Sandy King (sanking@hubcap.clemson.edu)
Sat, 20 Feb 1999 15:20:22 -0400
Adam Kimball wrote:
>I know it has been mentioned before, but could someone provide a formula for
>Rollo Pyro- on or offlist? I'd like to give Pyro a try.
>
>-Adam
>
Leban/Rollo Pyro formula, as posted by Harald Leban on 13 January 1998.
Part A
Water 800ml
Sodium bisulfite 20g
Metol 20g
Pyrogallol 150g
ascorbic acid 10g
potassium bromide 1.5g
EDTA 2.5g
Water 1000ml
Part B
Water 800ml
Sodium metaborate 300g
EDTA 5g
Water to 1000ml
Distilled water recommended for stock solutions.
For use, dilute 1 part A + 2 parts B + 50 parts water.
Leban posted a slightly different formula on 18 January, without EDTA in
Stock B.
I see that Carl posted the original PMK formula in his message. Comparing
the developing agents in PMK and the Leban formula one will see that it is
really a much stronger version of PMK as regards the amount of Metol and
Pyrogallol contained in a liter of working solution, plus it contains
ascorbic acid, which cuts down on oxidation and is also superadditive with
Pyrogallol. This all means much faster developing times, but at some cost I
believe.
My tests with the Leban formula, which include plotting characteristic
curves for different developing times with several different films,
indicate the following.
1. For developing films to the same CI, times are indeed much shorter
with the Leban formula than PMK.
2. The characteristic curve with the Leban formula is less linear than with
PMK. There is a gradual rise in the toe and a very steep climb in the
mid-tones throughout the highlights. PMK has a straighter curve and levels
out in the highlights. This explains why you must *not* allow film to
develop too long in the Leban formula, as Kerik pointed out.Highlight
density will go off the board very quickly. This also suggests there is
actually more developing chemistry in the formula than necessary.
3. There is almost no fog with the Leban formula, and very little base
stain, but there is also somewhat less *image stain* as compared with PMK.
Consequently I consider the Leban formula much more than a slight
modification to PMK. It in fact behaves quite differently and requires
completely different processing times for all films.
For photographers who wish to simply cut down on oxidation to allow rotary
processing with PMK but keep developing times and other negative
characteristics as similar as possible to the original formula just add
2-5g of ascorbic acid per liter of Stock A.
Finally, I have both practical and theoretical reasons to believe that
Stock A solutions formulated with ascorbic acid do not keep as well as the
original formula.
Sandy King
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