[pure-silver] Re: D-76 and variations


----- 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.

The Agfa formula is similar but given as half the above strength, i.e., to be used without dilution for tray development or 1:1 for tank use.

This is likely the developer used for those nice, grainy, snapshot negatives you have from the 1940's.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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