[pure-silver] Re: 4X5 T-MAX 100; D76 (1:1); JOBO ROTARY
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 18 Feb 2008 14:23:14 -0800
----- 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
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
