Cor,
To your point, I did some research on the chemical conversions I found
the following two posts. In fact Lloyd's name was associated with the
posts.
I made the remark; it originally came from The Darkroom Cookbook, concerning
potassium carbonate, and I extended it to sulfite. The latter is available
from Photographer's Formulary at $16/lb. It doesn't specify the hydration
status; the ratio of K2SO3 to Na2SO3 is 158/126, or about 1.25. I believe
that the ratio of the carbonates is one of the hundreds or so errors still
in the darkroom cookbook (the "corrected" edition); K2CO3/Na2CO3.H2O is
138/124, so DIVIDE, not multiply, the amount of sodium carbonate by 0.9 to
substitute the potassium version.
I recently did a series of tests on Agfa MCC using warm and cold developers,
substituting only the carbonate, not the sulfite; and potassium makes a
final print that is noticeably warmer, especially after sepia toning. I
plan to mix the developer with both potassium salts next time I use a warm
developer; I guess I or someone ought to compare potassium carbonate
developers with each sulfite salt to see how big the difference is.
Note that with cold papers, the differences resulting from these kind of
changes is tiny, and often imperceptible.
I don't know how difficult K2SO3 is to keep in dry form; the jar is still
sitting on my shelf. I don't see why it would be any harder to keep than
the sodium version, which is ubiquitous.
You should be able to substitute potassium carbonate for sodium carbonate
without concern, however, keep it tightly capped and dry, since it
absorbs water from the air. The molecular weights are:
potassium carbonate K2CO3 138.2
sodium carbonate Na2CO3 106
sodium carbonate monohydrate Na2CO3*H2O 124
If potassium carbonate is used rather than anhydrous sodium carbonate,
the factor is 138.2/106 = 1.3X (1.30 g potassium carbonate used for each
gram of anhydrous sodium carbonate required).
If potassium carbonate is used rather than sodium carbonate monohydrate,
the factor is 138.2/124 = 1.11X (not 0.9X).
If sodium carbonates are substituted for potassium carbonate, the factors
are the inverses of those given above (anhydrous, 0.77X; monohydrate,
0.9X).
Both sodium and potassium carbonates give nearly the same pH, and the
differences in development should not be evident if the correct amount is
substituted. Using much less carbonate than specified may warm image
tone, but generally, developers don't affect tone very much compared
to other factors (paper, toners, etc.).
Benzotriazole might cool the image tone; usually, bromide (or developer
reuse) lends a warm or greenish cast, but improves high value separation
due to its restraining action. Both exposure (more) and developing time
(longer) should be adjusted if significant amounts of restrainer are used.
Adding more carbonate to a developer to which bromide has been added or
has accumulated, will cool the tone and decrease developing times, but
retain high value separation. Using the factorial timing approach
described by Adams is convenient to adjust times after additions (10%
solutions of KBr and Na2CO3 are convenient).
Tim
On 1/25/07 4:06 AM, "C.Breukel@xxxxxxx" <C.Breukel@xxxxxxx> wrote:
>
> }
>>
>> January 24, 2007, from Lloyd Erlick,
>> regarding Ansco 120 print developer:
>>
>> Thus: 12 g sodium sulfite anhydrous for one liter of *working*
> solution.
>>
>> The working solution I use contains 13.5 grams of potassium sulfite
>> anhydrous. I've forgotten the arduous calculation that led to this,
> but
>> the
>> solution works very nicely indeed. Maybe those more chemically adept
> than
>> I
>> am can correct my numbers ...
>
>
>
> ..ok I take the "challenge"..:-)..
>
> molecular weight sodium sulfite: 126,04
> molecular weight potassium sulfite: 158,26
>
> So 12 g sodium sulfite equels (158,26/126,04)*12 = 1,26 * 12 = 15,12 g
> potassium sulfite.
>
> A bit more than you use now, bit it ain't rocket scince, it probably
> won't matter too much..
>
> Best,
>
> Cor
>
>
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