[pure-silver] Re: 4X5 T-MAX 100; D76 (1:1); JOBO ROTARY

Richard, thank you for filling in "the rest of the story"
I have not used D76 in a long long time.
Jonathan

-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Richard Knoppow
Sent: Monday, February 18, 2008 2:23 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: 4X5 T-MAX 100; D76 (1:1); JOBO ROTARY 


----- Original Message ----- 
From: "mail1" <mail1@xxxxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, February 18, 2008 9:45 AM
Subject: [pure-silver] Re: 4X5 T-MAX 100; D76 (1:1); JOBO 
ROTARY


“The Film Developing Cookbook”, Chapter 5, Solvent 
Developers, explains the
in and out of D76.  A change in dilution changes PH which 
can affect the
activity of Hydroquinone. With the 1 to1 dilution the 
sharpness of the grain
increases due to decease of Sodium Sulfite. Changes in the 
gradation of the
film will take place, and the dilution also increases a 
shouldering-off of
the highlights typical of compensation developers.

Jonathan Ayers   [mail1@xxxxxxxxxxxxxxxxx]

    I am afraid there is a lot in Anchell's book which is 
just nonsense. The hydroquinone in D-76 is nearly inactive 
at the pH of the developer. It acts mainly to regenerate the 
Metol. The capacity of the developer is greater with both 
reducing agents than with Metol alone but leaving out the 
hydroquinone has almost no effect on the development ability 
of the formula.
    Sulfite has a several effects in developers. Its main 
function is to preferentially absorb oxygen to prevent the 
oxidation of the reducing agents by atmospheric oxygen. It 
also acts to prevent staining from oxidation products of 
development. Sulfite also is a mild solvent of silver halide 
(not metallic silver). This affects grain because it changes 
the way the developing agents can access the halide crystals 
and also changes the way morphology of the developing 
silver. Another way sulfite affects grain is because of 
"salt effect" which is the prevention of emulsion swelling. 
Some grain is caused by migration of developing grains in 
softened emulsion to form "clumps". This effect is much 
reduced in modern films where the emulsions are quite hard.
     Diluting a developer has some effect partly because of 
the reduction of the relative strength of the sulfite and 
the time of exposure to the sulfite. The change in pH from 
dilution probably has little effect.
     Packaged D-76 is buffered. The original formula was 
found to increase in pH slowly due to a slow reaction 
between the sulfite and hydroquinone. This reaction produces 
some sodium hydroxide. Actually, it takes place in all 
developers containing hydroquinone and sulfite but is mostly 
masked in higher pH developers like Dektol. By using a 
buffer of borax and boric acid it is possible to prevent the 
slow rise in pH and maintain constant activity. The formula 
for buffered D-76 is:

Kodak D-76d
Water (at 125F or 52C)                    750.0 ml
Metol                                       2.0 grams
Sodium Sulfite, dessicated                100.0 grams
Hydroquinone                                5.0 grams
Borax, granular                             8.0 grams
Boric acid, crystaline                      8.0 grams
Water to make                               1.0 liter

    This formula has the same activity as the freshly mixed 
standard formula but does not change activity with storage.

    There may be a small advantage in adding 0.5 gram/liter 
of potassium bromide to D-76 to eliminate the slight fogging 
characteristic of the developer when fresh.

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

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