Richard Knoppow (dickburk@ix.netcom.com)
Sun, 23 May 1999 01:01:14 -0700
At 12:53 AM 5/23/99 -0700, you wrote:
>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
>
I meant to add to this that the ratio of anhydrous to crystaline is about
50% for either salt. i.e. use half as much anhydrous as crystaline. Not
exact but close enough for practical measure.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
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