[pure-silver] Re: D-76 and variations
- From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 28 Nov 2005 14:17:08 -0500
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.
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of John Black
Sent: Monday, November 28, 2005 1:26 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: D-76 and variations
The problem with the rise in pH of D-76 with time is due to the
oxidation of hydroquinone. This is a fairly complex reaction in which
OH- ions are produced. It has nothing to due with either carbonates or
borax.
Oh.... other than buffering it, what was done about the pH problem with
storage? If hydroquinone oxidizes, is it still photographically active?
I could have sworn that there was an old formula or variation of D76
that had carbonate in it.
Pure Na carbonate solutions are quite alkaline but not of a long term pH
stability. There seems to be an interaction between CO2 in the air and
carbonate ion, or so I've been told. In paper developers that use
carbonate, a rise in pH is not noticeable activitywise.
JB
========================================================================
=====================================
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.
============================================================================================================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:
