FotoDave@aol.com
Sat, 22 May 1999 18:04:55 -0400 (EDT)
> Is the bicarbonate buffer agent that is said to be provided by the use of
> potassium carbonate crystals meant to apply to the stock or working
> solution?
I guess both, but for our application, it is the working solution that is
critical.
Basically any weak acid or weak base (like pot. carbonate) has some buffer
capability. It is only when it is very diluted, then we have to worry. My
books are all in the boxes since I just moved, so I don't have the FX-2
formula in front of me, but since it uses carbonate as alkaline and it is for
film (not paper), I can guess that the amount of carbonate is little in
working solution, that is why buffer capability should be watched.
However, I really do not see why crystal carbonate provides better buffering
than anhydrous. It might be because the crystal has water, so one must use
more, so it gives a false sense of better buffer, but the reason it is more
is simply because there is more water molecule. When dissolved into liquid to
the same pH, I believe crystal carbonate and anhydrous carbonate give you the
same thing.
In order to truly give better buffering, you could use carbonate +
bicarbonate to reach the same pH. Since you have a pH meter (if I remember
correctly), you can even use sodium carbonate (washing soda) and sodium
bicarbonate (I forget whether this is baking soda or baking powder, but you
can check the box).
> The Film Developing Cookbooks recommends as an alternate to potassium
> carbonate crystals the substitution of sodium metaborate at about 1.5X. Has
> anyone tried this?
I was going to suggest that too. Since you will need more sodium metaborate
to reach the same pH as carbonate, the buffer capacity is higher.
But to tell you the truth, I would not even worry about this buffer thing
until I use the basic formula and see the result. If your alkalinity declines
as development goes, at most you get some compensating effect, which I gather
for a few years of mails here, that most people from the alt. photo list seem
to like.
Dave S
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:39:34