[pure-silver] Re: Temperature Rule of Thumb
- From: "Nicholas O. Lindan" <nolindan@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 29 Jun 2010 00:56:08 -0500
Elias wrote
How can I compensate for temperature higher than 68 in my paper
developing? Should I try to cool things down?
To which Richard gave his usual erudite and
comprehensive answer. I would, however, like
to add a few points:
1) The Arrhenius equation (http://en.wikipedia.org/wiki/Arrhenius_equation)
gives the rate of many chemical reactions. In general the speed of a
reaction doubles for every 10 degrees C. As Richard mentioned, developing
involves many processes with different time constants and several that
are non-linear - therefore a simplistic application of the Arrhenius
relationship will not yield the exact time/temperature relationship --
but it will come close enough for most work. The Arrhenius relationship
is one of the fundamental features of the universe and is a good thing
to keep in mind for many diverse things including failure rates of
electronics and the keeping properties of cheese.
2) It is possible to vary contrast by increasing exposure and decreasing
development time. 'Soft contrast' developers like Selectol Soft are merely
slow acting developers. If you try to pull a print at 15 seconds with
Dektol
you will get a splotchy mess. Using a developer that takes 10 minutes to
develop to completion lets you pull the print early. If overdone DMax will
suffer severely. The technique will produce good results if the contrast
adjustment is limited to less than 1/2 a grade. If you are an Ansel Adams
reincarnation and desire to control print contrast to 1/100th of a grade
then a selection of developers and water baths at various temperatures is
the only way to get the results you seek if you wish to avoid multi-grade
papers.
In response to Elias' original question I would recommend just living with a
74 degree environment. By Svante's reckoning you should decrease developing
time by 1/4 to compensate, however the compensation will not be exact. If
you are making a series of prints that demand identical results then
temperature control may make sense -- but customers for the "real thing"
don't want identical results, the more wacky variation the happier they
are in picking "just the right vintage print".
--
Nicholas O. Lindan
Darkroom Automation
A Unit of Cleveland Engineering Design, LLC
Cleveland, Ohio
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