Richard Knoppow (dickburk@ix.netcom.com)
Sun, 23 May 1999 00:53:00 -0700
At 03:30 PM 5/21/99 -0500, you wrote:
>Does any one on the list use Crawley FX-2 developer? If so I would
>appreciate your comments about its qualities.
>
>In The Film Developer Cookbook the directions to mix FX-2 call for the use
>of potassium carbonate crystals, not anhydrous (the crystal form is said to
>give a slight bicarbonate buffer effect). What does this mean, and how
>might the same effect be gotten with the anhydrous variety?
>
>Sandy King
>
The original FX-2 formula is for a highly concentrated stock solution and
I think the preference for both the Potassium salt and the crystaline form
stem from their greater soluability.
In a developer the carbonate slowly hydrolizes to produce both the
hydroxide, which is the actual accellerator, and bicarbonate. Because of
the large resevoir of hydroxide in the carbonate it act as a good buffer
and the pH of the solution tends to remain constant
Sodium carbonate is usually preferred over the potassium salt because it
is not delequescent. Potassium carbonate is very delequescent so must be
stored very carefully to prevent moisture absorption and consequent loss of
strength.
Again it is this very quality which makes potassium crystals desirable
for highly concentrated developers like FX-2.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
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