----- Original Message -----
From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, November 28, 2005 11:17 AM
Subject: [pure-silver] Re: D-76 and variations
D-76 is very poorly buffered thus even a small amount of
oxidation is
enough to raise the pH significantly. There is a variant
which contains
sodium carbonate and sodium metabisulfite which creates a
carbonate/bicarbonate buffer.
Packaged D-76 probably contains some sequestering agent
which would help
preserve it. During the oxidation of hydroquinone,
hydroquinone
monosulfonate ion is produced. This is also a developing
agent although
it is not as active as hydroquinone itself. Potassium
hydroquinone
monosulfonate is Kodak's Balanced Developing Agent which
sometimes
appears in their formulas.
Sodium carbonate solutions will absorb CO2 from the air to
form
bicarbonate ion. But not enough to effect paper developers.
I think you are confusing buffered D-76 with something
else. Buffered D-76 uses a Borax and Boric acid buffer.
There is no variety of D-76 which contains either carbonate
or metabisulfite.
D-25, the extra fine grain developer uses Sulfite and
Bisulfite as a buffer system to achieve a pH of around 7.0
but this is to reduce the activity of the Metol and get the
very fine grain property.
Bisulfite is used in a few other developers, notably
Kodak D-61 and its Agfa equivalent Agfa 47. These were
widely used general purpose developers in the 1930's and
1940's especially for photofinishing work. They are too
active for modern films. The bisulfite is probably there for
some purpose other than buffering, there isn't enough. Here
is Kodak D-61a
Kodak D-61a Stock Solution Water (at 125F or 52C) 500.0 ml Elon (Metol) 3.1 grams Sodium sulfite, dessicated 90.0 grams Sodium bisulfite 2.1 grams Hydroquinone 5.9 grams Sodium carbonate, anhydrous 11.5 grams Potassium bromide 1.7 grams Water to make 1.0 liter
For tray use dilute 1 part stock to 1 part water. For tank use dilute 1 part stock to 3 parts water.
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