unfortunately, there are several reactions going on at once in a typical
photographic development bath. For example, consider a tank full of D76:
the primary development agent (the metol) is being exhausted by developing
the film, and regenerated by stealing electrons from the other developing
agents. A buffer reaction is keeping the pH of the solution stable, at
the same time. More complex developers will have sequestering agents
grabbing up development-inhibiting reaction products and holding them in
solution, etc. -- and all these reactions have different energies, thus
proceed at different rates. Get below or above some threshold
temperature,
and the overall reaction won't run as designed, period, and the
characteristic curve of the resulting negatives will be...different.
In any event, if you actually fit curves to the time/temperature data for
common films and developers (at some constant exposure and density) you
will find that they are, at least, shallow 2nd-order curves -- not linear.
And that's within a fairly narrow temperature range, all bets are off once
you get outside there. The film/developer testing page on Paul Butzi's
site has some nice examples of the data and the curves that fit it, and
they are *not* straight lines.
--
Thor Lancelot Simon
tls@[EMAIL PROTECTED]
"The inconsistency is startling, though admittedly, if consistency is to
be abandoned or transcended, there is no problem." - Noam Chomsky
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