Steve Shapiro (sgshiya@redshift.com)
Wed, 26 May 1999 05:49:02 -0700
Subject: Amount carbonate in developer, was Question about FX-2
Sandy,
I was just reading, last night about Maxim Muir's variation on the Windich
formulas in the Film Developing Cookbook that discussed exactly that thing.
Are you working from the Anchell, Troop book?
S. Shapiro
> Dave,
>
> I am skeptical of your conclusions about the effect of changing the amount
> of carbonate in a working solution. For the past several months I have
been
> working on an experimental pyrocatechin/metol developer with sodium
> carbonate as the accelerator. Working from concentrated A
> (Metol+Pyrocatechin) and B (10% sodium carbonate) solutions the film tests
> that I completed showed a signicant difference in developer activity (as
> measured by develolpment to a specific CI) between the following working
> dilution: 1) 1:2:100, 2) 1:5:100 and 3) 1:10:100
> (developer:carbonate:water). The actual pH varied very little as I recall,
> from about 10.3-10.5. Unfortunatley my notes are somewhat deficient in
this
> regard because although I took pH readings of all dilutions I had to
change
> calibration in mid-stream because of operational difficulties.
>
> Sandy King
>
>
>
> >I think we are over emphasizing the accuracy of carbonate. It is used
only as
> >the accelerator, and it is used basically only to set the pH.
> >
> >For a strong acid or base (such as Sodium Hydroxide), even if you double
the
> >amount, the pH change is at most 0.30 (pH is in log scale, so we get the
> >familiar one stop, 2 times, 0.30).
> >
> >But for weak acid or weak base (such as carbonate), the change for
doubling
> >the amount won't even be that high. The pH will remain about the same.
What
> >you get by giving more chemical is better buffering.
> >
> >
> >Dave S
>
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