----- Original Message -----
From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, November 29, 2005 10:38 AM
Subject: [pure-silver] Re: D-76 and variations
While there may be no official Kodak version of D-76
containing
carbonate there was a variant in the Dignan Newsletter 1973
for one
which uses 3.0 g of sodium bisulfite and 8.0 g of anhydrous
sodium
carbonate for the buffer system.
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of
Richard Knoppow
Sent: Monday, November 28, 2005 5:42 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: D-76 and variations
Since D-76 has become a sort of generic term for
developers using Borax as the accelerator, and since there
is a plethora of developers using other alkalies,
particularly carbonates, I don't think its valid to call
such developers D-76 variations. Borax developers have
certain characteristics stemming from the use of Borax
rather than other alkalies and the term should really be
reserved to differentiate them.
Something to note is that the function of Hydroquinone in
such low pH developers is different than in carbonate
developers. Carbonate produces a high enough pH to make
Hydroquinone active as a developer, Borax does not. There is
still an interaction between the hydroquinone and the metol.
Ryuji Suzuki's notes to me have caused me to doubt my
understanding of the so called superadditivity property of
M-H developers, mostly gleaned from rather old books, but
has not replaced it with anything else so I am left in doubt
about what exactly happens in D-76. Clearly, there is some
difference although it may be only capacity. Carlton and
Crabtree did test a version of D-76 with no Hydroquinone in
it as well as one with no Metol. The variant without Metol
barely develops at all, the version with Metol but no
Hydroquinone has nearly the same activity as D-76.
I don't know what Dignan did. Perhaps he adjusted the pH
of the carbonate-bisulfite developer to be the same as a
Borax developer in which case I would assume the
Hydroquinone would again be inactive as a developing agent.
Since carbonate produces outgassing in stop baths and fixing
baths I don't see that it has any advantage and maybe a
disadvantage. If the purpose was to prevent the increase in
activity he attacked it from the wrong end because the Borax
evidently has nothing to do with it.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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